Fast Pulse

[Starfire]

Photo shows a gunn squarewave osc with a less than 1 nanosec pulse train and sub picosec rise & fall time which is super clean. (no ringing)

It is at the limit of a 1ghz bandwidth scope to resolve. The scope is at 200ps/div direct (not a sampling scope)

Next trick is to extract a single pulse

[chrismb]

Photo shows a gunn squarewave osc with a less than 1 nanosec pulse train and sub picosec rise & fall time which is super clean. (no ringing)

It is at the limit of a 1ghz bandwidth scope to resolve. The scope is at 200ps/div direct (not a sampling scope)

John, please excuse my ignorance but are you sure you are measuring a square wave of 1GHz repetition with a scope with 1GHz bandwidth?

I thought these sorts of scopes were limited to resolving a rise time of a few 100ps at ~10mV/div?

[Starfire]

Chris,
The scope is a Tektronic 7104 using a multichannel CRT and is capable of measuring a 1ghz pulse train. The bandwidth figure refers to a minimum performance level for the instrument but it is capable of better. The exciting thing is it can't resolve the rise or fall time - anyone working with fast pulses knows it is near impossible to get rid of overshoot on fast pulses (ringing) and for this instrument not to show a fuzzy edge on the trace means it it not there.

I have used a sampling scope with much higher resolution on this oscillator with similar results, but prefer the 7104 - also have a 500mhz storage beast (Tek 7934) which I can use to capture a one shot - just about - won't show the detail but will show a capture.
I did a course on maintaining 7000 series at Tektronix Guernsey about 1971 and am Tek certified for 7000 series so know its performance and limitations

I have been trying to get rid of ringing on gunns for well over fifteen years.

The osc is built from a sample diode from Macom - more mechanical engineering than electrical and a bitch to get working - I am trying to get a single pulse.

[Doug Coulter]

Super high frequency overshoot would either be radiated away (even a tiny exposed conductor - like a probe tip or a transition to-from coax - becomes a good antenna) - or missed by the scope, even a tektronix analog (which gained much fame and adoration for only falling off 3 db/oct where all other brands were 6-12 or more due to peaking in the vertical amp). I still love my old teks. But regardless - that's one damn fine waveform and a good payback for all that work.

You'd really need a super wideband spectrum analyzer to see if you really had a square - harmonics falling off at the right rate. But when it's that good - who cares?

[Starfire]

Gonna try with a tunnel diode ( well two diodes as a filp flop) - the gunns are very tricky to get working at 1ghz - no problem at 10ghz - so I have to run them about 1/100 power and use a few special tricks. Have ordered a 3ghz Russian gunn so should be easer to get working and test this feedback clamping idea, if my memory holds out also bought ebay 300887755596 to try.

Would love a good spec., but funds limited