VLF meter situation resolved !
Posted: Tue Dec 05, 2017 3:57 pmHi Gang,
Yesterday I developed a hookup that kept VLF meter readings from 'double timing', but I noticed that below '0' volts, my meter just took a nap and waited for the waveform to rise above zero, while the stock meter double timed.
That hookup kept my needle from double timing, but it still wasn't correct.
So what's going on with this VLF double timing ?
Here's what's happening.
The stock meter sees both positive and negative 'voltages' (numbers) as POSITIVE !
So when the waveform dips below zero, the needle sees all those negative numbers as positive and starts moving upward again !
So why does this NOT happen at higher frequencies ?
Simple.
At higher frequencies the needle's ballistics PREVENT it from falling and rising that quickly, so the needle just goes to the positive value and can't fall fast enough, and the next negative value is seen as positive so the needle just stays put at the positive reading !
At audio frequencies we're given a pretty accurate reading, but at VLFs, the rate of change is slower than the needle's ballistics and the meter sees those negative numbers as positive numbers and starts rising again !
My half wave diode solution worked because it kept all negative voltages at ZERO, and the needle just sat at zero and waited for the positive cycle to begin.
It seemed to work, but the negative numbers were not getting read.
So I came up with a fix, I built a Dead Simple circuit that biases the meter above zero volts at all times AND tracks with the level control, so the meter can get hit with OVER +/-1 volt and not run into trouble.
Enjoy your new toy, open the box and see how I developed this circuit, and have fun !
Enjoy,
ROXY
Yesterday I developed a hookup that kept VLF meter readings from 'double timing', but I noticed that below '0' volts, my meter just took a nap and waited for the waveform to rise above zero, while the stock meter double timed.
That hookup kept my needle from double timing, but it still wasn't correct.
So what's going on with this VLF double timing ?
Here's what's happening.
The stock meter sees both positive and negative 'voltages' (numbers) as POSITIVE !
So when the waveform dips below zero, the needle sees all those negative numbers as positive and starts moving upward again !
So why does this NOT happen at higher frequencies ?
Simple.
At higher frequencies the needle's ballistics PREVENT it from falling and rising that quickly, so the needle just goes to the positive value and can't fall fast enough, and the next negative value is seen as positive so the needle just stays put at the positive reading !
At audio frequencies we're given a pretty accurate reading, but at VLFs, the rate of change is slower than the needle's ballistics and the meter sees those negative numbers as positive numbers and starts rising again !
My half wave diode solution worked because it kept all negative voltages at ZERO, and the needle just sat at zero and waited for the positive cycle to begin.
It seemed to work, but the negative numbers were not getting read.
So I came up with a fix, I built a Dead Simple circuit that biases the meter above zero volts at all times AND tracks with the level control, so the meter can get hit with OVER +/-1 volt and not run into trouble.
Enjoy your new toy, open the box and see how I developed this circuit, and have fun !
Enjoy,
ROXY