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[TenTec] "Tuning" antennas; baluns

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Subject: [TenTec] "Tuning" antennas; baluns
From: seay@Alaska.NET (Del Seay, KL7HF)
Date: Tue, 23 Sep 1997 07:56:32 -0800 (AKDT)

I think what we have here is a misunderstanding of each others terminology.
There are several absolutes involved.
        1: An antenna is resonant when standing waves exist along it's
           length. No amount of tranmission line massaging will change that.

        2: An antenna consists of the radiating elements. Hopefully
           a transmission line will not radiate rf.

        3: The transmission line delivers rf from the generator to the
           load. (Antenna)

        The antenna system consists of all of the above.

By the way, the Amidon baluns were operated well within their ratings and still
failed after short periods. The load on the baluns was approximately 300 ohms
and I never run more that 1500 watts of rf, the baluns were spec'ed at 3kw as
I recall.
73 de KL7HF

At 11:44 AM 9/23/97 -0400, you wrote:
>On 9/23/97 11:04 AM, rohre at rohre@arlut.utexas.edu wrote:
>>In fact, I hope all will agree or will measure,  that even with an antenna
>>matching device, (which for years was mistakenly called a "tuner"), you still
>>have standing waves on the transmission line, and the matching device is just
>>there to TRANSFORM a complex impedance at the shack end of the line to a 
>>value that more closely matches your transmitter.
>Not quite. In my book, a transmatch produces a "matched" or resonant 
>condition on the antenna "system" -- which includes the transmission 
>line. The resulting conjugate match is just as resonant as any other type 
>of antenna system.
>True, there are so-called "standing waves" on the transmission line. But 
>the presence of these waves has next to nothing to do with the resonance 
>of the antenna system. I'll give you an example -- a "resonant" dipole in 
>free space has a feedpoint impedance of around 70 ohms. Hook 50 ohm coax 
>to it and you have a mismatch that results in about 1.5:1 SWR. 
>Standing waves are only a problem in lossy transmission lines -- such as 
>coax. Open wire has so little loss that the standing waves can be safely 
>If you had a lossless 50 ohm coax, you could hook it to that 70 ohm free 
>space dipole and safely ignore the mismatch. Of course, with lossly coax, 
>that 1.5:1 SWR is probably much lower (feedline losses apply equally to 
>the reflected energy) at the transmitter -- probably around 1.2-1.4:1. 
>Low enough that you might ignore it anyway.
>>I hope this helps divide the concepts into their proper areas.  Antennas
>>resonate depending upon their physical structure and dimensions.
>No, antenna "systems" resonate depending on their ELECTRICAL 
>characteristics. A shortened dipole is no less resonant than a full-size 
>dipole, yet its dimensions are different.
>There's nothing magical about certain antenna dimensions or "resonance." 
>The overriding issue is concern for energy LOSS. Once you understand the 
>nature of energy loss in an antenna system, it is a simpler matter to 
>reduce such losses.
>Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr@radio.org
>Quote: "Not in a thousand years will man ever fly!"
>            -- Wilbur Wright, 1901
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