[time-nuts] AN/URQ-10A - on frequency doublers

[Richard (Rick) Karlquist]

The 5071A has a chain of doublers from 10 to 320 MHz.
One thing I learned in designing this is that it
is important to drive the doublers with pure sine
waves.  It might seem like if I double from 10 to
20, and then use that 20 to double to 40, it doesn't
matter if the 20 contains some 40 MHz 2nd harmonic
because after all I am making it into 40 anyway.
WRONG.  Without proper filtering, the spurs at
20 and 60 MHz come up due to the 40 at the input.

Another thing is that the filters should be designed
by transforming a low pass prototype to a bandpass filter
having a ladder network with series resonant tanks for
the series elements and shunt resonant tanks for the
shunt elements. For complicated reasons, this
works better than a low pass filter or a band pass
of the coupled resonator topology.  It is also
easier to tune up.  The 5071A chain uses off the
shelf components and has no adjustments.  Every
board just works at turn on.  Owners of 5061's
who have fooled with the multiplier in them will
appreciate this.

The lunatic fringe at NIST uses 2N2222 transistors
connected as diodes (collector to base short).  We
didn't have to resort to that in the 5071A.

BTW, a passive TRIPLER is also essentially perfect,
especially using Wenzel's circuit (see wenzel.com).

Rick N6RK

On 7/17/2019 5:43 PM, Glen English VK1XX wrote:
> Roy,
> 
> The passive frequency doubler is essentially perfect. It will add some 
> flicker noise. (There are documented methods like using CB connected 
> transistors etc however I suggest just build it unless you are after 
> doing better than the best labs in the world).
> 
> For all passive freq doublers, depending on where it is going, you might 
> want some selectivity to reject 4f, 6f etc , and also duty cycle affects 
> you might need to take notice of.The sort of input level you have 
> available, 3 to 10dBm is fairly suitable.
> 
> Expect conversion loss of 10 to 12dB , start with +10 is a good place.
> 
> You will most likely need some amplification post doubling to get back 
> where you want to be.
> 
> ...could buy off the shelf :  I would suggest this one : The balance is 
> good ensuring low odd harmonics :
> 
> https://www.minicircuits.com/WebStore/dashboard.html?model=RK-3%2B
> 
> For easy construction , for your 5 MHz doubler, I would suggest two RF 
> transformers and a bridge
> 
> like this: (schematic at the page) - see figure 4.
> 
> https://www.qsl.net/4f5aww/module5k.htm
> 
> you can use a centre tapped transformer, or 3 wire transformer.
> 
> OR, you could use a bridge frequency doubler .... has a little better 
> non even harmonic rejection...
> page 13:
> https://www.qsl.net/va3iul/Frequency_Multipliers/Frequency_Multipliers.pdf
> 
> 
> 
> glen
> 
> 
> 
> 
> On 18/07/2019 8:07 AM, Roy Thistle wrote:
>> Hi All:
>>
>> I tried to search for this, in the forum, but, I didn't find much.
>>
>> I'm interested in getting a AN/URQ-10A... I have the manual. It's an 
>> old on ship, frequency standard.
>>
>> Does anyone have recommendations, or issues, concerning these units?
>>
>> The one I am thinking of is a little bit high (about +10 Hz, I think) 
>> and can't be "tuned" back to 5 MHz, without... I am guessing 
>> calibration. But, I am wondering if... because of the positive drift, 
>> if the crystal is damaged.
>>
>> By the way, how and why 5MHz... because its not that useful! … at 
>> least today.
>>
>> Does a frequency doubler… assuming a lock on the standard... cause 
>> errors in the 10 MHz signal obtained?
>>
>> Best regards and wishes
>>
>> Roy
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> 
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