I was bored, so while surfing around the web I stumbled across an article on QRP Dummy Loads. Hey...something that I didn't know existed...I think I should build one to rid myself of this boredom. So I looked at a lot of plans, and settled on this one at: http://www.n5ese.com/dummy3.htm
I didn't need the second BNC connector to a voltmeter, so I just put in the resistor packs to come up with 50 Ohms at 8 watts max. My Yaesu FT-817ND only outputs 5 watts max, so the 8 watt capacity is a nice buffer. I have a Swan wattmeter to measure the radio output, and I put the dummy load after that. It worked great on the FT 817 as well as low power output on my FT-450D (went up to 8 watts intermittent). It did a fine job without heating up at all. Overall, the unit is only 3-1/2" long, and is made from 3/4" copper pipe and caps. The plans said it could go into a 1/2" water pipe, but the surplus carbon resistors I got were a little too large to fit as designed. It's still compact enough for me.
For you old timer hams and electronics geeks, keep in mind that this is a big deal for someone with very little electronics background, and virtually no assembly experience. I was patting myself on the back when the damn thing actually worked when I was done.
After working off a shitty piece of one-sided copper board, I finally got the solder connections to make so I could get down to the design rating. If I make another one I'll do things differently.
Took measurements across the bands, and both the R and SWR dropped along with the drop in frequency.
Now I think I'll make an oil cooled 130W model with an SO238 connector in a 1 qt. paint can filled with mineral oil. Gotta find some cheap 1K Ohm 3W resistors off ebay. My surplus guy wanted $1 each for them, and I can get the 20 pieces I need for $6.20 including the shipping. Sorry surplus guy, but you lose on this one.
I didn't need the second BNC connector to a voltmeter, so I just put in the resistor packs to come up with 50 Ohms at 8 watts max. My Yaesu FT-817ND only outputs 5 watts max, so the 8 watt capacity is a nice buffer. I have a Swan wattmeter to measure the radio output, and I put the dummy load after that. It worked great on the FT 817 as well as low power output on my FT-450D (went up to 8 watts intermittent). It did a fine job without heating up at all. Overall, the unit is only 3-1/2" long, and is made from 3/4" copper pipe and caps. The plans said it could go into a 1/2" water pipe, but the surplus carbon resistors I got were a little too large to fit as designed. It's still compact enough for me.
For you old timer hams and electronics geeks, keep in mind that this is a big deal for someone with very little electronics background, and virtually no assembly experience. I was patting myself on the back when the damn thing actually worked when I was done.
After working off a shitty piece of one-sided copper board, I finally got the solder connections to make so I could get down to the design rating. If I make another one I'll do things differently.
Took measurements across the bands, and both the R and SWR dropped along with the drop in frequency.
Now I think I'll make an oil cooled 130W model with an SO238 connector in a 1 qt. paint can filled with mineral oil. Gotta find some cheap 1K Ohm 3W resistors off ebay. My surplus guy wanted $1 each for them, and I can get the 20 pieces I need for $6.20 including the shipping. Sorry surplus guy, but you lose on this one.