[Lowfer] 518 kHz Navtex

[Garry]

Hi J.B.,

The good news is my LF setup is nothing special. I have a pair of 
Clifton Labs active antennas (they outperform the homebrew ones I've put 
together). They both use eprobes 4' in length and are mounted atop 10' 
poles at yard level. I used to have one up on a roof tower at 35' and it 
didn't do as well as near the ground. The key, as others have often 
said, is to try different locations to find which one maximizes SNR. 
Just moving tens of feet can make a significant difference. The more 
sensitive eprobe (by typically several dB over the other) has the 
feedline grounded to an 8' ground rod at the base of its 10' mast. It 
also has a common mode choke of over 100 mH ahead of the 100' LMR400 
coax run to the shack. There, ahead of the DC inserter, is another 
common mode choke. Despite substantial inductance there is often a large 
picket fence of 60 Hz harmonics (thanks ComEd). Fortunately that blends 
into the noise floor pretty well above 100 kHz.

I use SDR-IQs for my receivers running Spectravue software. One is 
externally clocked with a GPS-reference 66.666 MHz clock, the other just 
uses the internal XO clock. The former helps when monitoring things like 
Wolf but even the latter can handle QRSS60, opera32, and fst4w-1800 fine.

I also have an RSPdx receiver with the much more elaborate SDRuno 
software. Surprisingly it underperforms the SDR-IQs by several dB in SNR 
despite both having 14 bit A/Ds and the RSPdx being a newer design. I 
haven't spent much time learning how best to use SDRuno but feel I 
shouldn't have to. Spectravue is quite intuitive and does everything I 
care to do, especially when it drives Spectrum Laboratory via a virtual 
audio cable.

But the key to demodulating Navtex RTTY is to have the best, most 
sensitive software. For that I use SeaTTY. I think Jay, W1VD recommended 
that years ago when I started listening to Navtex signals. I tried a lot 
of other software and SeaTTY was the best. Perhaps Yand has caught up to 
it. I haven't tried the latest versions of it, or other software choices 
for that matter.

Interestingly last night west coast station Q didn't show up. Perhaps 
like area 4, station R in Puerto Rico it's been off the air. I misedd 
$12H in Tofino also but figure that was due to "local" station G being 
long winded and transmitting well past its 10 minute windows. 
Fortunately last night the very common problem of a station staying 
keydown after it was supposed to sign off didn't appear.

73 Garry, K3SIW, EN52ta, Elgin, IL