Advice on frequency measurement to 30MHz

[Andy Wood]

Hello,

A few ham friends and I are working on a project where we would like to be able to automatically switch in various filters based on the frequency of an Rf signal in the range 1.8 to 30MHz.

The project will contain a PIC (18Fxxxx) for various measurement, control and display purposes. We are currently in the early "block diagram" stage and have not yet decided on which device to use. I have used the CCP modules before for frequency measurement but not at this frequency (not even sure it can be done this way?). Are there any devices more suitable than others for this application? Maybe a prescaler needs to be involved?

Any advice would be greatly appreciated.

Andy

[Bruce]

Andy,

Have a look at this app note. It's for a 50MHz freq counter using an old C series PIC.
http://ww1.microchip.com/downloads/en/AppNotes/00592d.pdf

[Andy Wood]

Hi Bruce,

Thanks for the info. I now remember seeing that app note many years ago.

I also found this thread which has helped me get something up and operational on a 16f877 for starters.

http://www.picbasic.co.uk/forum/showthread.php?t=1137

I used Timer1 (T1CKI) as the input (as it is 16bit) and Timer0 with a period of 1mS for the timing. I had to fudge the resulting values just a bit as there is a small error due to timer resolution and program overhead.


Andy