What details might I need to be aware of when monitoring the remote meter outputs of a Wattcher Series RF power monitor?

Bird has had some customers wishing to use DC outputs of the remote monitor ports (forward and reverse) as inputs to a digital system. Perhaps they are using a programmable digital multimeter, a digitizer, a data logger, or other data acquisition hardware - in any case, they are sampling the Bird wattmeter analog outputs and making it usable in their software environment. 

While the manual indicates that the output voltage will range from 0 to 1.038 V, the one thing you should note is that the level will not be linear. This aligns with how the elements work with the internal meters of the Wattcher Series, not to mention the classic Bird Model 43, each which whose meters have a resistance of 1400 Ω. 

As an example, we used a 100H element for the forward power measurement in a 3170B meter with line section. Our signal generator was configured for a 2 MHz frequency while stepping the output level such that it ranged from 100 to 10 W in 10 W increments. The table of results is shown below:

W	V
100	1.08
89	1.017
80	0.947
70	0.884
60	0.807
50	0.705
40	0.603
30	0.483
20	0.343
10	0.206

What is more informative on the behavior is when we plot these values on a chart, clearly showing the non-linear behavior:

To be able to properly account for the behavior in your software/program would first to establish a lookup table or equation representative of the meter output. While the table of values provided above acts as a reference, you will want to characterize your own meter + element combinations for a set of values that are most representative of your system.