Dear Gary, LF Group,
The attachment shows a spectrogram of the last hour or so of your test, up
to around 2251utc - earlier periods were similar. The upper trace is G0MRF's
beacon, which is quite local to me, and the lower trace is G4WGT. As far as
readability goes, the transmissions that are fairly yellow were printing out
with few errors; this was about 20dB above the "blue" noise floor on the
spectrogram. I would estimate that this mode will work with similar signal
levels to CW - the "yellow" signals would have been comfortable audible CW
copy. As you can see, the periods of QSB are quite variable - For a short
QSO of a couple of minutes, this wouldn't be a problem, but long QSO would
require standing by waiting for the signal level to build up after a fade -
also rather like CW.
I used MMTTY for reception - with 23Hz shift, the signal has to be tuned
quite accurately for best reception, perhaps within 5 Hz, and I found it was
neccessary to turn the AFC off to avoid it wandering off towards G0MRF's
CW/PSK31 signal - the separation between the two signal carriers was only
100Hz, so not surprising I suppose. The bandwidth of the narrow RTTY looks
quite similar to PSK31.
Thanks for the test,
Cheers, Jim Moritz
73 de M0BMU
G4WGT_02.jpg
Description: JPEG image
|
