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[aprssig] HF options - Further Thoughts

Dave Baxter dave at emv.co.uk
Fri Dec 21 09:09:39 UTC 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
also.

Dunno about any licencing for non ham use though.

Just an idea.

Dave G0WBX.
 

> -----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 
> well.    
> 
> [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]
> Home Page:          http://wa8lmf.com  --OR--   http://wa8lmf.net
> 
> NEW!   World Digipeater Map
>   http://wa8lmf.net/APRSmaps
> 
> JavAPRS Filter Port 14580 Guide
>   http://wa8lmf.net/aprs/JAVaprsFilters.htm
> 
> "APRS 101"  Explanation of APRS Path Selection & Digipeating
>   http://wa8lmf.net/DigiPaths
> 
> Updated "Rev H" APRS            http://wa8lmf.net/aprs
> Symbols Set for UI-View,
> UIpoint and APRSplus:
> 
> 
> 
> 
> 
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