Friday 24 December 2021



Super simple to build! It only consists of 16 parts and it literally takes a few minutes to put together. A great beginner project.

The QRPGUYS call this their "LED Tuning Indicator" but most other people would call it an SWR Bridge. I purchased it because I was just a little concerned that I might harm the finals in my QRP-Labs QDX while tuning-up.

I use an Elecraft AT1 tuner which is remarkably fast at finding a match, but for the sake of $20, it's just not worth the risk. With this bridge fitted inline, the QDX will never see more than a 2:1 mismatch. It's rated at 10W PEP or 5W CW which is perfect for the QDX.

All you need to do is fit it between your transceiver and ATU and flick the switch to the TUNE position before tuning up as normal. As the tuner gets closer to a good match, you'll see the onboard LED glow dimmer and dimmer. When your tuner finds a 1:1 match, the LED should extinguish (although it may actually stay on VERY dimly).

So once you've found your match, just flick the switch back to OPERate and away you go. Leaving the switch in the TUNE position will result in your transmitted power being reduced by a factor of 4 (approximately). This can be handy for when you wish to reduce the transmitted power of your QDX for WSPR tests.

When I'd built the little kit, I attached it to the QDX and gave it a go. It worked perfectly on all bands and had ZERO impact when in the bypassed mode for normal operation. Very pleased with this little device and I look forward to playing around with some more QRPGUYS kits in the future.

Kit available >> here <<

Here’s a video of the kit in action with my PreppComm MMX (which is notoriously easy to blow up 😂

Just to clarify, this device (apart from being used in-between a radio and a tuner) can be used without an ATU to help you to determine how close to resonance your antenna is. You could adjust the length of your antenna and monitor the brightness of the led after each adjustment. When the led no longer lights up, you've reached the sweet spot.

Here’s a >LINK< to the manual.

Thanks for visiting the Blog. Feel free to leave a comment below.

73, Tom, M7MCQ.

#qrpguys #qrp-labs qdx #swr-bridge


Larry C said...

Where can I buy this kit?

Roy Appleton said...

Good article! You might add one thing, a link to the QRPGuys product page. Roy WA0YMH

Ian.L said...

Hi Tom, might seem like a silly question but if I've got this right its for use with a manual ATU and you tune up without any power until the LED goes out/dims? You then go to the operate position which bypasses the bridge and tune if need be as normal. Is this correct?

MadDogMcQ said...

D'oh!! Sorted Roy. Thanks for visiting the Blog.

Merry Xmas!

MadDogMcQ said...

Link is now in the article Larry :-)

Merry Xmas.