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Author Topic: 80M - 10M EFHW with no variable cap  (Read 9997 times)

cockpitbob

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80M - 10M EFHW with no variable cap
« on: May 26, 2015, 11:04:32 PM »
There's a new company started by a former Cushcraft antenna design engineer that appears to have done what I wanted to but couldn't. A 1KW, 80M-10M EFHW coupler with no variable capacitor (like LNR Precision's couplers).  The price is steep($99), and it weighs 1lb, but if it does what they claim, it would be fantastic.

I've designed a 100W and 10W EFHW coupler similar to LNR Precision's (no variable cap to tune when changing bands).  I take a slightly different approach and don't have that "damping" capacitor across the primary winding, but essentially the same thing.  The best I could do is 40M - 10M.  I couldn't get one to go out to 80M or much beyond 100W.  Transformers are very tricky things.  The small ones don't have enough inductance to work at low frequencies (3.5MHz).  The big ones have too much stray inductance and capacitance to work well at high frequencies (28MHz).  1kW isn't much for a balun, but it's a lot of power to put through a 7:1 step-up transformer.

I'm really having a hard time not calling B.S. on this:
Quote
Just adding a wire radiator of ~130 feet makes this antenna resonant on 80/40/30/20/17/15/12/10m.
Power Handling:1kW I.C.A.S
Especially the 1kW.  I can't believe a transformer that big will work at 28MHz, or pass 1kW at only 3.5MHz.

So, anyone know about MyAntennas.com?  No reviews on eHam yet.

I really want one.  Even if it only works for 80/40/20 ad 100W, that would be a nice simple, end fed, no tuner antenna.  Great for NVIS in a go-kit.

KK0G

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Re: 80M - 10M EFHW with no variable cap
« Reply #1 on: May 27, 2015, 08:38:18 AM »
Resonant on 80/40/30/20/17/15/12/10 with just a 130' wire?! Uh...... so is a dummy load :o . I'd be highly suspect of any antenna manufacturer making such a claim.
"Those who would give up essential liberty to purchase temporary safety, deserve neither liberty nor safety" - Benjamin Franklin

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gil

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Re: 80M - 10M EFHW with no variable cap
« Reply #2 on: May 27, 2015, 11:06:57 AM »
Yeah, I'd wait for a review.. Or make sure they have a return policy..

Gil


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E73M

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Re: 80M - 10M EFHW with no variable cap
« Reply #3 on: May 29, 2015, 10:18:55 AM »
Hello guys,

I found this forum mentioning my antenna so here are few bits of info for you regarding my ENDFED Half Wave - EFHW antennas.

First , transformer...
 it was very hard to make wide band transformer to cover 80-10m with low insertion loss and to maintain impedance transformation ratio over that bandwidth. It took me few months of testing and winding the transformers. Well, at one point I also could not believe it is possible but it is... I do not about other transformers of this kind but I have doubts bout their loss, actually I have built some of those small ones with huge loss, 2-3db, especially lowest and highest frequencies(80 and 10m), that is why it can not take power.

Now, 130 ft of wire and 8 band resonances. Actually we are talking about half wave on 3.6MHz and its harmonics, just multiply it by 2-8 times  and you will get 7.2/10.8/14.4/18/21.6/25.2 and 28.8MHz. With a small compensating coil at start of the wire all those high resonances are moved lower in frequency to fall into band limits (except 10MHz). No big mystery here.

For the original poster, version of my transformer for NVIS is named MEF-110 which works from 1.8MHz to 10MHz (covers 20m with a bit higher inswertion loss 0.66dB)
MEF-110-KIt has only 0.28dB loss on 1.8MHz, 0.36dB on 3.5MHz and 0.41dB on 7Mhz  see the image of actual measurement here


I really do not want to use this venue for marketing purposes (I advertise on several web sites and QST) but had to answer  few of your doubts.
After all I am not new guy on the block, my designs are being sold every day by other companies and I never even thought about return policy on my new products.

Hope I have shed some light on this topic...

 73 Danny Horvat N4EXA aka E73M


cockpitbob

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Re: 80M - 10M EFHW with no variable cap
« Reply #4 on: May 29, 2015, 11:08:16 AM »
Danny, thanks for finding us and posting :D .  You've found a small group of EFHW zealots.  We're also QRP fanatics, so if you start making tiny, light, broadband, 10W EFHW couplers you'll really have our attention.  We like the SOTA tuners, but you have to tune them and they aren't water proof.

OK, I'm impressed.  I've done several of my own and couldn't get a 100W coupler to go wider than 40M - 10M.  At even 50W the flux at 80M was high enough to really start warming the core.  I have no idea how you keep the core from saturating at 3.5MHz and 1kW.  I know you can't give away your secret sauce, but I'm dying to know what core material you use (I use -43).

I was wondering about that coil in the wire.  Thanks for clearing that one up.

73,
Bob

gil

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Re: 80M - 10M EFHW with no variable cap
« Reply #5 on: May 29, 2015, 01:20:38 PM »
Welcome aboard Daniel,

It does seem a lot of us like end-feds for their efficiency and ease of deployment. We are certainly interested in portability, small stuff.. You might want to check out Bob's thread on a 40/30/20m trap antenna...: http://radiopreppers.com/index.php/topic,990.0.html

Nice QRZ page, I like your beam antenna.

You're right about where I land after a couple skips to Eastern Europe, so maybe I'll hear you sometimes, if you use CW...

Gil.

cockpitbob

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Re: 80M - 10M EFHW with no variable cap
« Reply #6 on: May 29, 2015, 03:29:56 PM »
Danny, I wasn't going to say anything since you probably get hounded to build niche products, but since Gil brought it up... ::)

I'm having to make my own tiny QRP traps for wire antennas because I can't find anything out there to buy.  40/30/20 is probably the most popular choice in QRP rigs and almost everyone I've read about puts pluggable links in the antenna because no one makes trail-friendly traps.  Links are fine except you have to lower the antenna to change bands.  I doubt the market is real big, but if you were to develop a QRP end fed coupler and a line of 10W trap antennas, or just the traps people could splice into their wires, you would sell a few and generate more traffic in your web site.

Meanwhile, I just wasted half an hour at lunch fussing with my traps because I had a bad length of coax making my analyzer tell me stupid things.  All that time I was saying, "gee, I wish someone would make QRP traps." ;D

Rob80

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Re: 80M - 10M EFHW with no variable cap
« Reply #7 on: November 15, 2015, 11:40:31 AM »
Looks like a copy of the endfed antennas from the dutch guys.
« Last Edit: November 15, 2015, 11:55:40 AM by Rob80 »

Lamewolf

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Re: 80M - 10M EFHW with no variable cap
« Reply #8 on: December 08, 2015, 07:20:02 AM »
Resonant on 80/40/30/20/17/15/12/10 with just a 130' wire?! Uh...... so is a dummy load :o . I'd be highly suspect of any antenna manufacturer making such a claim.

What gets me is that they call it an end fed "half wave".  Well, its only a half wave on one frequency, then a multiple of that on the harmonics, ie: second harmonic its a "full wave" !

cockpitbob

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Re: 80M - 10M EFHW with no variable cap
« Reply #9 on: December 08, 2015, 08:45:18 AM »
I think everyone calls that style "half wave" mainly because to be resonant the length needs to be some multiple of a half wave (half, one, one and a half, two....)  His antennas are getting solid reviews on eHam so they must work.  I'm just jealous because I've designed this type of antenna but couldn't get the kind of wide band performance he's achieved.  Mine will do 40/20/15/10 (the SWR is getting a little high on 10).  His does those plus 80.  For a transformer that's an incredibly broad frequency range.

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Re: 80M - 10M EFHW with no variable cap
« Reply #9 on: December 08, 2015, 08:45:18 AM »