Thank you very much!!! KE8BBT I'm changing my 7 year old RG58 to LMR400. At the antenna I have RG213 so I can easily get 5 loops. But then I have an 80 foot run so I'm using the LMR 400 after the lightning arrestor. Then at the entrance/bonding box (KF7P) I'm using RG213 as my feed into the house because of its flexibility.
The key bit of information I had been missing was that the choke increases the outer braids impedance. Once you said that it was clear to me why chokes work and why. Thanks
Great Video! Very informative. Baluns have always confused hams, myself included. I think I grasp it just a tiny bit better than before, & that's worth it's weight in gold to me, as Radio is a means of self sufficiency and Emergency Communications.
Hey mike bought your slim Jim j-pole and it is Amazing!!! Got all kinds of compliments on my signal reports. Can’t say enough good things about your antennas. Great purchase. satisfied customer. Thank you sir
I'm an electrical engineer (FYI). The way I like to visualize what's going on is the following. First of all, in any transmission line (any line that carries alternating current), any change in impedance along the way will result in some current passing through that point and some reflecting back along the way it came. The line looks infinitely long if the load is only resistive, which means that at the particular applied frequency, the capacitive and inductive reactances balance each other perfectly. A 'change in impedance' means a change occurred somewhere along the line that added/subtracted either capacitive or inductive reactance (or both) and they no longer cancel each other out. In other words, if you measured the instantaneous voltage present right at that point where the impedance change occurs and looked left and right, the different directions from that point have different impedances and will therefore see different amounts of current from that point into the two directions. In a dipole antenna situation, both wires of the dipole are by default equal in all regards (assuming no other factors such as conductors or ground planes too near the wires). But each half is 'fed' by something different ... the center wire of the feedline on one, and the coax shielding on the other. If you take an imaginary walk down the dipole wires to their connections, then those connections are what I referred to as a 'change in impedance' above. The input impedance of the center wire on the feedline (resistive+reactive) is different than the input impedance of the coax shield (resistive+reactive). If you further assume that it is reflected current coming down the dipole's wires towards those connections, it's fairly easy to see that some power will be reflected back along the dipole wire and some will pass through the connection into the wire and coax shield (separate from each other). But the feedline wire and coax shielding have different impedances (!) ... the result is that the 2 sides will NOT be the same in terms of current being reflected back into the dipole wires and current that was able to pass through the connections. Play with software such as EZNEC and you can see this modeled nicely. You can view this as current on the coax-braid side of the dipole existing in the dipole wire and a 'little bit leaking into the coax'. If you could stop the 'leakage' into the coax, then according to Kirchhoff's Current Law, the dipole wire would then carry ALL of the current and it would equal the current in the center-wire side of the dipole. This is where a choke comes in ... they are inductors. Inductors resist instantaneous changes in current. As the current in the dipole wire rises at the connection point, the inductor (the choke) resists current flowing down the coax shield and thereby forces it to stay in the shield side of the dipole wire. The only gotcha is that different frequencies require different inductances in the choke - air core ('ugly baluns') have narrow high-impedance characteristics versus frequency while ferrite-core chokes have broader ranges of high impedance versus frequencies ... and not all ferrite cores are created equal. Here's a good resource (hint: choose 11 turns of RG58 on a stack of two FT-240-52 ferrite toroids) www.karinya.net/g3txq/chokes/
Great job teaching this and it applies to common mode rejection such as in circuits with splitters . I am a scientist and appreciate your teaching in this area TNX.
Thank you for this video! From a practical point of view, how can one measure the efficiency (attenuation, bandwidth, optimum frequency, ...) of a coax choke balun?
Last year I put h/b dipoles into my attic and a h/b 60m inverted vee outside. I tried a ferrite ring choke of the correct grade at the aerial end of the inverted vee but noticed my SWR changing slightly when I touched the coax cable in the shack. My theory was that due to the wavelength r.f. was getting onto the coax after the choke so I put it in the shack and no problem. The coax must be in the r.f. field. My inverted vee is very unbalanced as one end is near the house. The same with my h/b 2m 2 element collinear so I put the choke about a ¼λ from the aerial. SWR reading okay. The dipoles I never checked but put the chokes in the bedroom shack thinking the coax is in the r.f. field. SWR okay. Maybe a few snap on ferrites spaced out along the coax at the aerial as well might stop r.f. being picked up on the coax. I think I'll try this. Interestingly I looked at two aerial manufacturers, one said a choke at the aerial and the other said at the tx. G4GHB.
Hi I am De kc5ulu . Love the presentation you give . I have a problem with sleeve chokes they work great but I've been told by several hams that I am wrong in the way that I build them I've also noticed articles that all contradict the way I'm doing it. I use the 1/4 wave formula 234/frequency to get open air length of my antennas , I use the same for my coaxial chokes but , I have been told by many I need to allow for the velocity factor of the coax I'm using, which in this case is rg8x however the whole reason for the choke is to increase the impeandance on the outside of the coax so the signal will go down the inside 50 ohm cable and not the outside. I did finally make a choke using the coax velocity factor of the 8x but it was to short and didn't work for me so went back to the way I doing it . I encase my chokes with heat shrink and it may slow the signal some but I can't tell, it still works the same. I am building 2 meter quad antennas I don't use ferrite beads or wind up coax due to weight and or windloading . So what I am asking is this way I am doing it right or not?
1) What's the difference between a Voltage balun and a Current balun and why should I use one and not the other ? 2) Which is the most appropriate balun for a half wave centre fed dipole for 2-30Mhz fed with 50 ohm coaxial cable ?
Thank you KB9VBR, excellent clarity describing the application of a balun and choke. You're an awsome Elmer resource. BTW, 'enjoying my KB9VBR j-pole and like to brag about how well it works.
Can you recommend the best 100W mobile unit for my vehicle. Also, a recommended mobile antennia..I do like the idea of owning a unit that automatically locates the repeaters as you travel through different states. Thank you.
I posted a question 2 years ago and see no response , ok then I sense have proven my point on sleeve chokes , just don't allow any coax velocity factor since we are only working with signals on outside of coax. Now it would be nice if you mention what can happen when you have high common mode current on the outside like it can radiate just like the antenna but causes the pattern to be way off ,it also receives outside interference causing more noise on the receiver it also can create rfi and those signals can get into all your sensitive electronics and gfi breakers not to mention it will produce a shock hazard. If you don't care then watch out for angry neighbors because you're most likely giving them interference . The more informed you are the better you can protect your hobby.
Wow very informative, Sir, asemble antenna like j-pole and ground plane what exact measurement for ham radio 5 watt cignus v85, and 10 watt Baofend UV82
Ignorance is not bliss, I was robbed. Actually I understood a few things which is remarkable for me. How do baluns work that aren't wired to the antenna. I've seen little antennas used for TV and radio as well by friends living in apartments that can't mount a large mast or have any length to run any type of wire. Guess it's like putting in an inground pool and you live on the 8th floor. The folks below probably wouldn't appreciate it much. Any the baluns aren't wired in, its basically just attached to the mast itself. It's larger the coax attaches to it but it's just snapped on. I'm guessing the mast is aluminum does it somehow travel down the mast without actually being wired to it? My ignorance makes the question a bit dense I know but thanks anyway if you get a chance to answer the question.
I have seen a lot of different ways to wind balancing. One wines 2wires around the toroid then goes over to the other side and wound the other way. The other has 2 sets 2 wires wound one on each side, called a current balon. I am not sure what they do different.
Ok wow! Super simple and it worked!!! I’m not a technical guy; I like to talk on the radios not build and modify the dern things, but this was so easy and it took my SWR from about 1.9 to 2 down to 1.5 On my 2m 70cm mobile with tram antenna trunk lip mount 50rg coax bout 20ft. Thank you for the information
I made a 20M Dipole Antenna. I will not be using this 20M dipole for any other frequencies other than the 20M that it was made for. Is a balun needed for this a 20M Dipole antenna? Again I will not be using this 20M dipole for any other frequencies other than the 20M that it was made for. I also have an isolator. Would I need both? Do they pretty much do the same job?
Thanks for a very good and informative video. I am in the process of making an HF broad band terminated dipole antenna and was wondering if creating a loop as described in this video would make an effective choke for my antenna. Any information you provide will be appreciated. . . Thanks!
I understand for the most part but I assume no balun or RF Choke would be needed on a QRP rig using balanced line to a dipole? And would a RF choke not be needed for QRP using a long-wire to a antenna tuner?
If a choke is needed to block rf from coming back down the shield braid , would adding the choke (turns of wire) at the braid connecting to the antenna rather then the whole coax. I'm considering a jpole 2mtr/ 70cm feeding coax of rg8x. You mention the clam shell chokes, Can I use one taken from old power cords to get a home brew antenna build secure from the common mode currents? I am still confused how the choke does not also impede the rf going to the antenna ? Thanks.
Mike, In the process of constructing a fan dipole, My plans include adding slide on 12 ferrite beads and make a cover with PVC pipe and 2 end caps. I will be using 100 feet of RG8X... Any suggestions..... Thank You
I'm not sure of your question. Are you looking for a source for the ferrites or a better method of putting them on the cable? Instead of using a PVC tube, which could collect water and freeze, I'd probably secure them with heat shrink tubing or electrical tape. Then you wouldn't need to remove the connector on your cable in order to install the choke.
Mike, Van Gordon made a G5RV 20 years ago. The choke was made with slip on ferrite beads (10). He would use PVC pipe and 2 end caps. The caps would be sealed. I think your idea is the best idea. Thank You and keep up the great work. Thanks Again Chuck KK4CV
I tried an experiment with 400 ohm TV antenna feed line, and cut it to the proper length for a 2Meter antenna, and I wrapped a small piece, 1" X 3" trailer flashing aluminum panel, watching to make sure i did not touch the elements , but started there, and after checking the SWR several times, it went down from nearly a 2 to less than 1.5.within a 10 millimetre section, going down the antenna first, then going back up above the connection. after another two times adjusting, it went to a flat zero. No SWR was seen on the meter. Did you ever try one of these experiements, ? My J pole still works today, whether it is outside hung high in a tree, or within my hamshack. and I have worked several local hams straight, using no repeater aid. Let me know what I did right for once if you will please Sir. Thank you for your time. KB4AKS "A"lways "K"eep "S"miling
I have a Palstar AT4K with a 1.1 internal balun.I have a 450 balance line coming in to a DXEngineering 1.0 balun. My question is: Using a separate Palstar on a separate TX should I not use the DXE balun since I have an internal balun ?
+Familia Román Soler 1:1, 4:1, etc are ratios of impedance. Normal impedance for amateur radio equipment is 50 Ohms, so a 1:1 balun will convert a 50 Ohm balanced antenna to 50 Ohm unbalanced feedline. Best example would be converting a 1/2 wave dipole antenna (which actually is 70 Ohms, but close enough for this illustration) to 50 coax cable. A 4:1 balun will convert an 200 Ohm impedance down to 50 Ohms. Some examples of antennas that could have 200 Ohms of impedance at their feedpoint include HF verticals or off-center fed dipoles (like the Carolina Windom). If you are planning to feed these antennas with coax, you will most likely need a 4:1 balun to match the impedance at the feedpoint. A commercially built antenna will most likely tell you if you need a 1:1 or 4:1 balun. If you are building an antenna, using an antenna analyzer like the MFJ-269 will tell you what the impedance is at the feedpoint, which will then indicate what type of balun is needed.
+Familia Román Soler The Double Bazooka should have an impedance of 50 ohms at its feed point. A 1:1 balun would be sufficient, since I assume you are planning to feed the antenna with coaxial cable. If your impedance is above 75 Ohms or SWR above 1.5:1, then I'd work at adjusting the antenna length to bring the SWR, and impedance back down.
Nice have you on my subscribtions. No one answere a question as fast as you. I have a 13 years old kid looking into ham radio. And his complain al the time is no body answere my questions. Thanks a million.
+GoohtWillIndustries Great ideas! My go-to source for information on baluns is usually the ARRL Handbook. But that information can be very technical and the book, unfortunately, is densely written. I'll add homebrewing 1:1 and 4:1 baluns to my list of topics for a future video.
Type 31 mix has a top frequency of about 300 Mhz and Type 43 mix is suitable for frequencies up to 500 Mhz or so. You can use Type 31 ferrites for VHF applications, but you will receive diminishing returns as the transmit frequency climbs.
For 2 meters i'm using RG-8X cable that has a foam dielectric. Wouldn't it be better to wind the 5 turns of cable side by side as opposed to jumble winding? Also should one use a full wave length of coax (62" of RG-8X)' for a 2 meter choke?
+Dan Druff Winding the coax side by side as opposed to the 'jumble winding' will give you a higher level of choke impedance, so it would be a preferred method. But since we only need to increase impedance to about 750 ohms or so, the jumble method works fine for VHF/UHF frequencies. On the HF bands it would take more turns of coax, so careful winding makes a big difference. As for your second question, I haven't heard of using a full wavelength of cable in the construction of a choke, and couldn't find a reference to such in my quick search. But I did a quick calculation and if you used 5 turns of coax in a 4 inch diameter circle, the total amount of coax you'd be using is close to 62 inches, or a full wavelength on 2 meters.
+KB9VBR Antennas ........I've seen home made 2 meter chokes wound 15 times, (RG58) around a 3/4" pvc form. Is there any advantage or disadvantage to this procedure as opposed to winding one 5 turns, 4" in diameter?
So what about an endfed like chameleon emcomm III? Is their “system” already designed appropriately, or is there still benefit on chokes or ferrite beads
That's an interesting question and my answer has a bit of speculation as you can't open up their transformer packages and inspect them. But I do know that Chameleon uses a 5:1 impedance transformer in their antenna systems. End fed style antennas can send RF energy back down the outside of the feed line if they aren't properly grounded and/or have a counterpoise. The Chameleon Emcomm III base antenna does have both counterpoise and ground, so a choke balun should not be necessary. But the Emcomm III portable does not. Their MPAS system comes with 50 feet of coax with an integrated choke, so I'm going to infer that the Emcomm III portable would benefit from a choke also.
KB9VBR Antennas ....I have my portable setup with both a ground and multiple counterpoise. Also....I actually have opened up the transformer. The bolts on the side to attach the antenna etc came loose, and the only way to tighten was to open it. It is packed full of what I would guess is dielectric grease. At least I hope that is what it was since I “topped it off” before closing it up again 😁
all choked up. haha i see what you did there :-) thanks this video helped explain a few of my questions. Is a chock as effective as a balun? it seems like a simpler solution, Im still trying to figure out what it means when all the rations they have on baluns
A choke is a similar to a balun, but serves a little different purpose. Both use ferrite chokes or coils of wire to change the impedance of an antenna system. But there is where the similarity ends. Chokes are used to raise the impedance of the outside of conductor of a cable to reduce stray RF interactions. A balun matches an unbalanced feed line to a balanced antenna by changing the impedance between the two. Despite serving different purposes, the terms tend to be used interchangeably.
oh ok that makes since thanks for the info i really appreciate it. by the way i missed a typo. i meant to say "ratio" not "rations", but i have been doing more reading and pretty sure i get that now. now if i could find a source for information explaining how you know how many turns to use. i see a lot of people saying to use so many turns but most give a different value, i would assume there is a way to calculate that?
There are formulas and charts for calculating how many turns of coax you need for a choke to be effective at a particular frequency. If you want to dig into the theory, both the ARRL Handbook and Antenna book have extensive sections on the subject.
To match the impedance on a delta loop I am told to use a 1/4 wave length of 75 ohm cable at the feed point. Is it better to do the 5 loops with it at the feed point? do I need a 1:1 current balun also ?
The 1/4 wave length of 75 ohm cable is used for a different purpose than the balun. It is changing the impedance to 50 ohms at the feed point. The 1:1 balun doesn't change the impedance, but does keep stray RF from returning back down the outer braid of the coax. You may need to add the balun, I guess it depends on your install and if the return RF energy is causing problems.
I don't think a choke is necessary for most mobile style antennas. But if you are getting RF interference in your vehicle- for example: In an older vehicle I drove‚ 6 meters would mess up the AM/FM radio; then adding a choke would be a good idea.
So when I get your J-Pole tuned to GMRS frequencies does it hurt to make that five wind four inch loop for good measure for my Midland MXT115 radio or don't worry about it. I am new and starting out and do not own a good antenna analyzer yet but plan on doing so someday in the future.
@@KB9VBRAntennas I put the 5 turns at a 4 inch loop on my LMR-240 cable from USACOAX. Everything seems to work great. I will do a video soon on the install of the GMRS radio in my Polaris Ranger of your antenna and the cable. Excuse my ignorance but what is the magic math and science behind the 5 turns at 4 inches close to the antenna. I get the increased resistance it causes. Just curious about the reason for the number and diameter of the turns. Thanks Kevin
Possibly‚ it depends on what the QRM is. If the QRM is man made like electrical noise the isolator may help filter it out. But you may be better off by first trying to figure out what the noise is and if it is coming from inside your home or another source. Once you know the source of your noise‚ the better able you will be to remove it.
Iam trying to install a HF rig in my truck radio is a Kenwood 440s it has internal tuner also have an LDG external tuner the antenna is a MFJ with the wander lead I get the antenna tuned then it changes usely after I key the mike or turn the transmit power up. Do I need a choke or balun for this ?
Would it be a mistake to use a common mode choke when using an automatic antenna tuner? It seems to me that the tuner needs the returning current feedback to lower the swr thereby maximizing the antenna rf output?
Both Type 31 and Type 43 mix ferrites will work for VHF frequencies, but Type 43 has better common mode suppression than Type 31 at the higher frequencies. Both will work, but you can by with less individual chokes using the Type 43 mix ferrites.
So the best choice of ferrite bread would be the highest impedance at radiated frequency (e.g. 400 Ohm at 433mhz UHF should be fine)? E.g. this example: cdn.lairdtech.com/home/brandworld/files/28B0315-100.pdf How to chose ferrite bread for higher frequencies e.g. wifi 2.4Ghz when most datasheets just go up to 1Ghz... ? Would the 28B0315-100 be ok?
I have a question, if anyone would be kind enough to answer :) I'm not a 'Ham', just an amateur that likes pratting with antennas for receive only say, airband... So, would my diy dipole for aircraft freq work better with a 'choke'? Does an antenna that is optimum for transmitting, automatically translate into being at optimum for receive also? thanks :)
The choke's primary purpose is to keep RF energy off the outside of the feed line while transmitting. But it can have some benefit with receive only antennas, mainly cutting a bit of the receive noise. You won't notice this noise much with FM, but it could help with AM and sideband modulation reception.
thanks very much for replying quickly :) I wondered if it would help because it's the balanced-unbalanced thing (receiver is 50Ω), then again - I guess that's a balun? I might try both then :)
Not convincing to me I'm afraid. If you make a coil of coax, both centre and braid are coiled and both will act as chokes to RF. Why should the braided part be more of a choke than the centre conductor? The RF energy travels on the surface as he explained (skin effect) so can't see the value.
Peter, in a sense you are correct. But consider this. The purpose of the outer braid is two fold: it creates the return path for the electrical energy as part of the RF circuit, but it also provides a shield so that the inner conductor doesn't radiate. It works like a Faraday cage. In coiling the coax the inner conductor is protected by the outer braid, thereby not creating the inductance. The outer braid has no such protection, so the inductance is present in the coil which increases the impedance, stopping the flow of return RF energy.
+Geronemo Bauer Either type 31 or type 43 ferrites are suitable to use as a coax choke. The Type 31 is good for HF and VHF applications, while the Type 43 will also work with UHF frequencies. The number of beads depends on the frequencies for your antenna. Lower frequencies will require more beads than higher frequencies. For VHF, 3-4 would be sufficient. With an HF antenna it could require up to 10. Beads only need to be placed near the antenna end of the coax and not the radio end.
Built a 40 Meter NVIS dipole, the article I followed said to do a balun- 6 turns at 6-8" diameter. Is this correct? I'm using 49 ft. of RG-58U total length(including balun), with RG-8U to run to the station. Anything you would change in this setup??
+Steve Tomlinson With RG-8U I'd go for at least 7 turns in a 4.5 inch diameter circle. ideally for 40 meters, 10 turns of coax would give you the highest level of impedance on the outside braid. Here's a chart that can help you determine how many turns of coax you need for your antenna based on coax type and frequency: www.karinya.net/g3txq/chokes/
+Steve Tomlinson RG-8U should be flexible enough to bend that tight. Although some brands of cable may be stiffer than others. Worse case scenario, you could use a lighter weight cable to build your balun and just connect it in-line with the rest of the antenna system. At 40m, your losses would be minimal.
Thank you, KB9VBR, I do have a question. Does a BALUN replace the Ladder-Line? Well, I do have a question. NORMALLY a G5RV antenna is supplied with "Ladder-Line as a feed line" IF you install a 1:1 balun. It has a SO-239 Coax connector. Can you connect the coax directly to the BALUN? Is the ladder line now useless?
With a G5RV antenna, the ladder line is actually part of the antenna. At the lower frequencies the ladder line radiates. That's why the line needs to be cut to a specific length. At the end of the ladder line you should have a 1:1 current balun and then feed the antenna with coax. I wouldn't attach the ladder line directly to the tuner as that could introduce RF into the shack.
Thanks for the clarification. No, there shouldn't be a balun in the center connector between the dipole elements and the ladder line. This should be a direct connection. The balun goes between the coax and the ladder line.
Inexpensive G5RV antennas, like the MFJ-1778, have a direct SO-239 connection between the ladder line and the coax. This will work, but you run the risk of RF energy traveling back down the outside of the coax feed line. If you are having trouble tuning the antenna on 40 and 80 meters, this may be the reason. Removing the coax connector at the end of the ladder line and replacing it with a 1:1 current balun, like the MFJ-918, will increase the antenna's performance on those lower bands.
Conventional wisdom states that antennas like the J-Pole work best if you put a few loops of coax near the feed point. But why is that? My latest episode of Ham Radio Q&A delves into that subject and delivers the answer. . . th-cam.com/video/zpUSe0yrxjs/w-d-xo.html
SWR is a differential mode measurement and has no effect on common mode current. Air wound chokes are narow band and are most effective at their self resonant frequency. Too many or too few turns can make common mode worse. Let's say the feedline common mode impedance is net inductive. If your air wound choke is net capacitive, the choke can increase common mode currents. W8JI has a nice white paper on this. Model a 1/4 wave ground plane with (4) radials and then add a vertical 1/4 lambda wire on the shield side pointing down- you will see a lot of common mode current. (4) radials are not sufficient to get rid of common mode. You canot say that type 43 is the best ferrite material. For broadband common mode impedance you would like to select a material that will display large resistive values at the frequency of interest. A common mode choke on a DC grounded J pole, if designed correctly, will attenuate feedline common mode, but will do nothing to common mode on the metal mast. In summary, way too simplistic a discussion of baluns, UNUN's, and in some cases incorrect.
Thank you very much!!! KE8BBT
I'm changing my 7 year old RG58 to LMR400. At the antenna I have RG213 so I can easily get 5 loops. But then I have an 80 foot run so I'm using the LMR 400 after the lightning arrestor. Then at the entrance/bonding box (KF7P) I'm using RG213 as my feed into the house because of its flexibility.
Very timely. I upgraded to General this month and had to start dealing with a lot of theses issues on lower frequencies.
The key bit of information I had been missing was that the choke increases the outer braids impedance. Once you said that it was clear to me why chokes work and why. Thanks
Glad I was able to clear that up for you.
Simple explanation of a complex subject; well done. Thank you!
Wonderful! Thank you so much.
5:00 how to make RF choke.
Great Video! Very informative. Baluns have always confused hams, myself included. I think I grasp it just a tiny bit better than before, & that's worth it's weight in gold to me, as Radio is a means of self sufficiency and Emergency Communications.
Thanks for making me that little bit wiser.
Hey mike bought your slim Jim j-pole and it is Amazing!!! Got all kinds of compliments on my signal reports. Can’t say enough good things about your antennas. Great purchase. satisfied customer. Thank you sir
I'm an electrical engineer (FYI). The way I like to visualize what's going on is the following. First of all, in any transmission line (any line that carries alternating current), any change in impedance along the way will result in some current passing through that point and some reflecting back along the way it came. The line looks infinitely long if the load is only resistive, which means that at the particular applied frequency, the capacitive and inductive reactances balance each other perfectly. A 'change in impedance' means a change occurred somewhere along the line that added/subtracted either capacitive or inductive reactance (or both) and they no longer cancel each other out. In other words, if you measured the instantaneous voltage present right at that point where the impedance change occurs and looked left and right, the different directions from that point have different impedances and will therefore see different amounts of current from that point into the two directions. In a dipole antenna situation, both wires of the dipole are by default equal in all regards (assuming no other factors such as conductors or ground planes too near the wires). But each half is 'fed' by something different ... the center wire of the feedline on one, and the coax shielding on the other. If you take an imaginary walk down the dipole wires to their connections, then those connections are what I referred to as a 'change in impedance' above. The input impedance of the center wire on the feedline (resistive+reactive) is different than the input impedance of the coax shield (resistive+reactive). If you further assume that it is reflected current coming down the dipole's wires towards those connections, it's fairly easy to see that some power will be reflected back along the dipole wire and some will pass through the connection into the wire and coax shield (separate from each other). But the feedline wire and coax shielding have different impedances (!) ... the result is that the 2 sides will NOT be the same in terms of current being reflected back into the dipole wires and current that was able to pass through the connections. Play with software such as EZNEC and you can see this modeled nicely. You can view this as current on the coax-braid side of the dipole existing in the dipole wire and a 'little bit leaking into the coax'. If you could stop the 'leakage' into the coax, then according to Kirchhoff's Current Law, the dipole wire would then carry ALL of the current and it would equal the current in the center-wire side of the dipole. This is where a choke comes in ... they are inductors. Inductors resist instantaneous changes in current. As the current in the dipole wire rises at the connection point, the inductor (the choke) resists current flowing down the coax shield and thereby forces it to stay in the shield side of the dipole wire. The only gotcha is that different frequencies require different inductances in the choke - air core ('ugly baluns') have narrow high-impedance characteristics versus frequency while ferrite-core chokes have broader ranges of high impedance versus frequencies ... and not all ferrite cores are created equal. Here's a good resource (hint: choose 11 turns of RG58 on a stack of two FT-240-52 ferrite toroids) www.karinya.net/g3txq/chokes/
Thank you for a very well explained definition of baluns and their use.
finally someone that can explain a balun .thank you very much, great vid
Great job teaching this and it applies to common mode rejection such as in circuits with splitters . I am a scientist and appreciate your teaching in this area TNX.
Loved the clear, concise explanation with the illustration!
Thank you for this video! From a practical point of view, how can one measure the efficiency (attenuation, bandwidth, optimum frequency, ...) of a coax choke balun?
Last year I put h/b dipoles into my attic and a h/b 60m inverted vee outside.
I tried a ferrite ring choke of the correct grade at the aerial end of the inverted vee but noticed my SWR changing slightly when I touched the coax cable in the shack. My theory was that due to the wavelength r.f. was getting onto the coax after the choke so I put it in the shack and no problem. The coax must be in the r.f. field. My inverted vee is very unbalanced as one end is near the house.
The same with my h/b 2m 2 element collinear so I put the choke about a ¼λ from the aerial. SWR reading okay.
The dipoles I never checked but put the chokes in the bedroom shack thinking the coax is in the r.f. field. SWR okay.
Maybe a few snap on ferrites spaced out along the coax at the aerial as well might stop r.f. being picked up on the coax. I think I'll try this.
Interestingly I looked at two aerial manufacturers, one said a choke at the aerial and the other said at the tx.
G4GHB.
Finally a good video explaining these things... great!!
Great presentation really helps me understand about Baluns thank you
I used a ferrite bead, looped it only once (so it goes 2 times through the bead) and it works wonders.
Finally a choke video I can fully understand thank you A+
We can all use a little more radio theory. Great presentation. Very understandable.
Great explanation. Thanks for taking the time to explain.
A pop can with 6 loops. Then can removed. And loop taped . Forms a good choke for a quarter wave. Dipole. The swr drops off and the radio runs cooler.
Hi I am De kc5ulu . Love the presentation you give . I have a problem with sleeve chokes they work great but I've been told by several hams that I am wrong in the way that I build them I've also noticed articles that all contradict the way I'm doing it. I use the 1/4 wave formula 234/frequency to get open air length of my antennas , I use the same for my coaxial chokes but , I have been told by many I need to allow for the velocity factor of the coax I'm using, which in this case is rg8x however the whole reason for the choke is to increase the impeandance on the outside of the coax so the signal will go down the inside 50 ohm cable and not the outside. I did finally make a choke using the coax velocity factor of the 8x but it was to short and didn't work for me so went back to the way I doing it . I encase my chokes with heat shrink and it may slow the signal some but I can't tell, it still works the same. I am building 2 meter quad antennas I don't use ferrite beads or wind up coax due to weight and or windloading . So what I am asking is this way I am doing it right or not?
Another excellent video!
1) What's the difference between a Voltage balun and a Current balun and why should I use one and not the other ?
2) Which is the most appropriate balun for a half wave centre fed dipole for 2-30Mhz fed with 50 ohm coaxial cable ?
too bad no one replied
@@gaptastic Luckily i know now....
I have coiled RG8 and ferrite beads ordered...
Such a great lecture on a difficult topic for me as a new General. Super high yield. Thank you!
this is one of the best explanations of balus I have heard, thanks. kf7rcm
This is SOOOOO helpful! Thank you sir!
Thank you KB9VBR, excellent clarity describing the application of a balun and choke. You're an awsome Elmer resource. BTW, 'enjoying my KB9VBR j-pole and like to brag about how well it works.
Thanks for the compliments. I'd glad to hear that the antenna is working great for you.
Easy the best video on this subject thanks for the time and effort 👍👍
Thanks for a great answer. That really helps.
Thank you, great video!
Great straight forward explanation. Thank you....
Can you recommend the best 100W mobile unit for my vehicle. Also, a recommended mobile antennia..I do like the idea of owning a unit that automatically locates the repeaters as you travel through different states. Thank you.
I posted a question 2 years ago and see no response , ok then I sense have proven my point on sleeve chokes , just don't allow any coax velocity factor since we are only working with signals on outside of coax. Now it would be nice if you mention what can happen when you have high common mode current on the outside like it can radiate just like the antenna but causes the pattern to be way off ,it also receives outside interference causing more noise on the receiver it also can create rfi and those signals can get into all your sensitive electronics and gfi breakers not to mention it will produce a shock hazard. If you don't care then watch out for angry neighbors because you're most likely giving them interference . The more informed you are the better you can protect your hobby.
Nice explanation, thanks! So we want to keep the RF of the outer side of the bride on the cable, right?
Wow very informative, Sir, asemble antenna like j-pole and ground plane what exact measurement for ham radio 5 watt cignus v85, and 10 watt Baofend UV82
ANSWERS TO MY QUESTIONS,, GREAT VIDEO
Thank you for the video.
Ignorance is not bliss, I was robbed. Actually I understood a few things which is remarkable for me. How do baluns work that aren't wired to the antenna. I've seen little antennas used for TV and radio as well by friends living in apartments that can't mount a large mast or have any length to run any type of wire. Guess it's like putting in an inground pool and you live on the 8th floor. The folks below probably wouldn't appreciate it much. Any the baluns aren't wired in, its basically just attached to the mast itself. It's larger the coax attaches to it but it's just snapped on. I'm guessing the mast is aluminum does it somehow travel down the mast without actually being wired to it? My ignorance makes the question a bit dense I know but thanks anyway if you get a chance to answer the question.
Well explained !. .
Thank you. You are helpful.
*Deadpan* In this episode I get all chocked up.
I have seen a lot of different ways to wind balancing. One wines 2wires around the toroid then goes over to the other side and wound the other way. The other has 2 sets 2 wires wound one on each side, called a current balon. I am not sure what they do different.
Ok wow! Super simple and it worked!!! I’m not a technical guy; I like to talk on the radios not build and modify the dern things, but this was so easy and it took my SWR from about 1.9 to 2 down to 1.5 On my 2m 70cm mobile with tram antenna trunk lip mount 50rg coax bout 20ft. Thank you for the information
Excellent and informative.
I made a 20M Dipole Antenna. I will not be using this 20M dipole for any other frequencies other than the 20M that it was made for. Is a balun needed for this a 20M Dipole antenna? Again I will not be using this 20M dipole for any other frequencies other than the 20M that it was made for. I also have an isolator. Would I need both? Do they pretty much do the same job?
I would use Mix 61 for VHF/UHF
Thanks for a very good and informative video. I am in the process of making an HF broad band terminated dipole antenna and was wondering if creating a loop as described in this video would make an effective choke for my antenna. Any information you provide will be appreciated. . . Thanks!
Mike you need to update the links for the chokes you are referring to in your VLog.
Thanks for letting me know. This video, and a few other of my earlier ones are scheduled for an update this fall.
Hello Micheal. The link for the RF chokes on DX Enginnering site is not working anymore. Also, neither is the Palomar baluns link as well.
I understand for the most part but I assume no balun or RF Choke would be needed on a QRP rig using balanced line to a dipole? And would a RF choke not be needed for QRP using a long-wire to a antenna tuner?
Excelent explanation..Thanks !!
If a choke is needed to block rf from coming back down the shield braid , would adding the choke (turns of wire) at the braid connecting to the antenna rather then the whole coax. I'm considering a jpole 2mtr/ 70cm feeding coax of rg8x. You mention the clam shell chokes, Can I use one taken from old power cords to get a home brew antenna build secure from the common mode currents? I am still confused how the choke does not also impede the rf going to the antenna ? Thanks.
Which antenna type have most gain?
Can I do this for 2 meters? Get a slight amount of noise from the tv.
Thank you. Well spoken.
Mike, In the process of constructing a fan dipole, My plans include adding slide on 12 ferrite beads and make a cover with PVC pipe and 2 end caps. I will be using 100 feet of RG8X... Any suggestions..... Thank You
I'm not sure of your question. Are you looking for a source for the ferrites or a better method of putting them on the cable? Instead of using a PVC tube, which could collect water and freeze, I'd probably secure them with heat shrink tubing or electrical tape. Then you wouldn't need to remove the connector on your cable in order to install the choke.
Mike, Van Gordon made a G5RV 20 years ago. The choke was made with slip on ferrite beads (10). He would use PVC pipe and 2 end caps. The caps would be sealed. I think your idea is the best idea. Thank You and keep up the great work. Thanks Again Chuck KK4CV
I tried an experiment with 400 ohm TV antenna feed line, and cut it to the proper length for a 2Meter antenna, and I wrapped a small piece, 1" X 3" trailer flashing aluminum panel, watching to make sure i did not touch the elements , but started there, and after checking the SWR several times, it went down from nearly a 2 to less than 1.5.within a 10 millimetre section, going down the antenna first, then going back up above the connection. after another two times adjusting, it went to a flat zero. No SWR was seen on the meter. Did you ever try one of these experiements, ? My J pole still works today, whether it is outside hung high in a tree, or within my hamshack. and I have worked several local hams straight, using no repeater aid. Let me know what I did right for once if you will please Sir. Thank you for your time. KB4AKS "A"lways "K"eep "S"miling
4:58 vhf/uhf choke. 5 turns, 4" loop.
I have a Palstar AT4K with a 1.1 internal balun.I have a 450 balance line coming in to a DXEngineering 1.0 balun. My question is: Using a separate Palstar on a separate TX should I not use the DXE balun since I have an internal balun ?
Every other article I read says mix 31, which is correct?👍
Can you make a balun sma adapter for ht radios that have bad swr
How about toroids for VHF?
And what about Biquad Antennas? Is it necessary to apply a balun?
Hi my name is Julio call sign WP4PBO. My questions is about 1:1 & 4:1 BALUN. When I'm suposed to use ether or.
+Familia Román Soler 1:1, 4:1, etc are ratios of impedance. Normal impedance for amateur radio equipment is 50 Ohms, so a 1:1 balun will convert a 50 Ohm balanced antenna to 50 Ohm unbalanced feedline. Best example would be converting a 1/2 wave dipole antenna (which actually is 70 Ohms, but close enough for this illustration) to 50 coax cable.
A 4:1 balun will convert an 200 Ohm impedance down to 50 Ohms. Some examples of antennas that could have 200 Ohms of impedance at their feedpoint include HF verticals or off-center fed dipoles (like the Carolina Windom). If you are planning to feed these antennas with coax, you will most likely need a 4:1 balun to match the impedance at the feedpoint.
A commercially built antenna will most likely tell you if you need a 1:1 or 4:1 balun. If you are building an antenna, using an antenna analyzer like the MFJ-269 will tell you what the impedance is at the feedpoint, which will then indicate what type of balun is needed.
Thanks for the fast response. I'm building a doble bazooka for 40m. Any advice on the balun subject.
+Familia Román Soler The Double Bazooka should have an impedance of 50 ohms at its feed point. A 1:1 balun would be sufficient, since I assume you are planning to feed the antenna with coaxial cable. If your impedance is above 75 Ohms or SWR above 1.5:1, then I'd work at adjusting the antenna length to bring the SWR, and impedance back down.
Nice have you on my subscribtions. No one answere a question as fast as you. I have a 13 years old kid looking into ham radio. And his complain al the time is no body answere my questions. Thanks a million.
+GoohtWillIndustries Great ideas! My go-to source for information on baluns is usually the ARRL Handbook. But that information can be very technical and the book, unfortunately, is densely written. I'll add homebrewing 1:1 and 4:1 baluns to my list of topics for a future video.
Thank you.
Would a slim jim be the same as a j pole in that it acts like a 5/8 ground plane? would a slim jim even benefit from a balun?
You say use type 43 mix beads however the link only shows type 31 or am I not reading the description correctly thanks
Type 31 mix has a top frequency of about 300 Mhz and Type 43 mix is suitable for frequencies up to 500 Mhz or so. You can use Type 31 ferrites for VHF applications, but you will receive diminishing returns as the transmit frequency climbs.
For 2 meters i'm using RG-8X cable that has a foam dielectric. Wouldn't it be better to wind the 5 turns of cable side by side as opposed to jumble winding? Also should one use a full wave length of coax (62" of RG-8X)' for a 2 meter choke?
+Dan Druff Winding the coax side by side as opposed to the 'jumble winding' will give you a higher level of choke impedance, so it would be a preferred method. But since we only need to increase impedance to about 750 ohms or so, the jumble method works fine for VHF/UHF frequencies. On the HF bands it would take more turns of coax, so careful winding makes a big difference. As for your second question, I haven't heard of using a full wavelength of cable in the construction of a choke, and couldn't find a reference to such in my quick search. But I did a quick calculation and if you used 5 turns of coax in a 4 inch diameter circle, the total amount of coax you'd be using is close to 62 inches, or a full wavelength on 2 meters.
+KB9VBR Antennas ........I've seen home made 2 meter chokes wound 15 times, (RG58) around a 3/4" pvc form. Is there any advantage or disadvantage to this procedure as opposed to winding one 5 turns, 4" in diameter?
So what about an endfed like chameleon emcomm III? Is their “system” already designed appropriately, or is there still benefit on chokes or ferrite beads
That's an interesting question and my answer has a bit of speculation as you can't open up their transformer packages and inspect them. But I do know that Chameleon uses a 5:1 impedance transformer in their antenna systems. End fed style antennas can send RF energy back down the outside of the feed line if they aren't properly grounded and/or have a counterpoise. The Chameleon Emcomm III base antenna does have both counterpoise and ground, so a choke balun should not be necessary. But the Emcomm III portable does not. Their MPAS system comes with 50 feet of coax with an integrated choke, so I'm going to infer that the Emcomm III portable would benefit from a choke also.
KB9VBR Antennas ....I have my portable setup with both a ground and multiple counterpoise. Also....I actually have opened up the transformer. The bolts on the side to attach the antenna etc came loose, and the only way to tighten was to open it. It is packed full of what I would guess is dielectric grease. At least I hope that is what it was since I “topped it off” before closing it up again 😁
Instead of a 'Direct match", what do you think of an 'Inductive Match' to a J-Pole?
jerrykr7kz@aol.com
all choked up. haha i see what you did there :-) thanks this video helped explain a few of my questions. Is a chock as effective as a balun? it seems like a simpler solution, Im still trying to figure out what it means when all the rations they have on baluns
A choke is a similar to a balun, but serves a little different purpose. Both use ferrite chokes or coils of wire to change the impedance of an antenna system. But there is where the similarity ends. Chokes are used to raise the impedance of the outside of conductor of a cable to reduce stray RF interactions. A balun matches an unbalanced feed line to a balanced antenna by changing the impedance between the two. Despite serving different purposes, the terms tend to be used interchangeably.
oh ok that makes since thanks for the info i really appreciate it. by the way i missed a typo. i meant to say "ratio" not "rations", but i have been doing more reading and pretty sure i get that now. now if i could find a source for information explaining how you know how many turns to use. i see a lot of people saying to use so many turns but most give a different value, i would assume there is a way to calculate that?
There are formulas and charts for calculating how many turns of coax you need for a choke to be effective at a particular frequency. If you want to dig into the theory, both the ARRL Handbook and Antenna book have extensive sections on the subject.
ok cool thanks, google was not really helping me find anything i will look at those books
To match the impedance on a delta loop I am told to use a 1/4 wave length of 75 ohm cable at the feed point. Is it better to do the 5 loops with it at the feed point? do I need a 1:1 current balun also ?
The 1/4 wave length of 75 ohm cable is used for a different purpose than the balun. It is changing the impedance to 50 ohms at the feed point. The 1:1 balun doesn't change the impedance, but does keep stray RF from returning back down the outer braid of the coax. You may need to add the balun, I guess it depends on your install and if the return RF energy is causing problems.
Good info!
Thank you for this video - 73
MrSuperheterodyne 73?
Would it be prudent to usa a choke or Balun on a mobil 50 w quad band FM radio antenna on an eternal antenna wire?
I don't think a choke is necessary for most mobile style antennas. But if you are getting RF interference in your vehicle- for example: In an older vehicle I drove‚ 6 meters would mess up the AM/FM radio; then adding a choke would be a good idea.
Very good.
So when I get your J-Pole tuned to GMRS frequencies does it hurt to make that five wind four inch loop for good measure for my Midland MXT115 radio or don't worry about it. I am new and starting out and do not own a good antenna analyzer yet but plan on doing so someday in the future.
The same rules apply when using a J-Pole style antenna for the GMRS frequencies. I'd recommend the choke balun if you can do it.
@@KB9VBRAntennas I put the 5 turns at a 4 inch loop on my LMR-240 cable from USACOAX. Everything seems to work great. I will do a video soon on the install of the GMRS radio in my Polaris Ranger of your antenna and the cable. Excuse my ignorance but what is the magic math and science behind the 5 turns at 4 inches close to the antenna. I get the increased resistance it causes. Just curious about the reason for the number and diameter of the turns.
Thanks
Kevin
Wait! did you say energy radiates into the Aether! 3:50 So TESLA is Right Aether force is REAL!
Have you ever known Tesla to be wrong?
I have an ldg ru-9:1 in on a long wire I get some qrm could I insert the mfj 915 isolater on the coaxial and would it help with the qrm.
Possibly‚ it depends on what the QRM is. If the QRM is man made like electrical noise the isolator may help filter it out. But you may be better off by first trying to figure out what the noise is and if it is coming from inside your home or another source. Once you know the source of your noise‚ the better able you will be to remove it.
Iam trying to install a HF rig in my truck radio is a Kenwood 440s it has internal tuner also have an LDG external tuner the antenna is a MFJ with the wander lead I get the antenna tuned then it changes usely after I key the mike or turn the transmit power up. Do I need a choke or balun for this ?
Possibly. If you are using an external tune, the internal tuner in your rig should be turned off. Otherwise the two will fight against each other.
Good video.
Thanks!
So, would you advice using a balun on 10 and 11m using a 9ft tank whip, mag mounted on a vehicle using Ultraflex 7? Thank you!
mokotram
Would it be a mistake to use a common mode choke when using an automatic antenna tuner? It seems to
me that the tuner needs the returning current feedback to lower the swr thereby maximizing the antenna
rf output?
No still use a balun. This will reduce the common mode current on your feedline, which in turn will mean your tuner has to work less hard anyway
Thank You
Why Ferrite Mix 33 over Mix 31?
Both Type 31 and Type 43 mix ferrites will work for VHF frequencies, but Type 43 has better common mode suppression than Type 31 at the higher frequencies. Both will work, but you can by with less individual chokes using the Type 43 mix ferrites.
So the best choice of ferrite bread would be the highest impedance at radiated frequency (e.g. 400 Ohm at 433mhz UHF should be fine)? E.g. this example:
cdn.lairdtech.com/home/brandworld/files/28B0315-100.pdf
How to chose ferrite bread for higher frequencies e.g. wifi 2.4Ghz when most datasheets just go up to 1Ghz... ?
Would the 28B0315-100 be ok?
I have a question, if anyone would be kind enough to answer :) I'm not a 'Ham', just an amateur that likes pratting with antennas for receive only say, airband... So, would my diy dipole for aircraft freq work better with a 'choke'? Does an antenna that is optimum for transmitting, automatically translate into being at optimum for receive also? thanks :)
The choke's primary purpose is to keep RF energy off the outside of the feed line while transmitting. But it can have some benefit with receive only antennas, mainly cutting a bit of the receive noise. You won't notice this noise much with FM, but it could help with AM and sideband modulation reception.
thanks very much for replying quickly :) I wondered if it would help because it's the balanced-unbalanced thing (receiver is 50Ω), then again - I guess that's a balun? I might try both then :)
Not convincing to me I'm afraid. If you make a coil of coax, both centre and braid are coiled and both will act as chokes to RF. Why should the braided part be more of a choke than the centre conductor? The RF energy travels on the surface as he explained (skin effect) so can't see the value.
Peter, in a sense you are correct. But consider this. The purpose of the outer braid is two fold: it creates the return path for the electrical energy as part of the RF circuit, but it also provides a shield so that the inner conductor doesn't radiate. It works like a Faraday cage. In coiling the coax the inner conductor is protected by the outer braid, thereby not creating the inductance. The outer braid has no such protection, so the inductance is present in the coil which increases the impedance, stopping the flow of return RF energy.
can I put 43 material beads on coax, where near radio or antenna or both, how many 5 10?
+Geronemo Bauer Either type 31 or type 43 ferrites are suitable to use as a coax choke. The Type 31 is good for HF and VHF applications, while the Type 43 will also work with UHF frequencies. The number of beads depends on the frequencies for your antenna. Lower frequencies will require more beads than higher frequencies. For VHF, 3-4 would be sufficient. With an HF antenna it could require up to 10. Beads only need to be placed near the antenna end of the coax and not the radio end.
Built a 40 Meter NVIS dipole, the article I followed said to do a balun- 6 turns at 6-8" diameter. Is this correct? I'm using 49 ft. of RG-58U total length(including balun), with RG-8U to run to the station. Anything you would change in this setup??
+Steve Tomlinson With RG-8U I'd go for at least 7 turns in a 4.5 inch diameter circle. ideally for 40 meters, 10 turns of coax would give you the highest level of impedance on the outside braid. Here's a chart that can help you determine how many turns of coax you need for your antenna based on coax type and frequency: www.karinya.net/g3txq/chokes/
+KB9VBR Antennas Isn't RG8-U too stiff to turn onto a 4.5" diameter? Thought maybe you meant the RG58-U. Thanks for the insight..
+Steve Tomlinson RG-8U should be flexible enough to bend that tight. Although some brands of cable may be stiffer than others. Worse case scenario, you could use a lighter weight cable to build your balun and just connect it in-line with the rest of the antenna system. At 40m, your losses would be minimal.
+KB9VBR Antennas My new DX Engineering coax is really stiff, but I found some older 8-U that will work. Thanks for your help..
Thank you, KB9VBR, I do have a question. Does a BALUN replace the Ladder-Line?
Well, I do have a question. NORMALLY a G5RV antenna is supplied with "Ladder-Line as a feed line" IF you install a 1:1 balun. It has a SO-239 Coax connector. Can you connect the coax directly to the BALUN? Is the ladder line now useless?
With a G5RV antenna, the ladder line is actually part of the antenna. At the lower frequencies the ladder line radiates. That's why the line needs to be cut to a specific length. At the end of the ladder line you should have a 1:1 current balun and then feed the antenna with coax. I wouldn't attach the ladder line directly to the tuner as that could introduce RF into the shack.
My question WAS. Do you connect the dipole WIRES to the 1:1 balun in the center AND connect the feedline coax directly to the Balun?
Thanks for the clarification. No, there shouldn't be a balun in the center connector between the dipole elements and the ladder line. This should be a direct connection. The balun goes between the coax and the ladder line.
I'm confused. The G5RV has a coax connector. (How would you connect a balun to a SO-239?)
Inexpensive G5RV antennas, like the MFJ-1778, have a direct SO-239 connection between the ladder line and the coax. This will work, but you run the risk of RF energy traveling back down the outside of the coax feed line. If you are having trouble tuning the antenna on 40 and 80 meters, this may be the reason. Removing the coax connector at the end of the ladder line and replacing it with a 1:1 current balun, like the MFJ-918, will increase the antenna's performance on those lower bands.
Blink brother Blink!!
Conventional wisdom states that antennas like the J-Pole work best if you put a few loops of coax near the feed point. But why is that? My latest episode of Ham Radio Q&A delves into that subject and delivers the answer. . .
th-cam.com/video/zpUSe0yrxjs/w-d-xo.html
KB9VBR Antennas Thanks for the lesson. Just found your channel. My ability to post is screwed up, so I`m commenting here.Joe KC3BXZ
KB9VBR Antennas
Good Job thank you KE0EOB
lmr-400 on an aluminum dual band j-pole. Do I need just one Type 43 mix or more and how do i calculate how many I need. thank you.
Ugh on the explanation of electrical and rf energy... SWR is much more than just rf going back down... ugh...
Ugh
Great info! KM6IKH 73
SWR is a differential mode measurement and has no effect on common mode current.
Air wound chokes are narow band and are most effective at their self resonant frequency. Too many or too few turns can make common mode worse. Let's say the feedline common mode impedance is net inductive. If your air wound choke is net capacitive, the choke can increase common mode currents. W8JI has a nice white paper on this.
Model a 1/4 wave ground plane with (4) radials and then add a vertical 1/4 lambda wire on the shield side pointing down- you will see a lot of common mode current. (4) radials are not sufficient to get rid of common mode.
You canot say that type 43 is the best ferrite material. For broadband common mode impedance you would like to select a material that will display large resistive values at the frequency of interest.
A common mode choke on a DC grounded J pole, if designed correctly, will attenuate feedline common mode, but will do nothing to common mode on the metal mast.
In summary, way too simplistic a discussion of baluns, UNUN's, and in some cases incorrect.