[HBQRP] requesting information on feeding balanced antenna with a L match atu

[Jim Scott]

Hi all,

(tossing in my 2 cents)

I know QRP ops thrive on efficency, always wanting to squeeze every milliwatt into that antenna! That goes without saying.

However, for discussion, one might consider the following. I've used big loops for years. I prefer 2 wavelength variety since they appear somewhat as an omnidirectional endfire array. I have built them for both 40m and 75m.

Big loops have a higher termination impedance (generally between 100-200 Ohms), so I feed them with ladder line and use a balun tied at the transmitter end. I have found them to be very effective. They are low Q, essentially omni-directional, low angle radiators with gain over a dipole. Downside, they are large!! A 75m 2 wavelength square loop is approximately 130 ft on a side. As for transmitting on higher bands, we found it produces lobes for harmonic bands, but yield higher gain where it does radiate. You do need the tuner for this.

I never ran QRP on one, but I would submit that if one was going to use a horizontal loop, this could be the best way to feed it without a large expense. 

73,

Jim Scott
WB0IYC 
Life Member ARRL
FISTS 15327
Joplin, MO EM27RC
http://www.wb0iyc.com



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-----Original Message-----
From: Rick Bennett [mailto:kc0pet at embarqmail.com]
Sent: Monday, July 10, 2017 07:55 PM
To: 'VU3SXN / KC3CWD'
Cc: 'hbqrp'
Subject: Re: [HBQRP] requesting information on feeding balanced antenna with a L	match atu

Shubham,Not sure if anyone else has responded. Unfortunately feeding a loop antenna for multi-band operation and high efficiency is somewhat complicated. If you were just going to operate at the resonant frequency, then matching for high efficiency is not difficult. The problem comes when you go to a different band. So if you are optimized for 7 MHz, then when you feed say 14 MHz to it, the feed point impedance is going to be very different. Even if you can match your transmitter to the coax, you are going to have a lot of coax loss. Many years ago I put together a full wave loop antenna and used an SG230 automatic feed point tuner (they were pretty expensive) directly connected to the loop. It worked OK but not great. I could tune it to any frequency I wanted to, but the performance was another issue. On the resonant frequency it performed OK and maybe some other frequencies (not necessarily the ones I was interested in) it was OK but for the most part I would not have called it a multi-band antenna. After that experience I have switched to using fan dipoles, off center fed dipoles or various forms of simple wire antennas for multi-band operation.All that to say, have you considered a different type of antenna? There are many, many designs for multi-band antennas out there. Just food for some thought and research.Rick, KC0PET----- Original Message -----From: "VU3SXN / KC3CWD" To: vu3sxn at gmail.comSent: Sunday, July 9, 2017 6:48:47 AMSubject: [HBQRP] requesting information on feeding balanced antenna with a L	match atuHi,I am trying to feed a resonant length 7 mhz full wave delta loop 41 meters of total length with an L-match ATU,Since the l match is a non balance tuner and a full wave loop is a balanced antenna , so can please provide few of your expert tips that how can I feed this balanced loop antenna to a unbalanced l match antenna tuner, I am planning to use this loop antenna on all the freq from 7 to 30mhz will also try it on 6m,I have few options in my mind but I am confused what arrangement to use..Option1. Use a 1to1 current balun between loop antenna to l match tuner,Option 2 use a 1to4 balun between loop antenna and l match tunerWill these baluns feeding the loop antenna will be efficient as I use homebrew rigs with 15watts output and I am trying to make it very efficient ….Vu3sxn / kc3cwdShubham tiwarireply at -- vu3sxn at gmail.com______________________________________________________________HBQRP mailing listHome: http://mailman.qth.net/mailman/listinfo/hbqrpHelp: http://mailman.qth.net/mmfaq.htmPost: mailto:HBQRP at mailman.qth.netThis list hosted by: http://www.qsl.netPlease help support this email list: http://www.qsl.net/donate.html______________________________________________________________HBQRP mailing listHome: http://mailman.qth.net/mailman/listinfo/hbqrpHelp: http://mailman.qth.net/mmfaq.htmPost: mailto:HBQRP at mailman.qth.netThis list hosted by: http://www.qsl.netPlease help support this email list: http://www.qsl.net/donate.html