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RF decibel meter

Big brother is watching you

Please visit my recently started old and vintage microphone blog

This time I’m trying to make another nice an quite cheap add-on to the possible lab eqRF decibel meter siteuipment farm for Ham and it will be a RF decibel meter, then I will test if it’s working and how good or bad.

This DIY is rather easy to make as the PCB is to buy here, making or finding the PCB is usually the most difficult part of a DIY work. For this realization you will need at best a signal generator for calibration even if it can be done without. All the informations you need to make this RF meter could be found here.

On the picture, you can see the front and the back from this RF decibel meter. Very little components are used, 5 components are SMD 1206 type, not the smallest one and still easy to work with. The SMD are soldered on the back of the PCB. Really no special, expensive component or hard to find parts.

How does it works? The table of my measurement below will let you know. The three first row from left are the input signal strength (50ohm) then the predicted DC output for the meter and the last three column are the actual value at 1MHz, 10MHz and 100MHz. You can see the derivation of the measured value vs the predicted value and decide if the precision match your need. You can also calibrate where you want to counteract the deviation.

I found this kit to be a nice ad-don even if the both I built started to work correctly above -69dBm, +38dBu (+-79uV RMS) and not +32dBu as announced, but it’s not a commercial DIY kit so nothing to claim, Hi.

dBm

dBu

V RMS

DC (has to be)

1MHz (was)

10MHz (was)

100MHz (was)

-77

+32

39.8uV

300mV

404mV

400mV

400mV

-67

+40

0.1mV

400mV

424mV

424mV

415mV

-57

+50

0.31mV

500mV

504mV

503mV

464mV

-47

+60

1mV

600mV

604mV

601mV

548mV

-37

+70

3.16mV

700mV

703mV

701mV

649mV

-27

+80

10mV

800mV

801mV

799mV

748mV

-17

+90

31.62mV

900mV

901mV

899mV

844mV

-7

+100

100mV

1V

999mV

996mV

941mV

+3

+110

316.23mV

1.1V

1.099V

1.093V

1.032V

+10

+120

1V

1.2V

1.164V

1.161V

1.07V

As usual, enjoy and replicate.

 

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