EMRFD Message Archive 11777
Message Date From Subject 11777 2015-10-13 15:00:37 John Lawson Re: emrfd] QST SA 110MHz bandpass filter nearly complete but I have Vince,I used #18 wire for my coils.....check you wire size as one of the troubleshooting steps.......Finally, I worked with the coupling wires and the piston cap adjustments until I arrived at the proper shape of the filter as shown by a sweep of the filter, then I could get a good look at the inserti 11778 2015-10-13 17:07:41 Phil Sittner Re: emrfd] QST SA 110MHz bandpass filter nearly complete but I have
I second John’s comments. My unit has an insertion loss of 5dB as well and was a snap to calibrate. Over coupling leads to the double humps you have but I don’t know how that impacts the insertion loss. Use of larger wire improves the Q of your inductors and lowers the loss. The easy way to deal with the coupling is to use a longer length than specified and then trimming each of them in small increments (equally) until you see the bandwidth expected. If you trim too much it’s not expensive to replace the wire. This filter was for the original SA design. I also just finished building Ashar’s configuration but found better return loss with the w7zoi approach using the piston trimmers and 18 gauge wire.
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