Oscilloscope testing help.

[8113 Northern MN]

Alright so I finally have 3 scopes in my shop. I know some basics on how to use them in basic electronic settings but have never been taught how to use one with a CB. I know you can look at your modulation and output signals through these.

Since this has been my go to place for learning the tricks and trades of CB mods and testing figured Id ask someone here if they know of a good place to show me a step by step procedure to properly set up the scope for use in testing my CBs. Id like to know the best settings on the scope and connection points within the CB itself in order to take a look at these signals. Any help is appreciated!

 

[The DB]

Alright so I finally have 3 scopes in my shop. I know some basics on how to use them in basic electronic settings but have never been taught how to use one with a CB. I know you can look at your modulation and output signals through these.

Since this has been my go to place for learning the tricks and trades of CB mods and testing figured Id ask someone here if they know of a good place to show me a step by step procedure to properly set up the scope for use in testing my CBs. Id like to know the best settings on the scope and connection points within the CB itself in order to take a look at these signals. Any help is appreciated!

Take a look at w2aew's youtube videos, he has several that may be of use to you. While they don't deal with directly tuning radios, they may be of use to you, and are, at the very least, a good place to start.


The DB

 

[GnG8d]

He has some really interesting videos, I've subscribed to his channel for sometime now.

 

[Robb]

You need to homebrew an RF sampler for testing the radio's output; or you will fry the scope!
But for checking internal signals, all you will need is a probe or test leads.

 

[Tallman]

There are ways to observe the signal with out directly connecting to high power areas. One way is to wrap a lot of turns of insulated wire around the coax to make a common mode inductive pickup. This would be used just to observe the output signals. Get some 10:1 probes and you should be good for up to 200 volts or more.
When you use the scope for alignments you are looking for a peak or a dip. The dip would be for adjusting harmonic filters. Peaks for transmitter outputs.
Don't bother getting the scope calibrated since it is used for observation only. If you have a frequency counter get that calibrated instead. I worked one job where we had to set a frequency to "Exactly 6.8 divisions scope set..." turns out the frequency adjustment was better accomplished with frequency counter. Too much math and time for one adjustment.

 

[Tallman]

Every scope I have ever seen has a probe calibrator built in to it.
Always has been 1 kilo Hertz at various output levels. The 1 KHz will get you into the range for audio with the time base settings.

 

[Captain Kilowatt]

There are ways to observe the signal with out directly connecting to high power areas. One way is to wrap a lot of turns of insulated wire around the coax to make a common mode inductive pickup. This would be used just to observe the output signals. Get some 10:1 probes and you should be good for up to 200 volts or more.
When you use the scope for alignments you are looking for a peak or a dip. The dip would be for adjusting harmonic filters. Peaks for transmitter outputs.
Don't bother getting the scope calibrated since it is used for observation only. If you have a frequency counter get that calibrated instead. I worked one job where we had to set a frequency to "Exactly 6.8 divisions scope set..." turns out the frequency adjustment was better accomplished with frequency counter. Too much math and time for one adjustment.

I disagree about the calibration. The vertical amplifiers should be calibrated so that the display amplitude is accurate. If an adjustment calls for setting the level at 400mV you want to make sure it is 400mV unless you prescribe to the "crank everything for max 'cause more is gooder" theory.

 

[GnG8d]

I disagree about the calibration. The vertical amplifiers should be calibrated so that the display amplitude is accurate. If an adjustment calls for setting the level at 400mV you want to make sure it is 400mV unless you prescribe to the "crank everything for max 'cause more is gooder" theory.

I would offer that a resonant circuit should be peaked to perform as designed. If components aren't changed/added/removed or modified and the bias voltage/voltages are set properly, the rest of the circuit should be "peaked" to maximum for proper operation. So using a scope to peak some test points and a DVM to verify voltages at other test points doesn't really require a lab certified scope.

You don't intentionally detune the tank (resonant) circuit in your tube gear do you?

 

[Tallman]

I disagree about the calibration. The vertical amplifiers should be calibrated so that the display amplitude is accurate. If an adjustment calls for setting the level at 400mV you want to make sure it is 400mV unless you prescribe to the "crank everything for max 'cause more is gooder" theory.

The FAA (Yes I know it is not the FCC) told me on so many occasions the trouble they had on Oscilloscope calibration. They recommended to the manufacturer's that they inspected to just place a tag on the scope for "Reference only and not for measurement." All volt/ohm meters, Distortion Analyzers, Watt meters, Spectrum Analyzers, and RF voltmeters had to be current on calibration. The FCC agreed when they came through. All of our equipment and products were under the scrutiny of both agencies.
But for me personally the absolute accuracy of scope readings is just unnecessary expense. But that's just my opinion.

 

[Tallman]

I would offer that a resonant circuit should be peaked to perform as designed. If components aren't changed/added/removed or modified and the bias voltage/voltages are set properly, the rest of the circuit should be "peaked" to maximum for proper operation. So using a scope to peak some test points and a DVM to verify voltages at other test points doesn't really require a lab certified scope.

You don't intentionally detune the tank (resonant) circuit in your tube gear do you?

NO. I re-tune to factory specifications or better. The dip I was referring to is the harmonic filter out put.
Some of the equipment I use work on has been "Aligned" by one of their friends and now they have problems. I have quit working on those. One came in with all of the slugs cracked and broken. Since they were effectively locked up I sent it back and told them to send back to the manufacturer. Turns out his Tech. buddy was using metal precision screwdrivers.

 

[8113 Northern MN]

Thanks alot guys. Between this thread and inbox messages ive been given a ton of information regarding this and as I continue to study this scope and how to properly use it all of this is great help!

 

[GnG8d]

Between this thread and inbox messages ive been given a ton of information regarding this

Why do people do that? Forums are for the open sharing of information and ideas for the benefit of people browsing and trying to learn. That's hard to do in private messages.

Think of a forum where all questions asked could only be answered in PM, it wouldn't be much of a forum would it?

 

[Captain Kilowatt]

The FAA (Yes I know it is not the FCC) told me on so many occasions the trouble they had on Oscilloscope calibration. They recommended to the manufacturer's that they inspected to just place a tag on the scope for "Reference only and not for measurement." All volt/ohm meters, Distortion Analyzers, Watt meters, Spectrum Analyzers, and RF voltmeters had to be current on calibration. The FCC agreed when they came through. All of our equipment and products were under the scrutiny of both agencies.
But for me personally the absolute accuracy of scope readings is just unnecessary expense. But that's just my opinion.

Depending on what you want out of it I guess. if all you want is waveform shape and relative amplitude then fine however if you are looking to properly align a piece of equipment then you need to know that it is accurate and actually allowing you to do the alignment procedure as it should be done. I worked on commercial broadcast gear for 22 years and always had to make sure the test gear was functioning properly before jumping into an alignment of something. The digital control circuits demanded proper amplitude and frequency which were easily checked with a properly aligned scope. Again, if all you want is relative readings then fine but don't touch my gear.

 

[GnG8d]

Depending on what you want out of it I guess. if all you want is waveform shape and relative amplitude then fine however if you are looking to properly align a piece of equipment then you need to know that it is accurate and actually allowing you to do the alignment procedure as it should be done. I worked on commercial broadcast gear for 22 years and always had to make sure the test gear was functioning properly before jumping into an alignment of something. The digital control circuits demanded proper amplitude and frequency which were easily checked with a properly aligned scope. Again, if all you want is relative readings then fine but don't touch my gear.

I've never seen a manual calling for p-p or even peak voltages. Using a scope over a meter just means you'd have to calculate the rms voltage.

 

[Captain Kilowatt]

I've never seen a manual calling for p-p or even peak voltages. Using a scope over a meter just means you'd have to calculate the rms voltage.

What meter would you use to determine an RF signal of 50 microvolts at 1.296 GHz was indeed the proper value? It won't be a VOM or a Bird. LOL I guess I just see the difference between a CB'er wanting to peak and tune his radio and a real tech wanting to do a proper alignment on a higher end piece of gear. No disrespect meant, I am just saying.....