[OZAPRS] APRS sat settings

vk2tv aprs at exemail.com.au
Fri Nov 11 11:24:20 AEDT 2022

Are there any satgates within 100km of Sydney that would cause a problem 
for their "local" stations? In my years of running a satgate I don't 
remember logging very many Sydney stations through ISS, PSAT, Bricksat, 
et al. The stations I usually gate are in vk5, vk3, vk4, vk1 and zl, and 
all a long way from here, making me a non-"threat" :) One exception is 
VK2EVB in Coffs Harbour (100+km) whom I can't hear direct.

The path "VIA=ARISS,SGATE,WIDE2-1" certainly doesn't create issues other 
than it makes the packet longer which "might" make it more vulnerable to 
not being decoded. If that path works for any particular individuals, 
use it.

As for HF aprs I fully endorse the value of using 30m, for those whose 
licence permits it. I ran 30m aprs for a number of years when out on the 
farm, logging aprs stations from all over Oz, Europe, the Caribbean and 
down near Antarctica. I also had a 40m port for aprs, and I tried 20m 
too - three separate rigs. 20m was a dead loss with a dipole antenna, 
and 40m was way too noisy - atmospheric. My site noise was always S0.  
Prior to turning to 30m aprs I ran a HF BBS and 30m walked all over 20m 
and 40m for reliability for Oz paths. The down side to 30m is that it 
tends to be somewhat unreliable and unpredictable for distances less 
than about 500km, that finding after considerable years of BBS and aprs 

A bit OT for the topic, but relevant to the conversation for best HF 
performance: to enhance the success rate of HF packet (including aprs), 
keep packets short. Parameters such as maxframe, paclen and frack 
settings are not what one would use on VHF, and "better suited" values 
make a world of difference on HF.
maxframe - use 1.  Better to get one packet through than to lose 2 or more!
paclen - maximum of 64 but preferably 32 or 48.   Same rationale as above!
frack - use 13 seconds.   This one made the world of difference. A 
typical VHF setting of 3 to 7 seconds would retry out, almost 
predictably when the band was noisy or badly affected by phase 
distortion. Longer frack time didn't eliminate those issues but did 
provide a better "buffer" against their effects.

Consider setting a txtail value (try 200mS and adjust as necessary) to 
ensure the end of the data stream isn't cut off by a tx dropping off 
before the packet has been cleared. I had zilch success on HF without 
some txtail time.

The channel access parameters listed were arrived at courtesy of 
Flexnet, the German packet software from the 90s, that dynamically 
auto-set the parameters listed above, and it was Flexnet that repeatedly 
arrived at those figures that served me well for some years, long after 
I shifted the system to Linux and kernel ax25.


Ray vk2tv

On 10/11/22 22:14, Terry wrote:
> The seems to be diversity of paths used for the ISS.  I think Ray's 
> observation (VK2TV) is pretty well on the money.
> However AFAIK the ISS is the only satellite operational at present, 
> and even then the digipeater goes 'off air' at times for a variety of 
> reasons - EVA / docking with another spacecraft / school contacts and 
> other events.  It's currently been off air for nearly five days as I 
> write, so it's not as reliable as one might hope ( I speculate that 
> sometimes they simply forget to turn it back on again). The other 
> factor can be that its orbits over a given spot on the earth's surface 
> are such that a mobile station might only be heard for a series of two 
> or three passes in any given 24 hours.   There are (from memory) about 
> three satgates in the SW of WA and from what I can see, VK5ATN-3 is 
> the only one in SA.   There are a few more in the eastern states one 
> in Tassie. The coverage over AU is pretty good but a satgate in the 
> northern part of the continent would be welcome to fill the gaps that 
> do exist. Even so, some satgates in Indonesia do have a reach which 
> does extend coverage into the northern and central  parts of WA.
> Personally I would still choose 30m for that kind of trip - I think 
> that on balance you'd be 'seen' far more often on there than what the 
> ISS is able to offer.  In the meantime keep an eye on 
> http://www.ariss.net/  and watch the orbits on a program of your 
> choice.   At present, the ISS offers useful daytime passes for 
> Australia, but in time that will change (as it does) to passes 
> possibly less favourable for the intended purpose.
> 73
> Terry
> On 10/11/2022 4:38 pm, vk2tv wrote:
>> I don't know if anything more than just VIA=ARISS is "really" needed 
>> in today's environment. Comments from anyone??? My satgate (near 
>> Kempsey), one of a few in Oz, just listens for traffic on 145.825 and 
>> gates it to the aprs-is.
>> Ray vk2tv
>> On 10/11/22 16:47, Bob Cameron wrote:
>>> Just wanted to check this. One never knows how dated Internet info is.
>>> I successfully beacon on 30m on my VK travels (permanently on road). 
>>> I am about to wander over to VK6. The 30m will be a good test of the 
>>> usual VK5 IGate I get into as it seems there is no 30m RX/igate in VK6.
>>> I do however want to setup a fallback to use satellite and wanted to 
>>> check if;
>>> is valid. Would someone please verify this for me?
>>> Tnx Bob VK2YQA-12
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>>> OZAPRS at aprs.net.au
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