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Dummy Load Not Working

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FiveFilter

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I just got a couple of 50 ohm dummy load devices from ebay for testing purposes; one 5W and the other 10W rated. I screwed them into the antenna slot of my SWR meter and tried to read the SWRs with my radio. It showed the SWR in the red on all channels with both dummy load devices. I tried them on another SWR meter with the same results.

I noticed on the new dummy load devices that the center probe of the connection is very short and very small compared to what is usually seen on antenna coaxes. Could it be that the new dummy load devices are not making contact appropriately? Would there be any danger of shorting something out if I used a piece of aluminum foil in the connections to make sure they are making a proper contact? Any other ideas of what might be going on?

Thanks!
 

RFI-EMI-GUY

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It sounds like the dummy loads have male type N connectors and you are screwing them onto female SO-239 connectors. You need an appropriate adaptor if you haven't already crossthreaded the connectors.

Sent from my SM-T350 using Tapatalk
 

FiveFilter

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RFI-EMI-GUY, you are exactly right. After your comment, I went back to the listing and there it was as plain as day, "type N connector" for this item. Now I get to look for the adapter. Thanks for the guidance!
 

prcguy

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First I would check the dummy load connector center pin to ground with an ohm meter to see if it reads close to 50 ohms. If you have two different dummy loads that read bad I would suspect the meter or your setup.
prcguy
 

FiveFilter

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Yep, I checked the ohm values of the two dummy load devices between the center pins to the outside grounds and both of them read exactly 50 ohms.

The problem I have is like RFI-EMI-GUY accurately suspected, the dummy loads I bought have type N male connectors, which don't fit the SO-239 female connectors on the SWR meters I have. It's the ole "round peg into the square hole" drill.

I've got an adaptor coming in the mail to make them compatible.
 

FiveFilter

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So today in the mail I got my type N female to SO 239 male adapter, screwed it onto my new 50 ohm dummy load, which I then plugged into the the antenna port of my SWR / Watt meter, which was then plugged into the antenna port of my radio.

Eureka! It worked as advertised.

My little Uniden 520 pro compact CB showed a perfect 1:1 SWR against the perfect 50 ohms resistance, and produced a 3 Watt deadkey signal when plugged into my Jeep Wrangler's power port with the engine off. I think the little Uniden will be producing pretty close to the legal 4 Watt signal limit with the engine running and the alternator providing a more typical power supply of 13.2 VDC as compared with the engine-off 12.5 VDC I tested it on. Since it was raining in the aftermath of TS Cindy, I stopped my testing with that.

It's nice being able to confirm your equipment is working properly.

Thanks for the help fellas.
 

prcguy

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Glad to hear its working. Something you might consider for checking SWR meters in the future is a second 50 ohm load and T adapter. When you have the T adapter on the antenna jack of the SWR meter and two 50 ohm loads attached to the T adapter with no cables, or two short identical length cables, the SWR meter should read exactly 2:1.
prcguy


So today in the mail I got my type N female to SO 239 male adapter, screwed it onto my new 50 ohm dummy load, which I then plugged into the the antenna port of my SWR / Watt meter, which was then plugged into the antenna port of my radio.

Eureka! It worked as advertised.

My little Uniden 520 pro compact CB showed a perfect 1:1 SWR against the perfect 50 ohms resistance, and produced a 3 Watt deadkey signal when plugged into my Jeep Wrangler's power port with the engine off. I think the little Uniden will be producing pretty close to the legal 4 Watt signal limit with the engine running and the alternator providing a more typical power supply of 13.2 VDC as compared with the engine-off 12.5 VDC I tested it on. Since it was raining in the aftermath of TS Cindy, I stopped my testing with that.

It's nice being able to confirm your equipment is working properly.

Thanks for the help fellas.
 
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