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RE: Source for F to N/SO239 Adapters



Bob said...

> But why bother.  THe signal out of the Drake is so great, and so far above
> the noise floor of your IF receiver, that it won't make any difference..
> I'd just leave the F connector and save your expensive coax for something
> else.  Just run RG-59 cable TV coax down to the shack.

IMHO Bob's right...

Here's part of a spreadsheet I use to calculate losses, which I stole from
the AMSAT digital satellite handbook:

System_Noise_Figure=

10*LOG
(  10^(Preamp_NF/10)+
  (10^((Rx_Noise_Figure + Cable_Loss)/10)-1)/
   10^(Preamp_Gain/10)
)

With all figures in dB, preamp/converter at the antenna.

If your NF is low, your conversion gain sufficient and you don't have any
in-band strong signals, you can get away with quite a lot in the feeder
department.

Seemingly as long as the preamp/converter gain can override the effects of
feeder losses, the system noise figure is not far off the preamp/convert
noise figure.

The figures seem to bear out empiracally with my configuration - even
running over 180' of Westflex W103 cable (similar to 9913) at 2.4GHz things
seem to be acceptable. Of course if you're running 144MHz IF things are even
better as the coax losses are far less.

Of course transmitting's a different kettle of fish, and strong signal
considerations usually preclude the benefits of using wet string and high
gain preamps on 2m & 70cm.

73 Howard G6LVB

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