[time-nuts] FTS 1200

[EWKehren at aol.com]

Ed
I think so too. I hope if it is a shorted capacitor it stays but looking at 
 for instance at the bias of a 10811. There would be no capacitor right at 
the  diode. I have the tuning network for a 1130 and it shows a 20 K to an 
internal  +12 V
Bert
 
 
In a message dated 8/10/2012 2:01:22 P.M. Eastern Daylight Time,  
ed_palmer at sasktel.net writes:

Bert,

I wasn't suggesting amps of current.  A normal  reverse-biased diode 
would give nanoamps of current flowing out.   Microamps (or more) of 
current flowing in would show that the internal  biasing of the varactor 
was messed up.  A bad diode could also show  current flowing in, but your 
success with negative voltage biasing  suggests that the diode could be 
okay.

Ed

On 8/10/2012 11:31 AM,  EWKehren at aol.com wrote:
> Ed
> I did not see any current, but that  is also due to the fact that there is
> most likely at least 10 K  between pin 2 and the varactor. Most likely if 
it
> was  biased for  instance + 12 Volt, there would also be a resistor before
> the   diode. I suspect John is right that with my + voltage the diode was
>  forward  biased and blocked oscillation.  Maybe this one was  strictly - 
tuning
> voltage, hope so. I  will run it for a time and  observe stability. May be
> similar to HP 10811 bias.
>  Thanks   Bert
>   
>    
>   
> In a message dated 8/10/2012 11:28:46 A.M.  Eastern Daylight Time,
> ed_palmer at sasktel.net writes:
>
>  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,  EWKehren at aol.com  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,
>> bg at lysator.liu.se   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,
>>>   jmiles at pop.net  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

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