[time-nuts] Secondary phase noise standard & FE405

Bob Camp kb8tq at n1k.org
Sat Nov 12 17:52:30 EST 2016


Hi

Yes, the FE-405 uses a DDS and a cleanup. Inside the cleanup loop the DDS spurs come 
straight through. Since the FE-405 compensates for all sorts of things, the DDS moves
around a lot. Even a one bit change on a DDS will move spurs around. With an ever changing 
DDS, you have an ever changing forest of “stuff” on the output. 

Not the best thing for a “standard” …..

Bob



> On Nov 12, 2016, at 4:24 PM, Gerhard Hoffmann <dk4xp at arcor.de> wrote:
> 
> I have made an experimental secondary phase noise standard, as F.Walls
> 
> would call it. In the end, it's inspired by his paper.
> 
> 
> There is not much to it. There is a Mini Circuits PSC2-1 splitter that is
> 
> fed from an oscillator or other source. The splitter divides it into a
> 
> clean output that goes to another SMA.
> 
> The other half is to be dirtyfied. It is fed into another PSC2-1 that is
> 
> used as a combiner. Its output goes to the signal source analyzer via
> 
> a third SMA.
> 
> 
> The dirt input is either  a 4th SMA or a noise generator. That is switched
> 
> by reed relays. The noise generator consists of a 60 Ohm resistor and
> 
> currently 2 LMH6702 stages for +20 and +40 dB. I'm not sure if the
> 
> 60R really defines the level, but the gain is at least flat from AF
> 
> to > 100 MHz. If not yet, it can be made so. I have already a
> 
> solid step attenuator so I can get rid of those reed relays.
> 
> 
> I checked it this evening with my FE405 osc I bought earlier this year
> 
> and that has enjoyed a good month of continuous running by now.
> 
> I observed
> 
> 1. that the FEI delivers only 3.5 dBm
> 
> 2. that there are lots of birdies far out.     Is that normal, maybe from the DDS?
> 
> 
> The addition of the noise reference lines seems to work properly.
> 
> oscillator:
> 
> < https://www.flickr.com/photos/137684711@N07/30824608092/in/album-72157662535945536/ >
> 
> low calibration line:
> 
> < https://www.flickr.com/photos/137684711@N07/30824607162/in/album-72157662535945536/ >
> 
> high calibration line:
> 
> < https://www.flickr.com/photos/137684711@N07/30824607552/in/album-72157662535945536/ >
> 
> Later this evening I'll add the pic of the tin box. I need a USB cable...
> 
> :-)  Gerhard
> 
> 
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