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Test Equipment Anonymous (TEA) group therapy thread

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tautech:

--- Quote from: bd139 on May 26, 2018, 08:57:05 am ---Yep keep and use. These when they are working have the best display quality of any analogue scope IMHO.

Also I have a cunning plan. I’ve been working on a spectrum analyser for about 2 years on and off. This conveniently will fit inside a vertical plugin. So I will disassemble the duff one and reuse it then be able to slide the SA into the vertical slot, plug the sweep out from the timebase plugin into that and use that as the sweep gen for the SA.

The SA is a pretty dumb one btw. It’s basically a dual conversion receiver with two IF’s. The first LO is voltage controlled. Mix with minicircuits DBM. Second mix is SA612. The output is an AD8307. With some cal and praying this gives around 90dB of dynamic range and a sweep span of about 500KHz to 200Mhz and switchable bandwidth of 1MHz for a band scope of 1Khz for measurements which is perfect for HF. Capability is all based on the only helical filter I could get my mucky fingers on.

--- End quote ---
Interesting project.  :-+
I'll keep my eyes open for news of its arise from the ashes of a D83.  :o

bd139:
If I ever get it working. VCO is unusably unstable at the moment and the crystal filter I built was shit because I had no idea what I was doing when I built it.

There’s a similar design here (which mine is not based on but the topology is about the same) for the interested. They’re not all that complicated :)

http://www.hanssummers.com/spectrumanalyser.html

AF6LJ:
Ant free running VCO that runs at more than a few MHZ is a real challenge to stabilize, without incorporating some form of closed loop frequency stabilization scheme.

bd139:
Indeed. Also linearity is a problem when the tuning is a varactor.  To be honest it doesn’t require masses of long term stability as I will use a marker generator to align it periodically.

At 200Mhz it drifts up to 1MHz/min though which is shit. Haven’t had time to fix this as I keep buying broken test gear :D

nixiefreqq:

--- Quote from: bd139 on May 26, 2018, 08:57:05 am ---
 I have a cunning plan.


--- End quote ---

you made me laugh out loud.


what was that guys name?    (baldrick?)

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