50 to 75 Ohm Balun Construction 1.5.1
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- เผยแพร่เมื่อ 5 ก.ย. 2024
- Documentary of the construction of a transmission transformer with a ratio being 1.5.1 power handling 1kW 100% duty.
This transformer can be used for matching different feeders or equipment in the 1-30Mhz HF region. I will be using this as a buffer transformer to feed a 4:1 balun thus creating a 6:1 balun.
I hope this is useful for someone out there. 73
Parts recipe:
4 lengths about 300mm of 1.25mm copper enamel wire
1 length of about 300mm of 1.7mm copper enamel wire
1 Jaycar LO1238 (Mid Perm) core warped with plumbers tape.
I was in need of a 35 to 50 ohm transformer to match up my 40m beam, wound up 5 turns on an FT 240-43, worked out the first try, nice flat response across the entire HF band.
Thanks for your fine tutorial
Clay, I4LEC
Thanks for the positive comment Clay. Much appreciated.
Hope all is well with you. A few folks are complaining that this is an Unun, rather than a balun, who cares. One would typically use this , at least here in the states, to help make use of the amazing amount of 75ohm cable available from the old cable industry. Its perfect for that. Hope you are able to keep making videos because considering the dates on these videos, you were definitely a little ahead of your time. Could it be that you have another channel with more videos ? Thanks.
I found the source document you were using.. Amidon W2FMI Transmission Line and Transformer Handbook. Thanks for sharing... I'm going to build a pair, so I can use RG-11 Feedline with a 50 Ohm Radio and Antenna.
Many thanks for this video,have a lot of 75 ohm coax,will make this ballun.Simion PZ1EW
So for what can i see, this is a UNUN and not a BALUN, I´m right?
Thank you for providing this. However, like many videos, the hardest part is left out. Trimming the ends, stripping the wires, soldering, etc.
I am new to making balun, with little knowledge of how to correctly solder the windings. Even though I have read the associated source document, it am still unsure. Can anyone post a comment about which get soldered to which, e.g. 3 to 5, 5 -? , etc.? It is unclear to me in the video.
What I see in your schematic it is 4:5 not 1:Sqrt(1.5) In a transformer n1/n2 = V1/V2 = I2/I1 = SQRT(Z1/Z2) or Z1/Z2 = (n1^2) /(n2^2) so for 50 to 75 you need turn ratio of SQRT(75/50) = 1.224744871 or 1:1.224744871 or 4:4.898979486 which is close to 4:5, but not exactly. So you have to tune your transformer a bit.
I am having trouble determining the order of the colored wires from the video. Could you clarify?
I am in need of a 50 to 75 ohm transformer such as this to go from 50 ohm feedline to a 5/8 vertical (75 ohms) antenna but for 6 mtrs. What core material should I use? Thanks in advance, Steve KD1DT
Jerry Sevick's, Transmission Line Transformers Handbook, page 12, says that the 1.5:1, 1-HU75, UNUN you are building, is a 75 to 50-ohm device in one direction but a 50 to 32-ohm device in the reverse direction. If this is true, I have just learned something, as standard transformers boost voltage in one direction but reduce voltage in the reverse direction. Maybe impedance transformers work differently. If you can shed light on this, please do. Thanks, Jack
Jack Cureton Sorry Bill I dont have the time...
I would like to build 1.5:1 balun (or UnUn) for my 100MHz 50Ω 7dBi Yagi. (Simple FM stereo dipole impedance is 73Ω in free space, but with other Yagi elements it is 50Ω - it is similar to JAMPRO J3YF antenna). Your SWR is worse for higher frequencies with 1.5:1 balun, so for 100MHz it will be useless? What is the best for 87.5-108MHz FM stereo? Folded dipole + coax balun 4:1 instead? Or Yagi with J-Pole radiating element?
sir you mentioned magnet wire ,what is difference between enamelled copper and magnet wire. regards
Thank you for this nice video! I do have a question. If you were to use this 1:1 Balun, what method have you chosen to check for common mode currents first before checking for VSWR? Thank you and 73's de K8KEM. David in Ohio
Can you use Wire from a transformer winding instead of magnet wire?
They are synonymous as far as I know, so you should be fine.
Have you built a 300 to 75 OHMS balun Sir ??? Coaxial rg-6 connection on one eng and a two lead wires on the other ???
kool video, how can I make 6:1unun?
Thanks for the video. Very well done.
Frank Kf4xy
Why are you calling this a "Balun" - is this an impedance transformer or do you intend to adapt a balanced load to an unbalanced load?
Right ReBus. I believe you can turn this into a BALUN if you connect the shield of the 50Ω coax (going to the green winding); and then put the center conductor of the 50Ω coax to the black conductor where he shows it at ground, and also make that one of the balanced leads at that point as well. If you know otherwise, please comment.
You tried air core?
First attempt at 1.5:1 has resulted in very poor performance. Not sure what is causing the problem. The SWR climbs to > 1.15:1 at 12 MHz, to > 1.25:1 by 18 MHz, and climbs steadily to >1.55:1 by 30 MHz, and 1.8:1 by 40 MHz. The resistance climbs fairly smoothly from 49 ohms at 1.8 to 79 ohms at 28 MHz, and then levels and drops through 40 MHz. The reactance climbs steadily from 1.8 - 14 MHz, dips back to zero by 18 MHz and remains zero through 28 MHz, where it then begins a steep and realatively smooth increase to 33 ohms at 40 MHz.
Something "muy mal" is happening here.
I've verified that I've used the correct materials. I checked each winding for shorts, opens, etc before making any connections. Verified that my turns and connections matched the buffer balun in this video precisely. Used the same meter, cable, connector, etc that I used in the 4:1 testing.
The unexpected increases in pure resistance are puzzling... (as is the reactance curve, too)
I don't know what I did (or didn't do). I'm puzzled. Will post back if I discover the issue...
+Clay Autery Dear Clay, I am very pleased with your work and result on the 4:1, let me also revise my notes on what I encountered during construction. It sounds like it is almost working just not as broad, I think this may coincide with Sevick's recipe. Oh its starting to come back now... Cores. I think I experimented with different core material and found that higher permeability was good for the 4:1 but a lower permeability was better for the 1.5.1 from memory when tested independently. However having said this when I used all 1238 cores and connected this together it provided satisfactory performance to 30Mhz, i.e. 1.1:1 1.3:1 vswr. I think I used a green core and it seemed to work good. A good way to check and play with performance of unknown cores is I used the thin strands from cat 5 lan cable as my test 1.5:1 cores. (much easy to use this thin telephone wire for experimenting) I think you are very close to sinking the ball. Try and just connect the two baluns " just for giggles" and see what is played. I will check my notes and get back to you, but I hope I have left some clues that can solve the puzzle. Again well done on the 4:1 really! And I hope it has put some muscles on your fingers. Beats using the hand clamps in the gym.. Also Teflon tape on the core is supposed to prevent the enamel copper wire from scratching.. and the teflon tubing just aids in keeping the wires together when winding.. I got a full day today so I'll check back tomorrow I hope this helps cheers .E
+remingtoncountry1100 Gotcha... Well, here's what I did... I clipped all the connections loose and took one turn off the core... (It was 5, if you use the conventional center pass count technique, and I reduced it to 4). Reconnected everything very carefully and deleted the use of tinned copper ferrules to join 2-3, 4-5, and 6-9 (on the off chance that it was creating some additional reactance... who knows). Just used tight lap joints with minimal solder for good connection. Double, double checked to make sure I was getting the wires well-cleaned of the coating(s).
Anyway, testing it... Basically, it performed "better". Still not broadband, and the pure resistances still went to 72 Ohms tops, but I raised the freqs at which the SWRs increased by about 2 MHz at the lowe end and about 8 MHz or so at the high end. SWR at 30 MHz was down by about .2 at 30 MHz (1.35 < x < 1.44.... Reads as 1.4:1).
This removal of 1 turn DOES tend to make sense, since the original Sevick design called for 4 turns rather than 5 (of course he used a completely different core).
I am going to grab some more 14 AWG Thermaleze, some different cores, et al. and play around to try and get a broader bandwidth. I'd like to hold the SWR to < 1.25:1 thru 35 MHz if possible, and eliminate as much of the reactance as possible and keep it as close to purely resistive as possible.
Time to do some research and math.
Anything you can find in your notes would be great...
I will hook this 4 turn 1.5:1 mod to the 4:1 and see what the Antenna Analyzer shows...
I have seen two cores taped together and windings wrapped around both, would that solve your problem?
Hi , i have an old MARCONI 100db step attenuator with 75ohm input and output..can i use this to change the input output to 50ohm as i will be using it for 27mhz?
Regards
Andrew
Just wind a balun for whatever ratio you need. The frequency is usually wideband. Refer and search for Jerry Sevic balun handbook and good luck.
Adding note here: Nominal characteristic impedance fro the transmission lines in this balun should be approximately 61 Ohms [sq. root of (50 x 75)] Actually some bit higher since the ferrite core'd dielectric effect must be considered. Just passing on what I learned today.
Learned that my 1st attempt failure is LIKELY due primarily to construction technique issues... windings not tight enough, wire spacing not consistent throughout (even though I made a ribbon with tape clamps), etc, etc...
Ordered the T-150-KC cores (coated) to try some experiments with winding techniques and varying wire coating thickness, spacing, et al to set impedance somewhere north of 61 ohms to see if I can knock out the wild resistance and reactance curves and broaden the bandwidth.
+Clay Autery Hi Clay just got in after an exhausting day. I will be busy for the next couple days and could not find my note book today. At the end of the day This demo show a balun that costs tens of dollars to construct and can handle legal limit in most countries and over 3-4 times legal limit in Australia. I just checked my 6:1 again it is 1.1:1 from 1Mhz or transmission power of 99.8%, or a loss of .010dB and 1.2:1 30 Mhz with a transmission power of 99.2% or .036 dB of loss at 30 Mhz difference being .6 TX power over 30M. By adjusting my spacing of the connecting wires I got almost 1.1:1 on 30 Mhz and yes I am using all the same cheap jaycar core. So in conclusion I have made a minor rendition to Sevick's W2FMI-6:1-HB300 by using two cores, (even 2 stacked cores) for the 4:1 section and using different brand cores than Sevick. Sevick also states this is a 1-30Mhz not a 1-52Mhz and states a flat response from 1-30, but no graph is shown in the text that I took the recipe from. Define flat? Is a table flat? to some yes to others no.. and I am not going to buy the latest and last edition this month to see if he added performance curves before he passed away. If you are chasing the extra performance and think it is worth the effort and a receiving station will tell the difference?, then sure fine go for it. This would be braking the 3 db rule of for sure.. For me and most, the difference in loss is minimal and wont seriously disrupt the transmitter and receiver path loss calculation to a point of concern. Yes I used to gold plate myself but pragmatism these days and accountants along with HR directors draw the cost benefit analysis formula out and stops engineers " over engineering " . Let me know how you end up with your project.
+remingtoncountry1100 I hate those kinds of days! Hope tomorrow is easier on you, even if you are super busy. Seriously, don't worry about making a special effort to hunt/look anything up. You are absolutely correct about the "over-engineering" or "chasing the last 10%" or whatever term is applied.
I could probably hook it all up right now and forget about it, and it'd work just fine... after all, it's mostly just being used to hold the SWR down a bit on a loop so the on-board antenna tuner doesn't have to work so hard, although it's nice to know that virtually all the power is leaving the radiator and not being wasted as heat. Bottom line for me... MOST of this entire exercise is for the sake of learning to understand "how the watch is built" versus "looking to see what time it is".
How high of per ability core do I need for 144 MHz?
Is it possible to buy a 1:1.5 balun for VHF/UHF?
Only vhf
can you suggest a circuit to match 50 ohm to 75 ohm at 400 to 600 Mhz
Hi, I am thinking perhaps coax balun may be more appropriate at these frequencies and something in line of D match sometimes called delta balun. I also recall an paper describing using a fat section of inner to outer tubing in the form of a "patch connector" to do it. The problem was the B/W was bumpy to say the least. Not sure on your application so I am merely humoring a couple of suggestions so you can do some more research. I hope that is of some help.
It's a little hard to see the phasing but nicely done.
What core did you use?
+Msagro5 Hi the parts list is provided in the video description, it is a china generic. Search jaycar and the part number. very cheap for local sourced.
This is UNUN not BALUN :-(
I believe you can turn this into a BALUN if you connect the shield of the 50Ω coax (going to the green winding); and then put the center conductor of the 50Ω coax to the black conductor where he shows it at ground, and also make that one of the balanced leads at that point as well. If you know otherwise, please comment.