On 3/14/2019 5:15 PM, charlie carroll wrote:
Measuring at 50 MHz, the difference in loss / 100 feet is about 0.4dB
for the 2 cables. Make it a 1/4 section at 80 meters and you're near
0.1 dB difference in loss. Good luck making meaningful measurements.
Cables using CCS behave like solid copper at VHF/UHF, but NOT at 1-5 MHz.
And there's the issue of cable shielding, which is a weakness of CATV
coax cables below VHF/UHF. This can be an issue in multi-transmitter
environments, and it can be an issue if you're listening through your TX
antennas.
I've addressed this set of issues extensively in my recent app note on
chokes and transformers for RX antennas. On my website,
k9yc.com/publish.htm and in the most recent NCJ.
Bottom line -- I use nearly 2,000 ft of flooded Commscope RG6 in my RX
antenna systems, and use chokes to minimize common mode current, which,
through a mechanism quantified as a cable's Transfer Impedance, couples
common mode shield current to the inside of the coax. That flooded
Commscope RG6 works well IF we keep common mode current under control,
and the "flooding" material that closes nicks on the outer jacket
happens to be something that varmints don't like to munch. And I use big
50 and 75 ohm coax with a beefy copper shield and hard line for my TX
antennas.
73, Jim K9YC
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