Where do I begin to figure out why this doesn't work ?

[Hextejas]

I built this field strength meter on a breadboard and I need guidance to figure out why it doesn't work. Where in the circuit to take readings, etc. The power on LED comes on but that's it.
I tested it by having it near my radio as it pressed the transmit button.
Thanks.

[rstofer]

Check for 5V at the output of the 7805L (the junction between C3 and R2 relative to Gnd or the (-) side of the battery.
Check for 5V on pin 7 of U1
Check for any output voltage on pin 4 of U1.
Wiggle pot R6 and see what happens to the output of U2A.
Check the voltage on C6
Disconnect the LED Voltmeter and take the measurement with you DMM.

[virtualparticles]

The AD8307 will output 0 volts at -84 dBm in and 25mV per dB above that level. So 2.1 V at 0 dBm for instance. The actual RF sensitivity will vary quite a bit depending on what sort of antenna you use and will vary with horizontal or vertical attitude depending on the polarization of the received signal. The LM358 is configured to provide a gain to that output of 0 to 0.323 (2.2/6. depending on the position of the 100k pot. So with 0 dBm in you should see 0.678V with the 100K pot at the top.  I'm not sure what the "LED Voltmeter" business is all about but you can just take the output of the LM358 into a voltmeter for your readout. You can create an arduino based voltmeter with an LCD display for this or just purchase one on Ebay.

It's quite difficult to predict the amount of RF power that will be coupled to this circuit from the antenna. That depends on the gain of the antenna at that frequency. Usually a circuit like this is just fed with an electrically short "spike" which is excited by the electric field of the EM wave. So calibrating this will be a challenge but you should be able to see the difference between RF and no RF.

[Datman]

It's a power meter, more than a field strength meter...
Try lowering the 6k8 resistor to 100 ohm, increasing gain. You could have to adjust offset.