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FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator

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radiolistener:

--- Quote from: maxwell3e10 on August 23, 2019, 10:23:36 pm ---because the wavelength of the signals is so much longer than typical cable length.

--- End quote ---

you're also needs to take into account that usual coax cable has velocity factor about 0.6, it means that wavelength is almost twice smaller in the cable in comparison to the vacuum.

In the vacuum 1 meter wavelength is 299.8 MHz. But in the cable 1 meter wavelength is about 197.8 MHz.

Also you're needs to take into account double cable length, because reflected wave needs to move forth and back. By take this into account, 10 MHz = 29.98 m * 0.66 = 19.79 meters wavelength in the cable / 2 = 9.8 meters.

For 10 MHz, 9.8 meters is longer than 1 meter cable, but not so much...

For 50 MHz difference will be even smaller: 50 MHz = 5.99 meters * 0.66 = 3.95 meters in the cable / 2 = 1.98 meters. As you can see 1 meter cable is pretty close to 1.98 meters. So we cannot treat it as "much longer" at all... :)

maxwell3e10:
Yes, I agree with this. 10 MHz is kind of borderline above which one has to start thinking about impedance matching and termination.

There was a discussion on some other thread if 10 MHz clock distribution requires proper 50 Ohm termination on each end. In principle, yes, especially since the cables involved are often fairly long. In practice, not always. Some instruments have 50 Ohm impedance for external 10 MHz reference input, others have higher impedance.

radiolistener:
From my experience with these BNC to alligator clip cables:
https://www.aliexpress.com/item/32822207220.html

the critical frequency is about 2-4 MHz, above that I can notice significant error. I tested it with low bandwidth sine wave. It doesn't means that there is complete fail, no. You can still see the signal, but above 2-4 MHz you can notice difference with properly matched cable.

radiolistener:

--- Quote from: maxwell3e10 on August 23, 2019, 11:05:46 pm ---Some instruments have 50 Ohm impedance for external 10 MHz reference input, others have higher impedance.

--- End quote ---

I think it depends on how device using it. Some device may ignore distortions and even may be tolerant to jitter. But some devices may be very sensitive to external 10 MHz purity.

rhb:
@ maxwell3e10

BTW What's the "3e10" supposed to mean? 

You seem very busy avoiding identifying and explaining my 485 photos.

Generally this thread has degenerated into a "3 Stooges" skit with an occasional straight man walk on.

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