Topband: RG-6 coax

[ZR]

----- Original Message ----- 
From: "Jim Brown" <jim at audiosystemsgroup.com>
To: <topband at contesting.com>
Sent: Wednesday, April 10, 2013 12:49 PM
Subject: Re: Topband: RG-6 coax


> On 4/9/2013 9:19 PM, donovanf at starpower.net wrote:
>> CCS RG-6 may be a problem for powering some remote devices such as 
>> preamps or relays through the cable because CCS RG-6 has significantly 
>> more DC resistance than SC RG-6.
>
> If you can find a proper (that is, complete) technical data sheet for 
> whatever coax you are considering, it will include values for the DC 
> resistance of the center conductor and the shield. Likewise, a proper 
> technical data sheet for a remote device should include the DC current and 
> the minimum voltage needed at the remote device for it to work reliably.
>
>  Having this data, and the length of the coax, it's a simple matter to 
> predict whether the cable resistance will be a problem.
>
> It's important to remember that the center conductor is not the only 
> issue -- MOST RG6 coax is designed for use at VHF and UHF by cable TV 
> systems, and their shields are optimized for use at those frequencies. The 
> foil + braid shields of these cables tend to be relatively thin, so their 
> DC resistance tends to be fairly high.
>
> I don't worry a lot about RF loss in RX antennas for topband and 80/40M, 
> but I do worry about shield resistance, because high shield resistance (at 
> the frequency of interest) degrades shielding.

ALL CATV coax is designed for performance down to 5MHz as data, signaling 
and other narrow band applications operate below the TV channels.
Many towns and cities have all their computers linked, traffic control, 
alarms and more on cable these days.

The only real test of a cable is to terminate it at its characteristic 
impedance, insert a swept high level signal and then walk it with a sniffer 
such as CATV field crews use.
Terminating and listening on a receiver is acceptable if all you are 
interested in is a narrow range of fairly low signal strengths.

Carl
KM1H