We have an HP8662A and when we go from 118.0000000 Mhz to 117.9999999 the output has some discontinuity during the change. Other frequencies seem alright within at least 5 Mhz of this value. Does anyone know if this is a common characteristic of these units or is our unit faulty ? Thanks, Garnet.
There's a whole lot of switching going on inside that box. The reference range is switched in octave bands from 640 MHz down, and there are several VCO tank circuits to keep the noise low at any given frequency. How long is the glitch?
I've got a .PDF of the 1981 HP Journal issue that was dedicated to the
8662, and I don't see any switching logic in their block diagrams that looks like it happens at 118 MHz.If you're just seeing the signal drop out for a few milliseconds, I suspect it's nothing to worry about.
-- jm
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Thanks for the HP Journal - very interesting. Would be nice if the colored text parts had scanned in as well though. In our application if the signal drops out for more than 270ns we loose everything and have to start over so its a bit inconvenient. Guess we might be looking at a replacement generator sometime soon ......
They seem pretty legible here... are you using a reasonably up-to-date Acrobat Reader version on a 16/24/32-bit desktop display?
Yep, I think you're going to have to use a conventional sweep generator for that application. The 8662 will definitely hiccup when it switches VCO or reference ranges, and probably in a lot more places than that. I think their time-to-frequency spec is a few milliseconds at the very least, and the transition will be far from continuous.
-- jm
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