The "Dee Ultimate" meters I saw being promoted a few years back were touted as the same design as a "Dozy" meter.
Don't know, never have seen one in the flesh.
If that's what's inside, it's a "Passive" peak-reading meter.
Puts a capacitor big enough to "filter" the modulating audio between the diodes and the meter's coil circuit. For you geek types out there, it's called an "integrator" and makes the pointer respond to peak power, sorta.
Since you are borrowing power from the RF signal to push that pointer against its return spring, the inertia of the needle and coil will cause it to "average" the peaks and valleys in your audio waveform. This tends to cancel them out, so that a (only) 100%-modulated AM signal swings upward only slightly if at all.
The capacitor behind the "Peak" switch on this type meter is being 'charged up' by your RF signal passing through. It gets discharged back into the meter's coil circuit during the "valleys" in your modulated audio waveform.
SO LONG AS YOU CHARGE THIS CAPACITOR FASTER THAN YOU DISCHARGE IT, the meter won't fall back (much) during the 'valleys' in the audio waveform. Provides a "peak-reading" function that LOOKS purty.
But on the low-power scales, there isn't as much current available to charge that "peak" capacitor. The capacitor never gets fully charged before the meter's coil starts to discharge it during the valleys. It's not unusual to whistle into a radio and see 18 Watts PEP on the 100 Watt scale. Flip to the 1000 scale, and the same radio shows 25 Watt peaks. Your mileage may vary. All 'passive' peak-reading meters share this flaw, to some degree.
On the highest power scales, this kind of meter can read within 90 or 95% of true PEP power. But it depends a LOT on the audio waveform. And it's not all that friendly to SSB signals. Works better on AM.
An "active" peak-reading meter requires a power source of some kind. Battery, AC cord, something. Sure wish I could remember the name, but one company made one without a power cord, only a battery. It would 'hog' a few milliWatts from your RF and charge a battery from that. You had to run over 100 Watts PEP to do it, but so long as you would transmit before tha last charge ran down, the peak-hold amplifier circuit would be powered indirectly from your radio's RF output. The more often you talked on it, the more charge would be stored for running the peak-reading amplifier.
Main advantage of the "active" peak meter is that the "peak-hold" capacitor now discharges a LOT more slowly, and holds the meter needle firmly at the peak-power level, whatever power range you use. The amplifier circuit inside drives the meter's coil without drawing a lot of current away from the peak-hold capacitor. Won't be 'stingy' on SSB, either.
Drawbacks are more parts, more expense, needs a power source, only a little more accuracy, depending on how you use it. Or a lot more accuracy, if you use SSB.
But when the "Dee" meters were introduced, they were a "Dozy" with a different name on them. Something about a trademark lawsuit over the name "Dozy", I think.
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