of a Yaesu FT-7800R UHF/VHF Transceiver
The FT-7800R is an economical, no frills mobile radio for 2m
and 70cm, with 50 watts and 40 watts respectively.
The removable control head and power saving features make it a good choice for my
Cabin space is limited and the vehicle has a clean look, so utilitarian items such as
radio equipment is best when hidden.
Audio is piped into the the stock car stereo system via an FM MP3 player-to-radio type
The antenna system uses a Diamond Super Gainer and has exceptional gain, at 7.5 db for the
The base unit was mounted to a home-brew rack that was
zip-tied to under panel of the rear speaker deck.
I used the area where the amplified bass speaker would go.
Power was routed directly from the battery using 30 Amp / #12 gauge red/black automotive
wire. The line was fused on both positive and negative close to the battery.
The route went through the front right quarter panel through the door wiring harness
grommet then underneath the carpet / upholstery trim pieces where it was hidden from view.
Then behind the rear folding seat to the shown location. Automotive flexi-tubing and
tie-wraps were used in exposed areas and against metal car body parts and in the engine
I use 6" (1/8" thick) PVC trim used for siding and attached a stock piece of
1/16" aluminum purchased from the Depot. The corners were rounded.
The PVC channeling was used to reinforce the flimsy aluminum. The aluminum was used just
for heat dissipation.
The 7800R has a decent heat sink and a fan, but does generate a bit of heat when in use.
Since the 7800R's speaker is located on the base unit and the radio is therefore contained
in the trunk, I needed to use an external speaker.
I tried using a decent separate speaker but learned that as the vehicle hit highway speeds
and the air-conditioning fan caused the output to be inaudible.
The solution was to pipe the audio through the car's stereo system.
This was a great idea as the stereo automatically increases the volume according to the
vehicle's speed. Other features included options like volume and mute control on the
Unfortunately... There is no iPod or aux port on these models of GM stock stereos.
Replacing the stereo was out of the question as the security, chime and many other systems
of this vehicle are controlled from the stereo unit. To save costs, no doubt on mixing and
matching factory options, simply by combining control of the creature comforts in one
There is an $80 adapter to using the system's CD changer option, but it still requires
external power to the adapter and there was also a know incompatibility with some models,
and many of the models had the same numbers and appearance.
Therefore the solution would be to use an FM transmitter. One often found at Walmart to
plug your MP3 player into.
I therefore gutted one, tweaked it and added a small switching power supply to it to bring
the 12v from the system to 3v.
I ran into a serious problem when the audio from the 7800R was distorted and the volume
was insufficient. Impedance matching was then necessary to the FM transmitter module.
Adding a capacitor and PA transformer added ground loop isolation and eliminated much of
the bass from the ham rig's audio.
Car audio systems love to amplify and compress the bass component.
Finding this solution took the majority of time, in fact three weeks and there was much
experimentation. Finally an Altoid's tin was used... what else for a ham?
You can see the power supply along side the transmitter. The on board regulator and on/off
switching control plus the stereo pilot tone controller were disabled on the transmitter
The unit was Velcrow-ed behind the car stereo dash unit and power was linked to the
vehicle's RAP 12v circuit relay that provides 15 minutes of power after the car is shut
off and the key is removed.
Power to the car stereo and transmitter is shut down upon the opening of any of the doors.
Along with the 7800R's power off feature, there is no way to drain the battery when the
occupant is away from the vehicle for long periods of time.
Here is the final installation of the control head. I used a goose neck flexible arm mount
purchased from Mount Guys.com. It is bolted to a convenient center console bolt under the
passenger seat and has enough holding power to mount other heads.
Space was left on the rear speaker deck mount assemble for an additional HF rig.
The antenna uses a K-400 mount and has proved to be sturdy.
This is the EmComm Jump Kit. It's a fairly inexpensive Stanley FatMax bag from Walmart,
that has many radio shaped pockets and a plastic bottom. With handle straps and sturdy
I've been filling it with whatever I can find around the house. Weather radio, connectors
and etc. It could come in handy in an emergency deployment.
73, De Mike Maynard, K4ICY