[TowerTalk] Coax cable economics. (was Mosley

[Patrick Greenlee]

Will someone please explain why what I'm about to write is not true (if 
that is the case.)  I'm trying to follow the "debate" regarding coax 
losses and their effects on transmit and receive.

The receiver has an inherent internal noise floor which can be 
qualitatively observed by shorting the input coax fitting and cranking 
the RF and AF gain up.  If the signal portion within the "signal + 
noise" coming through the coax to the rcvr goes sufficiently low it will 
be irretrievably lost in the receiver's internal noise irrespective of 
other considerations.  Coax losses on receive could in some weak signal 
situations attenuate the signal sufficiently to reduce it below the rcvr 
internal noise and make it unrecoverable.

Clearly, I'm no expert, just trying to understand the topic under 
discussion.  Critiquing the above could help me understand the matter 
better.

Patrick   NJ5G

On 2/19/2015 6:52 AM, Jim Thomson wrote:
> Date: Wed, 18 Feb 2015 21:22:02 -0800
> From: Jim Brown <jim at audiosystemsgroup.com>
> To: towertalk at 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 at contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk