On Wed, 10 Jul 2002, Brendan Moran wrote:

>> I really don't know the answer but maybe you could use a spectrum analyzer
>> and a noise source. This will not tell you the impedance but you should be
>> able to improve your circuit by trial and error. It may also show you any
>> resonances in band, and noise peaks. A dense 'fence rail' signal may
>> replace the noise generator and make the noise floor easier to see on the
>> specan when you tweak the circuit.
>
>Well, I have been developing a sort of a theory of operation when working
>with analogue circuits:  Never use trial and error where calculations will
>do the job.  So, I admit that I don't particularly like the idea of using
>trial and error to solve this problem.

If you don't have the parameters for the circuit the next best thing is to
get some real world data to give you a starting point.

>Aside from that, I didn't list the noise figure meter because I didn't think
>it was relevant.  The problem I've had with it, though, is it measures
>consistently higher than I expect.

>For example: I have an antenna pre-amp with a rated NF of 0.5dB.  It has
>50-ohm in and 50-ohm out ports.  When I hook it up to the NF meter, (which I
>have calibrated using a noise source and the same 2 cables off the noise
>source, only with a F-BNC to F-BNC connector, that I use with the antenna
>pre-amp) It gives me 11dB or so.  Hardly an acceptable error.
>
>It's primarily for that reason that I didn't mention the NF meter.
>
>Anyways, got any clues on that one?

Nope. I know too little about your circuit to be able to help. Sorry.

Peter

--
http://www.piclist.com hint: To leave the PICList
mailto:piclist-unsubscribe-request@mitvma.mit.edu