m0vey

Amateur Radio

Homebrew Remote ATU MFJ993

Homebrew Remote ATU MFJ993

 Okay, so technically I'm using a commercial atu . The homebrew part has been to mount it in a waterproof case & make an atu that's supposed to sit in your shack, work as an exterior atu at the feedpoint of my aerial. Similiar idea to an SGC atu , but with the ability to handle more power at a fraction of the cost.

 

        I've enclosed some pics so you can see how I mounted the auto atu in a waterproof electrical enclosure. The enclosure has a lip with a rubber seal to make the case waterproof.

 

First, I mounted the atu in the case using some corner brackets. I used the original screws of the MFJ993 to fasten the brackets to the atu. Next, I fixed the brackets to the case (like in pic atu2) . After i drilled holes in the base of the case, I used some small screws with bolts on the ouside of the case.

 

Next, I fitted a surface mount so239 to the case using a 16mm wood bit to drill the hole. This is to attach coax from my transceiver.  I also fitted 2 banana plugs to the case. A black one to couple the earth to the atu & a red one to couple the wire of my inverted L antenna to the atu.  I also drilled a hole to allow me to bring cable into the atu, supplying 12v from my shack psu to power the atu.  I fitted an on/off 12v toggle switch in my shack, to allow me to power the atu on & off.  The hole I drilled in the atu was sealed up with silicon once I installed the power cable.

 

  You can see on pic (atu a) how I made the connections from the atu to the so239 & banana plugs on the case. I also used a pl259 elbow joint on the atu , to couple the coax from the atu to the chassis mount so239 without any kinks in the cable.

 

 Once I'd made all connections & connected the power cable using a choc bloc inside the atu, I fitted  the case to my fence at the base of my antenna. For this I used 1 1/2" screws.   I made sure the power switch was turned on on the atu & another switch set to auto before I sealed the unit using the 4 supplied screws.

 

  Next it is just a case of selecting the antenna in the shack, switching power to the atu & using about 15w on fm to tune the antenna.   My antenna is around 126 feet long inverted L with a 40 foot vertical section.  I've had reports of being 1-2 spoints stronger than I was originally as there are now no losses in the coax, with my antenna tuned at the feedpoint.

 

Remote ATU Take 2

 I decided to do a modification to the MFJ993 .

The mod was to fit an so239 so that I could use the atu to tune coax fed antennas , instead of it being just a long wire tuner.  

 My Inverted L will tune all freq's from 160m - 10m  . My noise level has also reduced again.

Tests this afternoon showed a noise level of s 2-3 on 160m !!