RadioBanter - WEFAX & RTTY

On Thu, 23 Oct 2003 17:48:32 +0100, "Roger Cordrey"
wrote:

I need to obtain an SSB receiver suitable for receiving WEFAX and RTTY (as
well as audio weather transmissions) with an output which I can use to input
to a PC running something like JVFAX. I know nothing at all about this sort
of radio reception, but anticipate some problems with any sort of
sophisticated unit as I need to use this on a boat cruising in UK, Europe
and Med.

Would I be better off with portable, battery powered receiver - or installed
RTX with backstay antenna etc.? And can you suggest/recommend make/models
appropriate to your advice?

Roger,

I'm a bit of a premium radio fanatic when it comes to home use.

However, for my Hunter 310 I bought an Icom R-75 receiver to feed my
laptop for HF-Fax, Halifax (CFH) RTTY weather broadcasts and NAVTEX
broadcasts. The receiver works well with either its AC power brick on
AC shorepower, or directly from a 12v accessory socket.

Best of all, it's a pretty good approximation to my mulit-$k rackmount
receivers for US$450 (from Ham Radio Outlet).

Another possibility you might consider (as I did) is the somewhat
dated (but still very good) Yaesu FRG-100 (at the same price).

Yet another receiver option is the Ten-Tec RX320. It's a better
receiver than either the Icom or Yaesu, using digital signal
processing for its IF filtering and demodulation functions.

It also runs on 12vdc, either from an included power brick or boat
power, and only costs $300. However, it is a "black-box"
computer-controlled receiver, that would require you to use additional
(free) software to control it.

The advantage of the R75 is that I can listen to broadcast programming
(or voice weather broadcasts) without powering-up the laptop.

As you probably know, the best freeware fax decoder software is WxSat,
but I find the little $35 software combo SeaTTY to be a very good buy
for decoding HF-Fax, RTTY and NAVTEX messages in a simple and
convenient package. Both packages merely require a soundcard - no
serial-port hangers-on.

(I also have the Hoka Code300-32 suite of professional decoders for my
digital intercept hobby, but that's over-complicated extravagence for
cruising weather broadcats.)

In any case, you need to be able to tune so that the audio tones
coming out of the receiver to your soundcard are reasonably close to
the standard values for best decoding.

With a professional (rack-mount) receiver, you just use CW mode with
an appropriate BFO offset value. However, with consumer-grade
receivers (including most recreational boating "sideband radios") you
have to use SSB mode. This requires you to de-tune from the listed
frequency by the amount that you'd have offset the BFO in CW mode.

Having the ability to quickly tune to this "diddled" frequency by
recalling a digital memory when underway is pretty desirable in any
but the smallest seas. This could be from a laptop over a cable, but I
find the R75's built-in memories with the ability to label them as
"CFH" or whatever a big help.

If you want to do FEC-mode (NBDP) broadcast reception, you'll
appreciate the R75's "RTTY" mode, which is jst CW mode with the
required BFO offset as a canned value appropriate for 170Hz RTTY.

However, if you want NAVTEX, unless your boat (and those at nearby
slips) don't have battery chargers on, you'll need an optional 500Hz
filter to get a reasonable signal-to-noise ratio on 518kHz.

The (cheaper) 500Hz filter at the 9MHz IF makes the most difference,
and adding the more expensive 500Hz filter down at the 455kHz IF is
only a minor further improvement that, in my judgement, is a lower
priority than the oven-controlled "high-stability" frequency standard.
(which you can also live without unless you experience very wide
temperature swings in the cabin. I assume you'll not try any of this
shirtsleeve environment equipment in your cockpit.)

Good listening,
Al
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Location: 42N39, 71W09 (Near Boston, MA)
HF Antennas: 65ft TFD, 45ft T2FD, 28ft vertical, 65ft doublet
HF Receivers: Ten-Tec RX340, RX320, Harris R2368, Cubic R3030A
Decoders: Code300-32, Universal M-8000, PK-232MBX/DSP
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