Schematic Rise

This is a simple and low cost wide band VHF field strength meter. The field strength is measured by converting the radio signal to DC and measuring it.





The RF signal will be picked up by the coil and rectified by the diode D1.Even a very small DC voltage is sufficient to alter the biasing of FET and it will be reflected in the meter as an indication of the presence of a radio signal. The meter can be calibrated by adjusting the preset R2 to make meter M1 read ZERO in the absence of any radio signal. This schema is not very sensitive, but can sense radio signals from hand held FM transmitters up to a distance of few meters( ideal for theoretical demonstrations).



Notes.

* The schema can be assembled on a general purpose PCB.
* Use a 9V PP3 battery for powering the schema.
* Use a 250uA FSD current meter for M1.Using a lower FSD meter will improve sensitivity.
* The coil L1 can be made by making 6 turns of 20 SWG enameled copper wire on a inch plastic former.
* The antenna can be a telescopic whip antenna.

I think most of you like to make transmitters today Im going to give you a video transmitter.The special thing of this transmitter is you can operate this schema with 9V power supply and you can send signals about 100M.I have used this diagram for my security camera system its working well and also when we do a concert or a musical show we need to send live videos to a big screen or a projector normally video transmitters are quite expensive but you can build this schema with less than $10 Here I used Bc 108 Transistor If you are unable to find Bc108 you can use similar Transistors like BC337, BC546 , 2N2222

 












Note


# Build this schema on a PCB
# without connecting an antenna dont give the power to the schema
# Build this schema in a little space