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It may seem a "strange topic" for these parts - CALIBRATION

guitar_199

guitar_199

Sr. Member
Mar 8, 2011
987
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Deer Park, TX
I threw a question on this subject out in a Vintage Test Equipment group on FB and the discussion really grew interesting. No pick on... no sarcasm..... I was kind of disappointed actually.

SO I thought I would drag it over here....

Does any one here worry about calibration of all of your test equipment?

It seems rather expensive for someone working on a "home" level. ONE place here in Houston quoted me something like $5000 to calibrate my service quality Beckman 1.3 Ghz frequency counter. I kind of lost interest after that.

But one suggestion they had that seemed to "ring reasonable" was.... a GPS disciplined 10Mhz Oscillator.

With THAT one at least has a reference to keep the frequency counter "in check" and I am thinking that the freq counter is one you would really want to have right.

It just seems to me that as LONG AS your scope can see the signal... that for the most part you are probably okay.

In a way.... I even lump the "spectrum analyzer" the same way. It can still be used for valuable purposes EVEN IF you are not using it for critical level measurements. I figure that if you have a reasonably good power meter.... that the spectrum analyzer can still display the spectrum and let you know if you have spurious content showing up in weird places.

So.... what do you all think? (other than... that I am overthinking things????)

Do any of you do things to check the integrity of your gear?
Do any of you consider this topic important... especially if you repair radios for others?

Just curious....
 

oh this is a nice can of worms ya got there!

I guess i can offer some perspective, but at the end of the day it's still just an opinion.

on a conceptual level, calibration is super important.
but why?
because without it no work can be performed to a professional level?
NO FREAKING WAY!

It's because we have to have some sort of standard for things to be measured against.

do we need a reference for what "one pound" is"
of course.

Do you need your home scale calibrated to know whether or not you're losing or gaining weight?
of course not.

Use this idea when thinking about equipment that is used to find peaks and nulls.

For radio purposes, an oscilloscope is a good example.

Has anyone ever seen any alignment manual tell you to measure a certain voltage level using your oscilloscope?
NO.
they may give you a general reference so you can tell if an oscillator is operating properly or something like that. "1-2v P-P typical" is something you might see.

But they are never going to tell you to peak L10 until you see exactly three divisions on your scope when set to 1v per division, or something like that.

why not?
because that's not really how scopes are used in our world.
can you use a scope for voltage measurements?
sure.

are there better more accurate tools for this?
you bet.

I have three oscilloscopes. only one of them i bought new.
it was expensive.
the ONLY reason i bought it (aside from having the money at the time) was because i wanted to calibrate my wattmeters, and a scope is great to do that with, IF you can count on its accuracy.

i checked my new scope against both of my 20+ year old scopes, and they were all within a line thickness of each other.
the expensive one sits in the closet, and i run the old tektronix for daily use.

now a frequency counter does need to be accurate, but how accurate?
we have to stop on the right side of the decimal at some point dont we?
just how far that is depends on the kind of work you're doing, and your budget.

for radio work, 1hz accuracy is all you're going to need.

can you get a better counter than that?
absolutely!

will anyone besides you know or care?
nope.
(well i know of one guy out in the desert who might, but he only talks to himself anyway so...)

If i were to show you just how far you have to turn your clarifier to tune in a station that is 10hz off freq. you'd laugh.
let's just say it ain't much.

Are there really any radio operators out there who just stare down their clarifiers refusing to turn them?
no.
if you want to talk to someone and their voice is just a bit "ducky" for your tastes then you just tweak the clarifier and there they are.

I'll be ballsy and say it flat out.
Aligning a CB radio to within 10hz accuracy is FINE!

i however like to get to 1hz if i can, but trying to do this on a Ranger chassis will drive you batty!

i bought a rubidium oscillator years ago and gave it to a friend who was in college at the time and had access to super expensive test equipment.
it was like 10.000.000.3xx or something like that.
better than i'll ever need.

went home to calibrate my three frequency counters that go to 1hz resolution.
NONE of them needed to be adjusted.
two of them are over 15 years old, and read 10.000.000.

i send out fluke voltmeters for calibration for work once a year.
been doing this job for 10 years and i have yet to see one come back saying it needed adjustment.


so, is calibration important?
yes.

am i concerned about any of my equipment?
not in the slightest until it starts acting funny.
LC
 
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I believe it is really important to have your meters reading correctly if your going to be making adjustments inside your radio. For example in my years of accumulation of meters I have 3 slightly different Dosy meters that have basically the same SWR readings but all 3 read different on dead key and modulation and that is frustrating. The first one I bought I had a local cb repairman calibrate it to match his bird meter but he was a young man starting out so I can't say my confidence level is extremely high in the job he done. My plan is to get a well know repairman to fix a radio for me and take his settings and adjust all three meters to read the same and that should be close enough for working on only my radios. I would never think of working on someone else's.
 
I use WWV to align my frequency counter (first time last year). I'd be screwed without WWV as I don't have a fancy atomic reference at home.
edit: gonna warm it up and check it again tomorrow now that I am thinking about it...
 
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Well, I remember in the good ole days when the FCC had certain requirements for a CB to be on frequency now this was before PLL circuits and OCXO'S and TCXO'S were not used in any old tube CB radios and the frequency tolerance was to 20hz one way or the other and the test equipment produced for the express purpose of working on CB that was widely used at the time was accurate enough to get the job done. ( HICKOK, B&K and SENCORE) The point is now with the exception of certain manufacturers you have to work at making a radio operate off frequency assuming you want it to be off frequency. I heard Fine Tune talk about how amazingly accurate his and only his test equipment apparently is I just turned him off and have never turned him back on.
 
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My Frequency counter and signal generator came from an engineering firm that does design work for the defense department. They are from the 90's and were just sitting in their lab as they have upgraded their equipment a few times since they were using what I now have. I did a search for calibration labs in my area and found 2. It is possible that since I am a few hours from Washington DC there seems to be a lot of defense contractors in my area and these labs are needed. I paid $125 each to have them calibrated at one of the local calibration labs. I thought it was important to have the signal generator calibrated as when I set the S9 level during the alignment I wanted it to be somewhat accurate. I have tested the freq counter against a reference oscillator since the calibration. It was dead on. I then take the signal generator and set it to 10 MHz and connected it to the freq counter and it is dead on as well. Not that those tests are as good as a calibration but it does show that they are still on. I also agree that the scope and spectrum analyzer are more of a reference rather than a lab grade accurate measurement device for me so I am not as concerned about their calibration.

For those of you that are looking for equipment…. When I dropped off my equipment for calibration the lab had a bunch of equipment on the shelf. I happened to ask about them and was told that they get unused equipment all of the time. They told me that if I ever needed anything to call and they would see if they had something that fit. Most of the equipment was lab stuff like gas analyzers but you never know. If you have a lab around you call and ask. I happened to be talking with a person that worked at the defense contractors and told him that I was working on setting up a bench at the house to work on radios. He was very excited to hear that anyone would do that as everything today is so disposable. He was my connection to get the older equipment I have. You just never know…
 
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I have had two airplane radios that were out of cal on transmit but fine on receive. Calibration is important.

Given that I used an old frequency generator to verify a new china made frequency counter and it was pretty close. Make sure that if you are doing calibration work that your equipment checks against other stuff.
 
I usually take the worst BNC cable I have (because it has poor shielding) and connect the signal generator directly to the counter with it using a 50Ω terminator. I then tune the HF radio to WWV and increase the signal generator output just until I hear a change in the received audio. Then I get the frequency close enough to hear the beats, then adjust the generator level so the beat sounds best, then fine tune the gen frequency for zero beat. When adjusting the counter, I always overshoot the adjustment every time. It takes me forever with how sensitive the adjustment is in my counter
 
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