[OZAPRS] What's Happened to HF APRS in VK?

Chris Hill chris.hill at crhtelnet.com.au
Mon Oct 13 19:37:35 EST 2003


Hi Warren,

Changing from LSB to USB does invert the "mark" and "space" tones, which
would definately be an issue for NRZ systems such as RTTY.

However, packet uses NRZI encoding, which only cares about whether a state
change has occured;  it doesn't care whether the change was "from a low
tone
to a high tone", or "from a high tone to a low tone".

Therefore, you can quite happily operate 300bps FSK packet using USB or
LSB,
just as long as you are transmitting and receiving on the right two
frequencies that everyone else is using.  (eg 10149.2kHz and 10149.4kHz
for
30m APRS operation).


I agree with you that running LSB with the displayed frequency (suppressed
carrier) being 10151kHz is undesirable;  not only will some rigs refuse to
transmit there, but we will indeed be transmitting out of band if there
are
any low frequency imperfections in the audio, due for (eg) alternator
noise,
AC hum etc...  a 400Hz "hum" on the transmitted signal would mean we are
transmitting energy on 10150.6kHz.  Not good.  Better to transmit using
USB,
safely inside the amateur band.


73 Chris




-----Original Message-----
From: ozaprs-bounces at marconi.ics.mq.edu.au
[mailto:ozaprs-bounces at marconi.ics.mq.edu.au]On Behalf Of Warren VK3BYD
Sent: Monday, 13 October 2003 4:43 PM
To: ozaprs at marconi.ics.mq.edu.au
Subject: Re: [OZAPRS] What's Happened to HF APRS in VK?


Hi Bob,

[SNIP]


> 2) If people are "confused" THen simply don't call it 10.151 LSB, but
call
>    it 10.147.6  USB.  Its the SAME frequency (assuming someone is using
>    an 1600/1800 Hz shift.  But the BEST way to refer to the global APRS
>    HF freuqnecy is 10.149.2 MARK and let the user do his own math based
>    on what TONES his TNC uses.
>
> They are all the same freq.

Are they all the same? Wouldn't swapping to USB invert the mark / space
thus
preventing you from decoding the signal on lsb?

Cheers
Warren.





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