[Moon] Re: [Moon-net] Noise Factor measuremnts Q.

[Dr. David Kirkby]

SM5LE wrote:
> Hi all
> 
> 
> 
> How much is a LAN's Noise Factor decreasing (getting worse) as the room temperatur goes warmer?
> 
> I did measure NF=0.3 at 17 dgr Celsius and now as it is 30 dgr in the room I measure 0.4 dB. Is that normal? Or do I have some instability (but I can not see any on spec. analyzer).
> 
> I do calibrate the NF meter HP8970A with noise source HP346C for every measurement.
> 
> It is on 1296MHz and cavity HEMT type.

You need to correct the cold temperature reference as ambient 
temperature varies. Some of the modern noise sources have a temperature 
sensor in them that allows the meter to do this automatically 
automatically, but the 8970A does not support such noise sources, so you 
have to set it manually.

On the 8970A it is "Special Function 6.0" that you need to change. The 
default according to my manual is 296.5 K (23.35 deg C).

BTW, I don't know if you are interested, but some time back I wrote some 
code that can be used to control an 8970A via a GPIB interface. It is 
useful if you want to collect data over an extended period of time. It 
only runs on UNIX/Linux and needs a National Instruments GPIB board. The 
software is in a VERY alpha state, as I never developed it much beyond 
solving my particular issue, but you can send arbitrary GPIB commands to 
the instrument.

http://hp8970.sourceforge.net/