________________________________
From: Richard Moore <[EMAIL PROTECTED]>
To: [email protected]
Sent: Monday, December 1, 2008 4:53:23 PM
Subject: Re: [time-nuts] time-nuts Digest, Vol 53, Issue 8
Yes my suggestion was to reduce the range not increase it. I was not sure if
you were using the 8 volt reference inside the OCXO or the on board 5V now or
as you say an external 8 volts. In any case using a lower reference voltage
does decrease the range and step size. With no way to adjust the 10Mhz voltage
point you could raise the lower limit by modifying the op amp to offset above
ground. If using Bruce's suggestion then switch between two different positive
regulated voltages and not regulated and ground with the analog switch.
I have several 10811's just don't know how good they are yet ...
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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 <[EMAIL PROTECTED]>
> 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
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