On Feb 21, 11:56 am, "Richard Fry" wrote:
Would it be worth the extra effort to try to get the base of the antenna
up to 40 feet rather than 25 feet?



Yes and no... Will help 40 a lot. 80 some.. 160, not a whole heck of a
lot.. 40 ft is still low in terms of wavelength on 160. Say you had a
ground mount with 60 radials.. To equal that ground loss with
four radials will require the antenna to be at about 1/4 wave height.

_____________

I know of commercial AM broadcast stations using 6-8, ~1/4-wave radials
elevated less than 20 feet over (rocky) ground, with an antenna system
radiation efficiency meeting the FCC minimum for broadcast station use.

How does that minimum compare to the usual 120 or so radials on the
ground?


Also this quoted conclusion hasn't been supported by the NEC evaluations of
L.B. Cebik as given in the paper linked below. Figure 16 in that paper
shows that the gain of a vertical radiator is within tenths of a decibel of
its peak maximum value with four radials each 1/4-wave long, when the whole
system is elevated only 0.075 wavelengths above the earth (about 41 feet at
1.8 MHz).

Well, a model can say one thing, and the real world performance
another.
I'm not saying it wouldn't radiate. It would. But it's not going to be
any world
beater for dx. For sure, it won't be living up to it's full
potential.
Four elevated resonant radials at 40 ft are better than 4 ground mount
radials, but
at that height you really need quite a few more if you want to equal a
stout
ground mount setup. If you have 60 radials on the ground, you need
about
20-30 at 1/8 wave up to equal the same appx ground loss. And 1/8 wave
on
160 is about 60 ft or more.
When I had a 40 meter ground plane at 1/4 wave up, "four sloping
radials"
I tried using it lowered to about 1/8 wave after working on it, and I
had the mast
down. I tried it for a night. It didn't work near as well as when it
was fully up to 1/4
wave when working most anyone. VK was probably almost 2 S units down
from my
usual report, just using that crude estimate to compare. It was
noticable for sure.
If you can get up to a 1/4 wave, and have at least 4 radials, then it
is pretty good.
And even that is not quite optimum, 10 would be better. It's close
enough though...
I've read of quite a few low band ops trying verticals, with low
elevated radials, with
usually a low amount. Most of them end up scrapping it after a few
nights of #$%&,
and laying out 30-60 ground radials. Most claim it woke the antenna
up.
I'm a great fan of elevated verticals on the low bands. The one I had
on 40 was very
stout. But I don't recommend them low to the ground with only a few
radials, unless
you are ready to accept the quite noticable hit in performance.
That's what can give the verticals a bad name..
You would probably be better off setting up a good mobile antenna on a
large truck and running
coax to it. :/ No joke.
But it wouldn't hurt anything to try out what he proposes.. If it
doesn't pan out, he can
always go back and lay the wire down. It would be much better than not
operating at all.
On 160, a lot will depend on the noise level.. Some nights a weaker
signal will do ok,
other nights, it's teeth grinding torture... On the low bands, I don't
like to throw away power to the
ground, that could otherwise be radiated if I can avoid it. Sometimes
it's hard to avoid
with some locations, restrictions, etc..
It's not that I try to discourage running less than optimum verticals,
I just hate to see
people try them, and then end up thinking most all verticals perform
about the same. If they
scrimp in some way, either with height, or number, they will lose
some performance.
MK