On Fri, Jan 20, 2017 at 10:30 am, kc0wox Leeper wrote:
Rule of thumb says the scope bandwidth should be about 10 times the signal displayed
I suppose I could mostly agree with that, though a 20 mhz analog scope should be good enough to diagnose this problem.
I assume his transmitter is running at 14 mhz. If you want to check signal shapes to see if there's a harmonic present at 14*3 or 14*7 mhz, then yes. ?If you just want to see if a 14 mhz signal is present and get a fair idea of the amplitude, then a scope with a bandwidth of 14 mhz or more is sufficient. ?A 14 mhz signal through a device with 14 mhz of bandwidth will be 3db down. At 3db down the displayed voltage on the scope will be down by sqrt(2), if it was really 1.414 volts pk-pk the scope would show 1 volt pk-pk. ?Good enough.?
Now if we're talking a cheap digital scope claiming a 20 mhz sample rate, then yes, likely not good for looking at a signal much faster than 2 to 4 mhz. ?Sample rate and bandwidth are two different things. ?A good quality digital scope will sample at 10 times the bandwidth of the vertical amplifier, the cheaper ones might limit the bandwidth to 5 times the sample rate.
Jerry, KE7ER
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