[time-nuts] XOR frequency doubler question 5/10 Mhz

[Chuck Harris]

Hi Paul,

It isn't that it is bad, it is just that 5 and 15MHz products at
8 to 10dB down isn't very encouraging.

To make decent use of this technique, I believe that you would have
to install 20 to 30dB of 5MHz rejection, and a 10MHz low pass filter
in the output circuitry....

And, that is in addition to making a simple very stable 90 degree
phase shifter.

The 5MHz rejection filter is necessary to prevent phase anomalies
from appearing due to the beating of the doubled 5MHz fundamental
with the XOR gate created 10MHz signal.

Any time you add filters, you are adding temperature dependent phase
shifters to your circuit.

-Chuck Harris

paul swed wrote:
> Experimenting with a 74ls86 XOR doubler for 5 to 10 Mhz. Typically this
> would use a 90 degree phase shift to the other gate. The gate acting as a
> mixer to produce 10 Mhz.
> The reason to experiment is that I have noticed most of the doubler
> discussions take a 5 Mhz square wave filter it to a sine wave, feed it to a
> multiplier scheme and then filter the output. The 7486 method eliminates
> one of those processes.
> I have accurate delay lines I can adjust in 2 ns increments (Allen Aviation
> lump LC).
> The output is a semi asymmetrical square wave due to some gate timing I
> need to deal with if possible.
> Setting the delay taps to 90 degrees produces a 10 MHz output with 5 and 15
> Mhz 8-10 db down. Lots of other higher frequency outputs. At this point I
> have no filtering on the output of the 7486.
> Purposely mis-adjusting the taps sets either the 5 Mhz or 15 Mhz level
> higher.
>
> Other noise and such are many DB down 50 plus.
> Why is this a bad method as compared to our typical time-nuts discussions?
> Regards
> Paul
> WB8TSL
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