A question to QRP PSK31 users and potential users: I am trying to design a way to transmit PSK31 with simple CW-only QRP transceivers. Besides the technical challenge of getting a good-enough signal quality that way, there is also a human-interface issue. I wonder whether people would choose to use such a system, given the limitation described below.
In normal use (with SSB rigs) one can see multiple incoming signals in the "waterfall", click on the desired one, and then the software generates an outgoing signal at the same audio frequency as the chosen incoming one. That way they end up on the exact same radio frequency.
My idea involves modulating the transmitter based on the envelope of the PSK31 signal output by the computer. The audio frequency of that envelope is ignored. That means that one would have to do without that nice feature of the PC software. Instead, one would need to do something like this: find the signal you want to respond to, then tune the rig's radio frequency so as to place that signal on the waterfall at the same audio frequency as the (CW) rig's tx/rx offset.
For example, if the transceiver transmits 700 Hz above (or below) the "carrier" frequency during reception, then the incoming signal should be producing a 700 Hz beat relative to the BFO. One can mark (via software or otherwise) that audio frequency on the waterfall to help with that tuning. With some radios one can also see the outgoing carrier on the waterfall by hitting the (CW) key for a moment. (Arranging a way to do that at low power, without actually transmitting, is an easy mod in some rigs.) The tuning can be made more exact if the waterfall can be zoomed in to show a narrower range around that frequency than the typical 3 KHz band. Some existing PSK31 software programs allow that, some don't.
OTOH if you are the one initiating the QSO (e.g. by calling CQ) and the other party (using a conventional SSB rig) replies right on your frequency, then all is good, you wouldn't have to do anything further to tune it.
This is not really different from the way we use the rigs for CW, where you tune the incoming signal to the same (or close to the same) audio pitch as the offset (and the sidetone, in the many rigs that generate the sidetone via beating with the BFO).
So, would you live with such limitations for the purpose of being able to use simple CW rigs (e.g., the SW40/SW30/SW20, the similar MFJ rigs, HW7/8/9, and so forth) for PSK31?
- Moshe, N1OVN