[time-nuts] what is the best way to multiply a 10 Mhz signal?

Mike Feher mfeher at eozinc.com
Tue Dec 21 13:18:38 EST 2010

Interesting. When I used to use and build DDSs back in the early 70's, we
typically used 2.56 times the maximum required frequency for a clock, to get
above Nyquist and allow adequate filtering stop-band rejection. At the time
we could not go much higher due to limitations in device speeds, especially
the D/A. Today you can easily use a much higher clock frequency which would
simplify filtering and reduce gain variations. At 70 MHz clock you are only
at 2.333 Nyquist. Even at 2.56 by the time you get to your desired goal of
30 MHz, you will have what looks just about like a square wave. So,
filtering will be a must, and, after filtering, you will find that your
amplitude output will greatly decrease with frequency. The other question is
phase noise objectives. If that is not a real concern, then as suggested,
maybe a simple locked VCO would be the way to go. 73 - Mike 

Mike B. Feher, EOZ Inc.
89 Arnold Blvd.
Howell, NJ, 07731
732-886-5960 office
908-902-3831 cell

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Stephen Farthing
Sent: Tuesday, December 21, 2010 12:57 PM
To: Richard (Rick) Karlquist; time-nuts at febo.com
Subject: Re: [time-nuts] what is the best way to multiply a 10 Mhz signal?

Hi Rich....

Thanks for the reply....I have an AD9834 DDS chip I want to use for a
Frequency generator with an accuracy of 1 Hz from 0-30 Mhz. . This part can
be clocked at 75 Mhz - but unlike other DDS chips seems to have no internal
clock multipliers. So it seems to me if I can some how generate a 70 Mhz
clock signal from my rubidium standard I can solve the problem.

73s Steve

On 21 December 2010 17:36, Richard (Rick) Karlquist
<richard at karlquist.com>wrote:

> I used to be in the synthesizer business (Zeta Labs)
> in a previous life.  I learned to ask the customers:
> what you are trying to accomplish as the end goal,
> before tackling a messy problem like multiplying by
> 7.  Maybe you don't need to multiply by 7, but we
> can't tell from your question.
> Rick Karlquist N6RK
> On 12/21/2010 8:35 AM, Stephen Farthing wrote:
>> Hi everyone,
>> I want to multiply the output from my Efratom 101 (10Mhz) to clock a DDS
>> at
>> 70 Mhz. Has anyone tried this?
>> Regards,
>> Steve G0XAR

It is vain to do with more that which can be done with less.
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