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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 16th Sep 2017, 7:00 pm   #1
ParcGwyn
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Default Valve Spectrum Analyser

After looking at the schematic of a Marconi OA1094A spectrum analyser I decided that it would be fun to sketch a circuit of a valve spectrum analyser. I have come up with a rough diagram of the signal stage of 0-30MHz spectrum analyser. The 2nd IF amp and log amp a copied fris could be om the OA1094. I have cheated a bit in using a varicap diode in the VCO and I am not sure about using a pentode in the first mixer.

The performance is likely to be quite poor but would make a fun project, next step would be a trinsitron timebase and a couple of longtailed pairs driving a VCR97.

Dave

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Old 16th Sep 2017, 7:52 pm   #2
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Default Re: Valve Spectrum Analyser

It might be a little bit in need of further development.... for one thing, the LO inductor forms a DC short across the varactor diode.

The logarithmic detector cn be done with a series of long tailed pair limiting amplifiers with a detector running off of each. The snag will be trying to get enough bandwidth t the impedance levels valves ned for decent gain. It could be done for the hell of it, but sometimes transistors really are the answer

David
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Old 16th Sep 2017, 8:10 pm   #3
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Default Re: Valve Spectrum Analyser

I'd love to see that in action if it worked. For the hell of it is reason enough
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Old 16th Sep 2017, 8:15 pm   #4
ParcGwyn
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Default Re: Valve Spectrum Analyser

I hope to have a go at building it some time, I have most of the components in the shed but it will need a bit of development, will have a play when I have time and post the results on the forum.

Dave
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Old 16th Sep 2017, 10:16 pm   #5
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Default Re: Valve Spectrum Analyser

It should be good fun.
Back in the day there were valved 'panadaptors' for receivers, which amounted to a narrow span analyser scanning across the IF.

David
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