[aprssig] Was 6 meter APRS, now 30M tone freq's and PSK

[Stephen H. Smith]

Bob Donnell wrote:
>  If the radio's SSB filter is a little wide, harmonics
> of those audio tones might not be well suppressed, which when using USB,
> from a carrier frequency of 10,147.600 kHz would result in emissions outside
> our band - 10,150.8 and 10,151.2 kHz.  
This doesn't seem to me to hold water in this case.  

1)  With the 1600/1800 tone pair, even the second audio harmonic would 
be at  3200 / 3600 Hz,   well above the cutoff of any normal SSB filter.  

2)  Most audio distortion is ODD harmonics which would place the 
distortion products even farther outside the filter passband.



>   I think I was the first person at AEA to talk to Bob
> Bruninga about APRS - at the time management there wasn't interested in
> committing programming resources to the idea, so it took another 3-4 years
> (?) before there was APRS support in AEA products.  

I didn't know there was ever any explicit support for APRS in AEA 
products.    What firmware version does a PS-232 need to have?   What 
APRS-specific features (i.e. beyond regular packet functions) did it 
support?
>  Phasing-type SSB rigs were likely worse,
> unless there was a quite good audio low pass filter ahead of the splitter
> and phase shifter networks.
>   
Presumably, mid-band audio tones (i.e. 1400/1600 or  1600/1800) would 
have had encountered fewer problems in phasing rigs, than tones at the 
far upper edge of the audio passband......

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Stephen H. Smith    wa8lmf (at) aol.com
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