"dummy load" question

[towerdog]

I found a wet dummy load the other day, a simple 1 gallon bucket with Rf connector. No markings or numbers.

I really do not want to open the thing and make a mess.

Question is, if I transmit into the load, should the SWR read a perfect match of 1:1 ratio. It should not reflect power back to the transmitter. Is this correct?

I would assume the impedance of this load is 50ohms, but could be wrong. It was used at a now decomissioned AT&T telephone microwave hop so it could be 75ohm or some other strangeness.

 

[Beetle]

You can measure the DC resistance of the load, and this value should be very close to the impedance. A good dummy load should be as non-reactive as possible, meaning that there should be close to zero inductive or capacitive reactance. This leaves only resistance as the impedance value.

If you measure close to 50 ohms, great. If it's 75 ohms or some other value you can still use the load; you just have to remember what its actual impedance is. And, use coax with the same characteristic impedance as the load. The transition between the feedline and the antenna (or dummy load) is the point that determines an SWR reading.

You might want to check the oil level in the load to make sure the resistance element is fully immersed.

 

[W5LZ]

If the thing isn't a 50 ohm dummy load, and if you don't have some reason to use a dummy load of whatever impedance it happens to be, I think I'd let someone else have all the fun of playing with it.
Of course, depending on how the thing is constructed, it really shouldn't be that difficult to 'convert' to a characteristic 50 ohms impedance. Just replace that resistive element. I'll bet that 'J' place in Mississippi would sell you one.
- 'Doc

 

[hookedon6]

heck. why waltz when you can rock and roll:laugh:

just load it up with a rig (at low power) and see what happens.