[TowerTalk] feedpoint choke for inv L

[Wes Stewart]

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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