There have been a few comments about Rx antenna chokes. What I built
may be of interest.
10 turns of RG179 micro TFE 75 ohm coax thru a Fair-Rite 2631101902 #31
core (1.12od x 1.125L x .54id). Wound thru a 3d printed form with 10
slots that keeps the turns disciplined in order.
Measured R 6.5k ohms on 160 and 5.8k ohms on 80m. These were used as
feedline chokes inside the matching and pattern reversing boxes for
DHDL's interconnected with triple shield RG6. An earlier version was
built with short BNC pigtails for other DHDL's. The internal to box
chokes have 2" leads so re-radiation should be minimal.
RG316 will work if 50ohm coax is needed and should have the same choking
results.
Prior tests of a commercial 3ft long "beads on coax" 160m choke yielded
about 1k ohms. Not practical IMO.
Grant KZ1W
On 9/12/2020 09:32, Richard (Rick) Karlquist wrote:
On 9/12/2020 5:26 AM, Mikek wrote:
My Technical knowledge is limited but, I have built directional
AMBCB antennas. Feed line isolation is critical to make a directional
antenna, directional! I have been criticized and been told, coax cable
does not pick up signal. Must be I don't use the right coax.
This from a previous post I made after I ran out and tested a 230ft
Coax and a 230ft 18ga twisted speaker wire, to see what BCB stations
they received.
You didn't mention what kind of coax you used, but unless you
proactively seeked out double shielded, it WILL leak. I used
to work for Hewlett-Packard/Agilent/Keysight. At one time, HP
has it's own captive wire manufacturing factory. One item of
interest for this discussion is that they made their own
TRIPLE shielded miniature coax to be used in instruments.
They had some connector vendor make special connectors to fit
this HP only coax. In the old HP measurement accessories
catalog, there were "RG-58" class test cables with BNC connectors
colored in HP "mint gray". These were not ordinary RG-58, but
were double shielded. Compared to the black Pomona test cables you
can buy from distributors, the leakage was drastically less.
It is also not surprising that CAT-5 cable has less leakage.
I have used it myself as feedline.
At BCB frequencies, you also have to contend with the skin depth
problem.
Rick N6RK
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