Modulation Meter Calibration ???

[FlyBoy50]

Been thinking of my 3 different Dosy Meters and the difference in the modulation readings on all 3. First off I bought a Dosy TC-4002-SW because I liked hooking 2 different antennas to it and a dummy load for my radio bench testing. After buying it my local guy that is into CB repair calibrated the watt meter to match the readings of his Bird meter which I don't seem to have a problem with. The part I question is the Modulation mode on the meter seems to be the most stingy reading ( more than a little ) of my 3 meters. The other 2 meters are a Dosy TFC-3001 & a Dosy TFC-3001-S which are close in Modulation reading but still different. The later being my favorite because I can check frequency reading on AM and SSB. The question being can the Modulation Meters be calibrated on all three meters to read the same reading. The problem being you don't feel like adjusting modulation on a radio if your not sure which meter is correct. And No I am not into radio repair but It would be nice to make a few simple checks & adjustments on my own personal equipment because my local guy is too busy with his regular job these days and it would be nice to turn down the dead key & turn up the modulation a little. Anything after that I'd leave it to the Pros because my investment for a hobby is over. Thanks in advance. Mike

 

[Eldorado828]

Been thinking of my 3 different Dosy Meters and the difference in the modulation readings on all 3. First off I bought a Dosy TC-4002-SW because I liked hooking 2 different antennas to it and a dummy load for my radio bench testing. After buying it my local guy that is into CB repair calibrated the watt meter to match the readings of his Bird meter which I don't seem to have a problem with. The part I question is the Modulation mode on the meter seems to be the most stingy reading ( more than a little ) of my 3 meters. The other 2 meters are a Dosy TFC-3001 & a Dosy TFC-3001-S which are close in Modulation reading but still different. The later being my favorite because I can check frequency reading on AM and SSB. The question being can the Modulation Meters be calibrated on all three meters to read the same reading. The problem being you don't feel like adjusting modulation on a radio if your not sure which meter is correct. And No I am not into radio repair but It would be nice to make a few simple checks & adjustments on my own personal equipment because my local guy is too busy with his regular job these days and it would be nice to turn down the dead key & turn up the modulation a little. Anything after that I'd leave it to the Pros because my investment for a hobby is over. Thanks in advance. Mike

The dosy meters don't have a true peak reading, it's done via resistors so no 2 meters will read the same and not very accurate either. If I remember correctly, the meters are adjustable through different pots depending on the range but I believe the pep readings will be dependent on the circuit components.

Without a true peak circuit that would require power from an external source, you'll only get a wide ball park reading.

Someone correct me if I'm wrong please.

 

[loosecannon]

what it really comes down to is whether or not a calibrated modulation meter actually gives you any relevant data.

For AM modulation, you can either adjust it with an oscilloscope for a clean waveform, or you can adjust it based on your ear, and scope patterns be damned.

a modulation meter, even if it's calibrated, and shows you whistling to exactly 100% on that meter, is still not a replacement for an oscilloscope, so if you don't know if the signal is flat-topping, you might as well just set the modulation by ear.

i guess there could be some value in being able to set the modulation where you like it by ear, making a note of what that equals on the modulation meter, and being able to go back and forth to that same meter reading.

the only advice i would have there is to use a 1Khz tone instead of talking or whistling in to the mic so you can get a more accurate reading.
youtube has hour long videos that are nothing but 1K tone.
LC

 

[Captain Kilowatt]

Those CB type modulation meters simply measure the difference in RF power from dead carrier to modulated RF and are not that great. An oscilloscope is best, or you can use a true modulation meter like the one I have. It does AM and FM modulation from 1.5MHz to 2.0 GHz but costs just under $1000 when new many years ago. They are available used on various sites for a few hundred.

 

[FlyBoy50]

If I remember correctly, the meters are adjustable through different pots depending on the range

There is 3 adjustment pots inside for the 3 different wattage ranges. There is another adjustment pot inside the one I had the cover off but I don't remember what it was for when I talked with a older Dosy tech long ago. I rather suspected the Dosys might be too low tech for really accurate work. When I checked my NOS Uniden PC-122 on my Dosy TFC-3001-S it told me the modulation was 100% out of the box which I questioned. I'll have to test it on my Dosy TFC- 3001 and see if it is lower. But I'll have to thank the 3 of you for chiming in and confirming what I feared.