Date: Wed, 18 Feb 2015 21:22:02 -0800
From: Jim Brown <jim@audiosystemsgroup.com>
To: towertalk@contesting.com
Subject: Re: [TowerTalk] [Bulk] Coax cable economics. (was Mosley
Antenna Question)
On Wed,2/18/2015 8:51 PM, Larry Loen wrote:
> The point of low loss coax is to hear them.
Not really -- that's only true with very small signal work in very quiet
locations. For the vast majority of us, and for nearly all real world
conditions, what we can hear is limited by atmospheric and man-made
noise. It's easy to figure this out -- if you start with no antenna
connected to your RX, then plug one in, and the noise increases by 10
dB or more, you are limited by the noise coming in on the antenna, and
lower loss coax (or even a more sensitive RX) won't help. What CAN help,
sometimes a lot, is an antenna that rejects some of that noise while not
rejecting (or rejecting less of) the weak signal you want to copy.
What low loss coax DOES do is make us louder in the other guy's radio.
73, Jim K9YC
## Excellent point. So if one has say an S-5 noise level on 20m, and even
lossier coax is then used, and noise level drops to S-4, the SN ratio on RX
has not changed at all ? You could simulate the same thing by adding
some attenuation in on RX.
## You are correct though, 3db loss in the coax means we just lost 3db on
TX..and RX. The 3db loss on RX wont be noticed, with any amount of noise on
RX present. The 3db loss on TX is a huge amount. All these losss add up
though...and fast.
## reduce coax loss by 1-2 db. Make the boom longer, add more eles. perhaps
another 1-3 db. Install yagi higher, perhaps another 2-6 db. Increase power
on TX
by 1-3db. All of a sudden, we are now 5-14 db louder on TX..and that’s
nothing to
sneeze at.
## On CW, with narrow filters being used, the RX noise level will drop by a
huge amount,
vs SSB filter widths. On 40-10m, that’s when u can get the RX noise level
way down to the
noise floor..at least on cw mode.
## Drives me nuts seeing power being burned up in the coax on TX. Use what
ever method you want
to measure coax loss, but the method of wattmeters on both ends of the coax is
a real wake up call.
Jim VE7RF
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|