[NLRS] Super tropo

[Doug Reed]

Hi Jerry.

Yup, I can agree with everything you said about packet. But I doubt the 
SSB advantage is a full 30dB, most references say 7 to 10dB. I usually 
expect reasonable packet decodes at 20dB quieting, around .5uv or less. 
I expect pretty much guaranteed packet decodes near 1uv. In SSB I would 
expect easy Q's at under .25uv and I know we've managed to work 10GHz 
SSB well into the noise level. But those are contest Q's, not what I'd 
call ragchew quality.

To me, if the APRS beacons indicate a 500 mile path, that path, or 
something longer, has already been open for SSB operations for quite a 
while. We're back to "If a tree falls in the forest but nobody hears, 
did it make a sound..." If nobody is transmitting, is there really an 
opening? If everybody is listening on 144.200 but nobody transmits, how 
do I know if conditions are good? Use 144.205 for voice keyer beacons?

The best thing about using APRS as a propagation indicator is that there 
are already thousands of beacon stations out there all across the 
country. It is not a perfect indicator because it could easily miss a 
weak opening. But it is active enough to catch most strong enhancements. 
In fact I'm inclined to argue it may be TOO active, too many beacons so 
they overlap!

And there are enough APRS receiving stations out there collecting the 
beacons and sending them to a central server that the information is 
captured and available for further processing. If you are of the "I'd 
rather do it myself" type, you can setup an APRS receiver and search the 
received beacons to extract your own personalized propagation 
information. I think there may already be some filtering routines in 
APRSISCE that will do it for you if you just specify what local station 
to monitor.

Is it perfect, no. I could suggest several options that are technically 
better, starting with CW Skimmer, PropNET or WSPRnet. If you have a 
handy SDR receiver parked near 144.265MHz you could use SDR and CW 
Skimmer to monitor existing CW beacons and forward the captures to one 
of the propagation sites. That would get you maybe 50 beacons across the 
country. And how many people would dedicate a receiver to do this 
monitoring? There are nearly 50 APRS WIDE digis and Internet gateways in 
Minnesota alone with many more active stations.

Yes, I would love to see a better system. But how do we get enough 
people interested to create the infrastructure. In broad numbers there 
are over 500 4-digit grid squares across the continental US. There is no 
way we'd get enough people interested in building CW beacons to have one 
per grid square. But there is probably near full penetration if using 
APRS. Or we could probably get by with the existing CW beacons if we had 
50 CW Skimmer stations monitoring propagation.

Until we get another, better, system for monitoring propagation, you can 
manually listen to CW beacons or you can watch for out-of-the-area FM or 
TV stations, or you can listen for distant NOAA weather radio stations. 
But all of these require your active attention, it isn't automated. Of 
all the systems out there, the APRS propagation monitoring map at 
Mountainlake seems to be the best option if you can apply a little 
mental enhancement to what the map shows you.

What I was interested in was having people mention if they make 2M Q's 
based on what they see on the Mountainlake map. This morning when the 
map was showing propagation from Mpls to Duluth, could Bill near Grand 
Rapids talk to Iowa or Missouri? Bill did say that conditions during his 
Q with W0GHZ was well above normal, but how much further could he have 
gone? DX Sherlock attempts to collect QSO logging info to indicate 
activity and pull more people in. But since it relies on someone 
noticing activity, it makes a poor indicator.

Anyway, my coax and antennas are so poor that I don't hear anything on 
the beacon frequencies even when Mountainlake is showing good 
conditions. :-)

For reference, I use these numbers to indicate the relative sensitivity 
and "QSO Ready quality" of conditions.
+10dB-	FM voice
0 dB -	SSB
-6 dB-	CW
-14dB-	PSK31
-24dB-	WSPRnet

I sometimes just lump CW and SSB together as 0dB, but that is a personal 
preference.... After considering FM vs SSB at 10dB, you also have to 
consider relative power levels. I'd guess the average APRS WIDE would be 
running around 40 watts. So on the order of 4 watts SSB should perform 
about as well. Or the other way around, a 100 watt SSB station has at 
least 14dB, over 2 S-units, advantage over an APRS station.

Anyway, unless we can find some other fairly constant signal(s) to watch 
as automatic propagation indicators, I still think Mountainlake is as 
good as we can find. There is always the other problem too, that during 
the weekday there are far fewer stations available to work....

73, Doug Reed, N0NAS.

Dr. Gerald N. Johnson wrote:
> You asked about the performance of APRS as a propagation indicator. APRS
> AFSK packet has two thresholds. First is that of FM some 30 dB stronger
> signal required than for SSB and then the typical PLL AFSK detector
> requires a virtually noise free signal, far better than just copyable
> voice so when APRS links see long they are STRONG. To FM AFSK, its DX
> when its "local" on SSB at the same distance.
...snip....
>Most of the digipeaters are running
> stock TNC firmware, not node firmware and so have no discrimination
> against distant signals.
> 73, Jerry, K0CQ