[TowerTalk] RG142 Measurements for chokes

jimlux jimlux at earthlink.net
Mon Apr 25 17:47:25 EDT 2016


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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