Icom 2720H in a Jeep Liberty

There has been much discussion about the mounting of a 2720H and the visibility of the control panel.  I have two of these rigs, one mounted in a pickup truck with the head turned slightly toward me and one mounted in a Liberty with the head mounted low and in the center.  The one in the Jeep is MUCH more visible than the one that is tilted toward me but neither one of them is bad.  Here's how I installed the rig in the Liberty including the antenna mount and the key-off control circuit for the radio.

I fabricated a simple aluminum bracket to mount the control head.  The bracket is attached to the bottom of the ashtray hole in the face plate.  It is very easy to remove the face plate.  All that is necessary is to remove the ashtray and remove one screw in the back of the hole.  The panel will then unsnap all around and pull right off.

Here's a shot of the head mounted and turned on.  You can see that the display is fully lit with high contrast.  It is very easy to see the display at all times... unless the shifter is in park.

The antenna mount was another problem altogether.  The Liberty has no surfaces that lend themselves to mounting an antenna except the roof. My wife has to park in a parking garage that limited the available space on the roof to the point that that wouldn't work.  I contacted Larson about a glass mount and they admitted it was a compromise at best so back to the drawing board.  What I came up with was the idea of mounting the antenna to the top surface of the bulkhead in front of the windshield and letting it protrude through the plastic intake air vent, below the windshield.  
I have always Liked Larson antennas and because of the height problem, went with the short 2/70 NMO that they make.  In addition, the base for this 2/70 is very short so only the antenna itself needed to protrude through the plastic cover.  The mount for the NMO kit is made of two pieces of  stainless steel.  You can see one screw in the rear of the overlapping section of the mount.  After the antenna was mounted and the angular position was determined, a second hole was drilled in the front edge of the mount to hold the vertical position.  Next I needed to determine the position of the hole through the plastic to clear the antenna mast.

To do this, I used a Larson NMO cap and chucked it in a lathe to determine the exact center of the antenna mount.  I drilled a hole through the cap and screwed in a sharp pointed sheet metal screw from the inside out.  I then installed the plastic air intake back on the car and pushed down on it to mark the underside to determine exactly where the hole for the antenna needed to be.  This actually worked very well and a 5/8 hole was carefully drilled for the antenna to clear the plastic.

As you can see, the installation came out very nice indeed.  The short antenna does not use a loading coil at the bottom so there was clearance (just barely!) under the plastic cover for the mount.  The antenna loads well and the SWR is below 2:1 across both the 2 meter and 440 bands.  The antenna is well off to the side of the line of sight so it does not interfere with driving at all.  I installed the base of the antenna the the fabricated mount, then the plastic air intake over it and then used an allen wrench inserted in one of the set screws to tighten the mast to the lower mount.

The last issue was the electrical work to make the radio do what I wanted it to do.  I wanted it to come on with the key in either the RUN or ACC position.  I also wanted to be able to use it without the key if I was doing an event and had the rig set up to cross-band repeat and was away from the car.  I contacted Icom to see if there was any issue leaving the radio itself turned on and shutting it on and off by controlling the power to the whole radio.  They indicated there was no problem at all doing that.  I used a 30 amp relay to control the radio.  The initial control of the relay was from one of the circuits under the dash that is at 12 volts with the key in the RUN or ACC position.  The other part of the control circuit was a bit tougher.  I wanted to be able to trigger the radio on and have it stay on without having to leave any other circuits on in the vehicle.

To provide the additional control of the relay, I used an SCR that is triggered by the running lamp circuit.  In that way, I can momentarily flick on the running lights and that latches the SCR and it then stays latched (powering the relay) until the key is turned to either the RUN or ACC position.  Doing that raises the cathode of the SCR to one diode drop below line voltage, back biasing the SCR and turning it off.  The 100 ohm resistor was necessary to desensitize the gate so that it wouldn't be turned on by things like the remote door opener.  Ask me how I know......  The components were soldered directly to the leads of the SCR and then heat shrink was put over the individual diodes and one larger piece of heat shrink was used to cover the entire device.  I snipped the heat sink tab off the SCR (so the assembly was smaller) since it is handling virtually no current and doesn't even get warm.  Incidentally, you can use any momentarily energized circuit for turning the SCR on.  There is no magic to the circuit I chose.  It would appear that there are a couple of unnecessary diodes in the circuit on both sides of the SCR.  These turned out to be necessary to achieve reliable turn off of the SCR.  Without them, it would occasionally remain on with a turn off pulse.

The protection diode (stops the pulse from the relay coil when it turns off) and the filter cap were mounted right to the bottom of the relay and soldered directly to the relay terminals.   I used a 30 amp 12 volt relay from AutoZone for the radio control.  That way, no high current is handled by any of the original Jeep wiring or switches.  The high current supply to the relay comes from a fused line directly connected to the power distribution panel under the hood.  I mounted the relay up under the dash (inside the car) and then drilled a hole and lined it with a  grommet for the antenna lead and the +12 volt lead to come into the passenger compartment.

Here's the schematic of the circuit.  None of the parts are particularly critical.  The diodes need to be about 100 volt parts and the resistors are 1/4 watt.  Although the schematic shows the trigger coming from the left front turn signal, I had to change that since the Liberty flashes the turn signals when you unlock the doors with the remote.  I ended up using the parking lamp circuit.  That way, I can just turn on the parking lamps for a second and it latches the SCR.

E-mail me at ultrasport(REMOVE)@mail.com
© Copyright 2002, 2003, 2004 Steve Das