[amsat-bb] Re: 75 ohm CATV Cable on 70 cm
sv1bsx at yahoo.gr
Tue May 22 02:19:41 PDT 2007
...yes, I tryed that on my 2nd QTH because my
experience with 100ft of RG213 was very bad on UHF.
It was Sunday - no chance to buy something better..
so I decided to replace the RG213 with 75 Ohm TV
Well, the receiving-difference it was spectacular!
With 75Ohm cable it was possible to hear Loud & clear
the FO-29 downlink, with RG-213 not good enough!
The same I noticed with other Satellites and weak
signal ground stations.
Later, after few weeks I replaced the 75 Ohm cable
with AirCom+. Nothing changed between 75 Ohm TV and
AirCom+ in the receiving! Absolutely equal receiving
between the two cables, even if the AirCom+ was "10
times" much more expensive cable!
But in transmittion, it's obvious that the 75 Ohm
cable has problem. It is not the mismatch (SWR 1.5)
but this cable probably can not drive output Power
bigger than 5-10 Watts. I confirmed that with 2-3 RIGs
and several type of antennas. If you have output Power
bigger than 10 Watts, is possible the RIG to
decrease the Power output (ALC action? protection? I
don't know!)a few seconds after PTT's press. (I'm
talking always for UHF band).
So, from my experience I believe that the 75 Ohm is
excellent in case you need a separate cable from
UHF-LNA output upto the Shack.
I noticed that the Loss for 100ft at 450 MHz is about
2-2.5 dB, very Low-value for a cheap cable.
For transmittion is a cheap choice, if you have up to
5-10 Watts maximum Power on UHF.
Hope that helps
73, Mak SV1BSX
--- Mike Miller <mmiller at nctc.com> wrote:
> Anyone have any experience using 75 ohm CATV cable
> on 70 cm?
> Mike KA5SMA
> Sent via AMSAT-BB at amsat.org. Opinions expressed are
> those of the author.
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