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What do i really need to align a CB radio?

jtrouter

Well-Known Member
Jul 7, 2015
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All right i have fixed the problems and recapped my Cobra 2000gtl, Now i am ready to tackle the alignment.
All of my Sams's books call for using a VTMM along with Signal generator, Scope . Now i do really need a VTMM?
I have cheap and good DMM i even have a Old analog voltmeter. Do i really need to go buy VTMM? Or use what i have
or what else do need. I should say i do have dummy loads, Freq counter, wattmeter, assorted plastic tunning tools Thank you
 

Spectrum analyzer wouldn't hurt, and while not the best, they can be had cheap:

Maybe a 5 pound sledge, crowbar, 10 feet of det cord. Oh, wait, you want it to work when you're done.
 
Spectrum analyzer wouldn't hurt, and while not the best, they can be had cheap:

Maybe a 5 pound sledge, crowbar, 10 feet of det cord. Oh, wait, you want it to work when you're done.
Ahh good one funny man
 
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Spectrum analyzer wouldn't hurt, and while not the best, they can be had cheap:

Maybe a 5 pound sledge, crowbar, 10 feet of det cord. Oh, wait, you want it to work when you're done.
Yeah, nah...the tinySA's aren't that good...at least the one I had for a short time wasn't. Bought it for a stand in while my HP8920A was out for calibration. No comparison...
 
DVM capable of reading 200Ma DC current (or cheap DVM and a stand-alone Ma meter), Frequency counter, signal generator, RF watt meter.
 
The VTVM had one thing going for it you won't find outside of a good o'scope.

Not for the sensitivity, but for the loading the probe tip places onto the circuit you're measuring.

The VTVM probe for DC Volts had a 1-Megohm resistor in the tip. This served to prevent the shielded DC-Volts lead wire from loading down a RF circuit. Textbook name for this is "isolation".

As a result you can probe into circuits with small RF signals without disrupting what's going on in the circuit. RF circuits that break into oscillation when your meter probe makes contact won't show you a correct DC-voltage reading. Turning an amplifier into an oscillator tends to skew the DC voltages in the circuit. A 'normal' modern-day digital meter has an unshielded wire a few feet long connected to the tip of its DC-Volts probe. That wire might as well be a large capacitor, and a feedback antenna both at once. Touch it to a sensitive RF circuit and it will either shut down halfway or become an instant oscillator.

Not a good way to get an accurate measurement. Closest thing to that type meter probe is a "times ten" oscilloscope probe. It's probably not as good for this purpose as the VTVM. But when meters went solid-state that 1-Meg resistor disappeared from the tips of meter probes.

And the means of duplicating the measurement shown in all those old schematics went down the drain.

Unless you keep one of those old VTVM's going.

Kinda. A good-quality times-ten probe is almost as good. And the 'scope can show you things that are going on the meter can't even guess about.

73
 
I have cheap and good DMM i even have a Old analog voltmeter. Do i really need to go buy VTMM? Or use what i have

The keyword?

1652022962155.png

Voltmeter - try to use anything that is analog, seriously.

Why? It can help "dampen" spikes and noise Prescence in the signal - for as you work to find the higher levels to peak to - references in the Service manual (Signal not it's noise or other artifacts like Noise floor hiss) you can use the Analog's meter own lag to develop that "Average RMS" due to this D'Arsonval movement design as a generalized indication of; "You're going the right way" or "You're too far into the weeds to pull you out"

We could get into the "nitty gritty" on differences that engineers have to design into electronics the new meters to mimic what replaces that, to use solid state versus analog movements that have been refined thru the ages to become the very things most people argue and fight over - both "on-Air" and the techs that do the very thing you are attempting to do on your own - everyday.

1652023496892.png
Simply because some meters are more divisive
about what is really being measured versus,
the ability to view a general rate of change to
indicate the direction you are trying to go.
So, since you're already using older radio equipment to begin with, the investment is really only your time and effort in familiarizing and even possibly cleaning the leads of the test jumpers to restore the OEM quality they originally had to get those reading correctly measured without the resistive effects left over from the "Oxides Of March" moving on thru April into May...

You also can use the radios own meters to VERIFY that which the older analog meter can - so you can use both more effectively in your restoration project.

Be sure to wish your mom a Happy Mothers' Day
1652024158166.png
Or at least remember her...

 
Last edited:
Marconi 2955B Radio Test Set will do everything you need in a single box.
The keyword?

View attachment 58848

Voltmeter - try to use anything that is analog, seriously.

Why? It can help "dampen" spikes and noise Prescence in the signal - for as you work to find the higher levels to peak to - references in the Service manual (Signal not it's noise or other artifacts like Noise floor hiss) you can use the Analog's meter own lag to develop that "Average RMS" due to this D'Arsonval movement design as a generalized indication of; "You're going the right way" or "You're too far into the weeds to pull you out"

We could get into the "nitty gritty" on differences that engineers have to design into electronics the new meters to mimic what replaces that, to use solid state versus analog movements that have been refined thru the ages to become the very things most people argue and fight over - both "on-Air" and the techs that do the very thing you are attempting to do on your own - everyday.

View attachment 58850
Simply because some meters are more divisive
about what is really being measured versus,
the ability to view a general rate of change to
indicate the direction you are trying to go.
So, since you're already using older radio equipment to begin with, the investment is really only your time and effort in familiarizing and even possibly cleaning the leads of the test jumpers to restore the OEM quality they originally had to get those reading correctly measured without the resistive effects left over from the "Oxides Of March" moving on thru April into May...

You also can use the radios own meters to VERIFY that which the older analog meter can - so you can use both more effectively in your restoration project.

Be sure to wish your mom a Happy Mothers' Day

View attachment 58851
Or at least remember her...

When i said old well its a Radio Shack/Micronta 22-220 FET VOM anolog
Is that old enough?
 
No one mentioned an audio generator. You're going to need one to align the transmit section.
 

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