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


jakob@...
 

I recently built the 50 Ohm 20 Watt dummy load from QRP-Labs. It works well with very close to 50 Ohm on most of the ham frequency spectrum. But I was not satisfied by the fact that I need a voltmeter and a calculator when I want to use the power meter feature in the dummy load. So I grabbed my parts box and built a power meter extension. It can measure instant power, peak power and average power over about 2 minutes, selectable with the rotary encoder knob. Press it to reset the peak value detection. It is built with an Arduino Pro Mini 5 Volt, a .91 inch OLED display and a 16 bit AD convertor ADS1115. The battery is a rechargeable 9 Volt type, good for about 24 hour of run time per charge. The software does linearization by interpolation between set points to compensate for the non-linear characteristic of the power sensor diode. I plan to extend the program to add a calibration feature for all ham bands form 160 m to 70 cm and store the set points in the EEPROM of the Arduino. I will see how far up in frequency I can go with the built in 1N4004 diode in the dummy load. The enclosure is from Amazon. 



William Jenrick
 

Sweet, Ill buy one!!!

On Thu, Apr 29, 2021 at 5:34 PM <jakob@...> wrote:
I recently built the 50 Ohm 20 Watt dummy load from QRP-Labs. It works well with very close to 50 Ohm on most of the ham frequency spectrum. But I was not satisfied by the fact that I need a voltmeter and a calculator when I want to use the power meter feature in the dummy load. So I grabbed my parts box and built a power meter extension. It can measure instant power, peak power and average power over about 2 minutes, selectable with the rotary encoder knob. Press it to reset the peak value detection. It is built with an Arduino Pro Mini 5 Volt, a .91 inch OLED display and a 16 bit AD convertor ADS1115. The battery is a rechargeable 9 Volt type, good for about 24 hour of run time per charge. The software does linearization by interpolation between set points to compensate for the non-linear characteristic of the power sensor diode. I plan to extend the program to add a calibration feature for all ham bands form 160 m to 70 cm and store the set points in the EEPROM of the Arduino. I will see how far up in frequency I can go with the built in 1N4004 diode in the dummy load. The enclosure is from Amazon. 




--
William Jenrick 


Vojtech Bubnik
 

Seeing your digital power meter, I would like to point to my self-powered Tayloe style digital power meter / SWR bridge design. The design is open and well documented and it IMHO a perfect companion to a small QRP rig that does not contain a SWR bridge.
BlinkySWR/manual-0.2-S.md at master · bubnikv/BlinkySWR (github.com)
Here is a picture of the prototype
bubnikv/BlinkySWR: Tiny, cheap, simple, accurate, self powered resistive SWR and power meter for SOTA and back packers (github.com)
and description of the design process
BlinkySWR/design at master · bubnikv/BlinkySWR (github.com)

I am not sure whether promotion of own products is allowed, I don't think I compete with any of Hans' products. If this is a problem, Hans please delete my post. The BlinkySWR could be purchased at BlinkySWR (remoteqth.com)
However the design is simple enough to be replicated. To be self powered, the LEDs need to be high intensity red ones and the linear regulator is quite special, it is a low quiescent current, low drop and high voltage type.

73, Vojtech OK1IAK


jakob@...
 

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.


Arv Evans <arvid.evans@...>
 

Very impressive. 

Arv
_._


On Thu, Apr 29, 2021 at 6:34 PM <jakob@...> wrote:
I recently built the 50 Ohm 20 Watt dummy load from QRP-Labs. It works well with very close to 50 Ohm on most of the ham frequency spectrum. But I was not satisfied by the fact that I need a voltmeter and a calculator when I want to use the power meter feature in the dummy load. So I grabbed my parts box and built a power meter extension. It can measure instant power, peak power and average power over about 2 minutes, selectable with the rotary encoder knob. Press it to reset the peak value detection. It is built with an Arduino Pro Mini 5 Volt, a .91 inch OLED display and a 16 bit AD convertor ADS1115. The battery is a rechargeable 9 Volt type, good for about 24 hour of run time per charge. The software does linearization by interpolation between set points to compensate for the non-linear characteristic of the power sensor diode. I plan to extend the program to add a calibration feature for all ham bands form 160 m to 70 cm and store the set points in the EEPROM of the Arduino. I will see how far up in frequency I can go with the built in 1N4004 diode in the dummy load. The enclosure is from Amazon. 



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.


KB9NBL
 

Jakob
Drop me the list of the parts used and a schematic if you have it.

Nice work!!

James



Robert AG6LK
 

Hi Jakob,

If you have a chance could you drop me a parts list, schematic and any other information you can think of. I think it looks great. I’d like to try my hand at building it also. My email address is amrmedic@...
I would greatly appreciate it. Thank you.

    73,
Robert, AG6LK


James Sweeden
 

On Thu, Apr 29, 2021 at 05:34 PM, <jakob@...> wrote:
The software does linearization by interpolation between set points to compensate for the non-linear characteristic of the power sensor diode.
I am interested in learning how this is done.  Can you point me to some good reading material?  Also would enjoy any other details of your build that that you would be willing to share.  Very nice project, well done!

James/KB7LJP 


Stig oz8pz-oz8wsp-oz8wsr
 

Hi all, i have been working with a SWR / Power meter for checking the output from the 
QRP  whisper transmitter, the output is about 0.2 Watt, so my normal power meter can't
measure the output. I have used some from the little ATU100 and a Arduino, so now i can
measure the output and the SWR. I have made dobbelt, so i can see 2 different TX.
I enclose some picture, how i have done it. The software is just simple.
73, oz8pz, Stig
Denmark

Den lør. 1. maj 2021 kl. 06.04 skrev James Sweeden <kb7ljp@q.com>:

On Thu, Apr 29, 2021 at 05:34 PM, <jakob@...> wrote:
The software does linearization by interpolation between set points to compensate for the non-linear characteristic of the power sensor diode.
I am interested in learning how this is done.  Can you point me to some good reading material?  Also would enjoy any other details of your build that that you would be willing to share.  Very nice project, well done!

James/KB7LJP