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R: R: G4COM Noise Meter and system tweaking...




----- Original Message -----
From: Russ Renaud <ae517@freenet.carleton.ca>
To: <domenico.i8cvs@tin.it>
Cc: <amsat-bb@AMSAT.Org>
Sent: Wednesday, July 04, 2001 1:40 PM
Subject: Re: R: [amsat-bb] G4COM Noise Meter and system tweaking...

>  I would have liked to have built a PANFI noise meter, but it was a bit
> costly.

In Italy we can buy a surplus  AILTECH  PANFI 75 ,30 MHz IF at about
 250 US $ in good conditions but without noise head.

> If I duplicate N6IZW's circuit, I would have approx 23 dB attenuation
> between the noise head and the preamp input. Is this amount of attenuation
> sufficient to mask the changing impedance of the noise head ?

23 dB is OK because the incident noise power will be attenuated by 23 dB
and the noise power reflected by the preamp VSWR will be attenuated back
23 dB as well.
Thus the noise diode,usually a NC 304 BL from NOISE COM,will not change
significantly its impedance because of the very low preamp  input return
loss or S11

I dont know the N6IZW's circuit but  i estimate that a noise head requiring
a 23 dB pad at the output to get a standard ENR of 5.2 dB should be supplied
by a standard pulsed 28 volts square wave and unfortunately the G4COM
circuit do not ! Take care of it.

> Thanks. I think I'll try > --
> 73 de va3rr/aa8lu

73 de i8CVS Domenico


> http://www.qsl.net/va3rr
> Check out the new Ship Station Regs at:
> http://www.tc.gc.ca/Actsregs/csa-lmmc/csa63.html
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