Frequency Generator

[Bryan]

Hey Guys,

I have a couple quick questions...

I've been diy'ing for a little while, and having a great time. Until recently, my only testing of the equipment has been my ear, and my fluke.

I recently bought a TEK 465, and would like to do some more complete measurements. So, I guess it is time to buy a frequency generator.

What should I be looking for? What are some good models, and approximately how much will I need to spend. I prefer to buy quality items once, versus purchasing crappy gear repeatedly.

Suggestions?

Thanks,

Bryan

[till]

you could diy: http://www-ee.eng.buffalo.edu/facult...413/tan005.pdf

i build one with 2 XR2206

Maxim has also a funktion generator IC they sent me as free sample.

[Bill Fitzpatrick]

I have both a HP 204C Audio Oscillator and 3310B Function Generator that I got on ebay. They have served me well.

[jackinnj]

my first frequency generator was a Heath HG5218 -- these are pretty inexpensive on EBay -- one practical suggestion however is to disconnect the meter -- in Audio Amateur in the early 1980's there was a POOGE article on the IG18 or 5218 which suggested this to reduce the meter's effect on distortin numbers. In fact they had a little transistor amp which isolated the meter.

you will often find the Wavetek sweep generators on EBay quite inexpensively -- I have a 182 which cost me $40 -- not as low distortion as the heath, but it really helps when you are working with filters.

sometimes you will find that serendipitous point on EBay when a nice piece of HP equipment has not bidders -- I have an ovenized HP3336B which cost me ~$100 == the only problem is that it uses mini-WECO connectors which are a tad expensive.

some equipment comes with freq generators -- like the HP339 distortion analyzer -- this unit has a very high quality oscillator -- distortion around 0.002%

the HP3581 wave analyzer usually goes for $50 - $100 and has a nice sweep oscillator -- it also has a very accurate audio voltmeter!

you really can't go wrong with the Krohn-Hite audio oscillators -- these are often pretty inexpensive and KH has an excellent reputation for quality.

things not to buy -- the old RCA and EICO tube based generators have pretty high distortion --

[Bryan]

OK Guys, Time to show my ignorance....

I understand the purpose of the Signal Generator, with respect to testing. My question is, what is an audio oscilator?

Maybe if you outline the types of measurements I can make with each piece of gear, this will help me along.

Correct me if I'm wrong.

Needed (Desirable) Equipment:

Scope (Tek 465)
Signal Generator
Audio Oscilator
Distortion Analyzer

Anything else?

Thanks,


Bryan

[Bill Fitzpatrick]

An audio oscillator will normally be confined to outputting low distortion sine waves in the audio band although most will go to at least 200K. A must have piece of equipment for generating the signal to measure frequency response.

A function generator will normally output sine waves, square waves and triangle waves. Some will also output pulses and ramps. A square wave is useful in audio - the others have limited value. The sine wave in a funtion generator is usually fairly high in distortion and not useful for distortion measurements.

A distortion analyzer usually confines itself to harmonic distortion analysis and of necessity has a built in, low distortion audio oscillator. There are also IM distortion analyzers available.

For serious audio work you should have an "AC Voltmeter", something similar to the older model HP 400EL. I like the 2 channel AC Millivoltmeter made by LEADER. You could use a scope instead of this meter but the meter's DB scale markings are almost essential.

If you are going to be designing and breadboarding opamp circuits you should also have a bench top power supply. It could be fixed at +/-12 volts but I like the adjustable, dual tracking supplies.

Some people like to have frequency counters as well but the dials on the oscillators are plenty accurate.

[Mikael Abdellah]

How about this: http://www.goodwill.com.tw/Products/GOS-620FG_E.htm

[darkmoebius]

Just this last month, I bought a whole bunch of test equipment including a pristine Tek 465 B , Wavetek 134 2MHz sweep/function generator, Universal frequency counter, Fluke 8050A bench DMM.

The biggest waste of money was the frequency counter because that 25+ year old Wavetek is dead-on accurate when I checked it. I got it for $50 off of eBay and it is in near perfect condition. They also have a lot of oscillators for sale at decent prices.

Although, the last week or so, I've been having second thoughts about not getting some of the oscilloscope software and running it all off of my computer. Obviously, it's not going to be as accurate as this other stuff, but it would be nice to have a distortion/spectrum analyzer and most importantly, the ability to post pictures of my measurments so others could tell me what the hell I'm looking at. (I really don't have any idea)

[jackinnj]

Originally posted by darkmoebius
...Obviously, it's not going to be as accurate as this other stuff, but it would be nice to have a distortion/spectrum analyzer and most importantly, the ability to post pictures of my measurments so others could tell me what the hell I'm looking at. (I really don't have any idea)

not necessarily so -- Test and Measurement had an article several months back praising sound cards -- these were in some applications where an engineer had to replace a piece of HP equipment which couldn't be replaced.

my computer is tied up most of the time with microcontroller software, or Excel, however. there's only so much multi-tasking you can do!

[Bryan]

Hey Guys,

Another couple questions.....

Does a function generator, set at say 40Hz allow you to play a tone through your equipment, or does one need a frequency generator for this.

Also, what do you guys think about the HP 331A and 334A distortion analyzers? They seem to be available and cheap on e-bay.

Thanks,

Bryan