[aprssig] Re: D700 vs Prius

Stephen H. Smith wa8lmf2 at aol.com
Wed Mar 28 18:05:28 EDT 2007

TGatje at aol.com wrote:
> Greetings,
> I am relatively new to this list but have seen some discussion of 
> installation of Kenwood TM-D700As in various vehicles.
> For a new wrinkle (for me) I want to install the radio in a Toyota 
> Prius. It, of course, has some issues.
> First, it has a relatively small capacity 12VDC battery. This battery 
> basically runs the control system and computers. All the heavy lifting 
> is done by the 200VDC battery. Therefore I believe I won't be able to 
> let the system run continuously when the vehicle is parked.
> Second, the Prius is basically a "drive by wire" vehicle, heavy on 
> computers and such. I'm worried that the presence of a transmitter in 
> the car may cause some malfunction. The last comment of the Experience 
> center was that unapproved modifications may void the warranty! 
> Contact with the dealer and the "Toyota Customer Experience Center" 
> have not been any help. I believe someone on this list mentioned 
> seeing a bulletin saying transmitters in Priuses are okay up to about 
> 100 watts but I've not been able to find anyone at Toyota to verify that.
> Third, suggestions on wire routing, power tap locations, etc would be 
> appreciated.
> Does anyone have any experience installing a D700 in a Prius? Or have 
> any advice on how to minimize problems? If you've seen their bulletin 
> on installed transmitters, please let me know where to find it.
> I

I have installed a D700 and a 100W HF rig in a Prius with no 
problems.    I installed a second battery (An Optima Spiracell Yellowtop 
42AH deep-cycle), with a Hellroaring Technology battery isolator in the 
sub-trunk, and connected it in parallel with the main 12VDC battery.  
The DC-DC converter that creates 12VDC from 240VDC can source 50 amps or 
more, so the power system has no problem charging the larger 12V battery 
when the engine is running. 

The Hellroaring isolator is a voltage-sensitive power-FET switch. When 
the power system on the input side of this device is at 13 VDC or higher 
(i.e. engine running), the switch conducts and connects the secondary 
battery to the charging system with less than .1 VDC drop. When the 
input side drops below 13 VDC (i.e. engine off), the isolator opens and 
disconnects the secondary battery.  All the radio and computer gear runs 
off the secondary batttey and can be safely left on.  The isolator also 
has contacts for attaching a "panic switch" to force the device on even 
if the primary voltage is below 13 VDC -- useful for jumpstarting from 
the secondary battery if the primary one runs down. 

For antenna mounts, I bent up some L-shaped brackets that added a small 
horizontal "wing" to each side of the tailgate hatch opening.    I 
placed two holes in the vertical part of the brackets with exactly the 
same spacing as the existing mounting screws for the hatch lifter 
pistons.  You just take out the two 11mm screws that secure the 
hatch-lifters to the trunk sidewall, slip in the brackets so they are 
sandwiched between the piston bracket and the sidewall, and re-insert 
the screws.   The bracket on the driver's is punched with a 5/8" hole 
for an SO-232 bulkhead ("barrel") connector. The right bracket is 
punched with a 7/8" hole and has a standard body-type NMO mount 
installed through it.  The SO239 side supports a Yaesu ATAS-100 HF 
screwdriver.  The NMO side supports a Comet 770 no-ground-plane-required 
2M/450 dual-bander. 

The chassis of both radios are also mounted in the subtrunk. I lined the 
floor of the subtrunk with a 1/8" thick aluminum plate cut to exactly 
fit  the floor of the trunk.  The standard mobile brackets for both 
radios are bolted to the plate as are several fuse blocks, the 
Hellroaring isolater and various other radio-related pieces of 
hardware.   Since this plate is resting in a plastic tray it is 
completely isolated from the car's chassis grounds.  I use the plate as 
a common point ground for all the black (negative) wires of the ham gear 
and related electronics.  ( I placed a single 1/4-20 1 1/2-inch bolt 
upwards from the underside of the plate. All negative power leads from 
the transceivers, second battery, isolator, laptop power supply, etc are 
equipped with 1/4" ring terminals, stacked on this bolt and locked down 
with a couple of 1/4-20 hex nuts.) A single 10-ga black wire (car stereo 
primary power wire) goes to the negative terminal of the car's existing 
12V battery in the right rear corner of the trunk. 

[The objective here was to absolutely minimize heavy DC currents from 
the ham gear current drain from circulating on the car's own chassis 
ground/negative power system.   This is to both minimize the chance of 
interfering with fly-by-wire electronics, and to minimize the amount of 
noise picked up by the ham gear via voltage drop over shared chassis 
grounds.  A single 10-ga black wire (car stereo primary power wire) goes 
to the negative terminal of the car's existing 12V battery in the right 
rear corner of the trunk.  ]

Up front there is plenty of room between the front of the console and 
the underside of the dashboard to mount the control heads of both 
radios.  Again, I made an L-bracket by cut an approximately 4" x 8" 
piece of 1/8" aluminum plate and bending it 90 degrees at the 
centerline, to yield a 4"x4" bracket on each side.   One 1/4" hole, and 
another 1/4-20 x 3/8" bolt with a pair of 1.5" dia fender washers 
secures the plate to the underside of the plastic dash  panel very 

The result of this is absolutely no interference with any of the car's 

However, on HF, the noise from the hybrid power converter generates a 
LOT of broadband white noise hash across the HF bands, making it 
impossible to hear anything under S8-S9 or so.    An inverter mounted on 
the electric drive motor converts 240 VDC to 440V three-phase  AC.  The 
noise generated from this 50 KW (!!) DC switching converter is a lot 
more than your run-of-the-mill 200W switching computer power supply!   
This hash SLIGHTLY desenses the D700 receive on 2M but has no noticeable 
effect on UHF.   It get especially severe when you hit the brakes 
activating the regenerative braking system or roll down hill. In either 
case, the motor reverses roles to become a generator driven by the 
wheels and generates a lot of popping grinding noise (sounds like an 
electric drill or mixer) overlaid on the smoother existing white noise.


Stephen H. Smith    wa8lmf (at) aol.com
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