Low cost (but good) directional coupler

Quote from DB8TF

I bought three of those directional couplers on eBay and they work very well for measuring PA output power.

The coupling value can be selected 10/20/30/40dB. (and some more)

Those directional couplers are sold by many sellers and also on amazon & Co. for a few bucks.

https://www.ebay.de/itm/1stck-…m:mT6rnKMBsPYpjotZjzsa11w

VY73 DB8TF

Also on sale at alliexpress, look out for shipping cost and time of shipping

It's not a bad price for a cast box with 3 connectors either!

Used these couplers earlier (before QO-100) on the radio club here. For the price it's not bad .. but check the directivity.

Yes, you can do that, but it's wise to calibrate it with a known source.

What I do, when I don't have a power meter attached, is measure the reflected voltage, then the forward voltage (connect the coupler reverse) and then RL = 20.log(Vr/Vf)

Quote from PA3FYM

Used these couplers earlier (before QO-100) on the radio club here. For the price it's not bad .. but check the directivity.

Also check the power ratings. Some are only 100W max. and I am not sure they will handle this continuously for a long time. SSB fine, DATV not. Not an issue for lower powers though.

I measured similar directional couplers with 20 dB and 30 dB coupling today. A PICO VNA 106, analyzer with a Rosenberger calibration set were used for measurements. Unused connector was terminater with ANRITSU 50 Ohm load with impedance match better than 40 dB. Results are attached. I guess, that couplers are really good and they worth your money. With AD8317(8) detector can be built very cost effectiv power meter or VSWR meter.

Rasto, where did you buy these? They look so nice : -)

Hi Remco,

I guess, that I ordered them from this source: https://www.ebay.com/itm/Femal…5a1fe4741805b19b11e7fa1f1

73 & GL,

Rasto

A75GR Rasto many thanks for the link,,

Hi Rasto,

thanks for the detailled measurement results. Very helpful for my project.

Did you also measure port 3 --> 2 ?

Hi Armit,

you can see a directivity. No problem, I can measure it, but in 2 - 3 weeks, when I will be in EU. I can also measure power level on port 3 with Load, Short and Open termination at ports 1 and 2.

73, Rasto

Due to this thread I also bought cheap couplers. I bought these in 20dB and 30dB versions.

My measurements as follows:

SA5PMG & A75GR Thanks for the measurements : -)

From the table above I conclude they are good (enough) up to 2.4 GHz, so perfect for 13cm / QO-100 experiments (like measuring return loss of antennas or calibration of output loops in (home brew) amplifiers)

I measured my directional couplers with 20 dB and 30 dB coupling between ports 2 and 3 today. The same setup as for previous measurement was used. Results are in attachments. Directivity for 20 dB coupler is 31 db @ 2409.8 MHz, for 30 dB coupler 25 dB @ 2409.8 MHz respectively.

Dear all,

I also bought a low-cost Chinese directional coupler for amazing 5,35 Euros including shipping and it performs really well.

Here is an evaluation report:

Evaluation report of a low cost directional coupler for 23cm and 13cm bands

Kind regards

Matthias

http://www.dd1us.de

Hello Matthias;

I have the same directional 30dB coupler and as you found it performs really well. For the cost over the frequency range they are very good units indeed.

Adrian