[aprssig] 6 meter APRS

[Stephen H. Smith]

Chris Moulding wrote:
> Yes, that's how it should work.
>
> It's early stages for the program but I'd like to run the PSK/QPSK 
> audio at 700 Hz so that with an
> audio feed from an existing HF receiver driving a 300 bd TNC running 
> at 1600 / 1800 Hz the
> PSK would be 1 kHz below the existing APRS.
>
> On 30m that would be 10.1483 MHz. Seems OK in Europe, would that 
> frequency be OK in the US?
>
> The receive side uses +/- 50 Hz AFC so the tuning would be easier than 
> existing packet. It's using
> the PSKCore DLL by AE4JY. A simple test program works well. It just 
> needs the interface to UI-View
> completing for the first on-air tests. I'd better get on with it!
>
 In North America, the standard HF APRS 300 baud AX.25 mark and space 
freqs are 10.149.200 and 10.149.400 (or in ITU/regulatory expression  
"10.149.300 +/- 100 Hz).    Most users here set a rig to 10.151 LSB. 
(Technically the suppressed carrier freq is outside the ham band but 
hopefully it is decently suppressed).  The net effect with 1600/1800 Hz 
tones is to land on the freqs above.    The net effect with an added 700 
Hz tone would place it 300 Hz OUTSIDE the ham band.  

The alternative to get the 1600/1800 Hz tones in place on 10.149.200/400 
is to operate UPPER sideband on 10.147.600.  This would place the added 
700 Hz tone at 10.148.300 which is well inside the band and should casue 
no problems.    Aha!  Just noticed this is exactly the frequency you are 
talking about above..... Looks like we have a universal channel!

[Other than trying to convince the majority of FM appliance operator 
newcomers to HF that are totally illiterate about SSB and it's frequency 
relationships, to understand that 10.147.600 USB has exactly the same 
results as   as 10.151 LSB on FSK packet.]     

I have no idea where this silly business of LSB "outside the band" on 
30M originated.  Not to mention the nuisance of having to "jailbreak" 
most current rigs to get them to transmit at a dial reading (suppressed 
carrier freq) above 10.149.999

The custom of LSB on 160-80-40 and USB on 20 and higher is a legacy of 
the first SSB designs in the early-to-mid 1950s. The very first hombrew 
SSB rigs used a single 9 MHz crystal lattice filter IF and and single 
5-5.5 MHz range mechanical VFO osc.   The 9 MHz IF and 5 MHz VFO were 
added in a mixer to get to 14MHz (20M). The same VFO was SUBTRACTED from 
the 9 MHz IF to get to 4 MHz (75 meters) with the result that the 
sideband was inverted to LSB.  One of the quirky results was the VFO 
dial actually tuned in the opposite direction on 80 relative to 20; i.e. 
the mechanical dial would show 14.000..........14.350 on 20 and  
4.000......3.500 on 80 on the same slide-rule scale. 

In the 1960's several low-cost commercial 80/40/20M tri-bander SSB rigs 
(the National NCX-3, the Hallicrafters SR-160, the World Radio Labs 
Galaxie III and the Eico 753 ) institutionalized this convention for all 
time.  None of these rigs could get onto the opposite sideband!

By the time 30M (and the other WARC bands) arrived on the amateur scene, 
ALL radios had long since been capable of operating on EITHER sideband. 
Why the 30M APRS types didn't go with USB (which is universal and 
mandatory in virtually all commercial/marine/military HF/SSB) on 30 is 
beyond me......  Since the established pre-WARC convention was "LSB 
below 10MHz and USB above 10", the new 30M band just above 10 MHz should 
have,by all reason, defaulted to USB.

------------------------------------------------------------------------

--

Stephen H. Smith    wa8lmf (at) aol.com
EchoLink Node:      WA8LMF  or 14400    [Think bottom of the 2M band]
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"APRS 101"  Explanation of APRS Path Selection & Digipeating
  http://wa8lmf.net/DigiPaths

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