Homebuilt Signal Generator

[Miguel Lopez]

Hello everyone

The need for a signal generator in an electronics workbench is out of discussion. I built a tiny signal generator in the past, that I've been using till now. It is very limited as it gives up to 50 kHz of sinewave. It has been very useful but now I need something else.

My intention is to built another sinewave signal generator with to independent outputs. One for low frequency (up to about 300kHz) and another output from 500kHz to about 5MHz, keeping distortion in low levels. The purpose of this device is to experiment with modulation and demodulation

I will also include two other outputs with 1kHz and 465kHz fixed frquencies in order to test radio and audio circuits, and use them as standards.

For the low frequency section and the 1kHz fixed frecuency, I used the attached circuit (R=1k).



I used an LM324 for the 1kHz output and LF353 for the variable frequency output. This variable output will have ranges (switching capacitors) and fine adjustment (single potentiometer)

On further posts I will show how I got throught this project.

 

[Colin Mitchell]

If you build a square-wave signal generator you can use its harmonics.

 

[Miguel Lopez]

If you build a square-wave signal generator you can use its harmonics.

I tried that some time ago, and I found that it needs a lot of electronics to get what I want, so, I think that this is the simplest way. Am I wrong?

Well, for the high frequency section and the 465kHz fixed frequency output I used the following circuit:

It is a version of the circuit found at this website:
http://my.integritynet.com.au/purdic/oscillators.htm

I added another transistor for amplification and another one for buffering the output. This is the first time that I build a circuit using FETs so, I'm very happy with the results. The variable capacitor is from a Soviet radio set and the coil was winded by me using Soviet RF cans from a B/W TV set. Coil L1 has twice the turn of coil L2.

Here some pictures of the whole arrangement for the HF section:

 

[Colin Mitchell]

If you want a known, fixed frequency, you can use a microcontroller.

 

[Miguel Lopez]

If you want a known, fixed frequency, you can use a microcontroller.

I can't. There is nothing like that here, and I lack the required knowledge to work with it.

I built the fixed frequency sections using the same circuit as for the LF and HF sections respectively, and I adjusted them in the lab, using a very accurate standard. I know they will have some drift in time and with enviroment temperature, but, well, my workbench is not NASA, so they are enough accurate for my experiments and work.

 

[Ian]

Hi @Miguel Lopez, this would make for a fascinating project log if you wanted to add it to this section (https://www.electronicspoint.com/projectlogs/) . I'm looking forward to seeing the progress!

 

[Miguel Lopez]

Hi @Miguel Lopez, this would make for a fascinating project log if you wanted to add it to this section (https://www.electronicspoint.com/projectlogs/)

How can that be done? I think that should be better once finished.

**************************************************************************

Resuming thread. I want to share some pictures of the LF section. As I said before, I switch the ranges by changing the capacitors in the circuit of Post#1. Then with a potentiometer I have fine frequency adjustment. The black knob in the PCB is the "Fine" potentiometer, which will be mounted on the front panel. All the outputs will have amplitude control too.

 

[Externet]

Hi tocayo.
Find this chip; and you will be very pleased. Performed like a charm in a project done 10 years ago.
----> http://www.intersil.com/en/products...g/other-miscellaneous/ICL8038.html?pn=ICL8038

Do not have any of those now; but can mail a XR2206 still in my parts bin.

 

[Miguel Lopez]

Find this chip; and you will be very pleased. Performed like a charm in a project done 10 years ago.

My source of components is scavenging old equipment mostly, so I don't think that I would be able to find something like that. Thanks for the advice anyway, Who knows.

but can mail a XR2206 still in my parts bin

Does the Embargo allow you to do that?

 

[Externet]

Do not know and do not care much.
I can try to go to the postal office and mail you an envelope with the chip. Am not selling anything anyway, and for hobby purpose. And if trouble happens, they will put me in ¿ jail ?. The world press will have a noisy ball with it.
Or do I have to mail such to someone in another country and have it resent to you ? Will see.

Worst case, other members elsewhere in the planet could mail it too. Give me your mailing address on direct message.

Edited. Checked :
---->http://pe.usps.com/text/Imm/ce_017.htm

 

[Miguel Lopez]

Here is how the SigGen cabinet looks like with all the modules inside.


And this is the front panel

 

[HellasTechn]

Miguel, Always involved in some interesting project dear friend ! I really respect you for that i have to admitt.

 

[Miguel Lopez]

Thank you very much for your compliment HellasTechn, I do my best.


Finally, here the SigGen in its final location (above my DC PSU), in my messy workbench, while testing a valve circuit.



Have to say that the Amplitude Modulation section is not built yet, as I will begin my experiments on AM right now, when I have a suitable device for this.

 

[CDRIVE]

Miguel, this is truly an impressive project. What you did was never commonplace but but did exist among my peers. That was a very long time ago.

Bravo!
Chris