12-03-2017, 07:29 PM
Hi Alan,
I have found that the design in an old ARRL FM and Repeaters handbook works well. I did it at UHF, but I believe that the article gives dimensions for 2 m and 6 m as well.
This is a design that uses bandpass cavities, adding a small inductance or capacitance between input and output to give a notch above or below the centre frequency.
Initially, I had a lot of difficulty getting the notches at +/- 5 MHz, because the article did not explain how to adjust that. I expect that this article may have been updated in more recent editions, but if not I can tell you how to do it. It's actually a great way to do notch filters as it gives you independent adjustment of the offset of the notch, and the depth of the notch.
In a high RF environment, I found it useful to have two notch filters and one bandpass for RX, and the same for TX, to give some extra receiver protection from transmitter spurii and strong signals in adjacent bands.
Best wishes,
Lew.
I have found that the design in an old ARRL FM and Repeaters handbook works well. I did it at UHF, but I believe that the article gives dimensions for 2 m and 6 m as well.
This is a design that uses bandpass cavities, adding a small inductance or capacitance between input and output to give a notch above or below the centre frequency.
Initially, I had a lot of difficulty getting the notches at +/- 5 MHz, because the article did not explain how to adjust that. I expect that this article may have been updated in more recent editions, but if not I can tell you how to do it. It's actually a great way to do notch filters as it gives you independent adjustment of the offset of the notch, and the depth of the notch.
In a high RF environment, I found it useful to have two notch filters and one bandpass for RX, and the same for TX, to give some extra receiver protection from transmitter spurii and strong signals in adjacent bands.
Best wishes,
Lew.