Would you accept constrained PSK31 operating procedures?


Michael McEwen
 

Fascinating concept...with my limited technical knowledge/skill, I'd like to try this...so far my PSK 31 efforts have been with my QRO rig at home station...it would be fun to put one of my laptops in my portable rig and try from a SOTA site...L'chaim...

_ _ ...   .. _ _ _

Doc K5OSA - QTH: EM04sr
ARRL  
4SQRP #801 - NAQCC #7625 - SKCC #10098
FISTS #17157 - OMISS #9886
LFSARC (Lawton/Fort Sill Amateur Radio Club)

Michael T McEwen
Lt Col, US Army, Ret

Cellular Phone:  580 919-9205
Residence:  580 529-3412


On Fri, May 22, 2015 at 3:53 PM, mbraner@... [4sqrp] <4sqrp@...> wrote:
 

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




moshecontra
 

First, PSK31 is NOT a frequency-shift modulation scheme.  It is PHASE shift.  In the simple (and most commonly used) BPSK mode, the phase is simply flipped 180 degrees - the frequency stays exactly the same.  (There is another mode, QPSK which shifts 90 degrees, that has some advantages, but is rarely used AFAIK.)  But in addition to the phase flip, in order to eliminate wideband splatter, the envelope is modulated, so that ahead of the phase flip the amplitude decreases gradually to zero, then the phase flips, then the amplitude increases smoothly to full power again.  If the envelope has the ideal sinusoidal shape, an "idle" PSK31 signal (a string of many zero bits) is therefore mathematically identical to a "two-tone" signal, i.e., two carriers that are about 32 Hz apart, beating with each other.  That's why it sounds like a warble.  The phase flipping is easy to add to a CW transmitter.  The correct amplitude modulation is the harder part.

Second, I am looking for a way to do it all with simpler equipment, not more complicated!  No Arduino for me therefore...  :-)  I can simply use my SSB rig and any old PC, but still would like to be able to do it with a CW transceiver.


Don Wilhelm <w3fpr@...>
 

Moshe,

One of the presentations at FDIM revealed a "how to do that".
The concept is to replace the VFO or VXO with a DDS, then use an Ardrino (or Raspberry Pi) to drive the DDS frequency control lines.
With the right programming, you can do JT65, RTTY, PSK or any of the other data modes that use alternating audio pitch to create the signal.
To accomplish the same thing using audio tones, you would need an SSB transmitter.

73,
Don W3FPR

On 5/22/2015 4:53 PM, mbraner@... [4sqrp] wrote:
 

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




moshecontra
 

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