[time-nuts] 5>10 doubler

Andrea Baldoni erm1eaae7 at ermione.com
Sat Jan 31 06:59:57 EST 2015

On Fri, Jan 30, 2015 at 07:35:34PM +0100, Gerhard Hoffmann wrote:

> As usual, it depends. If you want absolutely deep notches, it is
> easy with the usual molded chokes
> to produce craters at 5 and 15 MHz that meet at 10 MHz, even
> producing some loss there.

Let me sum up everything and please correct me:

the square-law characteristic of devices should be avoided, so the
configuration of the doubler must be some sort of "ideal" full wave rectifier

it's better to use diode-connected transistors like the 2N2222 because they are
less noisy than Schottky diodes at frequency < 40MHz (what about the normal
P-N diodes?)

matching is very important, so monolithic doubles or quadruples could be the
right choice, provided their other characteristics are compatible and the
substrate connection is not a problem

bandpass filtering must be avoided because of added unwanted
temperature-dependent phase shifts, so harmonic suppression should be obtained
by notch filtering

the notch filters could be made using quartz resonators but their high
impedance versus LC ones should be taken into account and, anyway, it's
difficult to find exactly tuned quartz (particularly for the higher harmonics
because of the overtone cut) - the sharpness of quartz filtering is not needed
anyway because the harmonics are distant enough for LC filters (what about
ceramic resonators?)

I add some questions.
I saw that most of the doublers out there are using a center tapped transformer
to obtain +-180 while the Racal circuit use a single ended input / balanced
output transistor discrete differential amplifier, thus combining phase
splitting with gain and impedance matching (but not isolation).
That configuration should be avoided because the transformer is normally a
better matched splitter?
On the base of many considerations, the Racal circuit is flawed in many parts;
it's anyway good enough for the counters it was designed for or the better
performance of other doublers will show up?

Best regards,
Andrea Baldoni

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