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Author Topic: PSK32 Narrow Filter - Type ??  (Read 2211 times)
N3HKN
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Posts: 245




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« on: November 20, 2003, 10:41:54 AM »

My rig is an Icom-746. As, I suppose, many hams suffer from strong PSK signals reducing their ability to receive weaker signals due to the AGC response to the strongest signal in the IF passband. Obviously with the 746 the audio DSP has no impact. However, the Passband Tuning can be adjusted to provide a narrow passband that helps quite a bit if the offending signal is not too close. A crystal filter seems to be the better answer to keeping the AGC from being activated by adjacent signals.

Thus my question - has anyone had any experience with narrow xtal filters to be able to offer an opinion on filter bandwidth and which IF (9mhz or 455khz) is the best place for the filter. I cannot afford to buy more than one filter.

Dick   N3HKN
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AA4PB
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Posts: 15066




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« Reply #1 on: November 20, 2003, 03:10:50 PM »

With my 756PRO I use a 50Hz filter for PSK31 so I would think the narrowest crystal filter you can get would be best. Make sure however that your radio will let you select that CW filter while in USB mode so that you can use it with PSK31.

Generally, the earlier in the receive chain your can get rid of the QRM the better. I'd put the filter in the higher IF frequency provided they are available in the bandwidth you want. A filter in either IF will prevent the AGC pumping however.
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Bob  AA4PB
Garrisonville, VA
N1ZZZ
Member

Posts: 213




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« Reply #2 on: November 21, 2003, 04:07:30 PM »

I have a 455Hz Inrad filter in the 9MHz IF of my 746.  I tell the radio that its a narrow SSB filter so that I can use it in SSB for PSK.  I use the IF shift to swing the filter bandpath across the waterfall.  IT works well, especially during contests.

GL 73 DE N1ZZZ
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