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[aprssig] How About 40M APRS

Ray Wells vk2tv at exemail.com.au
Thu May 29 23:41:35 UTC 2008


Stephen,

You might like to add to your list of tones.

The Baycom USCC card uses the AMD711 modem chip and has two tone pair 
options ...
1070/1270Hz
2025/2225Hz

I use the latter pair here on 40m.

Ray vk2tv

Stephen H. Smith wrote:

> g0jxn.jim wrote:
>
>> APRS on 10.151 MHz is in wide use in Europe including the UK. However 
>> before I operated APRS on that frequency I consulted the then 
>> licensing authority on the matter. The only comment was that I should 
>> use 10.147.600 USB to avoid the possibility of out of band carrier 
>> leakage.
>>  
>> 73
>>  
>> Jim, G0JXN
>
>
> Specifying the frequency this way (i.e. the supressed carrier 
> frequency rather than the actual RF frequencies of the two tones used 
> in FSK HF packet) is COMPLETELY MEANINGLESS  --unless-- you also state 
> the audio tone frequencies being generated by the TNC or other device. 
>
> ==== Yet another reprint of my essay on HF packet tones follows=====
>
>
> Packet data transmission is done by rapidly shifting an audio tone 
> between two frequencies traditionally referred to as the "MARK" and 
> "SPACE" frequencies.  On 1200baud VHF packet, these two tones are 1000 
> Hz apart and standardized on 1200 and 2200 Hz.   On 300 baud HF, the 
> two tones are 200 Hz apart and ARE NOT STANDARDIZED.
>
> Simply quoting the RF "dial frequency" (i.e. supressed carrier 
> frequency) for HF data modes is ABSOLUTELY MEANINGLESS unless you 
> qualify it with the AUDIO tone freqs being used by the TNC or other 
> device.
> o     The indicated "dial frequency" on SSB is the suppressed carrier 
> frequency.
> o     The supressed carrier frequency is NOT transmitted. o     What 
> IS transmitted are sidebands that are offset below the carrier freq on 
> LSB (or above the carrier on USB) by the exact value of the AUDIO 
> tones fed into the radio mic jack from the TNC, soundcard, modem, etc.
> Since the actual transmitted RF frequencies (on lower side band) are 
> the indicated suppressed carrier frequency (i.e. "dial frequency") 
> minus the audio tone frequencies, the actual dial frequency you want 
> WILL DEPEND ON THE PARTICULAR AUDIO TONE FREQS your TNC or other 
> device produces.
>
> -----> NOTE THIS ESSENTIAL FACT!!! <-----
> -----> Unlike 1200 baud VHF packet, there is no standard for the audio 
> tone frequencies used by various devices on 300 baud/200-Hz shift HF 
> packet! <-----
>
> Frequencies    Devices using them
>
> 1600/1800 Hz    Kantronics KAM, TAPR TNC2 (MFJ 127x. etc), TinyTrak
> 2130/2230 Hz    AEA/Timewave PK-232
> 1100/1300 Hz    TigerTronics TigerTrak (300 baud HF mode)
> 2100/2300 Hz    AGW Packet Engine softmodem (300 baud mode in free 
> edition)
> 1600/1800 Hz    AGW Packet Engine softmodem (300 baud mode in paid-for 
> "Pro" edition)
>
>
> The differing AUDIO frequencies are really not a problem on SSB and 
> are easily accommodated. (Unlike FM the audio pitch heard at the 
> receiving end is affected by the exact frequency the transmitter 
> and/or receiver is set to.)  You change the audio frequencies, as 
> heard at the receiving end, by tuning the transmitter to a slightly  
> higher or lower "dial frequency".  This, of course, results in a 
> slightly different indicated "dial frequency".
>
> [ This cuts both ways.  If the transmitter is off frequency, the tones 
> recovered at the receiving end will be correspondingly off-frequency.  
> Since the typical TNC or soundcard softmodem (i.e. AGW Packet Engine 
> or MixW in packet mode) will ignore any audio tones that are more than 
> about 20-30 Hz off, frequency setting is --VERY-- critical and high 
> frequency stability is essential.  You MUST be able to set the 
> frequency to within 10 Hz and KEEP IT THERE indefinitely.  This is 
> especially critical if you are going to transmit in the blind without 
> a signal to tune in on receive first!  Ideally you want a modern 
> synthesized rig with a TCXO high-stabilty master oscillator. ]
>
>
>
> The ==ONLY== constants are the ACTUAL RF freqs of the 200 Hz shift 
> mark and space tones on 30M APRS.  They are:
>    10.149.200
>    10.149.400
> NOTE: The traditional ham convention is to specifiy the actual RF 
> frequencies of the tones. The commercial/military/regulatory 
> convention is to specify the single frequency midway between the two 
> tones, along with the shift. In this format, the 30M APRS channel 
> would be quoted as:
>   "10.149.300 with +/- 100 Hz shift" or "200 Hz Shift Centered on 
> 10.149.300" .
>
>
> To produce the correct RF frequencies with a KAM, TNC2 or TinyTrak III 
> (300 Baud HF mode) whose default audio tones are 1600/1800 Hz, you 
> must set your radio to
>
> 10.151.00 LSB:
>   10.151.000 - 1.800  =  10.149.200
>   10.151.000 - 1.600  =  10.149.400 
> Or set the radio to 10.147.60 USB:
>   10.147.600 + 1.600  =  10.149.200
>   10.147.600 + 1.800  =  10.149.400
>
>
>
> To produce the correct RF frequencies with a PK232 whose default audio 
> tones are 2110/2310 you must set your radio to
>
> 10.151.51 LSB:
>   10.151.510 - 2.310  =  10.149.200
>   10.151.510 - 2.110  =  10.149.400 
> Or set the radio to 10.147.09 USB:
>   10.147.090 + 2.110  =  10.149.200
>   10.147.090 + 2.310  =  10.149.400
>
>
>
> To produce the correct RF frequencies with a TigerTrak whose 300 
> Baud/narrow shift audio tones are 1100/1300    (weird pairing centered 
> around the 1200 Hz low tone for 1200 baud packet -- but actually very 
> nice because the tone pairs are in the dead center of the typical SSB 
> filter bandpass and suffer the absolutely least amount of phase and 
> group delay distortion) you must set your radio to
>
> 10.150.50 LSB:
>   10.150.500 - 1.300  =  10.149.200
>   10.150.500 - 1.100  =  10.149.400
>
> Or set the radio to 10.148.10 USB:
>   10.148.100 + 1.100  =  10.149.200
>   10.148.100 + 1.300  =  10.149.400
>
>
>
> To produce the correct RF frequencies with the AGW Packet Engine 
> softmodem, whose default audio tones on 300 baud HF are 2100/2300 you 
> must set your radio to
>
> 10.151.50 LSB:
>   10.151.500 - 2.300  =  10.149.200
>   10.151.500 - 2.100  =  10.149.400 
> Or set the radio to 10.147.00 USB:
>   10.147.100 + 2.100  =  10.149.200
>   10.147.100 + 2.300  =  10.149.400
>
>
> Note that some HF radios with "DATA" or "FSK" modes offset the 
> indicated dial frequency to correct for the difference between the 
> suppressed carrier freq and the actual mark frequency, typically 
> assuming the lower tone is 2125 Hz (or sometimes 1800 Hz).  This will 
> force you to compute offsets different from what I have listed for 
> LSB/USB.
>
> AGAIN: Quoting "dial frequency" alone on non-FM modes is ABSOLUTELY 
> MEANINGLESS unless you qualify it with mode (USB/LSB/DATA, etc) and 
> the AUDIO tone freqs in question.
>
>
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