Building a Half-Wave End-Fed Antenna For 6m, Part 2.
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- Опубликовано: 8 май 2021
- Part 1: • Building a Half-Wave E...
Puzzling results building a transformer to adapt a 285cm military VHF antenna (incidentally a half-wave on 6m),as my chosen 49:1 gets reduced to a 12.25:1 when mounted on the radio. Then upside is that it works fine and improves the performance of my PRC-351. By how much remains to be tested... My field-strength meter test was thus invalidated and this experiment left me with more questions than answers. Maybe some of you experts out there have some insight and suggestions? In any case it was my first foray beyond the 10km limit, now that we can travel up to 30km. It was an excellent opportunity to meet up with my friends again and play radio in the mountains; beats watching TV any day!
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The length of the secondary winding's wire adds to the length of the antenna, from my experience. All my 6/10/17m efhw wires show that. When the length of the secondary wire at the transformer is, say, 40cm, your antenna wire should be 40cm shorter, in order to get it back to the resonance. When the number of secondary turns changes you have to adjust the length of the antenna wire accordingly as well. 73, om1zz
Glad to see Part 2 get posted. I came across part 1 a while back, which prompted me to build my own 6m EFHW to go with my Yaesu VX-7r. I used an FT-50-61 core with 49:1 winding and a bit over 9' of wire for the radiator. So far I've managed 3 QSOs on SOTA activations, one that was 63 miles point to point, the other two being a mere 25 miles. The best part, however, is that the new antenna is much more compact than my previous 6m J-pole. I can get the entire "station", radio/antenna/coax/throw-line, in my pockets.
The auto-transformer you build works better on HF then on VHF. On VHF (6M) you can use a simple L-C network. For example to transform from 50 ohm to 2500 ohm use: L = 1,1 uh and C = 8.7 pF. Use an air coil inductor and you can use a short coax cable as an capacitor. The performance will be much higher. 73 PA7N Erwin
Definitely, a toroid on 6m is really pushing it! Thanks.
Excellent post enjoyed it immensely.
Always enjoy your antenna building and balun building videos Gil. Well done.
Thanks Julian. Using a toroid for 6m is pushing it... It works, but must be a bit lossy...
Thanks gil
According to the toroids info site, a 7 turn over FT240-61 core gives an impedance of about 2650 ohms at 50.1 Mhz. Perfect for EFHW antenna.
Building a Half-Wave End-Fed Antenna For 6m, Part 2. 😁
😊👍😉✅❤️😍🙏🙏💋💋 terimakasih , videonya sangat bermanfaat sekali
Good job you didn’t let the glue loose too early Gil 😁
Hard to resist!
Awesome de YC2VOC
10:48
common mode current is low, but anyway coax acts as a counterpoise. And efhw impedance depends on counterpoise length and placement.
Nice setup as you say just luck just as long as it works doesnt matter why
Please, a couple of ideas and ect. Would it be possible to measure the impedance of your antenna at resonance (not with the toroid, but the actual impedance of that tubule antenna ? That way you would know more about what you need to match to. Also, That phone call at the end. Could you try turning off the special CC setting and letting us try auto translate , as I would like to see if it would have translated the phone call.
Happy to see some fpv footage! ;)
ruclips.net/video/EveETJnHrEA/видео.html
@@RadioPrepper Nice view! ;) I'm a bit jealous of those mountains! :)
Not even the best looking ones around!
Gil, another great video and mystery. Love the bushy beard and hat look just throw a Colt Navy into your kit and you are set!
Well, I have an 1897 Peacemaker, will that work?
@@RadioPrepper absolutely.. over here in Idaho it's a tad easier to get cap and ball over cartridges currently 🥺
Good experimentation and trial & error. As a past user/planner of this radio I'm not really sure why you got the results you did. Our conventional whip antennas/GSA/elevated GSA and inverted V antennas were just standard.
The location looked pretty good for 'Take-Off' and angles and slope.
Nice job.
Thanks. I will get a GSA eventually...
There is a site/list where you can find a torroid/windings and a piece of coax (rg58/teflon, on average 1pf/m) to get a real transformer for any frequency for a half wave. Sorry cannot produce this list directly. My 20m EFHW was made like this. My 40/20-10 is made on the 49:1 mechanism.
6:30 stunt mode enbladed ;) nice qth/p btw.
Excellent, I've been looking forward to part 2 :) Have you tried the 12.5:1 transformer on wspr or FT8 to see what the coverage was like on 6m?
Hi, at this time I have no radio that can use those modes on 6m, only FM.
I would be interested in what other people think of us who experiment with wire :-)
73 Bernd
I might make a video about experimenting...
Hello Gil, alias Doctor Glue. Nice Setup and how many OM are there? Wow! I wish you some nice sunny days at the mountains. =)
73 Jan / Germany
Thanks Jan!
You need to use a VNA to measure resonant frequency, SWR, impedance, etc. across the 6 meter band. That is what I use when building and setting up new antennas. 50 MHz is high for toroids.
I did, and it is at the very limit..
If you are trying to prevent internal damage in the transformer box try using polyester batting to cushion the transformer in the box. The batting can bought in bags, or could come from an old bed comforter, or any plush toy for the cost of nothing. If you think it may melt with your power levels, try fiberglass insulation (with gloves). You are the only ham I know of using epoxy in your enclosures and it always seems to ruin them. But of course the squirt of hot glue you used will work too.
Good one thanks. It won't melt with 4W 😉
I would have never expected that low of a feed point impedance. I figured 49 to 1 would be just right.
What I did not see was a 100 pf capacitor shunted across the input of the UnUn? What was your thought on not using one?
Nice video. Barry, KU3X/QRP
I don't remember, LOL.
Hey Gil, the results you got from removing toroid windings were strange. What material are they using in that case? As an Elmer and MIT Electronics Engineering grad by way of being an Air Force Col., told me repeatedly, radio is a black art.
I agree, strange.. The case is probably aluminum... The toroid is about an 9nch from it in the plastic box.
Interesting. I only have FT140-43 toroids here, but will try to remove turns on a 49:1 as well to see if swr will be better on 6m.
Please let me know...
@@RadioPrepper Update: Works like a charm. Well, almost. Best SWR I could get is 1.5:1 but thats good enough.
That is very good!
G, thanks a lot for another fine experiments vid! What do you think would happen if we replace the ferrite toroid with a normal metal bolt, the same size, then wind the wire around it? Or, around a bunch of washers of the same size stuck on a small pile with paper between each washer (if it is needed that the metal should be not homogenous chunk-I remember when I was young transformers were made of flat metal plates stuck in a pile, probably varnished each for separation..). I’d try but have not a single measuring equipment. Cheers!
I don't know...
@@RadioPrepper let me (us) know if you try pls, and will vise versa. Would be nice to not need to order ferrites.
I have a schematic somewhere for a coil based solution, will look for it..
Surely, all you need is a half wave dipole or a half wave whip? It's a clansman so get the matching clansman, round spike antenna?? Also The clansman is an FM only radio you need an antenna tuned to the FM part of the 6m band.
Yes. The only advantage here is that I can unfold and mount this antenna in ten seconds..
Well, sometimes you just need a little luck. 🍀
Why use a ferrite core at all?,.. an air core wound coil & variable cap would be easier,
Probably yes...
How much coax between the radio and the transformer with the transformer mounted to the radio?
An efhw requires either a counterpoise of enough coax to act as one of you get bad swr. The end feed point of a half wave is a VERY high impedance. Taking off turns does not match the super high impedance. Your results are suspect.
No it doesn't. Not at such a low power. A half-wave radiates practically all of the RF.
Just a few thoughts and ideas... Have you measured the velocity factor of your radiating element material with something like a Nano VNA? Radio waves travel slower than the speed of light through any element mediums and that will affect the true "1/2 λ" length vs what the math "says" it should be with a tape measure. You'll need to measure the "exact" length of a test piece of your radiating element material to measure the VF including a separate "short load" calibration of any jumper wires used to connect to both ends of your element material so they are zeroed out of the velocity factor for your element. A radiating element made out of say a copper or aluminum pipe will typically have a wider and flatter bandwidth and SWR than just a small wire, the wider the diameter the better, not that a roughly 3m pipe is "easy" for portable use but you might have some luck with very heavy gauge wire like for large car audio subwoofers as a radiating element?! 73!
It certainly would be more accurate to measure it, but I just don't bother..
@@RadioPrepper you may want to consider doing it at least once, it would help the antenna be more resonant with less "guess work" by clipping little bits off at a time and checking the SWR (and only to find "OOPS I clipped a hair too much off!"). 🤯 😁
True...
I am no antenna expert, but the general equations for antenna resonance, antenna radiation resistance, and empirical measurements of SWR, etc. don't necessarily account for antenna materials, configuration, and the local geography (i.e., the terrain). For example, I would be curious to see what your measurements are if you relocate your military rig and antenna to a location closer to sea level. It appears to me that your geographical location for testing your antenna and unun was in a mountainous/hilly region. Just like the old adage for real estate values, I perceive that antenna performance is very much influenced by "location, location, location." Great video, as usual. 73 de AE5ZX
Absolutely right.
I think you will find that the height (HASL) will not affect the antenna to any degree. Being close to a shore will change the ground conditions, though. But this has nothing to do with tuning the antenna and coupler.