[time-nuts] FRS-C TTL / sine outboard filter question

Adrian rfnuts at arcor.de
Wed Jun 23 15:50:46 UTC 2010

>> Mine is marked "TTL" internally.  The service manual has a chart 
>> showing the differences between the sine and TTL options, and I 
>> converted it to the sine version by changing a jumper to a resistor 
>> and populating an LC filter with 10uH and 100pF (~5 MHz).  I also 
>> terminated the RF connection on the connector board with a 47 ohm 
>> resistor to ground.
> It sounds like you made the changes to the A4 oscillator board, but 
> not the ones to the A3 power supply board (several inductors, 
> resistors and caps). I found that using a 1 uF for C16, instead of the 
> documented 0.1 uF, gives a better signal. See the top of page A-15 in 
> the manual.
Exactly that's probably the culprit.
If you need a sine wave output but don't want to change anything inside, 
just add a lowpass filter.
A 5th order LPF (three inductors/ 2 caps or vice versa) should give you 
a clean sine wave output.
Just add a coupling cap to remove the DC component.


More information about the time-nuts mailing list