PMRC Digital Education Net
Every Tuesday evening at 1900 (7:00 PM)
For the past year or more, we have been testing different FLDIGI op 'modes' to see what works well on the PMRC 2m FM analog repeater with multiple offsite inputs. We know that THOR and MFSK work very well, even up to MFSK128 and THOR 100, even for somewhat noisy signals.
There has been some question whether 8PSK(F) modes are robust enough to serve in any real emergency if we were called upon to deliver traffic to a gov't agency. The 8PSK (F) modes rely on a very high s/n ratio, often sufficient on a clear FM circuit, but not always. I notice a few stations who regularly check into the DEN have quite a bit of "noise" (background hiss sounds) when they check in by digi mode, as well as when they use their microphones. I'm not complaining about this; just pointing out an observation. Of course, I am very far from Roxborough but find I copy just about everthing, with an 11 element beam pointed towards Roxborough from an elevation of about 450 ft (my back yard).
Why don't we try this for the Tues night DEN on April 23rd.
If your transmitter has various power levels, choose HIGH power for this test.
Let's use 8PSK500F as our "check-in" mode at 7:00 pm tonight.
Be sure to turn ON the preamble constant tone (MENU under ID) for about 1 second, to have the repeater "catch" your signal. This means after you start to transmit, there will be a 1 second constant tone, and then the 8PSK signal will begin. That may help with multiple offsite inputs (the same applies when you talk with a mic). Key up, count to three, and then start to talk.
Turn off the FLDIGI "digital squelch" and turn off your radio's squelch.
These are very important. Don't worry about "trash" in the rx window.
Do not turn on AFC FLDIGI option.
Set your Transmit audio level to a reasonable volume (lower than your voice with your own mic). The worst thing to do for an FM circuit is over modulate (clips the signal).
Everyone: go to the FLDIGI MENU item for PSK modes and turn ON the TX "pilot tone" feature, and set the level to -20 dB. The Pilot Tone helps the software (in receive) to decode the sounds (it's really very technical). This means your transmit signal has an additional tone (you won't hear it).
For traffic, everyone prepare something really simple.... something that is a BLANK FORM FLMSG message with just a few lines of text.
Please don't send a long eml file that takes a few minutes with many blocks.
Then everyone will send their short FLMSG using the op mode 8PSK1000F, without selecting COMPress.
We will stay at 1500 Hz on the waterfall.
Center on the net control's signal on your WF.
SEND a TXID with your short FLMSG.
Everyone .... keep your RxID on at all times.
We will not do any "resends" during the net.
Once thru, everyone sends a FLMSG, and let's see who copies it.
After the digi net ends, we can discuss what we copied, and what we did not copy.... and guess why?
I suspect the "noisy" stations will have difficulty getting their messages delivered, as well as received ..... but who knows. I suspect signals that are "too hot" (too loud) may also not do well.
Everyone be sure that when receiving these 8PSK signals, your "diamond" in the bottom of the WF is lit GREEN (green is good).
Adjust your RX level (SignaLink is easy) for GREEN.
I'm looking forward to exploring 8PSK500F for checkins, and 8PSK1000F for traffic, via the 2m FM (analog) PMRC repeater.
During the net, keep a record of which messages you received with NO ERRORS, and which has a "CHECK SUM" error, and which had zero decode.
These test might give us some clues as to the effectiveness of the 8PSK mode for sending emergency traffic via this 2m FM repeater.