Sunday, July 17, 2011

EFJ Low Power Repeater Enclosure

Long story short…  I saw an E. F. Johnson-based mini-repeater up for bid on Ebay several years ago and got it for $130 shipped.

The receiver and exciter are from an EFJ UHF repeater.  Even though the enclosures look like complete mobiles, only half of each is in each enclosure.  An RC100 controller handles the ID, etc., and a Phelps-Dodge mobile duplexer rounds out the mix.  The original freq. was 444.575 which coincided with the Knoxville RACK repeater so I got a couple of crystals from ICS and soldered them in.  I tried to align the transmitter but in the end, Henry, WB4IVB aligned the whole shebang.  I actually have a 100 watt EFJ amp to go with the repeater. However, I sold the higher power set of duplexers and will have to find another set before the amp can be used.

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An empty McDonalds fry container is applied to ward-off evil spirits and repeater gremlins.  The trans-fat residue does the trick.

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The enclosure is an outdoor cable tv box you see adorning many power poles.  W4TEY found it at the Morristown Hamfest a few years ago and generously donated it to the cause.  It’s vented but in a way that helps keep water out.  The top portion has plenty of room for the repeater, controller, duplexers, and power supply.  A small fan would help but at 20 watts out may not be necessary with a commercial exciter.

Right now, I think the best use of this repeater would be at a medium profile site with a couple of beefy deep cycle backup batteries backing up the when PS.  If paired with a high-gain antenna, this modest set-up could really get out and be available during power outages.

I set up the Diamond 718 temporarily at the house to give it a whirl around town.  We’ll see how it goes.

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Steve, W4HKL

Friday, July 08, 2011


No pics of the inside…  it was late and I forgot.  Maybe later.  Basically, just strip the insulation off the wires and solder the heck out of the connections to the terminal posts.  Make sure you make good physical connections before you solder (washer and nut, good crimps, etc.)



Not sure why I need this…  except that I had the right parts laying around.

Steve, W4HKL

Diamond 718 Repeater Antenna -

“It’s Alive!!!!!!!”


The Diamond 718 UHF antenna that Mike, WM4MD graciously donated to me a while back is 99.99% ready to go.


After an unfortunate series of events a few years ago up on White Oak, the 718 turned Lawn Dart after it was dropped from near the top of the 100 foot tower.


“Ahhh…  the childhood memories these bring back…”

Lawn Darts

The top of the antenna is approx 8” below the top cap and the bottom section is approx 12” above the bottom mesh cap.  This should allow the standoffs to clamp onto the pvc without covering any portion of the radiating element.  The entire length of the antenna is approximately 15’3”.


Anyway, the antenna is now housed inside two sections of PVC – a 5 foot (2” diameter) base section and a 10 foot (1.5” diameter) upper section. Obviously, the antenna will have to be side mounted to the tower with both an upper and lower standoff to give it the necessary support.


The sections are screwed together and capped. All that’s left is caulking up the sections – after adding a coax pigtail to the antenna through the bottom mesh cap.


Tuesday, July 05, 2011

Part II - Replacing and Relocating The Battery In A Kenwood TM-331 (TM-241, TM-441, Etc.


I’ll type up the notes for this over the next few days.

I’m on Steve-Time…  W4HKL.

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Remove the plastic cover on the battery.

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This is the side we’ll pry up first.

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The polarity is as follows:

Top battery lead : Negative

Bottom lead: Positive.  You might want to pencil this in on the board somewhere to remind yourself later.


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Let’s get this show on the road…

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Use your fingers and the screwdriver…  get it up far enough to get some angle cutters in.

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Press the lower insulating pad back down if you can.

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Yes, the bottom of the battery is the positive side.

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I wondered why the TM-331 would retain memories most of the time yet sometimes lose them.

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0.15 Volts…  it should be around 3.0 Volts.

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Time to prep the batter holder, etc.

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This is more like it… and more likely to retain memory.

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Making sure the battery will be insulated from everything.





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Don’t tin these leads or you won’t be able to wind them around the battery holder terminals.  After winding, I bend the pins down a little to reduce the footprint of the holder.  This will have to fit inside the radio…

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I tinned the ends here before crimping them inside the old battery tabs coming from the board.


Soldering to the crimped ends lends a lot more mechanical strength to the connection as well as a good electrical connection…

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After you’ve heated the crimp… and also flowed a little more solder on the end of the tinned ends of the wire and up into the crimp…  test your voltage on the board.  It should be 3+ volts.

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Now tape it all up.

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Battery too…

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Note that I bent the wire well away from the solder joint in order to get the cord going in the right direction.

Congratulations!  You’re 10-20 minutes from being finished…

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Work backward…  and be careful.  Don’t get in a hurry.

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Routing the cables back into the RF section of the radio.

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Don’t forget this green wire loop.

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Again, I was lucky – the buttons were staying in place.  If you’re are “squirrelly,” you may have to keep the faceplate tilted and bring the radio up to meet it.


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Press all the button pads… make sure none are in a bind before proceeding.

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You can tell if one’s stuck, etc..

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Click… click…


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Now for this little SOB…  all I can say is take your time, work a little from one side and then the other… 

and hold your mouth right.


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Time to power up, enter a frequency, and give it a whirl.

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Powering down, cutting off the power supply, and then seeing if the memory is retained.

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Time for the moment of truth… will it work?