[aprssig] HF options - Further Thoughts
dave at emv.co.uk
Fri Dec 21 04:09:39 EST 2007
How about using PSK31 (or a variation) for this?
There are "PSK engine" DLL's available that'll do all the coding and
decoding DSP stuff for you, so long as you run them on a PC type system
(cheap enough, aren't there trackers that'll create PSK signals too?)
I can work all over Europe (and beyond!) day and night on 80/160m PSK
with less than 25W PEP out, and a definitely less than efficient antenna
system (electricaly short wire and ATU) from an "Urban" environment
Dunno about any licencing for non ham use though.
Just an idea.
> -----Original Message-----
> From: Stephen H. Smith [mailto:wa8lmf2 at aol.com]
> Sent: Wednesday, December 19, 2007 6:40 PM
> To: TAPR APRS Mailing List
> Subject: Re: [aprssig] HF options - Further Thoughts
> Scott Miller wrote:
> > I've had an inquiry about a project that would involve
> linking fixed
> > APRS stations at intervals of maybe 50 km, with not much chance of
> > digipeaters. Without favorable terrain, that seems a
> little doubtful
> > for direct VHF.
> > I've done very little HF myself in the past decade, and I've never
> > worked HF for local (relatively speaking) communications.
> Can anyone
> > suggest bands and equipment that would work well for this, assuming
> > 300 baud AFSK is used? Power consumption is a major concern.
> Just had some further thoughts. Do these stations need to be
> linked in a linear fashion (A---B---C) talking to each other,
> or is it just that each station needs to get what it hears to
> some common distant point; i.e. command post, net control or igate?
> If the latter, then an alternate approach would be to use the
> 10 Mhz "30 meter" band. 30M is open for hops of 100-500
> miles nearly 24 hours a day, and has very little
> interference on it since no voice ops are allowed on the band.
> The antennas become more reasonably-sized. (A full-sized
> 1/2-wave dipole is only 46 feet end-to-end, and a mini-dipole
> made from two 30M mobile
> whips end-to-end is efficient enough to actually be usable.)
> One would
> probably use the same NVIS approach of a horizontal dipole
> low to the ground for high take-off angle, as on the lower bands.
> If the "command post" or "igate" station was placed at
> least100-150 miles away from the area of operations, this
> should work reasonably
> [Note that the existing APRS HF system operates at the top of
> this band at mark/space freqs of 10.149.2 MHz / 10.149.4 MHz.
> There is an extensive infrastructure of igates and HF<>VHF
> gateways already in place on this frequency that ensures that
> you can transmit virtually anywhere
> in North America and be seen on the Internet. ]
> However, given the very low data throughput at 300 baud
> compared to 1200, and considering that you are occupying the
> channel for a radius that may cover 1/3 of North America at
> times (depending on propagation), you may be better off
> operating elsewhere in the band with your own network.
> especially if you are going to generate any significant
> volume of traffic.
> Stephen H. Smith wa8lmf (at) aol.com
> EchoLink Node: 14400 [Think bottom of the 2M band]
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