[time-nuts] time-nuts Digest, Vol 53, Issue 8

[Richard Moore]

On Dec 1, 2008, at 2:33 PM, Stanley Reynolds wrote:

> Message: 6
> Date: Mon, 1 Dec 2008 14:31:33 -0800 (PST)
> From: Stanley Reynolds <stanley_reynolds at yahoo.com>
> Subject: Re: [time-nuts] DAC resolution in GPSDO
>
> The oscillator I think has a manual adjustment. You could be using  
> the 5 volt provided on board or the 8 volt provided by the OCXO for  
> the ECC op amp. Note the ECC voltage is dependent on the control  
> board regulation some what even using an external reference. You  
> may want to manually adjust the OCXO closer to zero and set the  
> upper limit lower as well. By?using a external voltage divider on  
> the ECC voltage or lowering the gain (R7 & R8).

Nope, this Isotemp was made for OFC, labeled OSC092, or maybe OFC/ 
McCoy sold out to Isotemp. There's no external adjustment available.  
I used a 78L05 to make the +8V reference supply for the OCXO and it  
works quite well. I don't use the BertBoard's signal output chip at  
all, nor the RS-232 chip, so loading hasn't been a problem. Compared  
to my recently purchased Thunderbolt, running off the same antenna,  
the Zauhar GPSDO moves around by a few parts in 10E-10 to 10E-11.  
Using the +8V ref supply to make a larger range of DAC output makes  
the problem worse, not better. A 16-bit DAC would help, but this  
project has gotten more complicated than I wanted already -- see my  
webpage. The best solution now would be a good 10811A...

Dick Moore