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Difficulty decoding

Harley Burton
 

Hi. I am running Sound modem 0.97b and CCW 3.54. I decode a few stations fine but most of the time, unless I have my receive cursor absolutely correct on top of the receive signal, nothing decodes. Additionally, I don't see any signals in my second waterfall. Finally, I only decode AX.2T messages. I see PSK messages but nothing happens. All signals are received with plenty of signal strength and a good clean signal but no decodes.

Help!
Hathey
N5BFB
73's

Chris Moulding
 

In UX7HO Soundmodem is a feature that adds additional software receivers to decode stations not quite on frequency.

If you go into Settings then Modem settings on the left hand side is a box Add RX. if you enter a number say 4 then it will add 4 extra pairs of receivers either side of the centre frequency spaced by the frequency in the Add RX Shift box (default 30 Hz). You can also change Bits Recovery to SINGLE to help decode packets with some errors.

Adding software receivers requires more CPU cycles so if you add too many then your PC will be driven hard and may slow down or lock up. On a fast 2.2 GHz PC I run 5 pairs on a slow 800 MHz PC I run 3 pairs.

With APRS Messenger just wait for some more activity it's usually busier at weekends or when someone's out in the wilderness sending packets.

Regards,

Chris

WA8LMF
 

On 5/11/2018 12:53 PM, Harley Burton wrote:
Hi. I am running Sound modem 0.97b and CCW 3.54. I decode a few stations fine but most of the time, unless I have my receive cursor absolutely correct on top of the receive signal, nothing decodes. Additionally, I don't see any signals in my second waterfall. Finally, I only decode AX.2T messages. I see PSK messages but nothing happens. All signals are received with plenty of signal strength and a good clean signal but no decodes.

Help!
Hathey
N5BFB
73's


1)    You must be exactly on frequency (i.e. within about  +/- 50 Hz or so for classic AX.25 and within +/- 10-20 Hz for Messenger Digimodes).   The digital displays on modern HF rigs ARE NOT frequency counters. They only show the frequency you requested. The actual frequency you get depends on the calibration of a master crystal standard, from which the operating frequencies are derived via a frequency synthesizer.  Over time, as the crystal ages, the exact calibration can drift from the factory setting.   

To determine if the synthesizer is slightly off,   tune in WWV in USB mode (not AM) and zero-beat the WWV carrier.  This is easiest to do during the second half of each minute where there are only time ticks and no audio tones.   When the tone returns at the top of the minute, flip back and forth between LSB and USB.  The tone should have exactly the same pitch in both modes. If one is higher than the other, tune ever so slightly until the tones are as close to the same as you can get.   Now read the frequency display.  If it is NOT exactly 2.500.00, 5.000.00, 10.000.00, etc, but is reading something like 4.999.93 or 10.000.10 for example, note the error from the desired exact frequency.    Then offset any other frequency settings you enter by the same amount.    

[Or open up the radio and tweak the TCXO (Temperature Compensated Xtal Oscillator) to precisely zero-beat WWV with the dial set to the exact frequency. Usually this is a tiny trimmer capacitor accessed through a small hole in a metal can on one of the PC boards .]   Note that you will get the most precise reading of any error by using the highest frequency of WWV that you can hear; i.e. if the propagation is favorable, use 10.0 MHz or 15.00 MHz rather than 2.5 or 5.0.  



2)    The Sound Modem has the ability to handle two separate radio systems/bands on a stereo-input sound system - one radio/interface on the left channel and a second one on the right channel. If you are using a monophonic sound system (MIC inputs on soundcards are almost always single-channel) you only have one sound input, and only one waterfall will light up.     (Unless you have opted to set the sound modem to single-audio-channel mode, allowing you to process,  for example,  both 1200 baud and 300 baud on the same audio channel.


Stephen H. Smith    wa8lmf (at) aol.com
Skype:        WA8LMF
EchoLink:  Node #  14400  [Think bottom of the 2-meter band]
Home Page:          http://wa8lmf.net

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Long-Range APRS on 30 Meters HF
   <http://wa8lmf.net/aprs/HF_APRS_Notes.htm>