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Workbench/signal generator

2FB327

Active Member
Oct 31, 2012
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Looking for recomendations for a RF signal generator, from what I have read I need something in the 1-30MHz and be able to create a 1000hz tone.
If anyone could point me in the right direction, I have seen some old junk on the bay and a lot of the others seem like overkill.
Thanx in advance.
 

The more money you spend on a signal generator the more accurate the frequency output will be and the lower the signal can be turned down. Inexpensive ones will not have a frequency counter and will not turn down low enough to test for low sensitivity.

If your goal is to just align receivers for maximum sensitivity or trace a signal through the receiver, inexpensive ones will do. Although an expensive one can do many more things.

I learned an easy time saving trick a while back when it comes to aligning oscillator stages in radios. The service manuals always have you hunting down test points in the radios to connect a frequency counter to.

As I'm getting older I'm realizing it's becoming harder and harder to find these test points on the boards and some signal levels are low enough that many counters will not lock.

Using a quality HP signal generator and any HF radio, one can align oscillators without making any connections to the circuit. I've got a short piece of coax with a pickup loop on the end that attaches to the HF receiver.

I place this loop close to the oscillator in the radio I'm aligning to pick up its signal on the HF rig. I then set the calibrated signal generator to the precise frequency the oscillator should run at and adjust the oscillator frequency until it zero beats against the signal generator in the receiver. Alignment time can be cut by 80% and the calibration is still within cycles.
 
In Poland we have manufacturer of those: http://www.ambm.pl/index.php/urzadzenia-kontrolno-pomiarowe/dd1a.html
Freq range:: 0.1Hz-160MHz
Tuning step: 0.1Hz, 1Hz, 10Hz, 100Hz do 10MHz
Output amplitude: 50R/10k: 1mVpp ÷ 1Vpp / 2mVpp ÷ 2Vpp
Tuning step of amplitude: 1mV, 10mV, 100mV lub 0.5, 1, 3, 6, 10dB
Inequality: max -1dB / -4dB
Freq accuracy: -3...+5 ppm
Output impedance: 50R +/-10%
Artifacts and noise: 0.1Hz ÷ 20MHz: < -55dB
(related to 1Vpp / 50R) 20MHz ÷ 100MHz: < -45dB
100MHz ÷ 150MHz: < -40dB

It is AM/FM modulated 470Hz, FM deviation can be adjusted from 1kHz to 50kHz in 1kHz steps.

Nice piece of equipment, I own one and I like it a lot.
Mike
 
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I am a newbee when it comes to doing alignment work. My experience with learning alignments is that learning curve is steep at first, learn what is consistent about all alignments in general, and make consistency the rule of thumb. Some would say that is oversimplifying, I would agree with that too.

Aligning the receivers in an AM radio as opposed to a SSB radio has differences and similarities. The SSB radios are a little bit more complex.

If you are looking for a signal generator, think it is important that it has a calibrated output. Not just on freq with very little drift, but has a stable output as well.

When aligning, it is important that you feed the input of the radio with a 1uV signal. If the output is higher than 3uVs; the AGC ('Automatic Gain Control') will cut in and affect the radio's meter. At this point in the alignment, we are not concerned about what the radio's meter is doing; but we do not want the AGC to change our readings either.

What is best, is to have a 1uV signal into the radio and to use a SINAD meter connected to the radio's speaker jack. This will balance the gain that the circuit is getting by peaking the coils. The SINAD meter is balancing the gain against the noise and distortion of signal that is passing through the progressive gain stages. We don't want to overgain any one stage; so we make sure that gain is clean as we go through each one. That is the difference between aligning the receive with just a sig gen, and one that is aligned with a sig gen and a SINAD meter. The results can vary widely, as using the SINAD will have a sensitive yet much cleaner receive.

After the radio has been aligned with 1uV, then the receive meter is adjusted to 9 S-units with 100uV output from the sig gen.

But having a sig gen that has a calibrated/accurate signal output that can be adjusted and is on freq, is the one you want/need for an accurate job. Having a SINAD meter to do a thorough job is pivotal - IMO.

Those older sig gens really drift a LOT and it is hard -if not impossible- to keep the output voltage where it needs to be. Especially because they have no measurement/control in those older units. Started out with one, and I no longer use it. Makes a very fine door stop now - though . . .

1uV = one millionth of a volt p-p at a given freq.
 
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Thanks

Thank you all so much,
When reading some old info I found an article an made a loop along with and indoor antenna for my bench radio just to listen/receive I had no idea how valuable it is
I have two more questions:
1. In this video,Monitor your Ham Radio transmitter with an oscilloscope - YouTube what are the names/part numbers for the 4 BNC connectors mounted to the copper board? I sent him a response last week and didn't receive a reply. Also what are the cables called that go from the board to the scope (the blue and gray ones). I know I need 50 ohms and up till now the only connections I used were pl259's and so 239's. The choices are over whelming.

2.Help putting it all together, maybe photos from members or diagrams as to where to place T connection, etc.


Before I start alignment I want to try my hand at signal tracing using the scope and I have a stack of old Cobra 29's to repair. I have the factory repair manual, wiring diagrams etc.
Once again, thank you for all your help and have a good weekend.
 
What is best, is to have a 1uV signal into the radio and to use a SINAD meter connected to the radio's speaker jack. This will balance the gain that the circuit is getting by peaking the coils. The SINAD meter is balancing the gain against the noise and distortion of signal that is passing through the progressive gain stages. We don't want to overgain any one stage; so we make sure that gain is clean as we go through each one. That is the difference between aligning the receive with just a sig gen, and one that is aligned with a sig gen and a SINAD meter. The results can vary widely, as using the SINAD will have a sensitive yet much cleaner receive.

That's some good info right there. Modern radios can have too much gain with objectionable noise if they are not properly aligned. I've seen an IF strip in one rig that was tampered with. Some of the transformer slugs were obviously backed out of the coil form too far with much of the slug exposed.

I expected to hook the signal generator up and find very poor sensitivity based on my visual inspection. To my surprise it was very sensitive and very noisy. It appeared to be about twice as sensitive as its specs but nearly 10 times more inside noise that made the extra sensitivity useless because weak signals couldn't overcome the noise.

Some transformers may have more than one tuning peak. Good service manuals will tell you which peak is the correct one to tune for. It's almost always the one with the slug deeper in the coil form.

Other radios may have an internal IF gain control that must be adjusted after alignment. This insures the stage is not under driven and producing less gain or over driven and producing distortion or noise.
 
That's some good info right there. Modern radios can have too much gain with objectionable noise if they are not properly aligned. I've seen an IF strip in one rig that was tampered with. Some of the transformer slugs were obviously backed out of the coil form too far with much of the slug exposed.

I expected to hook the signal generator up and find very poor sensitivity based on my visual inspection. To my surprise it was very sensitive and very noisy. It appeared to be about twice as sensitive as its specs but nearly 10 times more inside noise that made the extra sensitivity useless because weak signals couldn't overcome the noise.

Some transformers may have more than one tuning peak. Good service manuals will tell you which peak is the correct one to tune for. It's almost always the one with the slug deeper in the coil form.

Other radios may have an internal IF gain control that must be adjusted after alignment. This insures the stage is not under driven and producing less gain or over driven and producing distortion or noise.
Thanks, Shockwave.

I've seen so many radios that guys aligned - myself included - using those old sig gens and just peak the coils to the max.

I work on radios for the locals in the South Bay Area. They get these radios from fleabay and some are in pretty strange condition/state of tune, but I'm sure you know what I mean.

Those first three RX coils do need to be close to the bottom! You are right about that. They can be peaked for higher gain, but many problems occur when that is done as you know. One common problem that is quickly noticed, is that the RX meter will 'ghost' false signals that aren't even present in the receive. Happened to me the first time I did a receive alignment - lol!

For those who are learning to work on radios, messing with the receive alignment is tricky business.

Learning to unhack radios and fix them is all new to me, but it has been both somewhat frustrating and mostly successful. Fortunately, I have only seen a small amount of them that stumped me. Chalk it up to experience, and experience as I have learned is everything in this game.

Shockwave:
Perhaps you can give us a breakdown of how you do RX alignments, a general guide, as I'm sure that myself and others may benefit greatly.
 
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Shockwave:
Perhaps you can give us a breakdown of how you do RX alignments, a general guide, as I'm sure that myself and others may benefit greatly.

The best advice I can offer is to obtain the service manual. The procedure can vary from model to model. The internet is a good source for free service manuals. At the very least a schematic is useful to find your way around the circuit.

If no info is available and you have to do it blind, start with confirming the PLL or VFO are on frequency. If the rig uses a VFO always adjust the coil for the low end of the band and the cap for the high end. Going over this a few times will bring the entire band into alignment.

I've given up my shortcut on how to align the AM and SSB oscillator stages with the calibrated signal generator and an HF receiver tuning for zero beat. But without the service manual you may not know the frequencies these oscillators are supposed to run at.

You could check the crystals but many use the same crystal for all three and just switch different tuning transformers inline through diodes to tune the offsets.

Without the service manual you'll probably have to tune the RF and IF strip towards maximum gain while observing the noise present in the generator signal. Do one stage at a time and check so if noise creeps in, you'll know what stage was the problem.

If one stage is generating objectionable noise when tuned for max gain, experiment to see which side of max gain (slug further in or out of the coil form) gives the best signal to noise ratio.

It's best to align the IF strip by injecting the signal generator directly into the first stage of the IF. That way you know the strip is tuned to the right frequency. I've seen people get the IF strip so badly aligned, you had to slide off frequency to hear an AM signal that was on frequency.

Remember your IF stage always stays on the same frequency regardless of where the receiver is tuned but the RF strip does not. Most CB RF strips should be aligned in the center of the frequency range they can cover. General coverage receivers will usually have bandpass filters in front of the RF strip that are selected by band. You may find some radios with a front end that is intended to be "stager tuned" to cover a wider bandwidth through one front end.

This means that parts of the RF strip are tuned for the low end while the next transformer may be tuned for mid band and the last stage of the RF may be tuned for the high end of the band. This equalizes the gain throughout the bandwidth of the receiver. These circuits are rare today.

If you're ever faced with having to adjust a potentiometer that you're not 100% sure is going to be the correct one, measure from the wiper to either end with your ohm meter and the radio off. That way if it was the wrong one you can set it back to the original value precisely.

I'm sure there is lots I've missed here due to time and space so I wouldn't consider this more than offering a few pointers. The service manual will cover much more detail. Experience in troubleshooting will help identify where the problem is. Often avoiding a complete alignment since the problem could easily be in a single stage. Good luck. If anyone has questions, ASK.
 
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Does anyone know the name or parts numbers?

. In this video,what are the names/part numbers for the 4 BNC connectors mounted to the copper board? I sent him a response last week and didn't receive a reply. Also what are the cables called that go from the board to the scope (the blue and gray ones). I know I need 50 ohms and up till now the only connections I used were pl259's and so 239's. The choices are over whelming
 
Thanks, I was just reading that one.
I want to order the BNC connectors/cables and just want to get the right parts.
I have no problems soldering and have done many pl259's but when you look in a catalog like jameco's there are a lot of choices.
 
Hi, get your electronics parts from Taydaelectronics.com
Tayda have everything you need.

PL-259 and BNC connectors from Ebay.

;)
 
I'll check them out, so far I figure I need 4 female BNC panel connectors, still not sure of the ends that go onto your scope or counter.
 

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