On 5/28/2020 12:20 PM, Raymond Benny wrote:
One way to tell if a choke is needed I would think, is to add say, a random
lenght of coax, 20 - 40 ft, to the shack end of you coax and see if your
SWR changes. If so, then a then a choke could help.
Jim, does this sound like a reasonable test?
No, I don't think so. The reasons for the choke are 1) to minimize noise
pickup on the coax from coupling to the antenna, and from there to your
RX; and 2) to keep TX RF off the coax shield. With the robust radial
system Tony describes, it seems unlikely that the coax shield would see
more than 1/60 of the TX current, or that the coax shield would
significantly change the feedpoint Z, or that it would contribute
audibly to RX noise.
If, however, the antenna was not ideally matched to the feedline,
changing the feedline length could change the Z at the transmitter. But
this would be a transmission line effect, not a common mode issue.
73, Jim K9YC
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