[time-nuts] funky frequency

Lux, Jim (337C) james.p.lux at jpl.nasa.gov
Fri Nov 20 01:43:38 UTC 2009


More likely it multiplies up to something useful.

For instance, for deep space communications, older radios multiplied up
something around 5 MHz to get the 2.x GHz or 8.X GHz transmit frequencies..
9.5625 MHz * 880 gives 8415 MHz, which is in the middle of the Deep Space
"space to earth" band.  The corresponding earth to space frequency would be
749/880 times that.  Similarly in the 2 GHz band, the ratio is 221/240.

The entire system is based on the crystal frequency chosen for your channel
and stuff is divided up and down.  Until very recently, you got an
allocation for your mission (many years in advance) and you'd order your
crystals, wait a couple years for them to be delivered, then install them in
your radio and tune it up.  If your mission happened to use a spare radio
from a previous mission, you'd hope you could use the same channel so you
didn't have to get a new crystal.


More at
deepspace.jpl.nasa.gov/dsndocs/810-005/201/201A.pdf


Not that your OCXO was used for that, but there are a remarkable number of
fixed frequency systems around with oddball frequencies.  I'll bet there's a
lot of terrestrial microwave systems that multiplied a ovenized oscillator
up to the frequency of use, and since they're on fixed allocated channels,
there's no particular reason why one frequency is any better than another...
They're all custom.


On 11/19/09 10:48 AM, "Don Latham" <djl at montana.com> wrote:

> I just found in my dusty junk, a couple of ovenized frequency sources at
> 5.199155 MHz, part# EROS-750-MA111 Dunno why I got these. Is this a magic
> frequency? It does not seem to divide down to a baudrate...
> Don
> 





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