Mode Zero

Hi all,

Has anybody designed a simple 2.4g RF detector circuit that would work with an existing analogue tx meter like we used to get on old tx's and easily fit inside the case. It only needs to show the presence of a transmitted signal; no accurate read out required.

Over to you clever people.

The reason is, I have a Kraft 76 series tx with a dual voltage and RF meter in I'm converting for my Kwik Fly 3.

Cheers,

Shaun.

Here ya go bud:

viewtopic.php?p=6272#p6272

Cheers pal.

I may have a couple of microwave diodes, I'll have a dig

I wonder if one of those UHF diodes, near a 2.4GHz transmitter, would provide sufficient voltage and current to illuminate a LED? One of those high efficiency, 'ultra-bright' LEDs will glow quite brightly on less than one milliamp, and might make a simple, cheap, 'transmitter is radiating' tester - either as a hand-held tool, or built into a transmitter.
A microammeter is obviously better, but more expensive, and less compact.

Would it work inside an ali cased tx Martin?

I don't know if it would work, at all, and I don't have any UHF diodes to try it with. A turn or two of wire to act as an inductor, in series with the LED, might help prevent the LED's capacitance from damping any current flow, and make it glow brighter.
If it does work, it should work equally well inside a transmitter case, close to the antenna feed.

Cheers

I'll get some UHF diodes ordered and play .

Martin wrote: ↑19 Dec 2023, 12:54 I wonder if one of those UHF diodes, near a 2.4GHz transmitter, would provide sufficient voltage and current to illuminate a LED? One of those high efficiency, 'ultra-bright' LEDs will glow quite brightly on less than one milliamp, and might make a simple, cheap, 'transmitter is radiating' tester - either as a hand-held tool, or built into a transmitter.
A microammeter is obviously better, but more expensive, and less compact.

Martin, the ultrabright LEDs have quite a high forward voltage, so even though they glow at quite a low current, from previous experience you are probably better off using the lowest forward voltage LED you could find.

Shaun wrote: ↑19 Dec 2023, 13:05 Would it work inside an ali cased tx Martin?

No! Well not with a Skyleader SLX case anyway.

I tried Phil's circuit and also bought a cheap commercial "microwave" detector meter (which was nothing more than an antenna, GHz diode and some capacitors and an uA meter). Both work well outside the case near the antenna, but inside it's like a Faraday cage and there was no real detectable signal in the case, even with the back off the Skyleader. Which when I think about it, is a good thing. I guess if you had a second external antenna somewhere near the Tx antenna it could work, but I don't know if it would affect the transmitted signal? There must be a way though.

The nearest commercial sets get to the rf power is the RSSI telemetry showing how strong the received signal level is.