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Old 2nd Dec 2019, 9:45 pm   #1
greenkit
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Default Farnell Modular Signal Generator

Does anyone have circuit information on this generator, built in the 1970s? A search on here revealed a launch notice from Wireless World, August 1972, but I haven't found anything else. My unit has the following modules:

MPS power supply
MSG1 0.1 to 12 MHz tuneable oscillator
MSA switched attenuator (up to 122 dB, claimed good to 1.5 GHz)
MSC calibrator (1, 10 & 100 MHz)
MSS sweeper.

Having been unused for many years, a first inspection revealed sticky switches, etc., all easily fixed. The -25V rail is up at -30V, with a substantial ripple at around 150 kHz that percolates through to the RF output, so there's a problem that a schematic would make more easily solved.

Is this a rare item?

Last edited by greenkit; 2nd Dec 2019 at 9:45 pm. Reason: spelling....
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Old 5th Dec 2019, 6:47 am   #2
Diabolical Artificer
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Default Re: Farnell Modular Signal Generator

Telford are pretty good for hard to find manuals and show quite a few for Farnell branded gear - http://www.telford-electronics.co.uk/manual.php?alpha=f . If not I'm pretty sure Farnell re-badged Scopex scopes as their own, maybe they did something similar with some of their sig gens? If you post some good pics of your sig gen someone here may recognise it as a type that has schematics etc more easily available.

Andy.
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Old 5th Dec 2019, 8:33 pm   #3
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Default Re: Farnell Modular Signal Generator

Hi there, you don't mention the model No.

I have an FG1, is it anything like this?

Paul B
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File Type: pdf FarnellFG1.pictures.pdf (449.9 KB, 101 views)
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Old 5th Dec 2019, 10:12 pm   #4
greenkit
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Default Re: Farnell Modular Signal Generator

Thanks to both for your interest and replies. I've attached 3 photos of the generator. Note the plug & socket method of distributing the power rails on the rear panel, quite unusual. It's a 'proper' Farnell effort as far as I can tell. I've had a quick look through Telford's list but nothing jumps out as regards module ID. The whole unit just seems to be known as a 'Modular Signal Generator'. The build is very similar to the FG1, not surprising as they're from the same era. I have had an FG1 for many years; it still works well and has needed very little in the way of maintenance.

I've been through a fair bit of Farnell test gear, but have never seen another one of these. Wonder how many they sold?
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Last edited by greenkit; 5th Dec 2019 at 10:15 pm. Reason: typo...
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Old 6th Dec 2019, 11:20 am   #5
Herald1360
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Default Re: Farnell Modular Signal Generator

A few 10s or maybe 200 or so, depending on where they started the serial numbers?
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Old 13th Dec 2019, 11:49 am   #6
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Default Re: Farnell Modular Signal Generator

Also looking for info, I have one but only the Power Supply and Oscillator units are fitted. What are tho other units? I can see Attenuator and Calibrator, what's the third?
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Old 13th Dec 2019, 4:12 pm   #7
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Default Re: Farnell Modular Signal Generator

Looks like Sweeper
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Old 13th Dec 2019, 10:28 pm   #8
greenkit
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Default Re: Farnell Modular Signal Generator

Confirmed as a sweeper, type MSS. For additional info I've attached a pdf of the original launch notice from WW 1972. Out of interest, Julesomega, which oscillator module do you have?
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File Type: pdf Farnell MSG.pdf (3.43 MB, 78 views)
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Old 18th Dec 2019, 12:11 am   #9
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Default Re: Farnell Modular Signal Generator

Mine is 10-100MHz. Don't recall looking inside, but the article mentions external freq control which sounds like it's varicap tuned, with a pot. for manual control. Pity, maybe of more use to you
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Old 21st Dec 2019, 11:02 pm   #10
greenkit
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Default Re: Farnell Modular Signal Generator

Thanks Julian; Farnell seemed fond of pot-tuned oscillators. My FG1 has a wire-wound main tuning control and discrete steps in frequency can be seen when adjusting carefully. I do remember they also made a small lab AF generator that had a variable (broadcast type) capacitor in a Wien bridge configuration; this was very smooth for manual sweeping, but probably at a cost. The first job with this one is to sort out the power supply and see where we go from there.
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