Hi J,
That sounds like a very good setup and it would be hard to improve on
it. The SWR should be low enough that using a tuner in the shack ( as
opposed to some sort of matching network right at the base of the
vertical) should work fine at moderate power levels. You might not have
to use a tuner at all. If you did put a fixed tuning network at the
base, just for 40 meters, you could get the SWR way down, and run the
legal limit maybe even with RG-58 (look up some data on coax power
handling before you try this, I'm sure you could run 500 watts, but 1500
maybe not) On the other hand if you use a fixed matching network for 40
meters, you will probably not be able to use it on other bands. You can
probably do pretty well with that antenna on most of the higher bands,
though it might be tricky on 20 meters, since the impedance of an end
fed half wavelength is pretty high. the radiation angle will be higher
as you go to higher frequencies, so it probably won't be the greatest
for DX.
If you've already got 65 radials, you probably cannot make it much
better even by doubling the number of radials.
You could remove a bunch of radials to increase your ground loss, until
the feed point impedance is very close to 50 ohms. That would make it
very convenient. It wouldn't work as well as what you have now though.
If you made it a bit taller, it could be easier to load up on 20 meters.
43 feet would be a 5/8 wavelength on 20, and it would still work great
on 40 and 30.
The point I was making is that low SWR does not mean better performance.
It often means poorer performance. I read and hear hams talking so much
about how great their SWR is, but seldom making any field strength
measurements. Most of the "performance" discussion is about anecdotal
data. "The Europeans are giving me good reports" That kind of stuff.
73 DE N6KB
On 11/7/2013 10:18 PM, Richards wrote:
Interesting commentary, Ken.
I DO have a 40m ground plan with 65 radials. And it has that
textbook 38 ohm low SWR you mention. It seems to work swell... but
your comment suggests it could be better.
A friend suggested I make it slightly taller and add some capacitance
until it presents a an inherent 50 ohm load. (I think that is what he
said... let's assume HE said it right, if this is not a good idea...
and presume I remember it wrong...)
So - What would YOU do with my antenna to make it work better?
(This is NOT an argument - it is a very serious question to me.)
-------------------- K8JHR -----------------------
------ Original Message ------
From: "Ken Brown" <ken.d.brown@hawaiiantel.net>
A quarter wavelength vertical over an excellent ground counterpoise
system has an impedance of about 37 ohms. If you don't need a matching
device to get a 1:1 SWR at the resonant point, then it is likely you
have about 13 ohms of loss resistance (the kind that produces heat,
versus radiation resistance, the kind that produces a radiated signal)
that added to the 37 ohms of radiation resistance makes a perfect
match to your 50 ohm coax. Very convenient. Not very effective. What
would you rather have? A low SWR or a stronger signal? Many hams have
chosen (perhaps unwittingly) a low SWR.
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