Re: 50 Ohm Dummy Load Extension #dummyload #power meter #dummyload #power


Arv Evans <arvid.evans@...>
 

Jakob

When designing and building your RF power meter if should be possible to
add extra functionality above the simple dummy load and RF detector, and
even more functionality than is provided by a simple resistive bridge. 

Several of the pass-through directional couplers like Bourne or Stockton
Bridge use current-transformer technique to sample RF current instead of
RF voltage.This seems to make it possible to calibrate for RF current and
RF voltage.  Knowing those values if should be possible to add calculations
to determine load impedance (calibrated with an accurate dummy load) at
the point between transmitter output and feedline input. 

A permanently attached remote sensor could be put at the
feedline-to-antenna-point to provide measurement at the far end of the
feedline with positive (FWD) and negative (REV) detection and summing
to feed the summed voltage to the radio room via the feedline.

If a swept or stepped RF source is available your RF instrument should be
able to perform swept frequency versus impedance tests and displays. 
Extrapolating forward, possibly illogically, indicates that the same instrument
could also be used to evaluate inductors and capacitors for value, and maybe
for Q-factor.

Arv
_._


On Fri, Apr 30, 2021 at 9:49 AM <jakob@...> wrote:
Hi Vojtech. There are many commercially available power/SWR meters out there that I could buy, but that is not my point. I want to have fun building something useful for my own use, and if someone is interested to do something similar, I would be happy to share information. I am not in business for ham equipment, and I leave that to professionals like Hans. By the way, I got caught with a fake Chinese copy of the  Adafruit 16 bit AD converter ADS1115. It only converts 12 bits and leave 4 LSB zero. I got it from Amazon some time ago. Just a warning if you want to copy! Now I ordered replacement from Adafruit directly. I need these extra bits to obtain reasonable accuracy in the single bit dBm range.

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