Data modes Filters and the passband

Hello operators.

Since the arrival of the ft-891, I’ve been learning how to more effectively utilize the filtering built-in to the radio. A few days ago, I changed my method of making QSOs and calling cq on digital modes. Here’s how it works.

In the old days I would have the filtering wide open (if I had it at all), watching the waterfall for any new stream that I hadn’t worked already. It didn’t matter if it was ft8, jt65, psk31 or psk 63, I chased the streams in the waterfall. Well that’s not a very efficient way of making contacts, so I switched it up a little. Now I find an empty place in the waterfall, shift over to the passband, then set my filter just over the passband limits, so that I can’t hear anything on either side of the passband. Anything inside the passband is free to come through. At that point I start calling CQ inside my passband. It doesn’t take long to rack up a line of stations who are probably normally chasing the waterfall. The filters and passband are working! Now we make the qso.

The benefits of this should be obvious but I’ll list a few.

  • Reduced qrm from nearby strong stations
  • Reduction in noise
  • If your filters work on both tx/rx stations around you are happy.
  • You’re hearing only what you want and need to hear for the qso

We can also apply this methodology to Station to Station field communications. You have a sked with the station on a certain frequency at a certain time. Assuming both of you have good frequency accuracy, and zero beat, you take the same steps of creating a passband like we did in the first example, but we open the passband a little wider until we hear that station. Then we can tighten it around the signal once we have them. This allows us to hear only what we want to hear and ignore everything else. Surprisingly this works for your winlink gateways, it works HF APRS, ALE, … as long as you know the bandwidth used by the station/mode you’re trying to reach/use. It’s also especially useful for the low power operator in the field.

I know this is standard going for the old timers, but not having had this capability in the past, I’m excited I’ve learned a better, more efficient way to operate.

Give it a try


Julian oh8stn

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