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Old 19th Oct 2014, 6:44 pm   #1
Radio Tech
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Default Signal Generator RF

Here is a nice little project for home construction I thought others might like to have a go at building, this one is my mark two version as the first one simply would not go no matter what I did. The case came from a factory that was shutting down so here are some pictures of the progress, I have included the circuit details which will not need much explanation, the veroboard that covers a hole is for a little three inch LS for a built in practice oscillator (Morse)

Regards

Ken
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Old 19th Oct 2014, 7:08 pm   #2
Bazz4CQJ
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Default Re: Signal Generator RF

Something that you might need to address later is control of the output level. Very often when aligning a radio, or fault finding, you need to start by injecting a high-level signal, then reduce to very low level as you progress. That means that the oscillator needs to be really well screened and the power cable well filtered and decoupled. Without those features, you'll radiate so much RF that it will limit the usefulness of the sig gen.

B
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Old 19th Oct 2014, 11:50 pm   #3
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Arrow Re: Signal Generator RF

An attenuator which 'tells the truth' over the required freq. and voltage-level ranges, and adequate screening, are probably THE two biggest challenges in the design and build of any signal generator. Moreover, as the freq. goes up, the problems also rise - and usually disproportionally. (Double the freq., quadruple the problems - or something like that. )
And it's those two factors (attenuators and screening) that significantly contribute to the cost of lab. type sig. gens.

Al.
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Old 20th Oct 2014, 3:18 pm   #4
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Default Re: Signal Generator RF

May I put that PDF document on http://www.vintage-radio.info/ please? It could be of interest to others.
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Old 7th Nov 2014, 2:32 pm   #5
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Default Re: Signal Generator RF

Hi Paul, yes of course by all means put the PDF of the circuit on your site, in fact anyone can copy it as far as I am concerned.

There are a couple more pictures that members might like to see so here they are, and it completes the project..

Regards

Ken
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Old 7th Nov 2014, 3:48 pm   #6
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Default Re: Signal Generator RF

This looks like the same circuit as the one in this thread

https://www.vintage-radio.net/forum/...ad.php?t=27184

There's also another version using the now unobtainable Denco coils.

Keith
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Old 11th Nov 2014, 2:00 pm   #7
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Default Re: Signal Generator RF

Thanks Ken, now added.
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Old 11th Nov 2014, 5:49 pm   #8
lesmw0sec
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Default Re: Signal Generator RF

Quote:
Originally Posted by Skywave View Post
An attenuator which 'tells the truth' over the required freq. and voltage-level ranges, and adequate screening, are probably THE two biggest challenges in the design and build of any signal generator.
Very true words. Some while back I completed a DDS signal generator. One reason it was worth finishing as a serious piece of kit was the fact that I had in the junk box, a nice attenuator from a defunct generator and which was controlled by external DC logic. A VGA did the 'set carrier' and modulation functions.

To make a reliable attenuator over a wide range usually requires some machining facility to isolate the switch sections and resistors. One of the best examples I have seen being the Marconi TF801 (I think!) VHF/UHF gen.

Les.
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