[R-390] 2nd LO xtal frequency

[Bob Camp]

Hi

I would double check any low level counter measurement with something designed for low level work. Even a spectrum analyzer would work for the offsets you are talking about. I’m not sure it’s really worth the effort, the oscillator is running way off by all you have checked. 

I’d check with the “usual sources” and see who has the crystals you need. I’d also see if a junker deck (with the crystals in it) would be a cheaper option.

Bob

On Sep 26, 2014, at 9:39 PM, Alan Victor <amvictor at ncsu.edu> wrote:

> Hello Bob, Craig, and all.
> 
> I agree with the shift in frequency about 1000 ppm. I was quite surprised.
> A simple measurment of course if you believe your PTO and 17 MHz 1st LO are
> spot on is look at the error on the kHz dial against WWV. However, I did
> measure the 2nd LO through a small 10 pF series cap. Yes, I pulled the
> oscillator a little but the zero beat shift was just 100's of cycles. A
> better method, form a small close field probe by soldering the center
> conductor of small coax, i.e. RG174 or better quality if you have it, to
> its shield. About a 0.5-to-1inch loop is all you need. The pigtail coax has
> a BNC on the end. I have a 40 dB gain preamplifier and run the preamp
> output into your counter. Doing a direct count, the 13 MHz xtal (for 10 MHz
> Rx) measured 12.986958 MHz. At this point I am searching the junk box and
> see what I can come up with for these various bands. Then its on to other
> problems.
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