RF Sampler

This page is work in progress and will be updated frequently. 

wip_c2

My OZ2CPU digitale RF mW-dBm-mV meter has a  input range from 1nW to 1W which is good enough for QRPp rigs and my TinySA has a imput limit of +10dBm / 10mW.  When you want to measure on equipment which gives more output power, you need a serious set of attenuators, or you could build yourself a 40dB RF sampler .

On the website of the OZ2CPU digital RF mW DBm mV meter the OM placed a section on how he build a one (scroll down to the section labeled "How To Measure High Power"). Which is also described on this page. Both seem to be inspired on Wes Hayward, W7ZOI, "Simple RF-Power Measurement," QST June 2001, pp. 38-43.

After reading these articles I decided that I want one in my shack and went to my local electronics store to get the parts. For the INPUT and OUTPUT connectors I have chosen BNC chassis part and for the sampling output a SMA chassis part. I used a double sided PCB of 1.6mm and on one side I cut out a 2.7mm path as a strip-line.

For the resistors I used 3 x 820 Ohm 1W resistors allowing it to handle 100W without a problem (if it's worth doing, it's worth overdoing).

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After construction I calibrated my NanoVNA H4 and tested it up to 900MHz in pass-through mode. 

rfsampler_01

As shown below, the impact of the cables can be seen in the S11 LOGMAG  measurement and the S11 SWR.
The S21 LOGMAG shows a nice flat (minimal attenuation) over the entire span. 

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Then I terminated the OUTPUT and hooked up the NanoVNA port 2 to the RF Sampler output.   

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As seen in the image below, for such a crude DIY rf sampler, the S11 LOGMAg is very acceptable (so is the S11 SWR). 
The S21 LOGMAG starts at -40 dB but starts to decrease to -43.7dB at 507 MHz and has more dips and hills (I didn't compensate for any frequency) 

rfsampler_07

Then I switched to a stop frequency of 150 MHz and repeated the 2 measurements. 

rfsampler_03

As shown below,  S11 LOGMAG  and S11 SWR are very accepteble. And the S21 LOGMAG shows a nice flat (minimal attenuation) over the entire span. 

 rfsampler_09

Again I terminated the OUTPUT and hooked up the NanoVNA port 2 to the RF Sampler output.   

As seen in the image below for this frequency range the S11 LOGMAg is very acceptable (so is the S11 SWR). 
The S21 LOGMAG starts at -40 dB and slowly decreases to -41 dB at 139.8 MHz.

rfsampler_08

As most of the time I'm building HF (and sometimes 2m) QRP stuff you don't hear me complaining. But I'm willing to try the capacitor compensation trick to get a more flat response. 

2 labels from my label write to give it a more complete / finished DIY look ;-) 

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Very happy with the result for now. But remember  

wip_c2

 

TODO : add photo's of test when using RF Sampler in combination with my OZ2CPU digitale RF mW-dBm-mV meter and TInySA.

 

To be continued . . . . . . 

Youtubes about this device

Also there are some nice Youtube video's about this device like :

#61: Basics of RF Samplers, Sampling-Tees, RF-taps, etc. by W2AEW.

#150 RF Sampler RF Tap 3 in 1 Home Build by Tony Albus 

How to Build an RF Power Tap by Level UP EE Lab, 

How To Build An RF Sampler Box by K7AGE

DIY 40dB RF Power Tap for Ham Radio by TheSmokinApe
 .

More interesting links about the RF Sampler

VK4HAT has build his own SMT RF Sampler and wrote some blog entries ( 1, 2, 3 ) about it. Nice work Rob. 

When you want to go big time (50dB up to 1.5KW), check out this article.

 


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