End Fed Half Wave Antennas VS Random Length End Fed Antennas
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- เผยแพร่เมื่อ 26 มี.ค. 2017
- Here's a few antenna matching devices I've gathered and some experience with the antennas.
CAPACITORS ARE 220 PF each and in series.
Interested? Join our FB page... End Fed Half Wave Antennas at / endfedhalfwaveantennas - วิทยาศาสตร์และเทคโนโลยี
This is one of those presentations most of us should bookmark and rewatch at the end of winter and mid summer to renew our understanding of important principles. So many people glom together all end-feds not realizing there are a few critical differences. Winding ratios, capacitor or not, counterpoise or ground and antenna length. Also, did you pick up where Steve shows the "random" lengths? They're not random! So pay close attention to the details. A random length end-fed for multi band operation and a EFHW for a particular band or an odd multiple. You can force an EFHW to do all bands just as long as you're willing to lose power as heat & sacrifice the transformer.
Wow!! Mr. Ellington, you did a SUPERB job of summarizing the different commercial bands of baluns, along with your own homebrew build! As Glen, below, points out, that this invaluable info needs to be 'bookmarked' for future referencing! Yes, what you accomplished is the VERY BEST that I have ever seen regarding this subject!! I THANK YOU for such an in-depth 'study'! Your schematics are the BEST, as well to help show what, and how, the physical/electrical construction was undertaken. 73's, Ron, K6PAM
Thank You Steve - for the presentation you gave us. Well done and I really appreciated watching it a few times.. Cheers 'n 73
great video, nice and clear. and concise... no robo voice, no rap music.
Steve-
Very informative. This video answers a lot of questions that I've had about end fed antennas.
Thanks for posting.
-Jaime N5NYB
Excellent overview - brought me one step closer to understanding the long wire/random wire/EFHW thing.
Probably your best and most informative video. Thanks for putting this up online.
Thanks Steve you've just answered my question on your previous video...very informative indeed.
What a cracking simplified explanation. Very good.
Fantastic explanation and really demystifies everything I was confused about on the impact of earth ground on these antenna types.
'Earth ground's are typically easier to deal with, length not being hugely critical as with radials in the air.
Great informative video. Well done. Thanks for taking the time to make and post it.
Barry, KU3X
Splendid video. Thanks for making it and buying all the ununs/baluns. Yeah, those "long-winded QSOs" are going to give these devices a workout on 80m.
I like your presentation a lot and thanks for the review. My neighboring ham friend and I built the ARRL 49:1 UNUN's and later I purchased a 2KW Balun Designs 9:1 UNUN. I haven't had the time to get set up to transmit yet, but, they both receive on the 68 feet of wire that came with the ARRL kit. I like the construction of both of the units well made and strong. Chuck / W7HDF.
Wow, Great roundup!
Very nice. Answers a couple questions i had.
Best explanation I have heard.
Good descriptive presentation regarding design aims. Thanks.
What a great video. Very informative. Most people think these things can handle 1500 watts continuous ......none do and it looks like you found that out. Another popular core material is #52.
Thanks for posting such a great video.
Barry, KU3X
Yes we converted to 52 mix a few years ago. Power is still time limited but much longer than 43.
Awesome video. Thanks. Great insights and explanations
Nicely done sir..... clear explanations and I am a member of the Facebook group. Glad you mentioned it. 73's de KF4LBG
Thanks for the terrific video, Steve. I use a compact 9:1 unun to supplement my 4010 efhw. Specifically, I bypass the efhw transformer ( covered in another one of your videos), clip on a few feet of additional wire and connect it to a 9:1 unun. That enables me to add 30, 17 and 12 meters, as well as 6 meters if I shorten the additional wire, all with SWRs between 1.3 and 2.3:1. As an added bonus, the additional wire and unun still cover the regular efhw bands (40, 20, 15 and 10 meters) with SWRs in the same range.
Quiet possible however the low swr you are getting is due to high ground losses so what you are seeing is deceptive.
@@n4lq Maybe, but it seems to be getting out OK.
Sure it may seem to be getting out ok buy you are still loosing lots of power whatever your ground system is or at least in your house wiring. Keep in mind that it take 3db in loss to even hear the difference but you are probably loosing much more. Still I have no doubt you will make plenty of contacts.
Congratulations!!
thanks for explaining the windings!
This looks like what I am going to start with. (MyAntennas EFHW-8010) It makes the most sense with my house and yard situation. I got my General in April this year and I have no HF rig. I am looking at either the IC-7300 or the FT-991a. Since I already have a FTM-100 in my shack I am leaning towards the IC-7300. I am also looking at getting a SDR Play RSPpdx unit before the IC-7300 to familiarize myself with the HF Bands before I jump into transmitting. I hope to take my extra sometime next spring as my book expires sometime next summer. I think getting some experience with HF is going to be a must.
OK. Thanks for the info. Yes you can hear different opinions. I have also this antenna. My coaxcable is 28m long. Then it should be I think work.
7:38 - Each coil winding element needs to be wound tight for two reasons. 1) All of the inductance parameters need to remain stable and not move as a result of possible thermal dynamics 2) Tightness helps prevent inter-element capacitance (the spreading apart or the squeezing together of the elements in the winding thereby possibly changing its capacitance. Free changes in LC are undesired variables that can effect the transformer's performance even with the correct winding ratio and therefore also the SWR at the frequency used.
This video is very informative. Have you ever compared end fed half wave performance with a resonant dipole at the same height? End Fed half wave vertical vs. resonant vertical with raised radials? Is there any benefit to a wire counter poise?
Steve, love your videos, some of the things you explain better than in other videos of the same subject. Thank you for that. My question is, I don't need to run 3KW through my unun, do I need to use three toroids? and if I only use two, what else changes?
Great video. Thank you
Nice video Steve with great information. Well done. I just joined your Facebook Group.
73,
George
K2WO
Orlando
I've had the same experience with Mr Becket's end fed random wire QSO King - "...it woooorks.... and you *CAN* make contacts on it, but...." - pretty much sums it up. It DOES work in a pinch, if nothing else is available, so long as it's feed point is high up and it's laid out in a straight line, but so does a coat hanger. :D
Fantastic video. Learned something here.
you answered so many questions thanks.
Thank You. Now i finally understand what this type of antenna can do and more importantly, how it does it!
I think the EFHW has its place: ie when you can only run a wire from your operating position because the real estate only exists in one direction. Or if you want to make a half wave vertical on low hf bands like 80m ... A very high tree could open interesting possibilities. However if you can run your wire so you have a dipole, a balanced line and balanced ATU will be better in a lot of cases. So many factors. Desired launch angle... do you want NVIS? Do you want long haul propagation? I think thats EFHW as a vertical as well as a centre fed dipole would be good to switch between
Thanks Steve, great video. I used the info to build a couple of models (2 and 3 cores) of the 49:1 transformers. I felt it appropriate to test the transformers directly as components before putting in the work of actually installing an antenna. This is easily done with a 2-port VNA and putting two transformers back-to-back. . I got enough toroids to build two identical transformers of each design, but got lazy and decided to run a test with the two unequal transformers back-to-back. Of course, they are both supposed to have the same ratio, but one might have greater loss than the other. It turned out that the combo lost as much as 4.2 dB on 80m and almost as much on higher bands. That's a couple of dB per transformer, not good! Then I tried it without the capacitors. Now the two transformers together lost only 1.6 dB on 80m, with similar results on 40m and 30m. 20m was higher, about 2.9 dB; 15m 4.2 dB; 10m 10.4 dB. I need to re-run the tests with identical pairs of transformers, but already it looks like the capacitors are added in the commercial units in order to claim reasonable performance on all the bands, while better performance can be achieved on the lower bands, at the expense of sacrificing the high bands, by removing the capacitors. The resulting lower loss on the low bands might make a big difference in power handling (this remains to be seen in practice).
In case a less experienced reader gets the impression from my comment that the commercial models using a capacitor are no good, let me clarify: Hams often use inefficient antennas that have losses of 20 dB or more, and still report fantastic results in actual contacts. Conditions and propagation cause that much variation. In this perspective a couple of dB is not much of a loss, and having "all" bands covered is indeed very nice! In practical use, the loss may be more likely to be noticed through overheating than from signal reports. Of course at moderate power, overheating may never be experienced.
Hello Erik. Others have used VNA's and gotten similar results. Try using identical back-back transformers and measure power in / out to a dummy load and see how much power is actually lost. Typically I hear 1db or so with the greatest loss on 80m as you said but usually a bit over 1 db. I find the capacitor has no effect anything below about 14mhz. I don't see how it could influence power lost on the low bands. When you do some more testing drop me an email. I'm ok on QRZ.com N4LQ
Hello Steve. I take back my statement that the cap's hurt the low bands. I had checked connections for tightness and didn't see any change, but when I took it all apart and put together again, I couldn't repeat the observation. I suspect my stainless steel hardware which may have had some oxide or silicone on it. I will email with numbers.
Good info to understand these magic boxes. :)
I believe you need about 3:1 for a 450 ohm antenna - remember the formula for impedance transformation involves a square root.
9 : 1 according to all the manufacturers. Well explained in books 👍
Great video thanks
Great video Steve ;-) I have a question. What SWR had you on the bands with 49:1 transformer endfed antenna? Did you need an antenna tuner? Thank you. Paul OM0ET
Generally the rig's internal tuner is all that's needed. SWR will normally be below 2:1 on all bands except 60 meters and the high end of 80m.
@@n4lq thank you very much Steve 👍 73 and good luck 🙋♂️
Looks good😁🌞🌎👍
What cores did you use on the three core 49:1 high power. A lot of articles I read says they use 52 mix but it is not supposed to be so good on 80 meters; they however did not mention a mix for high power covering 80-10. One thing to remember about winding cores it is the turns that go through the middle that count. It looks like 13 turns on the three core . stack. It seems like the article I have suggest 13 turns for the larger size?
Great video, thanks!
what core did the 1000 watt use . ? wanting to go this way . but wanting to build one myself. thanks
Hi. What about the frequency response of the auto transformer with a 3K ohm resistor attached? Mine have a flat 1:08:1 on 3.8Mhz, 1.2:1 on 7.150Mhz, 1.61:1 on 14.175Mhz, 1.65:1 on 21.225Mhz and 1.09:1 on 28.400Mhz (with 100pf cap installed, if not is around 2.7:1). Great video! Thanks!
I sure am glad I made my own. Those My Antennas are PRICEY. I bought the pieces and built my own for a fraction of the cost and it came out better looking! lol
That’s correct, the radiated power that your not sending through the transformer is going straight to the ground. Therefore decreased efficiency.
Very good video
Thank you so much!!!
*** EFHW 80-10 Antenna very good !!!
Hi Steve, really enjoying your videos! I want to learn Morse code, what method would you recommend? You also mentioned somewhere that you have sold your Elecraft K3, what rig would you recommend most for Morse primarily and also SSB?
Kind regards,
SImon
M0SYS
You might want to check out CWOPS. They can help. www.cwops.org/cwacademy2.html
As for rigs... The IC-7300 is the best deal going.
Steve - I've ordered the base model (EFHW-8010) for my IC-7300. I run CW barefoot all day long. Sound ok?
Steve,looking at the one you built, I have a question. It looks like you pass through the center 6 times, and then cross over (does the cross over count as a loop since it passes through the toroid?) And then it looks like you make 6 more passes through the toroid. so is this a 1:36 auto transformer?
You need to count the primary too because it and the secondary are wound together. I count 7 turns through the center and yes count the crossover plus add the outside ends as 1/2 turn each. Total is 14 or close to it. Counting just the inside wires doesn't give the whole picture. If it goes down the center then back up the outside, inductance is added for however far it passes the outside too. Note that on the first 7 turns I bunched up a couple of wires and it's hard to see both turns.
Excellent Steve I'm glad I've came across this channel loving the videos .I have a question if my end fed antenna is at say 840 ohms.and my rig is 50 ohms . how would you calculate this to know what balun I would need .would I just 17 x 50 = 850 ohms ?
Turns ratio is the square root of 840 / 50. Note that secondary turns count includes the turns wrapped around the primary.
@@avt3216 brilliant Steve I've did one with 130ohms fed into 50ohms coax .but I used my two inductors in series .in which case my coax inner inductor goes between the two coils and earth of coax to ground .my capacitor in parallel with two series inductors .works out nicely thank you so much Steve brilliant .these two coils in series are just voltage dividers I assume ?.
How well will a metal roof work, after a recent hurricane I actually covered a damaged existing very heavy roof with a second layer with the two coverings being screwed together reattaching both layers using metal screws so they are firmly attached?
Excellent comparison of make ups between the two types. I noticed the second auto transformer you showed was made with a 3:21 continuous winding, which still works out to 1:7 and 49 to 1 ratio. Logically it could also have a cross over at turn 11. What do you think about using 4:28 winding's (which is still 1:7) and should still be a 49 to 1 ratio? and perhaps with a cross over at 14 turns? or would the extra turns of wire material affect the outcome unless it were on larger cores?
It's a matter of inductance. For 160 you need the extra primary turn 3:21. For higher bands you need less inductance 2:14. Crossover is most helpful on the higher freq. bands and doesn't matter much on the lower ones.
@@n4lq Thanks, you've cleared up something i was wondering about.
Hey,
hooowww I thought you were let see show the antennas in action?
That would also seem very interesting to me!
oh well better luck next time.
success and best regards from the Netherlands!
Rob.
"Hint...Use about 25 feet of coax or more to act as a counterpoise." thanks very much for your answer. Does one need to worry about signal loss/ attenuation with a longer coax vs say a 20' coax? I just bought a Tecsun pl-660 and am wanting just to enjoy short wave listening like I used to years ago. Thanks again, Vic
No worries about coax until you get up to over 100 feet and VHF then you need to start paying attention to the type of cable.
Balluns are used to take an unbalanced (coax) feed line to match with a Ballanced twin lead antenna?. Correct me if iam wrong?, I'am new to the ham radio hobby.
Kind regards Eric Dee
THat's correct. What a current balun (it is not really a Bal -un because it does no conversion) does is via the inductance of the toroid when the current in is not equal to current out (yes that can occur if some of the current on the inside of the coax braid goes down the outside out of phase) ... it forces the current in both legs of the dipole to be the same. This imbalance could be caused by nearby entities (eg metal siding) or because the antenna is slightly longer on one leg than the other. There is also a Voltage balun that has the same effect in theory. This is a trifilar wound device. It does a conversion from unbal to balanced as well. The downside is that it effectively puts a three inductor short across the received signal. That a VB that works well at 30 Mhz might make the Rx a little deaf at 3 Mhz. Current baluns are the most common types for going from coax to an antenna. If you wanted to go from a 50ohm bal coax to 300 ohm twinax You'd use a 4:1 Bal to unbal which is a bifilar design. You can't get a precise match between 300 ohm and 50 because there is no such thing as a 6:1 balun. In terms of core sizes most Vendors agree that a FT 140-61 core is good to 100W PEP SSB as a current balun. The core in fact carries only tiny flux from winding assymetry if the antenna installation is clean. However under under assymetrical conditions it will.
I was trying to see where the Capacitors were soldered to.
one side looks to be soldered to the ground going out.
Where is the other side soldered to...
Very interesting this is what I need for my balcony I’m on the top floor (5th) and something end fed is what I have in mind I just applied to join the Facebook group and I would love to find out where to order the caps and the torrid core’s from ? anyway thanks for the video take care! 73 de ve3hip in welland Ontario Canada 🇨🇦
With the two twisted primary turns, the 1:49 transformer is NOT an autotransformer, it's a true transformer with two sets of windings. The two turns are NOT connected together at both ends, only at the bottom. I guess it COULD be wound as an autotransformer without the twisted wires and a tap at two turns. Would probably work equally well either way.
I home brewed a version of this transformer using two cores and a 100pf 5kv 'doorknob' transmitting capacitor. I used #16 wire, because that's what I had (and it was easier to wind than #14 would have been!)
For an end fed long wire a ground / counterpoise is not need if you matching network is above the ground 10ft and they do work well in a restricted space situation
Tnx again Steve for this great Video! Would like to see a video of you winding that 1:49. didn't quite get the way you wound it.. 73's de K8KEM
Ok I'll try to do that soon.
Thanks I'm moving into a new QTH and end fed or random might help me to be stealth
The ICAS rating of the EFHW doubled with the addition of 1 core. Yet it still got too hot with 500W CW. Cooling vs keeping dry sealed tightly.
ICAS is a bunch of bunk.... It takes 3 cores of 52 mix to be efficient enough not to reach Currie temp. when using 500w cw for long periods. With 240-52 mix I'm able to key down 500w for 15 minutes which is really good. The most heat happens on 80 meters. Other bands are fine.
Very good
If it keeps overheating maybe put it in mineral oil in a big sealed box with a circulation pump.
THANKS VERY MUCH
I wonder how this would work with if you made an EFHW fan dipole. I will have to try this. (40-30-17-12)
Also this answered my questions about the unun. I believe I will try a 43 foot vertical as I have heard good things about them.
Won't work at all. In fact you can't even put your finger near either end of the EFHW without wrecking the SWR. Fan's must be fed in the middle. 43 foot verticals work ok from 80 to 20 meters but they are too tall for low angles above that. They also need lots of radials and the tuner needs to be at the base of the antenna otherwise you suffer much RF loss in the coax.
The windings must be isolated from each other and the coils. I'm getting ready to build the 49:1 EFHW. I'm going to have the long wire in sections for each band. Using terminals to disconnect and isolate the sections not wanted.
Okay you said this a year ago. I'm curious as to the results?!?!??
Great vid! Which in your opinion works better, the 9:1 unun end fed, or the end fed half wave antenna?
By far the EFHW works better.
Thanks!!!
Michael Hilton sdr
Depends on what you mean by 'works better' ....
See 4:40 this video
Hey Steve , TU for ur research.. I duplicated 3 core/43mix and at 800 watts CW reached Curie Temp after 20-25 min, 500W CW No Prob..
Their specs show 0.5 Db loss that is 12% so at 50% duty CW and 500W is 30 watts about figures right since Curie Point for #43 is 130C !
73 de K2HZO Paulk
I would have liked to see them working in comparison
"ICAS" I can't always say.
I have the MFJ half wave end fed 10-80 antenna. I like the antenna but the swr is high on all bands especially 80. Even with a tuner all bands are around 1.8 after the tuner does it's job. MFJ told me just to use a ground rod with no counterpoise necessary. Any thoughts on this?
Lots of thoughts. That MFJ is not a good product. We have seen several connections fail inside the box. The vibrations seem to break them during shipping. I would stick with the Myantennas or Hyend brands. We would like to have you join our Facebook group for this antenna facebook.com/groups/EndFedHalfWaveAntennas/
Nice!
Steve,
What did you use for the Core? It looks like 3 magnets...if that’s the case, couldn’t you use 1 Larger Magnet with the 7 turns of the 14 gauge wire to accomplish the same effect?
Bill I think you should just order one already built from MyAntenna.com
Steve,
What did You Use to make your own device?
1) They are not magnets, they are ferrite toroids. 2) Inductance and turns ratio are what matter for calculating the number of turns.
Just trying to be sure but from what I see both the MEF-330 transformer and the one you wound are 13:2 and not 14:2 windings. That makes a 42:1 transformer which I suppose will work but give less than ideal matching.
hi steve, At 6:45 you say the capacitor value is 100 microfarad, isnt that really picofarad? In your video "Winding a transformer for End Fed Half Wave Antenna -- EFHW" at 6:50 you call it picofarad, so, which is it? I'm building this per your great video. thanks
Read description under the video. 100pf
ok thanks. I had ordered a bunch of those so thats good. www.ebay.com/itm/282636125854
Steve, at 6:45 the caps would most likely be 220 pf each, not microfarad, right? 73 Jan
YES 220 PF each...Sorry bout dat.
They are labled 221.
Hello Steve, Great video as usual. I am interested in the specifics of the transformer in the MEF 110 1k version. I can see in the video that it is NOT the same as the one for the 8010. I can see only one capacitor instead of the two 200pf.. also I noticed as you mentioned that the windings continue around the toroid in a clockwise direction. Can you describe specifically how the toroid is wound and what cap they are using please. I have one I wound already but would like to change it for 160. What length of wire do you recommend for the 160 version? I would imagine 260 feet or so?..Thanks and 73's.. de ka5wpm
I also have the same question... Anyone have the answer???
wonder what would happen if you tap a single wire into 49:1 instead of winding two wires together. will this work? this as well may allow some rheostat-style variable unun 🤔
What core are you using on your home built auto-transformer? I see that you are using three of them. And what wire do you suggest?
facebook.com/groups/EndFedHalfWaveAntennas/
@@n4lq And for those of us not on facebook: What mix(es) are you using?
Cheese cloth would be a better choice for those vents.
Keep in mind there are two different types of grounds. RF ground, and DC ground or electrical ground. When you’re talking the mirror image of the antenna or the other half of the antenna you’re talking RF ground. I believe some people sometimes don’t get that concept.
A question for my fellow hams. Under most circumstances is a balanced antenna better than an unbalanced antenna? I've been under the impression that a dipole are the way to go. I currently have a 40 m. Dipole over my house suspended from trees. It actually turned out really good once I got it moved around a bit. On certain frequencies I can get my SWR down to about 1.2 or 1.3 to 1. My goal is to build a 160 m dipole. But I have to coordinate with my neighbor for obvious reasons. 160 m band absolutely intrigues me. Ive heard guys a couple states away but the background noise floor is almost unbearable. 73s. Also, great video!!!
I don't understand the question "Balance in 10"....What do you mean?
@@n4lq sorry about that I was being lazy I didn't check with Google wrote from the voice recognition. I fixed the messed up part
The answer is no, balance is not the determining factor for "better". After all, an AM broadcast tower is totally unbalanced, not a dipole. The EFHW's advantage is number of bands covered without needing a tuner. Efficiency is actually pretty high. 160m is tough. 260 feet of wire! Otherwise it will need some kind of tuning system. There is a way to use the 80m version of the EFHW on 160m See my videos on that.
@@n4lq awesome thanks man.
Typically the more "metal in the air" the better, why a Dipole usually has an advantage, not needing as much RF grounding/counterpoise (not like station grounding/bonding). Being horizontal also helps eliminate QRM noise as most local QRM is vertical polarized. If you have a Nano VNA (like $60 USD) I'd look up video designs on how to build a "Bazooka" or "Double Bazooka antenna" for 10m-40m ETC and scale them up to 80/160m using _one_ Bazooka style element and instead of a 2nd pole use a 49:1 End Fed Half Wave transformer. An 80m halfwave element "might" give you 160m too?! but my "brainz is tiredz"...
The thicker or wider your antenna elements are, like thicker diameter copper pipe or even wider flat copper tape, the wider frequency bandwidth range you'll end up with vs a skinny arse little wire... That said, a Bazooka is an old military antenna design that uses copper braided coax and the benefits of the Bazooka style design is the copper braid acts as your main radiating element making it a VERY wide band and _REALLY_ quiet antenna as far as noise goes too! It then typically has either a tight coiled choke AKA "ugly balun" at the element base (usually for shorter 2m-10m antennas) or a short bit of ladder line soldered onto the tip for 10m+. Then see where that resonates on a Nano VNA, trimming a little off until resonant (BEST $60 you'll ever spend on amateur radio!). Something fairly cheap like RG-58 coax can easily be used for the elements too and the exposed solder joints ETC can be sealed up with liquid electrical tape over some adhesive lined heat-shrink to make it next to "Armageddon-proof".
I just like to call it duty cycle. It's close enough.
Hi I’m KP4ALM, were I can get those schematic for make those antenna
I'm kind of confused, a 43 foot wire against a goods ground constitutes a "sweet spot," in that several ham bands are in the neighborhood of being resonant, but are the expected feed point impedance of either a vertical or inverted "L" anywhere near 450 Ohms??? Isn't about a fifth or tenth of that????
Actually 43 is deliberately chosen to be NON resonant in order to avoid radical impedance's that are hard to match. This is a sort of an anti-sweet spot :*)
The EFHW's impedance at the end is around 2000 to 3000 ohms on all the harmonic related bands i.e. 80, 40, 20, 15 and 10 meters. This allows us to cut the antenna to length for the lowest band, 80 meters and provide a transformer to step this down to 50 ohms on all those bands. You are confusing the random length antenna with this one.
I suggest you watch my video that better explains this: th-cam.com/video/BpdpkUEW39o/w-d-xo.html
Were I not so dad-gum lazy about toroids I'd have spent a lot of days on this sorta thing!
*--VE6IU*
p.s. FWIW I liked tweaking so went QRP CW with fine dipole or maybe good vertical. What I //really// wanted to build was a big setup for 80m. I had lots of land, and lots of straight softwood trees for towers, so *_rhombic!_*
create video steve. Do you know how many winding the MEF 110-1K have? i seen 3 primary and 16 ore 18 secondary?
Thank you so much for answer.
73 Mark from Bavaria
3 primary and 21 secondary
thanks Steve, regards Mark
Tight winding keeps leakage inductance down. The reason behind winding it in two parts is probably to get input and output on the other ends physically. It also can reduce capacitance from beginning to the end too but I'd assume at HF frequency it makes no difference. On high frequency transformers it can make a difference.
Yes. The output tap needs to be as remote from the ground lead as possible. Just getting your finger near the output will skew the swr.
11:53 I.A.C.S. here would probably mean 1000 watts with a 50 percent duty cycle. ie rating for heat.
Even more confusing is some marketers use the XXX watts PEP I.A.C.S. term too.
Having fried enough things myself I ponder if folks ratings are real or are they some best case example too.
I think some types of balun configurations (current/voltage) have a higher loss when the VSWR is high thus the balun core really has to see even less I.A.C.S. power so is happy and not cooked. :)
If you have a thermal camera you can see the cores being hot, the leads wires and other parts too.
Another weird thought is IF a 1000 watt I.A.C.S balun if driven with a 1500 watt signal with a 1/3 duty cycle, would it be happy ?OK? ie is it just heat? or did the core saturate so one is really boxed in with little "headroom" above 1000 watts.
(*ICAS = Intermittent Commercial and Amateur Service)
They just make it up. I saw a test done for the Myantenna 2kw. He put 1.5kw into it for about 5 seconds...Twice and dubbed it ICAS. Yea right! Hopefully there will be a breakthrough because these things really work.
Just a stupid question (ok 2) only cause I'm not in the know lol,, but 1, why not oil filled like a paint can dummy load???
2, why not build these for sale?
I like ur design, seems robust compared to others, and I like integrity:)
Great video BTW!!
The problem with oil is due to the high impedance of the transformer. Oil will basically provide a short circuit due to its dielectric properties. Think of it as a liquid capacitor. I even tried using mineral spirits. It kills the transformer!
@@n4lq thanks for the quick reply!!
Ever thought of building these for sale?
Love the vids!!
To your knowledge, Steve, has there been any workups on a fan end feed half wave?
No because not only will it not work but it is not necessary. Another wire in parallel will totally disable the antenna.
@@n4lq Again, has there been any workup which support this?
@@JosephLorentzen Work up? Yes I worked it up. But why would you want to do it in the first place since it already covers multiple bands?
@@n4lq Eliminate the need for a tuner
@@JosephLorentzen YOU can model it, use MMANA-GAL, tell us how it goes!
I noticed the triple cores and understand that raises the efficiency from approx 65 to 85 %? is that correct?
I doubt if it's anywhere near as low as 65% but there is some difference in efficiency. The main factor is power handling capability and 3 cores provides a huge improvement.
I think in your case the capacitor is changing its value when heating thats why the SWR is changing
Nope. High temp. causes core permeability to diminish.
5:00 there is a big difference between the windings of both these 9:1 transformers... one got 9 turn like in the scematic but the high power one has only 7 windings and it is still a 9:1...
No, there is no difference. The turns ratio is the same. The total number of turns is adjusted for the toroid material and desired inductance at the frequencies used.
Should I have vent holes in the enclosure for 100 watts cw operation, single core? Thank you
Yes but not so much for cooling. A vent will allow moist air to escape otherwise when the transformer gets warm inside you will have condensation all over the internal parts. A single weep hole in the bottom isn't enough. A small vent like the one sold by Bud will do.