[NLRS] Super tropo

[Dr. Gerald N. Johnson]

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.

I used to be remote sysop for a number of Iowa packet nodes. Their 
default software settings would make a node accept a distant node as a 
direct link if it heard a beacon from it once, such as by aircraft 
reflection and then it would try only the direct connect to an 
unworkable node most of the day. During that time it would not connect 
to the nearest node and would put out beacons that it was "working" the 
distant node. It had to have settings to control what nodes it accepted 
as workable and that those sporadic nodes were not considered workable. 
A preferred list and then even under conditions of strong DX it would 
continue to connect and pass traffic automatically. So the properly set 
packet nodes wouldn't show DX propagation because it destroys the 
network functioning. The qrm possible doesn't help the preferred links 
though. The nodes broadcast shows only what it hears, not what it 
actually has passed traffic with, unless the distant modes are rejected.

APRS is beacon based, connections are almost not used. Every APRS 
station blatts a periodic beacon, with a generalized digipeater list and 
nearly all APRS stations act as digipeaters, plus there are dedicated 
digipeaters in the network. Some stations monitor and transfer to the 
internet for distant digipeats. Most of the digipeaters are running 
stock TNC firmware, not node firmware and so have no discrimination 
against distant signals.

73, Jerry, K0CQ

On 7/31/2012 9:58 AM, Doug Reed wrote:
>
>
> Interesting. On the Mountainlake 2M APRS web page at 9:45AM, there is
> one small spur of reception from Mpls to Proctor and a bunch of
> indication from Missouri and even more in Texas into Mexico. When I zoom
> in a bit on the map it shows a lot more widespread reception in our area
> reaching around the 5-state area, through Iowa into MO and KS, Wisconsin
> into MI and IL.
>
> So I would think that 2M should be good as well. Nothing showing on DX
> Sherlock on any band above 10M.
>
> 73, Doug Reed, N0NAS.
>
> Bill Davis wrote:
>> W0GHZ  50db above noise on 10Ghz this am -- even worked him portable from the dock SSB
>> K0AWU
>