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RF Signal Generator/Radio Alignment Question

J

JTuscani

Member
Aug 23, 2014
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Hello all,

New to the forums, have been reading for a while though. I have a question related to an RF signal generator I have recently acquired. Using a calibrated frequency counter the output of said generator is actually quite accurate and pretty stable. My question comes with the output voltage. I see that most of the service manuals for most common radios call for a 1uv or even .5uv signal when it comes to receiver alignment. This particular generator seems to only go down to about 20uv or so. The manual states that a 50-200 ohm resister should be used in series if you are injecting the signal directly into an antenna jack. This does not seem to affect the output. Is there something different I should do? Just FYI I have not done anything to any radios as of yet. I am simply trying to sort out the equipment before I start messing with some old CBs that I have laying around. I would like to just teach myself how to align and tune my own radios as a way to further my interest in the hobby. I currently have an oscilloscope, frequency counter, a multitude of digital and analog multimeters, and the above mentioned rf generator with a built in 1khz af generator. The model of the generator is GW Instek GRG-450B. Any information would be appreciated. I would like to learn as much as I can. Thanks.
 

Hey JT:

I started out a lot like you. But that signal generator just won't cut it; been there. A sig gen for working on radios really needs to be more reliable and accurate. The freq drift and output varies of the Instek is way too much for the kind of accuracy receive alignment calls for. Best to learn how to do the rest of the alignment process and leave the recieve alignment to the last, as it is a bit more tricky than most realize.
 
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I have seen your RF generator posts from a few years ago. What did you end up with? I was given this generator and I noticed the waveform at low power was extremely dirty looking, but I was hoping it would be fine to toy around with some old Cobra 29s or what not. Is something under $200 even feasible?
 
Hewlett/Packard Hp 8656B

I scored one used - of course - for just under $300. Extremely accurate and all of the features that one could need for RF receive work. Along with a sig gen, a SINAD meter is also key.
 
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I guess one of the old tube sig gen's probably wouldn't cut it either?:)

This would be a good thread topic to discuss imo, "tech equipment for the beginner". Some input on lower end, get ya by equipment that someone could learn on.

There are plenty of list out there, like this one:
http://www.hamuniverse.com/w4jbm/testgear.html
But they don't really give specifics on what the equipment specs should be to properly tune a radio.

I haven't pulled the trigger on any major gear myself, only because I'm a little confused on what to buy.
Again, jmo(y)
 
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mb91w126 said:
I bought mine from brltest. It was certified by them to be in spec. It's handy to have a certified piece of equipment, you can check the accuracy of other with it.

If you make them a reasonable offer, it will be accepted.
good luck!

http://www.brltest.com/index.php?main_page=product_info&cPath=44_4402&products_id=6507
Click to expand...


Thanks for the info. I sent a request, so I guess we will see what will happen.

In other news, I realized I also have an Agilent 20mhz function/sweep generator, but I am not sure how useful this would be. I believe it may be used moreso with FM? I could be wrong. Anyway, I am looking forward to being able to maybe bring some old radios back from the dead. I appreciate the feedback thus far and I know I have been searching for good info on some good starter gear. Thanks again!
 
JTuscany,

what you need to make your sig gen work with CB radios is a 20DB attenuator pad.
they are very simple to build and only involve a few resistors.
20DB equates to a 10X reduction, so that 20uV in becomes 2uV out.
then you can use another one in series to get to .2uV out.

Lou Franklin has a design for one in his Understanding and Repairing CB Radios book, but im sure you can find how to build one online somewhere.
LC

PS- dont forget to put a .01uF cap in series with the positive lead coming out of the signal generator.
 

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