Need a pointer.. A good starting out project for someone re-igniting the fire

[Duggyrh]

Hello all this year I will be an official OH (old fart) and taking up old hobbies old tech electronics and computers. so hear it is
I want a project to build a desktop function generator yet to a good level....I have come across so many eastern brands yet there are limits and i would like
slightly bigger limits and more expandable.

PROJECT:- Function Generator 5-10 Mhz... better if possible

Bit of fun...LOL
see what happens

Thanks all
Duggy

[David Hess]

Unless you use an integrated solution like DDS (direct digital synthesis), operation above 2 MHz becomes difficult and even then, designing and building a 2+ MHz linear output amplifier is not trivial.  With that said, what you propose is certainly feasible with an analog or digital design.

For analog designs, take a look at the Tektronix 1 MHz FG501, 2 MHz FG501A, 11 MHz FG502, 3 MHz FG503, and 40 MHz FG504 function generators to get some idea of what is possible and how it can be done.  They are fully documented in their service manuals which also include detailed descriptions of the circuits.  These are discrete designs except for general purpose logic ICs so very reproducible with common parts.  TekWiki has these service manuals.

[Doctorandus_P]

I do not want to disillusion you but if I look at the prices and specifications of for example the jds6600:
https://www.aliexpress.com/wholesale?SearchText=jds6600
Then there is no way you're going to get anywhere near those kinds of specifications without a very serious design effort.
And even if you try to design such a thing and you later discover you've been in your lab for months and then have made a thing you can buy for EUR 80 it takes the fun out of it. Even if you get all the parts for free and you've been working / hobbying for 50ct / hour it makes you scratch behind the ears and ask yourself what you're doing.

Old service manuals such as from the Stuff David points to is a good source for information, but when you've sourced the parts, made a PCB and found a housing to put it in it is probably already much more expensive.

I think there is more value / satisfaction in designing some custom gadget for a problem that has no solution yet, or  work on a desing to be shared with multiple people (preferably also share the design effort), but those projects are hard to find.

[David Hess]

Old service manuals such as from the Stuff David points to is a good source for information, but when you've sourced the parts, made a PCB and found a housing to put it in it is probably already much more expensive.

These old designs are more useful in providing insight into what is necessary.  For instance high performance function generators do *not* use operational amplifiers configured as integrators because the requirement for unity gain stability limits bandwidth limiting performance.  Even the various integrated function generators did not.  Instead they use current switched current sources to drive an integration capacitor which is a powerful but underappreciated technique with multiple applications.  Analog oscilloscope sweep circuits do the same thing but in only one direction.

Still, I wonder how well an integrator made with a current feedback amplifier, which requires some trickery, would perform except at low frequencies where high input bias current would be a problem.  This suggests adding a fast high impedance JFET buffer to the current feedback amplifier at which point the original current switched design begins to have greater appeal.

Then there is no way you're going to get anywhere near those kinds of specifications without a very serious design effort.

And even if you try to design such a thing and you later discover you've been in your lab for months and then have made a thing you can buy for EUR 80 it takes the fun out of it.

I agree that this is beyond a layman or amateur effort.  It is a weeks to months long project even for one experienced in this area of design.  More might be learned acquiring old function generators, refurbishing them, and studying how they operate.