odd results working at 250ksp/s
david.jacobowitz at gmail.com
Tue Oct 22 15:07:04 UTC 2013
I originally posted about 115.8 and 116.8 MHz, both square in the VOR band
of 108 to 117.95. I might have sent something else in a PM, but if so it
was a typo. :-) I am definitely only interested in the VOR band right now
-- though, as you say, it is adjacent to commercial FM with its high power.
My application is simple in concept: A fully auomatic VOR-based positioning
system, a fallback from GPS. I want to scan the entire VOR band, looking
for signals in the standard VOR format that can be demodulated. I do the
initial scan with a fast sample rate and FFT, just looking for peaks. From
those, I examine the signals to see if it looks like a VOR signal. From
that list, I will "park" on each signal long enough (~30s) to decode the
VOR's morse code station ID. From that, I will have a short list of VORs
that I can currently receive. From those, if the geometry is appropriate (I
know the VORs positions from a database) I can calculate a position.
The software then just round-robin tunes the VORs in range and continually
tries to calculate positions. If too many drop out, it returns to the
initial scan mode.
Not being able to receive this VOR or that VOR is not generally a problem,
but obviously, the more the better. With extra VORs I have better options
for choosing the closest ones or the ones with the best geometry.
This is actually quite difficult to test, because VORs can generally only
be received line-of-sight -- which means in the air. I'm a private pilot
but I found that flying and noodling with a laptop is too much trouble.
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