It has been interesting reading about the prescaler project. I designed the prescaler for the HP 5334B, and am familiar with the prescaler for the HP 5386. You really want a static flip flop like the 5386 used. The commonly available prescalers are "dynamic". They are designed to be driven by a clean signal from a VCO in a synthesizer. If you try to measure a signal with a wide band noise floor (such as an HP8660), most prescalers will miscount in the lower order digits. Only the 5386 will work correctly, in my experience. You won't notice this if you count some free running oscillator, because you don't know its correct frequency. Another issue is that some prescalers lose sensitivity at low and high frequencies. Trying to fix this by adding wideband amplifiers exacerbates the wide band noise floor issue. Signal conditioning with ECL line receivers is another non solution. You also need a power detector to gate the prescaler off in case the power is too high or too low. Of course, you get to determine where to set those limits, which tend to be frequency dependent. You can't rely on the idea that you can tell if the prescaler is miscounting by looking at the stability of the display. A stable display can be wrong, and a variable display can be correct and simply reflect the stability of the DUT. There is still the problem of the noisy source.
If you are trying to design a prescaler board, it is important to understand the intended application and properly test the board for that application. It is a lot more difficult than most people think it is. Rick Karlquist N6RK _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
