"Netgeek" writes:

Len,

Thanks for the input and observations! Comments follow:


Agreed - not that interesting to listen to, but the NAV
channels are exactly what I'm interested in - (both VOR
and LOC). The "experiment" I have in mind is a processor
controlled scanner of sorts that tracks multiple VORs
and performs as a backup to GPS. Hence the need for
fast/agile tuning (either PLL or DDS). As you may have
gathered - I'm not an "RF guy" by any stretch - but I'm
attempting to learn (out of sheer necessity 8-).....

HAH! I did **EXACTLY** that project back in 1996 or so.

Used the 145151 PLL that someone else reccomended.

The RX was the ... crud .. can't remember the part number ... That
motorola 3300 part that was so popular. 3356 maybe?

Used a cheap 567 to track the FM part of the signal, and a simple
envelope detector for the AM part. It was barely adequate for
close-in stuff, and for long range stations, the noise performance was
terrible.

The outputs of the two detectors went into a two-channel 8-bit ADC and
were read by the CPU.

Used a 68HC000 for the CPU, and had a database of VOR stations burned
into the ROM.

The cleverest piece of code was the CW decoder that was used to ID the
stations.

It would tune around, listening to IDs and take a
best-guess at where it was, then build a list of stations to scan,
stopping on each one for a second to get a RMI fix. (There was a
little crude LPF to help with the noise performance. Not that it did
much good... )

I found some nice 4-line x 20 char LCD displays at a local junque
shop, with ENORMOUS characters. 0.6" I Think .. Just HUGE for LCDs
.... It would do a scrolling display of the form

SJC 025 nm @ 036
OAK 044 nm @ xxx

etc.

All in all it was a fun project -- with lots of cool learning
experiences. In terms of practicality, the performance was never
spectacular, RF noise from the CPU section would get into the IF
(21.4 MHz)... it made a neat cockpit toy, but I would **NEVER** have
considered it even a backup aid to navigation.

Just writing about this is making lots of little details come back to
me. Feel free to e-mail and I'll bend your ear.

-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
Lawrence Statton - m s/aba/c/g
Computer software consists of only two components: ones and
zeros, in roughly equal proportions. All that is required is to
sort them into the correct order.