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Old 7th Sep 2016, 3:00 pm   #141
vintage_8bit
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Default Re: Marconi TF144H CT452A RF Generator

Jeremy. Just finished a restoration, so looking again at the genny. Could you confirm the latest resistor changes. I am in a good position now to construct my own board, or try yours? Colin
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Old 7th Sep 2016, 10:26 pm   #142
G0HZU_JMR
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Default Re: Marconi TF144H CT452A RF Generator

Hi Colin
I'm afraid I haven't been able to do much on this since the last update. My workbench is fully configured for other work at the moment. However, I did measure a couple of things a few weeks back. I measured the input impedance because you said it should look like 24R resistive.

So it is optimised for this across LF throught to 72MHz and beyond.

See the attached real and imaginary plot taken of the actual PCB using a VNA. The reference plane for the VNA is the little SMA connector fitted at the input. The data has then been post processed in a CAD program to show real and imaginary data and this is given in the graph below. You can see it is pretty close to ideal across the whole range. Red is real (about 23.7R) and blue is imaginary (close to zero) I also removed the trimmer and fitted a fixed resistor. The schematic hasn't really changed apart from this and see below for my latest (final?) schematic.

I also looked to see if there was the chance the complex instrumentation chip used on the board might leak low level interference back into the sig gen. So I tested it using a high gain LNA ahead of my spectrum analyser to see what leaked out of the input. I could find nothing right down to the limits of my test setup which is about -140dBm. So I don't think there will be an issue here.

If you pm me an address I can send it to you to play with?
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Regards, Jeremy G0HZU

Last edited by G0HZU_JMR; 7th Sep 2016 at 10:33 pm.
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Old 8th Sep 2016, 8:17 pm   #143
vintage_8bit
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Default Re: Marconi TF144H CT452A RF Generator

Hi Jeremy. I have sent a PM to you. Let me know if it dosent get to you. Colin
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Old 21st Sep 2016, 10:46 pm   #144
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Default Re: Marconi TF144H CT452A RF Generator

I have gratefully received Jeremys detector pcb. I have fitted it but unfortunately the modulation amp on the genny started giving a distorted output. This is now fixed so hopefully start making some measurements later this week.
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