Some time ago I started building the powerful dummy load (50 Ohms, 250 watts). Although I had had everything I need to start working on it, I didn't start the building because I was thinking I need the box I could hide the dummy load into. Recently I have bought the power amplifier so that I can't postpone anymore. I have some spare time (about an hour) so that I decided to start immediately.
My first design was the following: the resistor resides on the heatsink, the connector is connected to the resistor directly and secured to the same holes the resistor is secured to. But this approach requires metallic tubes of small diameter so that I decided to use the different approach. Below is a couple of pictures of the process.
First of all, I pierced two threaded holes for M3 bolts. This is the place for the connector which should be placed diagonally.
Then I made two more threaded holes for M3 bolts on the top of the heatsink. This is the very place the processor is attached to.
One more hole is for the RG-316 cable which should connect the terminal and the resistor. Also, I did some sanding to make the surface more smooth.
Then I soldered the piece of the RG-316 cable to the SO-239 socket.
The opposite end of the cable ready for soldering.
The inner world of the heatsink.
The resistor is secured and now everything is soldered.
The other view of the resistor.
The overall view of the device. The only one thing that is still missing - the cover preserving the resistor from being damaged.
The resistance is as expected.
Now it's time to check the dummy load on HF. I connected my RigExpert AA-30 using the 30 cm long pigtail made of RG-174. The SWR is pretty good. It is smoothly growing to 30 Mhz, although the value is still less than 1.1:1.
This is the overall view of the load connected to the AA.
Then I checked the SWR on VHF and UHF. I was surprised, but SWR was good on both bands too.
On more measurement. The range is from 137 to 950 MHz. As shown, from some point the SWR starts raising and I'm not sure I will use this load on frequencies greater than 500 MHz.
The conclusion. The load is compact, powerful, and useful. It has the fan allowing me to reduce the heating of the load to the appropriate value. I'm not sure I will use it with too high power, but who knows... But in order to use the fan, I need the standard 3.5 mm socket for connecting the 12V power supply. But this will be the next story.
My first design was the following: the resistor resides on the heatsink, the connector is connected to the resistor directly and secured to the same holes the resistor is secured to. But this approach requires metallic tubes of small diameter so that I decided to use the different approach. Below is a couple of pictures of the process.
First of all, I pierced two threaded holes for M3 bolts. This is the place for the connector which should be placed diagonally.
Then I made two more threaded holes for M3 bolts on the top of the heatsink. This is the very place the processor is attached to.
One more hole is for the RG-316 cable which should connect the terminal and the resistor. Also, I did some sanding to make the surface more smooth.
Then I soldered the piece of the RG-316 cable to the SO-239 socket.
The inner world of the heatsink.
The resistor is secured and now everything is soldered.
The other view of the resistor.
The overall view of the device. The only one thing that is still missing - the cover preserving the resistor from being damaged.
The resistance is as expected.
Now it's time to check the dummy load on HF. I connected my RigExpert AA-30 using the 30 cm long pigtail made of RG-174. The SWR is pretty good. It is smoothly growing to 30 Mhz, although the value is still less than 1.1:1.
This is the overall view of the load connected to the AA.
Then I checked the SWR on VHF and UHF. I was surprised, but SWR was good on both bands too.
On more measurement. The range is from 137 to 950 MHz. As shown, from some point the SWR starts raising and I'm not sure I will use this load on frequencies greater than 500 MHz.
The conclusion. The load is compact, powerful, and useful. It has the fan allowing me to reduce the heating of the load to the appropriate value. I'm not sure I will use it with too high power, but who knows... But in order to use the fan, I need the standard 3.5 mm socket for connecting the 12V power supply. But this will be the next story.
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