[time-nuts] Query about Austron 1150 oscillator

[AC0XU (Jim)]

I have an Austron 1250B, which has no fine frequency adjustment either on the front panel or through a rear connector.

I attached the datasheet for the 1150 oscillator module (with Skip Withrow's notes). The unit in my 1250B has no connection to pin 6, which is usually the reference for EFC, and which in 1250A units is wired to the control PCB. According to my DVM, pin 6 on the module itself has no conductance to any other pin. I thought that perhaps supplying an external reference voltage might allow the module to be tuned, but although pins 7 & 8, listed in the spec sheet as the EFC inputs, do have conductance to the ground pin, trying to adjust the frequency through these EFC pins does not work.

Does anyone understand why a customer would want a non-adjustable reference oscillator?

I am thinking about replacing the 1150 with another adjustable oscillator. This 1250B is nice because it has lots of buffered 5 MHz outputs, so I am inclined to rework it to make it more useful.

I have several adjustable 1250A models. They all have one annoying issue - the frequency adjust is so coarse that it is hard to adjust down to 10^-11 or better. I am thinking about adding a second 10-turn pot to the front panel, maybe 1M in parallel with the current 10K 10-turn pot. Has anyone tried that?

BTW, I looked into purchasing the digital pots that are in the FTS1050As. They are not a stock item but the manufacturer will make them on special order - for over $3K each in quantity!

Thanks-

Jim
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