"JGBOYLES" wrote in message
...
Comment I have is in your resistive divider. To keep the power
dissipations
in the resistors low, you will have to use large resistor values, but at
RF
these can be off 50 % or more.

Well, I hadn't thought of that, so I'm glad I asked the question. I had
planned on using a 200k 1/2 watt carbon and about 5k 1/2 watt for the
divider,
keep the leads short, and locate it a close as possible to what I think is
50
ohms in my system.
Do you think it would be worth the time and effort to do an rf frequency
sweep of the divider to see how accurate it is? I realize this method is
not
going to be dead accurate, but I was hoping for better than 50%.
73 Gary N4AST

Hi Gary,

I just measured some random 1/2W carbon resistors with an MFJ at 30 MHz.
This is not a precision instrument, but shows a trend.

Nominal Measured
5.6 K 0 - j586
220K 0 -j 600
1.8K 99 - j539 (convert this to parallel form)

As a sanity check

11 Ohms 12 + j4 (some lead inductance here)

What this is tending to show is that the resistors are showing a shunt
capacitance whose reactance is about 600 Ohms at 30 MHz. That is about 9 PF,
which seems high. I was expecting more like 1 PF. I want to redo this at a
higher frequency, might be out of range for the MFJ.

I notice my Kenwood power meter uses a capacitive divider for the voltage
sample. A friend of mine built a meter along the lines of what you want to
do. I will ask him what he did.

Tam