I have too few (~20) insulated, 55 foot long on-the-ground radials under my 55'
high inverted-L. In my desert conditions, running radials is quite literally a
pain, but I will add more as time permits. There are also a number of bare-wire
buried radials left over from an 80-meter project. I have however, disconnected
them with the idea that I am trying to collect displacement currents and return
them to the base without loss in the soil.
That said, and with deference to Rudy, whose papers fill a folder on my hard
drive, I still have a lightning ground consisting of four buried 2 AWG bare
wires from the radial plate to four 8' ground rods on 16' centers. So there is a
combination of radials and an earth connection. I wouldn't have it any other way.
Furthermore, the Heliax transmission line lays on the ground and there isn't a
piece of ferrite anywhere in my station, except for the molded on ones on a few
computer interconnects and the bead balun on my inverted-V. And... I use this
antenna for both TX and RX and I hear as well as, or better, than I can get out
using 500W.
Wes N7WS
On 11/20/2018 12:07 PM, Jim Brown wrote:
On 11/20/2018 3:10 AM, Rob Atkinson wrote:
If the ground system is at or below grade, you don't need a choke.
You DO if your radial system is limited, as you've stated below.
If
you find you do need one then that means you don't have enough radials
down. This is an example of ham antenna work where it is useful to
take a look at medium wave broadcast instead of re-inventing the
wheel. Broadcasters do not have chokes on their feedlines. That's
because they have a lot of radials and the feedline is (nowadays) coax
under ground.
AND because they don't have to LISTEN on that antenna.
But even if your feedline is laying on the ground you
can avoid having to fool with a choke provided you have enough
radials, so that the return current to the feedpoint is divided so
much that whatever is on the feedline is insignificant. And, you need
plenty of radials anyway, if you want to have a decent antenna. Put
down at least 60 radials and see if you have a problem with RF on your
coax....probably not enough to matter.
Right, but few hams have great radial systems for 160M, and most hams don't
live in the middle of nowhere where there's no local noise. A choke matters
when there are a few radials, short radials, elevated radials, etc. N6LF has
done extensive research, both modeling and measurement, on radial systems. One
of his results is that with a few radials, balancing current between them has
a strong effect on losses, and a combination of radials and an earth
connection is a bad thing. Use of a feedline choke is a good thing in that
sort of antenna system.
Hams are ferrite choke and
balun crazy...use them in many cases where they aren't needed....
Some hams have more demanding operating requirements than others. Chokes DO
matter, often a lot, for reducing inter-station interference in
multi-transmitter environments, like Field Day, SO2R contesting, and multi-op
contest stations. They can also matter when you have local noise.
73, Jim K9YC
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