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

paul swed paulswedb at gmail.com
Fri Feb 20 14:33:53 EST 2015


Chuck
Thanks and indeed I do need filters that I have not experimented with and
in that respect this would be more like some of the circuits discussed here
on time-nuts.
I am using nice controlled delay lines and at $66 each thats pretty
un-attractive.
But hey when you get them for 50 cents at a hamfest you can get crazy. Kind
of kicking my self as I think the guy had more. Wasn't sure what to do with
them.
So the next step would be a 5 Mhz notch.
Regards
Paul
WB8TSL

On Fri, Feb 20, 2015 at 11:28 AM, Chuck Harris <cfharris at erols.com> wrote:

> 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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