Bert’s low loss filter is NOT the one to use for a 28 MHz IF. It is intended to remove out of band interference and is essentially flat response from 1.21GHz to 1.31GHz-see attachment.
However, Bert made a very nice LO and image reject filter for me, which I use for 1296 MHz with 28 MHz IF. Loss, of course is slightly higher.
DB6NT also sell a suitable filter.
Hope that helps.
At G5LK/P we had a different problem in VHF NFD- yet another blown pre-amp on the Sunday morning, currently attributed to 4m getting into the control circuit. Sorry to those we could not hear in consequence, though we did manage an OK without it, with a bit of aircraft assistance.
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