[time-nuts] Suspected Spam: External clock for Analog toDigital Converter in GPSRx front-end Rx front-end

[Bilal Amin]

Hi John,

Thank you for your email. I am also looking at the PM method to solve my 
problem. I have a HP signal generator and I can use it to generate an RF 
signal and then modulate it with noise from the modulating input of the 
signal generator.
I need some suggestion regarding the noise generator. I don't have one and I 
never used one before. Any ideas regarding the noise generation.

Cheers

Bilal
----- Original Message ----- 
From: "John Miles" <jmiles at pop.net>
To: "Discussion of precise time and frequency measurement" 
<time-nuts at febo.com>
Sent: Saturday, March 03, 2007 1:13 AM
Subject: Re: [time-nuts] Suspected Spam: External clock for Analog toDigital 
Converter in GPSRx front-end Rx front-end


> Possibly, if the ready-made spread-spectrum clocks provide enough jitter 
> for
> him.  It shouldn't be hard to do it to an existing clock, though.
>
> The article by David Chu on time-interval averaging in the June '74 HP
> Journal issue talks a little about why phase modulation is preferable to 
> FM
> when you want to deliberately add jitter to a carrier.  A frequency
> modulator imposes a rolloff characteristic that shapes the spectral
> characteristics of the noise source in ways that you might not want, while
> making it harder to avoid changing the carrier's average frequency as well
> as its instantaneous phase.  He also points out that it's easy to add PM
> jitter by applying noise to a varactor-tuned tank circuit across the 
> signal
> path.  It all seems obvious and straightforward enough.
>
> Remember that the computer guys don't care what their average frequency is
> to any real degree of precision, because everything else is ultimately
> slaved off the main CPU clock.  If you use an FM technique and the
> modulating function isn't absolutely symmetrical, or the modulator 
> response
> itself is the least bit nonlinear, you will have to use a separate
> low-bandwidth PLL to keep the mean carrier frequency where you want it, 
> I'm
> thinking.  Way too complicated, considering the advantages of the PM
> technique.
>
> -- john, K5FX
>
>
>> -----Original Message-----
>> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]On
>> Behalf Of Hal Murray
>> Sent: Friday, March 02, 2007 1:17 AM
>> To: Discussion of precise time and frequency measurement
>> Subject: Re: [time-nuts] Suspected Spam: External clock for Analog to
>> Digital Converter in GPSRx front-end Rx front-end
>>
>>
>>
>> > How about using one of the "spread-spectrum" microprocessor clock
>> > generator IC's? These add a pseudo-random jitter to the clock signal
>> > so the interference from the equipment is slightly spread causing the
>> > equipment to pass EMC testing by causing an apparent reduction in the
>> > peak due to the bandwidth of the test receiver.
>>
>> I thought it was FM by a sawtooth, or something simple like that.
>>
>> I could easily have a fuzzy memory and/or there could be several
>> techniques
>> in use.
>>
>> --
>> These are my opinions, not necessarily my employer's.  I hate spam.
>>
>>
>>
>>
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>
>
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