Low cost (but good) directional coupler

• 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

At "Antons Funkperlen" website are photos from the inside: http://funkperlen.blogspot.com…htkoppler-fur-7-euro.html

Edit: attached a picture of a measurement on my 30db coupler

VY73 DB8TF

Images

Edited 3 times, last by DB8TF ().

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

Edited once, last by PH0RVK ().

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

Richard - M0VKK

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

• Is it possible to attach a Shottky diode, condenser + resistor to GND, at the coupler to measure the voltage with a DigitalVoltMeter ? So you can the measured volts calculate into Watt and dBm ?

Thomas - HB9SKA - JN47ck

• 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)

• This is a drawing from an OM I met, I try it to draw in ASCII:

---|>---o---o---> DVM

Shottky C _ R
_______ = _ =

Shottky

C = 100pF

R = 10kOhm

= = GND

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

What do you want to calibrate ? Which type of Shottky diode would you use ?

Thomas - HB9SKA - JN47ck

• 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 : -)

• A75GR Rasto many thanks for the link,,

DD0KP - Heiner - Waldkirch - JN38XC

• 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:

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.