Response to my gamma matching rules of thumb has been interesting.
Several individuals (including one extremely prolific station
builder) responded individually, and confirmed most of my empirical
observations. They also added that an omega match is useful in
achieving a better match without having to tweak the dimensions of
the gamma rod.
However, there was one very critical response. It is someone whose
technical credentials are beyond reproach, so there must be something
to his criticisms. He contended that:
1. The gamma attachment point must be as low as possible, failing
which the gamma itself becomes the radiator.
My response, although once again empirical, is twofold. Firstly: My
discussion was specifically confined to radiators with an electrical
length of less than a quarter wavelength. In these circumstances, I
maintain that longer is better. Secondly: I am not in a position to
express an opinion on what is radiating; I can only say that it
works. That being the case, I'm not particularly concerned whether
the tower or the gamma rod is doing the radiating.
2. The gamma diameter is immaterial, as only the transformation
ratio changes.
Quite so. However, the stated objective with my rules of thumb was
to provide a convenient impedance. That being the case, a diameter
ratio of as close as possible to 1:1 is preferable. The intention is
not to optimise one particular situation, but to maximise the
probability of having a convenient impedance when a random tower is
being loaded.
3. My suggested matching technique was dismissed as "not a match",
due to the 2:1 (or higher) SWR.
Guilty as charged. However, for those of us who struggle to find a
few hours a year to operate (normally the last weekend of several
months in the third quarter), a 1:1 SWR is a luxury one reads about in
books. I feel that, especially considering the low line losses on
LF, the idea of bringing the antenna impedance into a manageable
ballpark by preliminary matching and then using a suitably beefy
tuner in the shack is forgiveable. Should you harbour resentment
against the likes of me, I hope you'll find it in your heart to
forgive me.
Chris R. Burger
ZS6EZ
PS: Anyone who simply cannot find this forgiveness in his/her heart,
please shred your 3DA0/ZS6BCR, ZS0Z, ZS3Z, ZS6EZ, ZS6BCR, ZS9Z,
ZS9Z/ZS1, V51Z, 3DA0Z, A25/ZS6BCR, ZS6BCR/A22, 7P8EN and W6O QSLs and
return the remains to me by registered mail.
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