The previous two power meters I made in this thread used most of the entire range of the AD8307 log amp from about -73 dBm to +13 dBm. The "ham bands only" power meter could also measure higher powers with an external attenuator, but these meters were for direct measurement of power, not in-line meters to be used while operating transceivers.
In this case we are not interested in measuring very low signals such as a lab bench scenario testing our RF generator or other such interests. The measurement goal of this meter will be 0.5 W to 200 W to be used while transmitting and receiving. This equates to a range of +27 dBm to +53 dBm.
The coupled outputs, both FWD and REV (will use measured values in final design), are -50 dB. This results in a nice usable range for the AD8307 log amp of -23 dBm to +3 dBm input power. So I will be able to cover 0.5 W to 200 W input to the coupler easily.
Most of the basic details of these AD8307 power meters have been documented in this thread in previous pages so if you are curious just go back in the thread and look at the charts and data for the meters I already made. I may not repeat every detail this time but will concentrate on the differences between this and the previous projects, mainly the coupler and measuring FWD and REV power and SWR.
I gathered some of the parts to get started as you can see. What you do not see is an Arduino UNO board like I used last time, but an Arduino Mega board (and shield). I already had this, which was given to me for free (with a bunch of other such maker stuff that a local ham decided wasn't interesting to him any longer).
You may ask:
"But xrunner, why do you want to use a Mega board for this project? All those extra inputs are not needed and it doesn't have a faster clock than the UNO. That sounds pretty stupid!"
Not so fast! It does have more memory so that may be of some use (256 kB vs 32 kB). As I recall the other projects were right up to the memory limit.
"OK, you must be an inefficient coder if you need more memory. Is that the only reason you are using a Mega board instead of an UNO right now?"
I like to use graphics OK - sheesh! I also have another option I will be trying later on. The other two meters I made left a bit to be desired in terms of response time (i.e. laggy). What I'm going to try later on when I'm convinced this project is deserving of additional expenditure, is an Arduino Due board. This board has a more advanced chip that has a clock speed of 84 MHz as opposed to the UNO and Mega clock of 16 MHz.
"Hmmm - what does buying a Due board in the future have to do with what you are doing
now?"
Well, it also happens to be the case that the Mega and Due boards have the same pinouts. Therefore, when I get the Due I can simply unplug the shield from the Mega and put it directly on the Due.
Enough questions!
Anyway ... I need to check out some of the other parts. I guess I'd best see if the Mega board actually works at all so let me flash its LED.