Measuring 2.4 GHz SWR using a directional coupler

Measuring 2.4 GHz SWR using a directional coupler.

SWR meters for those frequencies are normally expensive. There is a way to do good measurements using a directional coupler. I got myself this one for 9 $:

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A simple BAT diode detector is easiy made:

1/2 BAT15-099

---|>|-------------------- | | |/ [ ] === O Volt meter | 1k | 1n |

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This 2.4 GHz linear:

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and a normal WiFi access point for test.

Good SWR (not much reflected):

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And with a metal object disturbing the antenna:

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By reversing in and output from the directional coupler you can get the forward voltage, and then you can calculate the SWR.

Here the method is described in more detail:

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Most expensive and most complicated part is the connectors, seems everybody uses something else...

So, some giggle Hertz tronix for the day.

Reply to
Jan Panteltje
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Oooooh. I want one or two. Thanks.

Nicely done. I prefer a bridge arrangement as in: I've built a few of these that work well. I suggest that you build yours so that the diode is easily replaceable. I keep blowing up mine with static electricity. PCB construction is nice, but just soldering the parts together in the air is good enough (if you have a good eye and steady hand).

I also use a return loss bridge: and an RF sweep generator.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
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Reply to
Jeff Liebermann

AD has a nice 2.7 Ghz Chip for this, so you can see gain and phase...

Ham use:

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Steve

Reply to
sroberts6328

On a sunny day (Wed, 28 Oct 2015 07:51:39 -0700) it happened Jeff Liebermann wrote in :

Do not open it, was full of what could be Beryllium dust, beryllium resistor inside? maybe it was just ceramic, but I could imagine a Chinese workshop.. Construction is nice tough, thick metal strips hold apart by some plastic type spacers.

But, but, that was also in the picture:

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Circuit diagram:
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PIC code in asm:
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That one needs some more work.

This is what it looks like after several diode replacements:

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The 50 Ohm SMDs are 2 x 100 Ohm on top of each other.

I have blown up about 3 BAT diodes now, using my Baofeng at 70 cm 2 W / 4 W. It is really a low power device, that is why I got the directional coupler, now I can live monitor SWR (reflected).

One interesting thing I found, when using the Raspberry RF out (can go to several hundred MHz)

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I consistently got strange readings. Finally realized that is a _square_ wave of several hundred MHz with harmonics into the GHz range, and reflections happen even in very short connection cables.

Interesting, had not seen that before.

Reply to
Jan Panteltje

Use a complete directional coupler; a meter on both ends - not terminator on one end and meter on the other (like you have now).

Reply to
Robert Baer

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