Illustrating IF vs. Audio Filtering for Improved CW Rcv

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Illustrating IF vs. Audio Filtering for Improved CW Rcv

Post by NG5NG » Sat Mar 14, 2009 6:51 pm

Filters help CW ops dig out low-level signals by ear. This shows how both IF and audio versions improve copy.

A sound file that contains a qso recorded from 7114 is located on the Yahoo board, under Files > Other Stuff. It is named "IF es Audio Filters - an example.mp3."

For the 1st 10 seconds you hear just my radio, no filters.

At t = 10 secs, I put in the 500Hz IF filter.
At t = 20 secs, I put in the audio filter.
At t = 39 secs, I take the audio filter out, leaving the IF filter.
At t = 43 secs, you have the radio by itself again.

The filters not only help uncover signals, but they isolate signals in busy bands. Recommend purchasing 400 or 500-Hz IF filters first, then get an active audio filter. If you can find a Datong filter, (FL-1, FL-2, or FL-3), buy it. Datong was a British company that made excellent products, but alas are no longer in business. You can find 2nd-hand versions on E-Bay, E-Ham, QRZ, and the like. In my opinion, they work better than DSP and require no fuss.

The SCAF-1 works well too. You can build it cheaply as a kit, purchased at To slice out signals from the noise, use the IF shift to cut out low-frequency distractions, and the SCAF-1 to cut out high-frequency QRM/QRN. The web site has sound samples that are accurate/realistic.

Here is a picture of my station:
It shows the SCAF-1 in use. I've since picked up a bug, BTW, and I'm getting ready to spring it loose on the CW populace.

2 cents from another newbie...


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Location: Oceanside, CA

Post by N6NQZ » Thu Mar 19, 2009 2:16 am

Interesting for sure. I too send English style. That's the way I started and feel more comfortable in that mode. For me it feels like I am more in control of the key than with the arm resting on the table. So I like the long arm and elevated type of keys. Lots of pro and con arguments about this subject but I realize, what works for me is not necessarily the best cup of tea for others.


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Joined: Thu Jun 08, 2006 10:59 am

Post by Rich » Mon Mar 23, 2009 3:04 pm

One more for the "English" style. I have never been able to lay any part of my arm on the operating desk, even the USAF AACS was unsuccessful in getting me to do so. So they lived with my very capable high-rise method. All my straight keys are high-risers too.
73 de N2UGB

Still a place for low-tech amateur radio in a high-tech amateur radio world!

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