[Fwd: [FoxHunt] Dick Smith Dop Scan]

[Bruce]

On Monday 25 March 2002 15:21, you scribbled:
> Peter, if you have scan ability I would really appreciate it !  It shou=
ld
> not be crazy big if its in Black and white so it might be easiest to
> e-mail.
> I thank you very much!
>
> I wish to get it running to help get others to see the fun in t-hunting=
=2E It
> seems people are amazed how easy it is to t-hunt with just and HT but t=
he
> dop scan attracts more new people.

Hmmm well easy !=3D dick-smith-doppler, at least in its original form!! T=
here=20
was an article written sometime (73 ? QST?) that took the DSE Doppler to=20
task, narrowed the filters, improved the diode switching etc, and made it=
 an=20
acceptable performer.=20
I'd suggest doing these improvements as a minimum to avoid undue frustrat=
ion.

Mine was never a DSE doppler to start with, but I did borrow ideas from i=
t=20
and other doppler circuits (see Joe's book) and made a home brew mismash =
with=20
8 antennas. At another stage I had the whole lot programmed into an EPLD =
+ 1=20
quad opamp.  It works, but never really well enough to get me really enth=
used=20
about dopplers.

Dopplers are comparatively deaf, fairly polarisation fussy and hopeless i=
n=20
multipath situations. There are also some RF problems with antenna mutual=
=20
coupling causing a directive pattern (when it isn't meant to be), and=20
switching noise (you can tackle this one with complicated sinusiodal=20
switching waveforms). They do give you "instant" bearings however, and wi=
th a=20
short pulse signal they might be the only practical option.

--=20
Cheers,
Bruce                                          ICQ: 32015991