Saturday, July 2, 2016

Wisp1 output power

Wisp1 output power

So, Alan/W7QO encouraged me to measure the output power of my Wisp1 board.  He was concerned that the Low Pass Filter might be reducing my output power. I hadn't made measurements since I was prototyping with an Adafruit Si5351 board. so it seemed like a good idea.

The LPF configuration is as I planned previously.

I ran a measurement of the output and found this:

It looks like 780 millivolts, peak to peak.  I used the calculations, as in the previous blog post, and came up with an output power of 1.52 milliwatts.  UGH!

I removed the LPF, pi filter (2 caps and inductor) and just put a 0 ohm resistor across the inductor pads.  The output power was much better.

It showed 1.90v peak 2 peak.  That yields 9.02 milliwatts without the LPF.  MUCH nicer.

Given the low power we're talking about with these boards, I'm going to  go ahead and skip the LPF at output.  At some point, I should go through the filter formulas again to see why I'm attenuating badly at 14 MHZ.

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