[CALV-AUXCOMM] Net in Lieu of AUXCOMM Meeting on Jan 16

[Shawn Donley]

All,


The NWS is predicting the possibility of some snow starting late Tuesday afternoon.   Rather than holding our monthly meeting, I'd like to have a voice net instead using the 146.985 repeater.  No reason to be on the road in bad weather.


As a follow-up, I'd like to spend some time after the voice net practicing Winlink peer-to-peer, via simplex or using either of our two digipeaters, K3CAL-1 and K3CAL-10 on 145.750 MHz..


Some thoughts to ponder prior to the net (and plan to discuss during the net)........


My own experiences so far with Winlink during various exercises, including the SETs and hospital drills, is that it's effectiveness rapidly declines with traffic load unless a plan is implemented and followed to spread folks out on different frequencies, or a time-based protocol is implemented (i.e. station x gets to transmit only between specific times).   The problem is packet collisions, which is further aggravated by the "hidden transmitter" syndrome.    That problem is nicely explained at  http://www.w4ghs.org/Winlink.pdf


Here in Calvert, our long and narrow county presents challenges with simplex communications, requiring the use of digipeaters both within the county for peer-to-peer and to reach most gateways, the exception being KB3FWW-10 which I can hit direct even with a low antenna.  Using digipeaters further aggravates the hidden transmitter syndrome.


A further limitation (my opinion) with Winlink is that only the targeted ( addressed To:) station can copy a transmission.  Others monitoring on frequency cannot.  This compromises general situational awareness and required multiple transmission sessions to "spread the same word" among participants. 


For these reasons, I'd like to experiment with some alternative digital protocols to use within the county.  We will still need Winlink capability to reach out to other jurisdictions and the internet.


One possible alternative approach that intrigues me is the Narrow Band Emergency Messaging System, or NEMBS.

NEMBS uses FLDIGI as it's core and, like Winlink, adds pre-configured forms to handle traffic.  FLDIGI implements a number of modem protocols like the familiar PSK-31 and the not-so-familiar such as MT63-2000L which is a robust mode with forward error correction.  On the VHF and UHF frequencies, fast modes with forward error correcting such as PSK-500R, PSK-250R and PSK-125R are available.   Unlike Winlink packet, FLDIGI only requires a sound card interface between the computer and radio.  In fact, for some of the modes it's sufficient to hold the radio microphone near the computer speaker to transmit, and hold the computer microphone near the radio's speaker to receive.


These robust "analog" modems allow anyone of the frequency to accurately copy a transmission provided they are running the same mode in FLDIGI.  Being inherently analog, the FLDIGI signals can use a voice repeater (like our 146.985 and 444.950) repeaters to extend range throughout the county.   Now you might say that doesn't solve the signal frequency issue, but most everyone in the county can copy 146.985 and know when it's in use to "wait their turn."   Plus stations that can copy simples can work simplex in these modes on a different frequency.


More information on the NBEMS can be found on the web site below.  Download and read the two pdf files there to get a much better appreciation of NBEMS.


http://www.arrl.org/nbems


Shawn

N3AE

Calvert EC