LF: DSP Experimentation, Antenna book etc.
Fri, 14 Apr 2000 08:15:58 -0400
Talbot Andrew wrote:
> If anyone wants to experiment with simple DSP techniques beyong just
> plugging in Gram etc, or even wants to try some programming without
> having to learn Windows API calls and how to use the soundcard, ICs for
> the serial port interface described in RadCom a good few years ago are
> still available.
> For those who don't remember the article, this was an 8 bit A/D
> converter digitising audio at 10000 / 7142 / 2500 Hz and sending the
> samples up the serial port to a PC. The idea being that this was a
> simple way for users to develop their own DSP type software in standard
> high level programming language without having to bother with the
> digitising side of matters. PC software available with the module at
> the time generated waterfalls and spectrum plots, although I have to
> admit that for these functions alone, these days you are better off
> using Gram and the Soundblaster. With slightly different PIC code for
> the interface, and a change of crystal, it will also work at 7200 Hz
> sampling instead of the overcomplicated sigma-delta interface specified
> for the VE2IQ software
> One function also available with this module was a simple downconversion
> from a 1000 Hz tone to zero frequency, the output consisting of Inphase
> and Quadrature components allowing phase measurements and vectorscope
> type programmes to be written easily. As far as I know, this function
> is not yet freely available for the S/B (sits back and waits for howls
> of refutation).
> A quick plug now - a commercial version of this interface with
> additional slow speed data logging functions built in, is available from
> HF Instruments - see their advert in the latest RadCom and web page
> HF-INST.CO.UK. The data logging function could be useful, for instance,
> for recording the AGC line over many hours while listening to a
> propagation beacon in the same way that a chart recorder would be used.
> To Larry and Co. if you have a 56002EVM available I now have some
> software for the PC that will let you sample a signal at 0.035 Hz (much
> faster rates are also of course possible), and produce waterfalls this
> wide looking in a bandwidth of 0.00012 Hz (yes, 120uHz). For QRSS
> that would require a dot length of 4 - 7 hours and around 12 days for a
> callsign. Rather silly but quite possible!
> I produced an overnight Dopplergram plot of the DCF77 time transmission
> and managed to clearly see some ionospheric spreading at night not
> present during the daylight hours. There really are visible ionospheric
> effects on 77 kHz signals but the picture is marred by the few mHz drift
> due to the Codec crystal changing the sampling rate as the room cooled
> in the night. If anyone wants a copy of this contact me directly on
> After reading all comments / discussions / arguments / heated debate
> about antennas recently ........
> Just found a very good book on antenna design on a work colleague's
> "The Handbook of Antenna Design" Vols 1 & 2 by A Rudge, K Milne et al.
> ISBN 0-86341-052-9.
> Thought by many to be one of the best books on antennas there is.
> After a serious bit of arm twisting I managed to borrow it from him for
> a few days. There is a decent sized chapter (over 100 pages) on VLF /
> LF antennas and another large chapter on HF ones.
> More importantly it does not have pages upon pages of squiggly maths -
> just simple equations that the average non-mathematician can actually
> use and plenty of diagrams and graphs to just read off the results.
> And finally ...........
> To those who complained they have never heard me on LF. I don't, and
> won't, operate normal speed CW. I hate the mode but will just about use
> it under protest on 10 GHz where it works well for rainscatter (and we
> keep to decent speeds with much repetition anyway). On LF I intend to
> stay with the far more effective (in S/N terms even if not in
> simplicity) PSK and other systems even if it means very few people to
> work ! Morse might be cheap and simple, but that is it's only
> advantage these days. CW may well be a skill, but not one I'm prepared
> to practice at keeping up (Sits back and waits for even more flak !)
> Andy G4JNT