[OZAPRS] We need a standard HF APRS Audio frequency pair

[Robert Thirkettle]

Hi Noel
I like what you say it make the problem a little easer for some people
to get their head around the problem. It represents the problem in a
slightly different way but the result is the same.  

Regards Rob Thirkettle ZL3RX          
Dept  Physics & Astronomy
University of Canterbury     
Private Bag 4800,         
Christchurch 8020,
New Zealand
Tel: +64 3 364 2510
Fax: +64 3 364 2469
mailto:rob.thirkettle at canterbury.ac.nz




-----Original Message-----
From: Noel Rowe [mailto:noel-r at clear.net.nz] 
Sent: Thursday, 4 December 2003 2:22 p.m.
To: ozaprs at marconi.ics.mq.edu.au
Subject: Re: [OZAPRS] We need a standard HF APRS Audio frequency pair


Mike, VK2BMM, recently posted here a detailed synopsis of the tone and
frequency issues relating to APRS on the HF bands.  He suggested that we
should refer to the "virtual carrier frequency"  rather than the dial
setting frequency that is the root of much confusion.

At a meeting held in Hamilton (central for ZL hams from Auckland,
Rotorua, and Tauranga) last Sunday to discuss APRS related issues, the
HF bands and the associated problems were debated.  It was suggested
that to overcome the "what frequency to quote" issue, that we should do
what was apparently the norm, at least arround here, back in the good
old RTTY days, and that was to quote the centre frequency of the tones.
This lines up nicely with Mike's thoughts.

All that is needed is for the operator to add together the frequencies
of the two tones to be used, divide by two, then use the result to add
to (for
LSB) or subtract from (for USB) the desired operating frequency (stated
as the tone centre, or virtual carrier as Mike expressed it) and the
result is the dial frequency.

The fact that it forces the operator to know (or to find out by looking
it up in the TNC manual or a help file) what the tones being used
actually are, can be seen to be educational and therefore a good thing.

As far as the LSB v USB debate for 30 metres goes, well I believe that
when the choice is to set a dial frequency in or out of the allotted
band edge, the "in band" setting must win every time.

Now, the tone centre is 10.149.300, my tones are 1600 and 1800, thats
3400/2 = 1700, dial set to 10.147.600 USB, ready and waiting!

Noel, ZL3GR.

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