it is not so easy to FM modulate a crystal oscillator, since the crystal
has a high Q therefore the modulation bandwidth of a crystal oscillator
is very narrow example: Q = F/dF -> df = F/Q if F = 10MHz, Q = 60,000
dF = 166Hz
73
KJ6UHN
Alex
On 9/5/2014 1:10 PM, Hal Murray wrote:
[email protected] said:
If I had 10Mhz or some other high frequency on the EFC line, would a typical
OCXO respond to that?
Some VCXOs actually specify their bandwidth. High audio is sometimes useful.
I haven't seen anything beyond that, but I'm just listening to discussions
like this one. There could well be applications that use a higher frequency.
One application is correcting for mechanical vibrations. This is interesting
in radar used on helicopters. (They do Doppler filtering to remove clutter.
The lower speed of objects that can get through the filter depends on the
clock stability.)
PCs often FM modulate their clocks. It's a hack to get past the FCC EMI
requirements. It spreads a spike in the frequency domain into a blob with a
lower peak. I think 30 KHz is typical. The PCI specs were tweaked to allow
this so they probably say something about the legal frequency limit.
PCs probably don't use expensive OCXOs, but that technology might get used in
other applications.
How do FM modulators work?
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