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Re: [TowerTalk] RG142 Measurements for chokes

To: towertalk@contesting.com
Subject: Re: [TowerTalk] RG142 Measurements for chokes
From: jimlux <jimlux@earthlink.net>
Date: Mon, 25 Apr 2016 14:47:25 -0700
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
On 4/25/16 2:37 PM, Dan Maguire via TowerTalk wrote:
Grant wrote:
If my calculated ft remaining is correct at 600 feet, then measured loss per 
100ft is currently 2.2 db at 30Mhz, 1.25 db at 10MHz and 0.5 db at 1.9Mhz.

The free TLDetails app (http://ac6la.com/tldetails1.html) includes Belden 83242 
(RG-142B/U) as one of the built-in line types.  The app can show a plot of 
loss/100ft vs frequency, like this:

http://s31.postimg.org/7qyn2cg8r/TLD.png

I'm afraid I'll have to challenge Grant on his assertion of 0.5 dB at 1.9 MHz.  
Clearly the correct figure is 0.494 dB.  :)


Now you're talking about the coding people getting a few microBel (that's .00001 dB) closer to the Shannon limit on deep space comm links. A standard joke around JPL telecom folks is that the coding people are pleased at extracting another 0.01 dB of link margin with a coding scheme that only requires a few tens of millions of gates to implement and consumes 5 watts, and then the spacecraft folks add 2 meters of coax at 8 GHz after the 10 Watt Power amp.


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