Mounting 2 way radio in trunk of Civic Hybrid

I'm looking to mount a 50 watt 2 way radio in the trunk of my 2004 Honda
Civic Hybrid. The remote head will be mounted somewhere below the stereo
and I have a glass mount antenna on the rear windshield. I know I'll
have to remove the rear seat to route the cabling, but how am I going to
get 12 volts to the radio? Is there a place I can tap in the trunk that
would power a 50 watt transmitter? If not, how would I run a power cord
from the battery to the trunk?

 

Hi

I don't think there would be enough power anywhere in the trunk to properly
supply power to your radio. A 50W output transmitter is probably 100W
input. At 12V that draws at least around 8.5Amps. Since it is in the trunk,
using any existing wire would just drop too much voltage across it (not even
taking into account whatever that wire was originally feeding). You would
not want to burden original wire with that kind of current. Also, since you
will not see 12V near your transmitter, it will most likely not put out 50W
but significantly less (it is not in direct proportion to the input voltage,
in most cases). The receiver will pick up all sorts of conducted
interference from whatever is on that wire - the modern GaAs fet radios can
be picky.
A better alternative would be to place the unit under a seat and feed it
through the firewall directly from the battery -- putting a fuse close to
the battery, of course. With the power source being close to the battery,
you also don't have to worry about alternator whine, etc. If you are using
the fattest wire you can stand, power loss will be kept to a minimum,
optimizing your output.

Unless through-glass antennas have changed a lot since I've attempted to use
them, they are not very efficient couplers - they also don't have a decent
RF ground so need antenna tuners, which are lossy. They tend to also be
fairly narrow band, so your SWR will not be optimum across our range. When I
checked them out, the best loss I could make was 6 dB on peak (not including
connectors), way worse off peak - so your 50W will most likely be at best
around 12 W ERP in a quarter wave whip on your center frequency. 6dB on
receive can make the difference between understanding a conversation and it
being lost. Don't count on the antenna gain to make up for this loss.
A better approach would be to drill a hole (trunk or roof) and put a
Motorola NMO mount on it: A roof mounted 1/4 wave will beat a through glass
5/8 wave hands down. That way you can pretty much accomodate any type of ant
enna without the rediculous loss of a glass mount.

Sorry I went slightly off topic here but some of this could be applied in
other problems as well.

Hope it is of use to you.
Remco

 

the first problem is getting past the IMA battery between the
seatt back and the trunk. careful, it is 144 volts DC.
personally i would run a fused wire direct from the battery
through the firewall and along the sill to the trunk. just have to do
a bit of fishing.
Chip

 

Thanks for the intelligent and well written reply. I'll probably go with
the suggestion to put it under the seat. As far as the antenna I'm gonna
have to stay with the glass antenna. The wife wouldn't be too happy
about drilling into the vehicle so soon. Plus I listen a lot more than
I talk. Maybe I could do a lip mount at some point.

Randall
KE0YG/8

 

Hey Randall

Yeah, I understand -- I have a wife too. When I was into the hobby, she
always complained about seeing wires and brackets..She has the class in the
family

I did drill a hole in my car when she wasn't looking. We're still together
so it worked out Just get her a nice box of chocolates right before you
show off your handy work on the lip mount. That box of chocoloates is a good
investment: a trunk mounted 1/4 wave will still outperform a glass mount
5/8.

73
Remco KB1ZB / ex PE1DGC

 

I agree with this comment. I put a 2-way dual band ham radio (50 watt vhf,
35 watt uhf) in the trunk of my 03 Accord, running +12 and ground directly
from the battery all the way back. Both hot and ground are fused at both
ends. I came through the fire wall, under the sill, etc. The control head is
in the little pop open compartment for sunglasses in the ceiling, and the
mic and speaker are in the pop open compartment under the radio/heater/ac.
Running wires was a long and tedious job, but the end result was worth the
effort.

I also agree with the comment another person made about glass mount
antennas, but alas, that is the solution I also selected. They are no where
near as good as a permanently mounted antenna. Be very careful how you mount
the glass mount - make sure it is not mounted over any of those fine wires
used for defrosting, and also make sure it is not mounted over any tinting
material.

Good luck.

Carl