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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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16th Sep 2017, 7:00 pm | #1 |
Hexode
Join Date: Jun 2005
Location: Aberystwyth, Wales, UK.
Posts: 358
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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 GW7ONS |
16th Sep 2017, 7:52 pm | #2 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,803
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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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16th Sep 2017, 8:10 pm | #3 |
Dekatron
Join Date: Jun 2016
Location: London, UK.
Posts: 3,687
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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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16th Sep 2017, 8:15 pm | #4 |
Hexode
Join Date: Jun 2005
Location: Aberystwyth, Wales, UK.
Posts: 358
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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 |
16th Sep 2017, 10:16 pm | #5 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,803
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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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Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done |