Re: R: [amsat-bb] G4COM Noise Meter and system tweaking...

[ae517@xxxxxxxxxxxxxxxxxxx (Russ Renaud)]

>The G4COM Noise Meter was described in RADIO COMMUNICATION January 1976 and
>it is a very old design presenting many limitations the most important of
>wich is due to the fact that it works using the audio of  a  receiver.

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

>I dont suggest to directly connect the output of  the above noise generator
>head to the input of your 2.4 GHz  preamplifier or converter because the
>output impedance of  the above noise head changes significantly from the
>OFF to the ON state when  pulsed by the squared signal coming from cursor of
>potentiometer RV3
>
>The result of this mismatch is that your preamplifier or converter cannot be
>really adjusted for the lowest Noise Figure because during the ON and
>OFF  state  of your noise head the gain of your preamplifier or converter
>connected to it changes as well  generating a false S/N measurement.

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?

>Unfortunately the power of the noise head at 2.4 GHz is very small
>depending on your microwave diode used for it  but it is possible to bust it
>building the very simple two stage MMICs wideband amplifier described by
>WB5LUA on the ARRL UHF/Microwave Experimenters Manual Chapter 7
>page 7-38 and 7-39  showing a gain of more than 15 dB at 2.4 GHz
>
>Now connect your noise head to the input of this 15 dB amplifier and
>connect to its output  a 6 turns helix for 2.4 GHz with a gain of  about
>10 dBi or any other antenna available for 2.4 GHz

Thanks. I think I'll try building a small amplifier to do this.  I'm 
hoping to use this method to adjust the matching on my helix...

Tnx es 73


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