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[TowerTalk] Radials, resonance and the MFJ259

To: <>
Subject: [TowerTalk] Radials, resonance and the MFJ259
From: (K4SB)
Date: Wed, 17 Dec 1997 22:14:47 -0800
> WC1M wrote:
> So, I went back and forth, lengthening the antenna until the >transceiver 
> reported minimum SWR at 7.150. At this point, however, the >MFJ reported 
> minimum SWR was ocurring at 7.300! I ignored the MFJ's >results and have been 
>  operating happily on 40M ever since (the antenna >is very broad; the SWR  
> hardly budges across the entire band.)snip

After reading this, and a couple of responses, I guess I'd like to put
my two cents in. Basically, this situation exists: At the antenna, the
SWR on several analysers is within that expected when the antenna is
tuned to the desired frequency. Also, the radial screen seems excellent.
However, some feedline length away, we find a completely different set
of SWR values.
So, first of all, there is entirely too much worshiping of the SWR god
here. The losses with an SWR of 2:1 on 40 are simply insignificant.
Secondly, what is the only thing which has changed? The inclusion of the
feed line. Since the SWR was not unity to begin with, the feedline will
display varying reactance in voltage and current at every phase shift.
It is not only possible, but probable that at some point, the feedline
very well may be in such a phase difference that an observed SWR of 1:1
would be present. Is this correct? No. The SWR of the antenna is still
what it was. What the transceiver is seeing is a combination of the
feedline and antenna, and until the antenna is adjusted by a matching
network to 1:1, it will continue to factor in the feedline. This is a
relatively simply device to build. Is it worth it? No

I would suggest a ground rod at the base of the antenna, connect to the
ground system, and really think the balun is a waste, but otherwise,
as noted earlier, if it works, use it as it is.
I don't know if the transceiver has a built in ATU, but if it does, it
should be capable od dealing with the mismatch.

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