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Are Dummy Loads Repairable

nokones

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I just learned that my Dummy Load took a dump and I am wondering if they are repairable and worth repairing? The casing/housing appears to be assembled with two halves and the N Female fitting has 4 screws attaching the fitting to the housing.

I didn't realize that my EMR Corp Model 1650 0-1GHz 125 watt Dummy Load failed on me. At first, I thought that the three radios I was measuring the RF output with the Dummy Load was in a dire need of an alignment and tune since I was measuring only 7 watts of output power. I measured the three radios with three different in-line Watt meters and one of the meters and slugs were calibrated last year by Bird.

So, I packed up the three radios and headed to a Motorola Service Shop in Tucson. As I was about to leave, the technician came out to my Jeep and told me the first radio is putting out 50 watts and is on freq. I said no way. He quickly checked the second radio with the same results, and the third radio was transmitting 40 Watts, but was a tad off freq and needed an alignment. I said do it.

The first radio was my Jeep radio so I put the radio back in my Jeep and remeasured the RF and it was at 48 watts. After the Tech tuned the third radio, I headed home and when I got home, my first task was to recheck the radios again. I checked two of three radios on the bench since they were loose, and they again only put out 7 watts.

So, I started replacing cables, cords, adapter connectors, ensured the power supply was putting out 14 volts. I bypassed my Anderson Distribution Block and directly connected the radio and controlhead to the power supply, only 2 watts were drawn from the power supply. So, I tried another power supply and still only two watts being pulled from the second power supply.

The only thing that I haven't changed was the Dummy load. My second Dummy load was only an UHF Dummy load and these three radios were VHF mobiles so I couldn't use the UHF Dummy load. However, I have NMO magmounts and a couple VHF mobile antennae so I hooked up the antenna to the radio in place of the dummy load. When I keyed the radio, 48 watts, hot damn. I reconnected the Dummy load, 7 watts, hooked the antenna back up, 48 watts.

I decided to get out my ohm meter and check the Dummy load resistance and it measured "OL". Although, I wasted a whole day going to Tucson with two perfectly good working radios, I did get one radio aligned and I did discover that the Dummy load failed and my meters and radios were not the cause of measuring 7 watts.
 

prcguy

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Simple open connections like right at the connector might be repairable but if the resistor itself has changed value or cracked open its a lost cause. I've accidently burned up more than one load over the years and was able to purchase an exact replacement resistor and repaired them good as new.
 

cavmedic

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Sep 2, 2012
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Pottstown Pa
Had a big one go bad in a Sinclair hybrid combiner. Whole shelf was replaced, intercepted it before it hit the dumpster, turned out the resistor had a cold solder joint and opened up. Unfortunately the two isolators bit the dust as a result, but now have a spare heavy duty load now along with the smaller ones from the circulators and some harmonic filters cluttering up the bench.
 

nokones

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Feb 19, 2011
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Simple open connections like right at the connector might be repairable but if the resistor itself has changed value or cracked open its a lost cause. I've accidently burned up more than one load over the years and was able to purchase an exact replacement resistor and repaired them good as new.
I found a brand new EMR Corp 1650, still in the box, for sale on eBay for $150, so I went for it, in the interest of time. When I get a boring moment looking for something to do, I'll try to crack the bad unit open and see if I can try to fix it. It'll be my first attempt of playing around with a resistor. I'm the type that will try to make an attempt to repair something before it gets thrown away in the trash. The problem with things these days is obtaining the parts for repairing.
 

prcguy

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This type of resistor is in many loads, some rated to 2GHz.

100-50TW_web%28640x640%29.jpg

I came across a pair of 100 ohm 800w versions and paralleled them to make a 50 ohm 1600w load on a forced air tunnel heatsink. I really need to put a copper spreader under the loads as the load to aluminum junction cant pull the heat away fast enough.

1736959977658.jpeg
 

W2JGA

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Oct 14, 2014
Messages
116
This type of resistor is in many loads, some rated to 2GHz.

100-50TW_web%28640x640%29.jpg

I came across a pair of 100 ohm 800w versions and paralleled them to make a 50 ohm 1600w load on a forced air tunnel heatsink. I really need to put a copper spreader under the loads as the load to aluminum junction cant pull the heat away fast enough.

View attachment 176288


Use liquid nitrogen..

 
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