[TowerTalk] Some thoughts on coax leakage

[Del Seay]

Adds a bit of legitamacy to buying the best.
When using hardline for runs, it's not easy to bring the hardline
to the rig, and most use short jumpers of regular coax. The difference
between using RG8AU, RG213, etc and using good RG-214 is amazing.
de KL7HF


Healy, Rus wrote:
> 
> Paul, KB8N, makes some good points about coax leakage. But consider
> this: 63 dB of coax leakage is an awfully large amount in a hamshack
> where cables are typically dressed close to each other over some
> distance out of the shack and out of the house. If we assume that two
> adjacent cables have 63 dB of isolation each, then we have 126 dB of
> total isolation between them (considering no other factors, yet).
> 
> This sounds like a lot, until you start thinking in terms of the signal
> levels we work with. 1.5 kW is about +62 dBm. Subtract 126 dB from this
> and you have -64 dBm. Folks, this is a *BIG* signal! (If S9 on your
> receiver just happens to be 50 microvolts, this is more than 10 dB over
> S9.) Any good communications receiver, even the low-end models that are
> simply not found in competitive multioperator hamshacks, can easily
> detect signals down to -137 dBm with a CW filter in line, and perhaps
> -130 dBm worst case with an SSB filter in line. This means that our coax
> leakage is at least *66 dB* stronger than the weakest signal the
> receiver can detect. Now add in coupling to cables from direct radiation
> from the equipment, antennas, and all other sources, and we're talking
> about mighty strong signals.
> 
> Isolation between two runs of hardline is much, much higher than this.
> And the all-important shielding hardline provides from coupled radiated
> signals from equipment chassis and antennas is perhaps even more
> significant. It is by no means false economy to use hardline to isolate
> stations from each other, IMHO.
> 
> --73, Rus, NJ2L
> nj2l@mdsroc.com
> 
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