The Dummy Load Projects

About two years ago I ordered a QRP Wattmeter kit from Oak Hills Research (OHR).  The kit contained everything I would need to complete the project and in a few hours over the course of about 2 days I had it fully assembled, tested and working.  Prior to this kit, I hadn’t done this kind of work since high school. 

I was actually very fortunate that while in high school, my band director Mr. Crawford NB5I put together a basic electronics and computer class.  I’m thinking this was either in my sophomore or junior year (1983-84).  This was in the timeframe when I was really interested ham radio and my off and on again attempts at learning CW.  The class was a welcome change to the reading, writing and arithmetic classes which I’ll admit did bore me.  It was really my intention to take this electronics class to help better assist me in learning all that a novice class amateur would need to know back then. I remember two things about this class.  One, I built a cool 12v power supply.  We had to design the project, etch the circuit boards, solder in all the parts and for it to work.  Mine did.  The second thing I remember about that class was burning the snot out of my first two fingers and thumb from accidentally grabbing the soldering iron at the wrong end.  Thank you Mr. Crawford for teaching this class.

photoNow skip forward some 25+ years, I had a ball putting that QRP wattmeter together and to find that it worked in the end with no burns on my fingers was all I needed.  I had been bitten by the bug.  I ordered a few additional kits from OHR.  These were two 10w dummy loads and one 100w dummy load.  The 10w models are pictured just sitting on top of the 100w dummy load.  These 10w models are great for the QRP rig. 

I’ll admit I started the 100w model about a year ago.  I managed to get ten of the twenty resistors soldered onto the board and life got busy and I moved it to the side of my workbench.  I’ve looked over at it several times and even grabbed the soldering iron a few times only to put it back with either no time or no interest to complete it.

Now that I have extra under my belt, I thought it was about time to get some of these half completed projects moved from the workbench.  This 100w dummy load only needs about a half hour more work and today was a good day to do it.  I fired up the soldering iron and soldered the remaining ten 1K Ohm resistors onto the board.  (shown below)

photo (2)

The next step was to test to make sure all the resistors were secure and see how close to 50 Ohms I would be.  I call 50.6 close enough for me. 

photo (3)

Now to mount the board into the chassis and complete the solder work to the SO-239 connector and chassis ground. 

photo (4)

Mount the top and secure the four rubber feet and we can call this one good. 

photo (5)

This is an air cooled unit.  The documentation states 100w continuous with high loads possible for shorter durations.  Considering 100w is as much power as I have, this will do fine.  I connected it to my FT-897.  Yep…it worked and did exactly what it should.  I tested up to 100w and the resistors heated up slightly with a 30 second transmit cycle. 

Both the 100w and the two 10w dummy loads were fun to build.  Today I ordered a nixie tube clock kit and it should arrive in the next week or two.  Tomorrow I’m checking out a new amateur radio club I’m considering joining.  So stay tuned…lots to blog about.

 

Until next time…

73 de KD0BIK

Jerry Taylor, KD0BIK, is a regular contributor to AmateurRadio.com and writes from Colorado, USA. He is the host of the Practical Amateur Radio Podcast. Contact him at [email protected].

3 Responses to “The Dummy Load Projects”

  • Fred W0FMS:

    Building is my favorite part of the hobby. (I’m really more of a sick engineer who does it for a living and for fun, but don’t let anyone know or I’ll never get a pay increase! :O) )

    I’m glad to see you getting back into that side of the hobby. IMHO, it’s the most personally rewarding aspect of ham radio.

    Cheers and 73 and get a solder burn and some lead poisioning for me.

    Fred, W0FMS

  • Michael N5TGL:

    Thanks for posting this. I’ve been looking for a QRP wattmeter.

  • KG7QDS:

    nice simple plan, thanks.

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