[time-nuts] ADEV

[Rex]

On 11/14/2010 7:24 PM, David I. Emery wrote:
>
> 3. External reference LNBs with 10 MHz (pretty universal) going
> up the cable that also carries power and brings the L band signal down.
> I'm not entirely sure how many of these designs simply bandpass filter
> and then limit the 10 MHz and use that directly as a PLL reference and
> how many phase lock a VCXO to the 10 MHz coming in.  Otherwise similar
> (and often  derived from designs for) the internal reference PLL types
> in 2 above.
>
> 	These ER types are more apt to be used for more exotic
> specialized applications where very high frequency accuracy or some
> degree of phase coherence  with other equipment or LNBs is useful.
>
> 	Obviously with the high multiplication factor, one needs a quiet
> reference inside the PLL bandwidth (and that is pretty wide to ensure
> reliable lock) - one suspects that issues with degradation due to
> mechanically induced noise and phase shift in the cables can be a
> problem.
>

I picked up an LNB a about 10 years back that used this external 
reference method.  The LO in the thing was a DRO that locked to a 10 MHz 
signal coming up the cable. The LO in this one locked to 10.750 GHz. 
Experimenting, I found that the DRO adjustment screw could be turned and 
it would lock every 10 MHz. I found it would lock as low as 10.690. I 
assume it would tune up about that far too.

I needed an LO in the 10 GHz area, so I hacked mine to use it just as a 
LO, not using any of the receive chain. Here's a page where I described 
the LNB and what I did with it.

http://www.xertech.net/Projects/sat_lo.html

Maybe the description there will help someone. If nothing else, it show 
pictures of what one external ref type LNB looks like.