Can someone move this to a better location if necessary?

I want to hook an analog meter to my Yagi antenna so the meter will max when the antenna is pointed directly at a cell tower.

My idea is to connect the antenna feed points to a Darlington 2 stage amplifier with a resistor to ground then connect a 50ua meter across the resistor. Would this work? Would a simple signal diode in the feed line help? I figure a 9V battery connected to the collector side and a 100 ohm resistor tied from the last emitter to ground. One feed point from the antenna to the base of the first transistor and the other feed point tied to ground.

I have measured the voltage across the antenna feed points and have observed a gradual increase in voltage from 3mv to 8mv as the antenna direction is slowly rotated to be pointing at the tower.

I have diagrams if that would help. I'm just trying to find the direction to the tower and do not care (for this application) what the actual field strength is.

Thanks,
Mike Taylor
Katy TX

 

This probably won't get an answer until tomorrow. There are only a few here that can work in the gigahertz range.

 

850Mhz. It is an 8 element yagi.

 

Assuming your antenna is sized correctly, and your amplifier will work at 850 MHz, you might want to at least use an envelope detector type of circuit. The topology in theory would be a diode in series followed by a capacitor and resistor to ground, in parallel. But unless the signal is large, the diode won't conduct. So maybe you could use an "ideal diode" circuit, which will rectify down to zero volts. Once that's working then you need to size the C and R so that the C won't discharge fast-enough to follow the carrier, but will discharge fast-enough to follow the change in power level due to pointing your antenna in different directions. Usually you would also want it to be able to follow whatever is modulating the carrier but you won't need to do that in this case. Construction for these frequencies will probably be your biggest problem. Maybe look at minicircuits.com and see how they do it. You will also probably need a buffer amplifier circuit, after the detector.

 

Give this article a look. A simple envelope detector is described with a schematic included if you scroll down a short way.

http://asliceofraspberrypi.blogspot.com/2013/10/adding-envelope-detector-to-convert-rf.html

Maybe it will get you going in the right direction.

 

How do you know that a particular bit of RF energy is a cell tower or something else -- a black helicopter for example.