Design help / ideas current sensor (2023 Update)

On a sunny day (Tue, 4 Jan 2022 22:15:45 -0800 (PST)) it happened Phil Allison snipped-for-privacy@gmail.com wrote in snipped-for-privacy@googlegroups.com:

My first big ham radio transmitter was about 250 W or more (tubes) and I could walk around in the garden with a neon light that would light up when transmitting. Now there is your indicator! Of course I had no license back then... But made a QSO anyways,

Sounds great if it's for something like triggering a babble-timer or a fancy neon "ON AIR" sign to impress the fam. God help him if it's for something related to the safety of himself or others. It is unfortunate he didn't specify cuz maybe he run off to build a THERAC 25 from ham radio parts.

On a sunny day (Wed, 5 Jan 2022 01:50:59 -0500) it happened bitrex snipped-for-privacy@example.net wrote in <ndbBJ.74583$ snipped-for-privacy@fx08.iad:

Yea, whats-it-called Darwin Awards. To add to the not so simple solutions I once made an AC current meter using an old audio tapehead:

gives mains AC current. mains wire glued in front of the headgap.

Jan Panteltje wrote: ================

** See: ** If you just added a second tape head - a few inches from the first - you could tell which way the electrons were moving.

.... Phil

All the transmitters I have seen under my 60 years as a licensed ham have an output for the PTT/Transmit mode signal. It is usually targeted for controlling an external power amplifier.

Why on earth cannot it be used? It is aeons easier to use the proper control signal than to synthetize something like it. The synthesized signal comes too late to be correct, by definition.

On a sunny day (Wed, 5 Jan 2022 00:26:06 -0800 (PST)) it happened Phil Allison snipped-for-privacy@gmail.com wrote in snipped-for-privacy@googlegroups.com:

Interesting, but those move fast, 300,000 km / second so in 1 mS 300 km, 1 ms is still 1000 Hz within audio range so say 100us = 10kHz = 30 kMm distance would do. Also it is not the same electron that comes out, those are more like dominos falling over, in the mean time they do a loop the loop around the copper atoms and occasionaly pass on momentum to the electrons in the next atom, that is why speed of electrickety is somewhat slower in a conductor. Somebody will correct this I am sure ;-)

No the electrons do not travel at the speed of light. Common fallacy.

see e.g.

Yes, they do tend to stick or even weld. If I recall, one traditional remedy was to use rhodium or iridium plating on the contact tips, and no gold.

And then there are mercury-wetted contacts, but Mercury is bad these days, probably because it worked so well.

Burglar alarm door switches used to have such plating.

Joe Gwinn

Tauno -- I see a PTT connector but it's an input that's meant for externally putting the xcvr in transmit mode. Don't see any sort of output that would mimic the PTT switch on the mic. There is also a din connector but from what I gather it's for data.

And this is a Yaesu model.

You could put a tee connector in the RF cable and tap off a few milliwatts into a diode detector and an SSR.

Maybe use one of the little Pomona boxes with a connector on each side. Gimmick cap pickoff.

jesus -- I didn't think of that ! and that's embarrassing. sometimes it's right ion front of your face. I hate it when that happens. yeah man -- you got it.

I would want something that's totally isolated from affecting the xcvr performance. A cap in series ? then the diode? Really all I need to do is grab a few millivolts or better yet, enough to power a sensitve optocoupler and still be self powered. (I'm not much of a designer anymore -- just breadboard till it works) :)

On a sunny day (Wed, 5 Jan 2022 16:25:37 -0000 (UTC)) it happened Jim Jackson snipped-for-privacy@franjam.org.uk> wrote in snipped-for-privacy@iridium.wfdf:

Thanks so about 1 mm / second

originally thought about doing something inline but didn't think of a tee connector -- using a box with so239 etc was too much hassle

Something like this should work. The gimmick is the cap.

Twist the gimmick until it works. It shouldn't affect the receive signal.

Or use the RF to light a neon and put that near a photoresistor. Or just look at the neon.

Directly driving an LED or SSR with RF might work, but some have a lot of capacitance.

What's this for?

something that won't sell. like everything else I've done. :) one thing that's nice about optoisolators I've used, is that it's amazing the range of voltage that will trigger them with just on resistor. I put a 1k on one I have and the npn output would react to everything from 3v to

20 or so if I remember right without drawing to much led current.

For higher powers or where safety is the concern it would be good to have two sensors; the primary indirect input current sensor detects non-activity, and the secondary RF sensor detects activity. It's simpler to build a fail-safe non-activity detector than it is to build a fail-safe activity detector - negligible input current is a pretty reliable indicator of non-activity. Then the state of negligible input current detected by the primary sensor actively holds the "SAFE" lamp or such on.

Power to the transmitter turns it off and then the RF detector confirms output activity. If the sensor or indicator for "SAFE" fails then it defaults to the (potentially) unsafe condition. And any incongruity in the states should also defaults to "unsafe."

But please refer any design of real-world health or safety critical systems to a qualified engineering professional, though, I'm definitely not entirely confident that's as bug-free as it can be either even with an ideal implementation.

Which Yaesu model?

Do you have its manual? Have a look of recommended linear amplifier connection. The T/R signal should be there.

It's an FT-840 but I want to do something universal if I can. Thanks sincerely for all the help. Many ideas to try.

There's no reason to help people who won't answer simple questions.