[time-nuts] TADD-1 six channel RF distribution amplifier

Bruce Griffiths bruce.griffiths at xtra.co.nz
Fri Mar 28 01:44:31 EDT 2008


Jeff Mock wrote:
> Bruce Griffiths wrote:
>   
>> Steve wrote:
>>     
>>> I'm thinking about using the TAPR TADD-1 six channel RF distribution 
>>> amplifier to distribute the 10MHz output of my Trimble Thunderbolt to a 
>>> few pieces of test equipment.
>>>
>>> What does the TADD-1 do to the phase noise characteristics of its 
>>> outputs as compared to the phase noise characteristics of  its input? 
>>> Improve? Degrade? Little or no change?
>>>
>>> Thanks.
>>>
>>> Steve K8JQ
>>>
>>>       
>
> I've been using a TADD-1 for about 6-months now and I'm quite happy with 
> it.  You certainly can't beat the price.  I added the optional 10MHz BPF 
> and tuned it with a tracking generator and spectrum analyzer.  The 
> outputs are very clean.
>
> I've never tried to measure phase noise, but the op amps and the rest of 
> the circuit seem to be good choices to me.  tvb did some analysis of the 
> box you might find interesting:
>     http://www.leapsecond.com/pages/tadd-1/
>
> jeff
>
>   
Jeff

As John Ackermann has often pointed out using a high Q bandpass filter 
is a particularly bad idea if phase shift tempco is important.

The best way to eliminate harmonics is to use high Q traps tuned to the 
unwanted harmonics, these have litle phase shift (and associated tempco) 
at the fundamental.

If you do use a high Q bandpass filter it may be necessary to regulate 
its temperature to stabilise its phase shift.

Some care in selection of filter components is also required to avoid 
significantly increasing flicker phase noise.

John has far some distribution amplifier phase noise comparison data at:

http://www.febo.com/pages/amplifier_phase_noise/


Bruce


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