The PMRC Digital Education Net

PMRC repeater: 147.030 PL 91

A voice and data net to discuss digital modes

Every Tuesday evening at 1900 (7:00 PM)

DEN  folks

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.


De  k3eui


Allstar is a voice over IP communication mode based on the Asterisk PBX platform.
An analog type transceiver is connected to other Allstar nodes via the Internet.

Doug, WA3DSP, developed the code to run Allstar with an inexpensive Raspberry PI.

For more information see:

Thanks to Doug and the Philmont club for setting this up.


If anyone is interested in HF NBEMS nets there is a group called Pa NBEMS Net

To join the group click here: PA NBEMS

NBEMS stands for Narrow Band Emergency Messaging System.

The Pa NBEMS Net meets every Sunday morning at 0800L using Fldigi at 3.583
Barry, K3EUI, is the net manager.

We would like to see more participation from the DEN members.