Shock-induced AL changes

So am I. :-)

Here is one, 12V/50A@50Hz synchronous rectifier with magnetic control:

Despite its simplicity turned out to be extremely rugged and reliable.

Yes, ths has already been done. I was told that this current-mode tuning was used in an East Germany military receiver due to its low noise. Be it as it may, I think they just didn't have suitable high-capacity varactors. OTOH, these theories are not mutually exclusive, so both reasons could be true.

Indeed, but you don't need to drill toroids for that purpose. Here is a magamp I made today to check the viability of the P40

6mm cores I bought in China. It turns out that a single layer winding can have as many as 55 turns, here you have two:

Then you stack them in a totem-pole way and wind the control winding through both rings at once, ending with this:

Then you just need to connect the two AC coils in a way the induced voltages oppose each other (best using a scope). The scope shows the magnetic coupling between the resulting AC winding and the control winding is almost non-existent.

Here are the measurement results for a 30 turns control winding and 2x55 turns AC winding. On the left is the control current, on the right the AC winding inductance in uH (@1kHz).

mA uH

0 12373 2.8 11732 6.1 10269 7.6 9432 9.3 8384 10.7 7485 12.5 6541 15.6 5054 18.8 3756 20.3 3438 22.0 3060 25.3 2437 28.4 2018 29.9 1853 31.6 1690 34.8 1440 36.3 1335 39.5 1144 49.1 765 60.4 506 99.1 173.6

the 10:1 inductance change boundary is crossed somewhere near 38mA, which makes it 30*0.038=1.11 ampere-turn. Very satisfying results.

Here is my testing equipment, made of IR21531 set to 309kHz and a 5x20 turns 1:1 isolation transformer on a core sufficiently big not to care about its own saturation, which allows me to have up to 4 isolated voltages in various configurations (e.g.

2*(2x12V in antiphase), good for push-pull magamps).

Best regards, Piotr

This is amazing. You have opened the door to LF and VLF spectrum analyzers.

These are impossible with varactors. DDS is noisy and contains unwanted spurs, and multivibrators and noisy and tend to drift. Your tunable toroids look like an excellent solution.

Here are some of the things you can do with a LF/VLF spectrum analyzer:

1. Find RFI/EMI sources in switchers, drivers, etc

1. Detect time transmission on VVWB on 60 kHz, DCF77 on 77.5 kHz, JJY in Japan on 40 & 60 kHz, Taldom in Russia on 66.66 kHz, BPC in Lintong, China on 68.5 kHz, MSF in Anthorn, UK, on 60 kHz

2. Listen to long-wave broadcasters in Europe

Add an ultrasonic transducer and a whole new world appears:

1. Find leaks in pressure lines

1. Listen to bats, insects and birds

2. Detect corona leaks on high voltage lines that generate RFI

1. Find arcover causing misfires in automobile ignition wiring

2. Detect bearing wear in machines

1. Listen to fish, crabs and other life underwater

The LF/VLF world is well worth exploring, and your tunable toroids make it very inexpensive.

1. This could be a real moneymaker - monitor arc welding to optimize arc

On a sunny day (Mon, 20 Nov 2017 03:54:47 GMT) it happened Steve Wilson wrote in :

Hey, those already exist and do not use transductors. Any FFT can be done on audio samples at any rate. Also magnetic tuned VFO is as old as the world, been there done that, and published it here.

Transductors are also as old as the world, in my first job we had those in big controlled rectifiers that you could not lift without a fork lift used for power stations, to charge big battery banks for telco, the transductors controlled by a thyristor controller for the 'bias'.

In many CRT color TV sets transductors were used for NS correction in series with the H deflection. Magnetic amplifiers: many books have been written on it.

I have designed and build a multi-channel LF transmitter (30 kHz to several hunded kHz) for some project, no transductors, just digitally switched inductors for tuning, a rack full, licensing was interesting, had to keep a log too. beep

Yes, they have been available for decades, AKA "dynamic signal analyzers".

--

John Devereux