[time-nuts] Rb as source for ADEV?

Bob Camp lists at rtty.us
Thu Feb 6 20:43:00 EST 2014


Hi

My intent was certainly not to stop anybody from doing anything with what they have. My concern is that this is a lot of work for modest return. A simple single mixer setup for  $20 would dramatically change things….

$3 mini circuits double balanced mixer
$3 op amps x 2
+/- 15 V supply you already have (hopefully).
$5 for a piece of perf board
$3 for 3 BNC connectors. 
$3 left over for resistors and capacitors. 

Offset the local reference one hertz or so and let the 5334 do it’s thing. Your resolution is now plenty good enough to see what’s happening. 

Circuit:

Mixer driven by your two sources
L/C filter between the mixer output and a positive gain op amp (OP-37 or similar)
Op amp set up with enough gain to give you 28V p-p when the mixer is saturated (OP-27 or similar)
Next op amp run as an inverter / limiter and driving the counter, use diodes in the feedback path to do the limiting. 

Not the most elegant circuit. Not the highest resolution possible.  Cheap / easy to build / simple to troubleshoot. Used a *lot* of times by a *lot* of people. 

If you want to get fancy terminate the mixer in 500 ohms at audio and 50 ohms at RF. Fancier still is to do some single pole R-C high pass / low pass in front of the first op-amp. Neither one adds much cost. They do make it slightly harder to build. 

To totally blow the budget go with an RPD-1 mixer rather than one of the simple ones. Termination would then be 500 ohms at RF and 5K at audio.  

Bob

Yes, I’m assuming you get the mixer at the hamfest / 20 piece price rather than just ordering one at a time from Mine Circuits.



On Feb 6, 2014, at 6:52 PM, Tom Van Baak <tvb at LeapSecond.com> wrote:

>> Simple answer - doing this directly with a counter is not the best approach. 
> 
> Most of us work with what we have. I think it's pretty cool what Bob is doing with a 5335A. Someday he may buy or build something better. Your best may not be his best, or my best. What is best at one tau is not at another. Time-nuts has never been about being best (otherwise we all loose to USNO); it's about learning and exploring this interesting field of time & frequency with what we have at home, whether it's the ADEV of 60 Hz or ADEV of a 5335A/GPSDO, etc.
> 
> /tvb
> 
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