[time-nuts] Thunderbolt spurs on 10MHz output at 100Hz and 200Hz from signal.

Bob Camp kb8tq at n1k.org
Sun Sep 18 09:35:14 EDT 2016


Hi

If you are measuring the OCXO, you should be getting around -155 to -160 dbc / Hz at 100 Hz offset. 
Depending on the particular board you have, and how it is powered, the numbers out of the TBolt
can be quite a bit worse than this. With a good supply, you should get within 5 db. There are a lot of
spurs, so you do need a pretty good (narrow bandwidth) analyzer to sort them out from the noise floor. 

Bob

> On Sep 18, 2016, at 8:42 AM, David C. Partridge <david.partridge at perdrix.co.uk> wrote:
> 
> I've just redone the measurement without the external attenuator and with 10dB attenuation set internally to the analyser.
> 
> The results are attached.
> 
> Dave
> 
> -----Original Message-----
> From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of Bruce Griffiths
> Sent: 18 September 2016 12:52
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Thunderbolt spurs on 10MHz output at 100Hz and 200Hz from signal.
> 
> The signal level is also very low.
> Brue 
> 
>    On Sunday, 18 September 2016 11:47 PM, Magnus Danielson <magnus at rubidium.dyndns.org> wrote:
> 
> 
> The phase-noise still looks fairly high. How do you measure this?
> 
> Cheers,
> Magnus
> 
> On 09/18/2016 01:27 PM, David C. Partridge wrote:
>> Now that's interesting I just re-ran the measurement, and got a quite different result which is attached.  The spurs have GONE.
>> 
>> My only guess right now is that the E4406A power supply is getting quieter as it has been on for longer (I've only had it powered for short periods before now).
>> 
>> Dave
>> 
>> -----Original Message-----
>> From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of 
>> Magnus Danielson
>> Sent: 18 September 2016 11:56
>> To: time-nuts at febo.com
>> Cc: magnus at rubidium.se
>> Subject: Re: [time-nuts] Thunderbolt spurs on 10MHz output at 100Hz and 200Hz from signal.
>> 
>> Hi,
>> 
>> On 09/18/2016 12:26 PM, David C. Partridge wrote:
>>> The local power is 50Hz, so I can understand the 100Hz spurs, but I 
>>> don't quite "get" where the 200Hz spurs are coming from.  Or is that 
>>> just BAU harmonics?
>> 
>> Consider full-wave rectification of 50 Hz, the power consumption load 
>> on the capacitor after the rectifier creates an inverse sawtooth wave 
>> of
>> 100 Hz, and sawtooth waveshape have both even and odd harmonics.
>> 
>> While much of this is regulated out in the next step, some of it makes it though.
>> 
>> Cheers,
>> Magnus
>> 
>>> 
>>> 
>>> Thanks
>>> 
>>> Dave
>>> 
>>> 
>>> 
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