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DON'T use a switching power supply on a powered RX antenna!

Moleculo

Ham Radio Nerd
Apr 14, 2002
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1,674
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I recently tore down and remodeled my shack. When I put things back together, I repositioned just about everything, including eliminating a couple of unnecessary power supplies. During this process, I decided to power the MFJ-1026 Noise canceller to a small switching power supply. This noise canceller is used with both the main Alpha Delta DX-CC multiband dipole and a receive loop run around the yard to help phase out local noise sources on the lower bands.

I thought I blew up the MFJ-1026 by running legal limit too close to the receive loop because all I could hear was static, noise, high pitched whine, etc., so I took it out of line and put it on the shelf. Fast forward a couple of months and I purchased a W6LVP Magnetic Receive loop. During a temporary install of the mag loop, I noted the instructions said to only use the supplied 12v power supply and never use a switching power supply as it will inject noise into the RX signal. A light bulb when on and I put the MFJ-1026 back in line, powered by a simple 12v motorcycle battery. The RX was perfectly clean on the original RX loop and the noise canceller worked exactly as expected. So then I hooked it up into a linear power supply with the same result. The entire time it was "malfunctioning" was due to the switching power supply I had plugged it into.

Lesson learned: NEVER use a switching power supply to provide power to an amplified RX antenna!
 

I tend to agree overall about the noise, but I have found most times it depends on the equipment used, and the quality of the switching supply.
To be clear, I use a Megawatt power supply for the rig with no issue. This experience was specifically about using it to inject 12v into the coax to power an amplified RX antenna.
 
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Seems that switchers are always a crap shoot with noise. Some will work fine where you use them, but some others may just go into crowbar somewhere else. The only thing you can do is try them and see if they'll work for you or not --- Or just keep the old Astron beast in line.
 

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