ANTENTOP- 01- 2020 # 024

Ferrite Clips and RF Current Sniffer

Take a look to RF Current Sniffer with meter Indicator. (Of course, it is possible use or analog arrow meter indicator either usual DMM.) On the ferrite clips wound three turns of the copper wire in 0.7-mm diameter (diameter of the wire does not matter, may be any suitable). Detector diode is 1N4148. This diode works up to 100- MHz. Lower part of the ferrite clips is glued to the PCB by epoxy. Upper part of the clips allows connect the clips to coaxial cable. Arrow meter (or DMM) is connected to the device through wires in length of 70- cm. Ever widespread current arrow meter with full scale 1- mA allows make very sensitivity measurements compare to current meter with LED indicator. Instead of analog meter it is possible use a DMM that is turn on to voltage range. DMM may provide another kind of measurements and you do not need adjust the POT that limit the current through the arrow current meter. Figure 6 shows design of the RF Current Sniffer with arrow meter Indicator.

So, with these two RF current meters I decided make measurements of RF current flowing on outer braid of the coaxial cable going from my Beverage Antenna (http://www.antentop.org/023/va3znw_beverage_023.htm). Of course, the measurement gives only quality result, not strictly science, but anyway I may judge how useful the ferrite clips are. The first measurements I made without RF choke (without ferrite clips on the coaxial cable). RF Current Sniffer with LED Indicator was installed on the coaxial cable coming from my Beverage Antenna and wiring in my shack. The LED may glow up at all bands- from the 160- to 6- meter. For glow the LED transmitter should run 80 W at 160 and 80 meter and 50- to 30 W at 40- 6- meter. Figure 7 shows glowing LED on the RF Current Sniffer with LED Indicator.

Then, ferrite clips were installed on the coaxial cable (see Figure 2). The RF current flowing on the outer braid of the coaxial cable is greatly reduced. At 160 and 80 meters, the LED has already stopped glowing, at 40 and 30 meters the LED is barely glowed at power of 100 watts. The "glowing" power on the other high-frequency bands also has significantly decreased. After this experiment I ordered another batch in 40 ferrite clips (ebay, from China) and I hope to significantly reduce the remaining RF current on the outer braid of the coaxial cable.

I used the RF Current Sniffer with Arrow Meter Indicator to measure the RF current on the power cord of my radio station. After the installation of ferrite clips the RF current has dropped significantly. After the installation of ferrite clips, at my opinion, noise on the receiver mode as well goes down. So, the ferrite clips improve my radio at two positions- at transmitting and receiving mode.

73! de VA3ZNW

Figure 5 Design of the RF Current Sniffer with LED Indicator

Figure 6 Design of the RF Current Sniffer with Arrow Meter Indicator

Figure 7 Glowing LED on the RF Current Sniffer with LED Indicator

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