[OZAPRS] 10MHz HF Gateway -Re: New to list

Ray Wells vk2tv at exemail.com.au
Fri Aug 31 12:26:50 EST 2007

Mike Zwingl oe3mzc wrote:

>just one comment on HF-APRS Gateway operation:
>in practice it is not the signal to noise ratio that decides about decode
>nodecode of an APRS beacon on 10Mhz.
I've only been on HF packet for about 8 years so I guess I've still got 
a lot to learn about it.

The two most significant things that affect the ability to decode HF 
packet are:
1. Noise
2. Phase distortion. Yes, even with just 200Hz shift it can be a real 
problem. It's more of a problem than noise at my QTH.

There is no doubt that a rig that drifts will cause problems, but with 
any modern synthesised rig the stability is excellent and unliley to be 
a consideration. Even my 23 years old Kenwood TS430 (which I'm currently 
using for the 30m gate) is more than satisfactory. I know the reference 
crystal is off by a100Hz or so but that's another issue that I can 
easily resolve when the need to do so gets to the top of my priority list.

>More important is to use a TNC that allows some frequency drift, like the

>DSP-TNC from SCS.
>The DSP-TNC is currently the only hardware that will simultaneously
>several APRS signals at same time in a 800Hz wide channel!
>So the frequency offset of a mobile station can be plus/minus 400Hz and 
>still have successful decode on 10.147,6 USB (10151LSB)
>See the result at VK6UZ-4 and VK8ZAB-4, Fritz and Alan are using these
>Most other TNCs/Soundcards require 30Hz accuracy in frequency, which is 
>almost impossible to achive.
>vy 73 de Mike
>ex VK3FPF/8
And how many are going to spend big money on another TNC when what they 
use works fine. We all know that Pactor-II is better than 0k3 packet but 
at near $2000 in Australia for the controller it would want to be.

VK6UZ and VK8ZAB are seeing lots of travellers in outback Australia, 
that's true, but have a look at where the travellers are, and then 
back-track to when they  were closer to stations in the eastern states 
and you'll see that other stations got hit more often. It's a matter of 
distance and propagation, not frequency drift in a mobile.

Far from being almost impossible to achieve, modern rigs easily maintain 
30Hz acuracy, and better.

I've had my TS430 in Central Australia on some of the most horrenous 
tracks you can imagine - try the flint country from the vk4/vk5  border 
up onto the Lamamour Plateau in South Australia, or the potholes and 
corrugations on the Birdsville Track just prior to it being graded. At 
no time did I detect the slightest stabilty problems, and I spent a lot 
of time listening to  both amateur and broadcast signals  (in SSB mode) 
while mobile.

On could be forgiven for thinking that you're selling those TNC's??

Ray vk2tv
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Ozaprs at aprs.net.au

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