Tuesday, May 24, 2011

Off-air frequency standard

This is an unbuilt kit for an Off-Air Frequency Standard from Spectrum Communications. It is a crystal calibrator phase locked to BBC Radio 4 on 198kHz with an output of 2V peak to peak at 10MHz.

I got this with the intention of using it to frequency lock my Elecraft K3 using the KREF3 module. Regular readers may remember that last year I purchased a surplus Efratom LPRO-101 rubidium frequency standard to calibrate my radios. But a rubidium frequency standard has a finite life which will be used up very quickly if it is turned on all day to use as a real-time frequency reference. My intention is that the off-air frequency standard will run all day and keep my K3 as accurate as I need it to be.

I ordered the full kit from Spectrum. I was disappointed to find that what looked like a die cast box in the picture is actually a plastic box with a grey metallic finish. If I had realized it was not a die cast box I would probably have opted for the cheaper PCB kit and ordered one of the nice extruded aluminium alloy Hammond cases for the project. I hope it will be RF-proof enough to work in my shack environment where up to 100W may be used into indoor antennas.

The other disappointment was the rather home made looking PCB which does not have a silk screened component overlay. There is a printed layout in the instruction sheet but relating the component positions to the holes on the PCB is easier said than done. My initial thought was that I am not going to be able to build this. What I will have to do is draw the component overlay on to the PCB itself prior to construction. But it isn't easy with my diminishing eyesight and need to use different strength lenses which makes switching between things at different distances a real trial. Having a silk screened PCB would just have made things a bit easier. I think my days of kit building are definitely numbered.
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