Hi Bert,
I see on the data sheet that the tuning voltage is supposed to be -10 to
+10 volts and that the supply voltage is +22 to +30 volts. I suspect
that one side of the varactor is supposed to be biased at one half of
the supply voltage. But in your case, it looks like that bias is now at
zero volts due to an internal short - either a short between traces or,
more likely, a capacitor failure. When you apply a positive voltage,
you're changing the DC voltages in the oscillator circuit which disrupts
the oscillator.
When you apply a positive voltage to the EFC lead, is there a current
flow into the lead? Since a varactor is always supposed to be
reverse-biased there shouldn't be any current.
Ed
On 8/10/2012 4:46 AM, [email protected] wrote:
Bjoern
Thank you for the link I am able to change the frequency 4 Hz from - 2Hz (
0V) to + 2 Hz (-12.2V) using pin 2. Reading the info that you got me
probably explains the slot next to the connector, but I experience a much wider
tuning range on pin 2 and John is right any positive voltage forward biases
the diode cutting off oscillation. Will do some testing.
Thanks again Bert
In a message dated 8/10/2012 6:28:17 A.M. Eastern Daylight Time,
[email protected] writes:
Bert,
Good that you got the EFC working! But I would be a bit suspicious of
needing -13V.
It seems from:
http://www.ece.gatech.edu/academic/courses/ece4007/08fall/ece4007l01/al4/dat
asheets/symmetricon_oscillator_instructionsheet.pdf
that the default EFC configuration is (0 to +10)V with a range of 4e-7
(2Hz). From the same document there are a lot of other EFC configurations,
but none that goes outside of +-10V.
My 1200 has about 3.5Hz tuning range on (0,10)V. Se attached jpg. I did
not check behavior on negative EFC voltage.
--
Björn
John,
that did the trick I can tune it with a negative voltage, minus 13 gives me
plus 2 Hz but this unit came out of a FTS 5000 and it had a positive
tuning voltage.
Bert
In a message dated 8/9/2012 9:13:29 P.M. Eastern Daylight Time,
[email protected] writes:
John
Oven did reduce in current and I can not imagine that it would be that
close with an overheated oven. At 0 V it is within .5 Hz of what they
normally are. Ground has no effect but even 0.8 V on pin 2 stops oscillation
That's a suspicious-sounding voltage. Are you sure you're not
forward-biasing the varicap? Maybe some of these OCXOs were specified
for use with negative EFC voltage.
If so, then driving the diode with a negative voltage should raise the
operating frequency (which is what you want.)
-- john, KE5FX
www.miles.io
_______________________________________________
time-nuts mailing list -- [email protected]
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
