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AF/RF Signal Generator: Which one?

Robb

Robb

Honorary Member Silent Key
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Dec 18, 2008
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Silicon Valley CA, Storm Lake IA
I was wondering which signal generator I should get. I've got a Tektronix 465 scope, a Protek freq counter, and a digital volt meter - so I just need a generator to do do my own tune-ups to my own radios. I don't need an expensive unit - just something that will work and do the job right.

I haven't a clue as to what brand to buy. I was looking at some of the older/low-dollar jobs. Again - I just want something that works and will do the job. I was looking at them on eBay for $15-30. They look old and funky; but will they do what I need? An RF generator that puts out an 30mv@1khz audio tone at 27.185Mhz to inject into the antenna connector of a radio to align the receiver.

eBay ? Signal Source, Function Generator and Pulse Generator items on eBay.com. Find IT on eBay.

Know what I mean?
 

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I have a couple of those old units. Never use them. They are not stable, give problems , ect. I use the Sencore cb42, the B&K 2040, and the IFR1200S. All on different benches now. But I guess you can say I am not the average "tinker".

What is the most you want to put into a generator?
Is cb all you going to be testing?
Will you be doing any trasmitter testing?

You can use the units you mentioned. It will work. But I would find on of the following
CT Systems
Motorola
Cushman
IFR (pricey)

Go to the clasified section of qth.com and put out a want add. I did that 2 years ago and got 20 replies in one day. 15 of those were under $300.
 
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I just work on my own stuff nowadays and have a few pieces of gear that gets me by. I use the following:

Wavetek 4104 AM/FM modulation meter.


4101.jpg



B&K Precision 3020 Audio Sweep/Function generator:

bk3020.jpg



Oldie but goodie Specialty Engineering Division SG-85/URM-25D RF signal generator good for 10 KHz to 50+ MHz.


URM25D.jpg



A Triplett 630-PLK for high voltage to 5000 volts and current measurement.


630PL.jpg


as well as a Hitachi 'scope and other analog/digital multimeters.
 
Radio Tech said:
I have a couple of those old units. Never use them. They are not stable, give problems , etc. I use the Sencore cb42, the B&K 2040, and the IFR1200S. All on different benches now. But I guess you can say I am not the average "tinker". What kinds of problems would I expect?

What is the most you want to put into a generator? As little as possible. It is an expensive hobby and I have to put limits on
Is CB all you going to be testing? Yes
Will you be doing any transmitter testing? XLNT point - YES

You can use the units you mentioned. It will work. But I would find one of the following
CT Systems
Motorola
Cushman
IFR (pricey)

Go to the classified section of qth.com and put out a want add. I did that 2 years ago and got 20 replies in one day. 15 of those were under $300.
Click to expand...

Thanks for asking!
And sharing what you use - too.
 
Robb said:
Thanks for asking!
And sharing what you use - too.
Click to expand...
Ok then.
Then this is why the generators you mentioned will not do what you need.
About all they can do is adjust RX sensitivity. Not the best either.
You will need to be able to generate a signal that you can attenuate. Throw in a tone at say 30 percent modulation. You may need a 455kz added and a noise generator.

Then there is the transmitter. Yes you can use a watt meter and a frequency counter along with a dummy load. But hey, let’s say you need to check a 2 meter mobile for deviation and frequency error. That’s FM let alone the receiver can not be tested with the old generator.

See the possibilities are endless. Those that mole posted are fine. May sound a bit high. I will say that my IFR was over 9 grand new. Around $1100 to $3500 used.
You should be able to find one that is suitable for around a couple hundred.

Now for another piece I recommend. Someone turned me on to this and it is great.
Look for a Sencore SC-61 scope. That thing is a dream!
60 mhz usable to 100. Has a LCD display.
You can measure voltage peak to peak and direct up to 2000 volts.
And you can measure frequency with a 10X probe.

I got mine on ebay for $149. Last week I had a rig in with not tx. 3 minutes with this scope and the problem was found. Coupling capacitor between the driver and final had shorted.
Sure makes trouble shooting easy.
 
Cat Driver said:
Better yet.....

Tone Generator Software - Audio Test Tone Generator Download
Click to expand...

I agree that the tone generator software is a great tool.
As long as the radio is working at some point.


I also want to say this to others that have nice service monitors/generators.
A few weeks ago I had a Drake L4B, A LK 800, and a LK 1000 on the bench.
My IFR was on with the test leads just hanging on the hook. I spent 2 days servicing the mentioned amplifiers. The next morning a fellow brought a rig in to look at. Told me it had a tx problem. I connected my IFR to the rig and turned the generator on at 1000mv with 1000 hz tone.
I heard nothing in the rx speaker. I turned and said to him that his receiver was also down.


I keyed the rig (100 watts) and showed nothing on the monitors built in watt meter. I spent 30 minutes trying to track down the problem.
To my surprised it was my IFR. There is no dummy load in this unit. They use a termination pad (50 ohm) that is heat sink to a module that bolts to the main chassis. The pad is a 40 ohm and 10 ohm resistor network with a big heat sink. After testing this I found the 40 ohm portion of the pad was opened. I called a guy and this tiny pad (about the size of a 2Cd2879) cost $205
For a quick fix I soldered a 40 ohm 2 watt resistor to the terminals and put it back together.
I can not key a rig into the unit but I can sample via the on air antenna port.

I remembered working on the amps and wonder if they could have got rf into the IFR and took out the pad or did it die from age. It does a lot of heating and cooling.

Now when I work on QRO stuff I turn off equipment and/or put terminators on the input.
This can save you some money down the road.
 
AS I am still trying to learn a lot, I thought I would start out simple and work my way up. That is why I want to mess with CB's first. It is why I am looking for simple test equipment that works and will do the job for both TX/RX. I got the Tektronix 465 by trading it for an A99 antenna. I bought the freq counter new on line from Protek. I already had the digital meter. If I can get decent at tuning up CB's and learning enough in the process, I might be able to move up to better equipment and learn more still. Got to start at the bottom and work my way up.
 
Radio Tech said:
I have a couple of those old units. Never use them. They are not stable, give problems , ect.
Click to expand...

ROBB -

Just about any signal generator is better than not having a generator.

I agree with RT that these older units aren't as good as the newer ones. But if they are in good working condition and are properly calibrated and aligned, they will be more than good enough for CB work. Especially if you're just looking for a learning tool. Sometimes I still use the Heathkit signal generator that I built from a kit 40 years ago, and it works fine.
I would stick with solid state and stay away from the tube sets. If you have to replace the tubes to get them working this will be more $$$. Try FAIR RADIO. Also hamfest swap meets are a great source. Whatever one you get, make sure it comes with the manual.
73s.

- 399
 
Last edited:
My vote for sig gen is the HP-8640B. They can be had on ebay for a little over $100.00 if you are patient.

There's even a complete maintenance page for these on the internet.

I had some really high quality antique sig gens and the HP runs circles around them.
 
Generating a precise and stable RF signal is so cheap these days, especially below 30MHz, such as this:
DDS-60 Kit from the AmQRP

They call it a VFO, but its output frequency is exactly locked to the divide ratio from a crystal.

With something as cheap as a DDS, you can concentrate your money on a quality step attenuator to enable you to do precise receiver sensitivity measurements.
Its also possible to do AM modulation on the RSET pin.
 

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