Transmitter tester, It's Alive, Alive!!!

[Dan/Panther]

In another thread we have touched upon a system for testing transmitters, and several ideas were bounced around.

Well I think I have run across a simple way to test transmitter. It doesn't give strength, but does tell you if it's good or bad.

Bill Cahill recommended wiring a speaker inseries with a battery, and the transmitter. If you hear sound at the speaker it's good. Made perfect sense to me.....

Well I didn't have a speaker handy where I was working, but I had some old phone parts, and decided to try the peizo microphone from and old cordless phone.
I wired the microphone in series with a 9 volt battery, and the transmitter.
Basically nothing exciting happened, UNTIL I brought the peizo microphone in front of the tramsmitter.
The feedback squeel was very apparent, and immediately I knew the transmitter was good, because if it were a dead one, I would not have gotten feedback, if I were simply shorting through the transmitter, I would not have gotten feedback.
That told me the transmitter was vibrating.
I tested this on a known DEAD transmitter, no feedback.
This defineately works for a good/no good tester, now to figure how to test for strength.

I'm thinking of adding a potentiometer in series, marked 1 to 10. Start at full volume, decrease the pot, the lower the pot goes without loosing feedback, the stronger the transmitter would be.
Is that thinking in line with sense, or nonsense.
Or any better suggestion.
If this works, I lay out what values I've used, and one other thing, a battery would not be the best power source, a wal wart would have a more consistant output over time, a weak battery would give false readings, or maybe even none where a good transmitter is being tested.

D/P

[Dan/Panther]

Well I got the prototype up and running.

Picture one is the complete unit with wall-wart. The meter is for the next step.
Absolutely blew me away when I opened the box, that I found to build the project, inside I found a small circuit board I had built a few years back for radio testing.
It's an audio output level indicator. I plan to add this to the circuit to have a visual to compare different strengths of transmitters.
The way it works is this.
In picture two the transmitter is mounted on the test pad., The contact brushes are placed over the ring contacts. The poteniometer is set for minmum, the power switch it energized, causing current to flow through the circuit, a high pitched feedback begins as soon as the switch is thrown. This tells you the transmitter is good, then by increasing the poteniometer, the feedback slowly decreases until it stops, this point is where you see how strong the transmitter is, the higher you turn the pot before you lose feedback the stronger the output of the transmitter.
This is where the meter comes in. When you first turn on the unit, the meter will register the output of the circuit with the pot down at minimum. the meter goes from 1 to 5, make a note of the reading gives you the first digit of the eventual value to be given the transmitter, the pot is also calibrated from 1 to 5. As you increase the pot the volume of the feedback decreases. When it finally stops , you read the number of the pot 1 to 5, the best rating would be 55, 5 for the meter, 5 for the pot, if the meter reads 3 when first turned on, and the feedback drops out at 4, the rating would be 34. Etc.
I know it sounds complicated and maybe some think not worth it, but it's really simple to use, and without the meter section very easy, and cheap to build.

D/P
At least it works.

[bingster]

Yankee ingenuity wins the day.  That's quite a nifty little piece of gear, dan.

[Dan/Panther]

Bingster;
Thanks for the compliment.
I was thinking, by creating a feedback situation might it actually loosen the carbon in the transmitter, and actually increase it's efficiency ?
Maybe by letting them sit and feedback for awhile it might help a weak transmitter. Kind of like rejuvenating a picture tube ?
As it is now, everyone recommends tapping the element on the table to loosen the carbon.

D/P

[McHeath]

Amazingly clever!  No wonder we were able to go to the moon back in the days of slide rules and pencils, guys like you figured out how to make rockets out of whatever was laying around. 

[Dan/Panther]

Funny you should say rocket, when I was 11, a neighbor and I were building a solid propellant rocket, when it prematurely ignited and darn near bilnded me in my right eye. Burnt it really bad, but I had a wonderful Dr., A Dr. Adrian, who it turned out  was practicing without a license. In my case Who the heck cares, he saved my eye.

D/P