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[aprssig] who hears my station

Stephen H. Smith wa8lmf2 at aol.com
Sat Dec 24 05:04:42 UTC 2005


Sct599 at aol.com wrote:
> In a message dated 12/23/2005 9:06:32 P.M. Mountain Standard Time, 
> wa7ixk at earthlink.net writes:
>
>     Sct599 at aol.com wrote:
>     > You could try using HF. There is an APRS network on 10.151mhz,
>     LSB, 300
>     > baud. There are HF to VHF gates and I-gates too.
>     > 
>     > Scott
>     ____________________________
>     I have never heard anything on that freq.
>     I do not try very often.
>       Have you tried it or just repeating hearsay?
>     I wanted to used it in the wilds of Idaho for my annual trip.
>     I wanted to add a TXO-9 and ping every hour with 5 watts with a 9
>     ft whip.
>     Don.t think it will work.
>     I only want one or two internet connections per day.
>     I am conened about frequency tolerance from 40 degrees F to 110
>     degrees
>     F. in the boonies.
>     i
>

"The wilds of Idaho" is exactly the kind of place that 30M HF APRS is 
ideally suited for.   The band is open to SOMEWHERE almost 24 hours a 
day.   It's not uncommon to get into an HF igate 500-1000 miles away 
depending on time of day. 

What is a "TXO-9"?  

HF APRS is conducted with standard 300 baud 200-hertz FSK normally 
generated by feeding shifting AUDIO tones, into the mic jack of an SSB 
transceiver.   The object of this is ultimately to produce an FSK signal 
that shifts back and forth between 10.149.2 and 10.149.4 MHz .    You 
MUST be within 10-20 Hz of these two freqs to be received by most fixed 
stations.     

o     5 watts is very unlikely to work well in the noise and qrm on 10 
MHz.  You really need a flull-powered 100W HF rig to be heard 
consistently. 

o    A solid 9' whip will feed directly on 10 or 11 meters where it is a 
natural quarter-wave long.  It will require some sort of matching system 
or tuner at the base on 10MHz (30 meters) where it will be far shorter 
than a quarter wave (or a loading coil inserted somewhere in the whip). 

=== Background on HF/SSB FSK (A post I have made many times on various 
lists) 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-FM 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" 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)


This is really not a problem on SSB since (unlike FM) you can always 
change the audio frequencies at the receiving end by tuning the receiver 
a little higher or lower.

[ 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 is ABSOLUTELY MEANINGLESS unless 
you qualify it with mode (USB/LSB/DATA, etc) and the AUDIO tone freqs in 
question. 









Stephen H. Smith    wa8lmf (at) aol.com
EchoLink Node:      14400    [Think bottom of the 2M band]
Home Page:          http://wa8lmf.com

"APRS 101"  Explanation of APRS Path Selection & Digipeating
  http://webs.lanset.com/wa8lmf/DigiPaths

Updated APRS Symbol Chart
  http://webs.lanset.com/wa8lmf/miscinfo/APRS_Symbol_Chart.pdf   


New/Updated "Rev G" APRS     http://webs.lanset.com/wa8lmf/aprs
Symbols Set for UI-View,
UIpoint and APRSplus:






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