Valve Spectrum Analyser - UK Vintage Radio Repair and Restoration Discussion Forum

ParcGwyn · 16th Sep 2017, 7:00 pm

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

Radio Wrangler · 16th Sep 2017, 7:52 pm

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

MrBungle · 16th Sep 2017, 8:10 pm

I'd love to see that in action if it worked. For the hell of it is reason enough

ParcGwyn · 16th Sep 2017, 8:15 pm

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

Radio Wrangler · 16th Sep 2017, 10:16 pm

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

16th Sep 2017, 7:00 pm	#1
ParcGwyn Hexode Join Date: Jun 2005 Location: Aberystwyth, Wales, UK. Posts: 358	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 Attached Thumbnails

16th Sep 2017, 7:52 pm	#2
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,869	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 __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

16th Sep 2017, 8:10 pm	#3
MrBungle Dekatron Join Date: Jun 2016 Location: London, UK. Posts: 3,687	Re: Valve Spectrum Analyser I'd love to see that in action if it worked. For the hell of it is reason enough

16th Sep 2017, 8:15 pm	#4
ParcGwyn Hexode Join Date: Jun 2005 Location: Aberystwyth, Wales, UK. Posts: 358	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
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,869	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 __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done