[OZAPRS] 30mx frequency

Noel Rowe noel-r at clear.net.nz
Wed Mar 31 12:40:39 EST 2004

Warren said:
>Hi Noel

>I am lost with this frequency conversion from LSB to USB,
>I keep ending up with 10,147.6
That is correct on 30m for someone using USB and a 1600/1800 TNC, which
includes me.  The handbook for a TNC will have the tone frequency it uses
specified in it.

>From Bob Bruninga web page the international frequency
>is 10,151 with 1600 & 1800 hz tones
That frequency is correct also, but only if you use LSB.  Because that
dial frequency, disregarding the SSB offset, seems out of band, it is for
peace of mind better to use USB so you can dial up "in band".  But in the
end, the side band doesnt matter as long as the tones produce the correct
RF frequency.
>Can you please show me the correct conversion steps. 
If you add the two audio tone frequencies used by your TNC together, it
will give you the difference between USB and LSB dial settings.  So 1600 +
1800 = 3400 and 10.151.000 - 3400 = 10.147.600, as shown above.

To start from the begining, on SSB the frequency transmitted at any point
in time is the dial frequency plus (for USB) or minus (for LSB) the
modulation frequency, regardless of whether it is speech or data.   And
for APRS on 30m the RF  frequencies generated by the tones (and used
internationally except at the moment in Oz!!) should be 10.149.200 and
What you do first is look up your TNC handbook and find the audio tone
frequency it is set up for, for HF use.  The rest is simple school
arithmetic.  Some minor fine tuning, a few Hz, may of course be needed
because of variations between our rigs.  And leaving the rig on 24 hours
helps to keep it stable. 
For using USB, you subtract the lowest of the two TNC audio tones from the
lowest of the two reccommended RF frequencies (10.149.200), and that is
the "dial frequency".   For example, for a PK232 TNC that uses 2110/2310
as its tones, 10.149.200 - 2110 = a dial setting of 10.147.090. 
For using LSB, the process is similar, but you add the higher of the two
TNC audio tone frequencies to the lowest RF frequency,  so using the PK232
as above but on LSB, it is 10.149.200 + 2310 = 10.151.510.
I should point out here that this is not really an SSB signal at all, that
is we do not need an SSB rig to transmit correctly.   A simple CW type
transmitter would do as well if we could pull the frequency 200 Hz,
between 10.149.200 and 10.149.400, as required for a rate of 300 baud.  We
only use audio to modulate our SSB rigs because we have the SSB rig
already!  It is a means to an end. But it is really a complicated way, to
use audio to get the RF frequency we need at any given moment. 

>I like Brian have heard very little aprs traffic on 30mx, and my mobile
>station is on air every working day.
>Even with all that monitoring I would be lucky to hear more than one
>a fortnight.
I am going to use HF mobile myself (as well as the VHF I always use) but
am waiting till we get this transtasman frequency difference resolved.
Overnight (starting at UTC 05:43 untill 21:15) I have decoded successfully
25 VK beacons, mostly from VK3WRM with a few from VK3MY-3, but I did it
only by fiddling the settings to allow for the localised Oz frequency use.
Remember that 30m is medium range HF band, I think about 500 to 5000 km is
regarded as the range, although I have decoded signals here as close as
50km.  We need  feeds to transtasman i-gates to intercept the traffic and
feed it "home".  And this is why we all need to be on a common frequency -
it doesnt matter where you are heard, as long as you are heard.
Hope this helps.  A list of setting for a range of TNC type has I see been
posted here, so should be of help to people.
Regards, Noel, ZL3GR.

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