RF communications - IF filter

The IF filter BW is chosen by the user if needed. You deermine how slow you want to sweep and how low you want the noise floor to be.

More or less noise should not control the resolution BW. I think the IF filter BW and also the combination of the sweep rate and the video BW can reduce the visual resolution on a display. But that may be different than what you are calling the resolution BW.

The shape of the IF filter itself affects the ability to resolve. If you have a pure tone and seep slow, you will see the shape of your IF filter. It should be well documented in your HP documentation, unless you are unfortunate enough to have to use a more modern piece of equipment with less documentation (just kidding, I am more lamenting than complaining).

I assume you are talking about an analog filter spectrum analyzer and not a synthetic one based on time samples and signal processing. In signal processing you would have the same filter limit, but some of them could be digital. You could also be using an analysis algorithm with a high resolution technique, in which case your resolution is not limited by spacing so much as phase cancelation in the data set you have.

hey...thanks for the reply..

yes its an anlaogue spectrum anaylzer and a rather old one.

you know with regard to the shape of the filter you were talking about..i have come across a 60dB to 3dB filter shape(thats the one the analyser is using). are you aware of any other IF filter shapes being used?

i also read up on residual FM on part of the local oscillator. it too limits the resoultion bandwidth. would you happen to have any idea on that?

thanks again..

The 3 and 60 only tell you part of the story, but probably enough for what you need. If I recall the equipment people tend to like to build the equivalent of "synchronous" filters. Maybe a google will show something.

If you are worried about the LO then you must really be looking at some fine detail. Most applications do not worry about the LO and those that do use specialty equipment for their close in phase noise measurements. Usually it is the high Q oscillator people.

If you can afford to look for a long time and you actually have two discrete signals of the same amplitude (probably an unlikely scenario) you are trying to resolve, you could dwell for a while and hope the averaging can help you resolve a little beyond the LO noise.

alright...

thanks...will try google...

will also take a closer look at the LO...

cheers