[time-nuts] Best phase detector / mixer for 100MHz?

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Bill,

>> One way to avoid the problem in the 1/f noise region is to avoid it.
>> Mix down to a few kHz and analyze you signal

This is a good point! Using my SW (www.hpw-works.com) simple set the x-scaling to a
center frequency & bandwidth of your choice with enough space in the lower region.
This is implemented out of the box. It's like a measurement using the d-jitter but
with a costume center frequency. See also the pictures on my homepage with zooming
into the 0.005 Hz region using a large sample size. 

Required is that the source oscillators are stable...  

Hanspeter


>> -----Original Message-----
>> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf
>> Of Bill Fuqua
>> Sent: Donnerstag, 29. November 2012 18:02
>> To: time-nuts at febo.com
>> Subject: Re: [time-nuts] Best phase detector / mixer for 100MHz?
>> 
>> At 03:56 PM 11/29/2012 +0000, you wrote:
>> > > By theory, yes... but we use a sound card with a lot of flicker
>> > > noise
>> > on the lower
>> > > end, also we have the 10...20Hz low freq. cutoff due the usage of a
>> > servo / single
>> > > 5V power. Also the raising noise below 100Hz (ADC serve & noise on
>> > > the
>> > ADC power /
>> > > input circuit) limits the performance.
>> 
>> One way to avoid the problem in the 1/f noise region is to avoid it.
>> Mix down to a few kHz and analyze you signal or if you must mix down to "DC"
>> then chop it to bring it up to a kHz or so and analyze it using a program such
>> as  spectrum lab or in software to internally mix back down to "DC" using
>> software digital mixer and then analyze.
>>   You can use a MOSFET analog switch to chop the signal.
>>    When you chop it you will have an carrier with upper and lower sidebands.
>> You can simply take the FFT data and either shift the bins making the carrier
>> (chopping frequency) the Zero or DC bin or even better yet add the upper and
>> lower sidebands so that you get a 3db improvement in S/N. I will be db since
>> the sidebands are identical mirror of each other, ie voltage doubles when they
>> are added increasing the signal by 6db but noise introduced by electronics on
>> upper and lower sidebands are not coherent and only increases by 3db.
>> 
>> 73
>> Bill wa4lav
>> 
>> 
>> 
>> 
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