RF Power Meter

This project is based on the Analog Devices AD8307 logarithmic amplifier. It has a dynamic range of over 80dB making it very useful for measuring a wide range of power levels from -70dBm (.1nW) to +13dBm (20mW) with a frequency response of 0-500MHz. The DC output is directly proportional to the logarithmic input and can be used to drive a panel meter.  The original design incorporating this chip came from a June 2001 article in QST by Wes Hayward (W7ZOI) and Bob Larkin (W7PUA).

Original circuit from June 2001 QST

I took this original idea, combined it with ideas from similar designs found on the web and created a PC board from scratch.  Initial testing seemed to show promise but I wasn't completely happy with the overall result so the project sat idle for several months until...

Update (Fall 2016)
I decided to start over using a pre-fabricated board developed by another hobbyist at the Yahoo group PHSNA (https://groups.io/g/PHSNA). This one had better RF shielding and was just a cleaner looking board. I also added a 20dB attenuator to the front-in to extend the upper range to ~1W (Note - technically I could have gone up to 2W and been within the chip's specs but decided to cap things at a more conservative 1W).

I got the two most expensive parts as free samples from Analog Devices but one part, the AD820 op-amp, came as an MSOP (micro small outline package) and the board called for a DIP (dual inline package). I built a breakout board for this part as shown below:

MSOP to DIP adapter

Still working on the finishing touches, but things are quickly wrapping up and should be finished soon...