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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