Saturday, September 26, 2015

RF Indicator

Indication of the RF has a very important role in transmitters. I saw this ckt on farhan's blog. It is a very clever and clear use of the simple diode detector. I was using the peak detector for Rf indications etc but this is a good one. Its simple, it works ,
please not :- it does not accurately measure or measure anything at all, it just indicates the RF level. When there is voice peaks, it flickers in sympathy with the voice.
For CW the presence of RF is easy task but for voice modulation its difficult. For my xtal controlled CW/DSB tx I use small homemade receivers but nearby receivers is being overloaded by the transmitters and we should not use our sensistive receiver during transmission. Its front end will be damanged....
Put it on the final linear the output. Ckt is self explained. Change the R according to the power level of the amp. Please don't use the preset or variable resistor, that might break disturb the Rf network.. he he..
For R try quarter watt carbon resistor, 10k to 4k7.... enjoy the flicker. Functionally similar was used in VWN- Tx but that was in DC current path.
In my experiments, I had used two linear amplifiers. One 2watt for driving my big 20watt linear. I did put this indicator on small 2watt linear.  At one point in RF when i increased RF level, there was constant light on LED, that means the High local stray filed from big amp was coupling and driving the LED. So I should have put the RF amp in small boxes and also put the this indicator on big keep this in mind when you are using two amplifier and two indicators shows the different dances... he he anyway it works.....
Wheel is here Enjoy.