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Tech237
Moderator
Username: Tech237
Post Number: 1300
Registered: 4-2004
| | Posted on Monday, February 15, 2010 - 7:03 am: | 
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Installing Radios in Vehicles
PART #1
Installing Radios in Vehicles
This is the first part in a series of articles aimed at installing radios in vehicles. During these articles we will take a look at antennas – location and mounting, radio location and mounting and running power and speakers.
Antenna Location
When I worked installing commercial two-way radios, I was often asked about why some antennas were located on the vehicles roof, some on the trunk lid and upper fender area and others mounted down on the bumper.
Common sense should tell us that some antennas cannot be mounted on the roof of a vehicle due to size and safety constraints. For example mounting a full length ¼ wave antenna for 28Mhz or lower is going to cause problems with low cables, covered car parks, bridges and drive-thru. (By the way the covered car park I learnt from personal experience – it cost me one Hustler mast and 30 fluorescent tubes.) The other reason some cannot be roof mounted is simply they are too big for the thickness of metal in a cars roof and will cause the roof to bend.(insert pix of 1800 and hustler)
If mounting an antenna on the car’s roof can cause problems why don’t we then mount all antennas on the trunk lid or lower? The answer to this is efficiency. To radiate the best it can, any antenna needs to be in clear surroundings, and as far away as possible from any parallel metal surfaces.
Mount a ¼ or ½ wave 2m antenna on the trunk lid and because the bulk of the antenna is below the metal roof of the car and close to the rear door pillars, it will not be as efficient as the same antenna mounted on the car’s roof. Also, as the antenna sways due to vehicle movement, the gap between it and any nearby metal surface changes. This, in turn, can cause the resonance, SWR and radiation patterns to change.
Now mount the same antenna on a bumper
mount, and as you can guess, things get even
worse, because more of the antenna is near a metal surface. However, some antenna can really only be mounted on a bumper level mount, so like most things, mounting is a compromise between efficiency, safety and looks.
Now Up to this point I haven’t mentioned On Glass antennas, and that was purely due to the fact I have not had any need use one. Now an On Glass antenna will not be as effective as a direct connected antenna of the same style and size, due to several factors.
With the antenna being mounted on a window we have little if any ground plane to work with, so how do they work?
The signal is capacitive coupled to and from the antenna with the glass being the dielectric of the capacitor. Now as the glass can be of varying thickness, this can change the value of the capacitor, which in turn, can affect how well the signal is transferred. Now add things such as window tinting (some of which can completely stop the capacitive coupling), the thin wires of the rear window demister and we can have even more trouble with an on-glass antenna.
Do they work? Yes, in fact a lot of cell phone antennas used this principle, but personally, I’d only use one as a last resort when no other type of antenna can be installed.
In short, always try to mount the antenna as high on the vehicle as possible contingent with safety and other important factors (“you’re not drilling a hole in the roof of MY car”, or not having a roof on the car).
Antenna Mounts
In the last section I made a comment about not being able to drill a hole to mount an antenna, there are several ways that you can work around this restriction by choosing different type of antenna mount. By this I mean consider using a magnetic mount on the roof instead of drilling a hole, or use an L bracket or trunk lip bracket instead of drilling thru the lid or fender.
Now I’ll be honest and admit, while magnetic mount may work I have never been really happy with them. Over the years I have been involved with radio, the majority of times I have had problems with electrical noise in a radio I have been able to reduce or eliminate the problem by replacing a magnetic mount antenna with a properly grounded style. The one occasion where this did not work was an early 60s VW Beetle, that no matter what was done, had unbearable ignition noise.
Other people swear by magnetic mount antennas, so as with most things caveat emptor. (insert pix of various mount and brackets)
Now trunk lid mounts have their own pros and cons, with the pros including such things as not needing to drill any holes, mounts are available for just about every style of antenna base, and the mounts adjust in all three planes so that the trunk does not have to flat in order to get a vertical antenna.
Conversely the two biggest cons, that I have found, are not all cars have a big enough clearance around the trunk lid to use a trunk lip mount, and the ground on a trunk lid may not be the best as, in most cars, it relies on the hinges. Neither of these are insurmountable issues.
The first can be overcome by making your own thin lip mount out of steel or aluminium, and the second by using ground straps from the lid to the chassis. More on these later on, when we look at mounting an antenna on the trunk lid.
Roof Mounting and Antenna
Roof mounted antennas, where feasible, are nearly always the best option. Just look at commercial two –way radio installs – nearly all have a roof mounted (or at least as high as possible mounted antenna). Installing an antenna in the car’s roof is not the daunting task it may seem – especially if a few precautions are observed. Note the roof mounted VHF antenna on the photos of the Pontiac earlier in this article.
Whenever I am going to drill into a vehicle’s roof for an antenna, I start by laying down a square of blue masking tape in the general location of where the antenna is wanted. This does two main jobs. Firstly it gives me a surface that I can mark on without worrying about the vehicles paint. Secondly, when it comes time to drill the tape helps to reduce the chances of the drill bit wandering and scratching the paint.
So how do I then locate where I am going to drill to mount the antenna? I use several methods to ensure the antenna is as near as possible to the center of the roof.
Firstly, I make a chalk line on the roof of the car (front to back) using body contours, inside rear view mirror and any other indications of the center line as aids. Now I repeat this only going from side to side. On most 4 door cars, this line generally is based on the leading edge of the door pillar, as this seems to be close to the mid-line, but also misses any internal bracing on the roof. Another good aid is to remove the roof mounted interior light and visually check. Once I have the location worked out, I'll transfer the lines to the tape with marker pens.
Now, I will drop the roof lining down and insert a length of wood under the spot where I'll be drilling. This piece of wood does two tasks – 1) it makes sure the roof lining stays away from the roof and reduces the chance of it being damaged by the drill, 2) once I see wood shavings coming up, I know I am through the roof.
Here is a couple of tips for when you install the antenna base through the hole you just drilled. On the outside you will normally have a rubber washer, I normally smear a THIN layer of Petroleum Jelly on both sides of this washer. This thin layer helps prevent water from creeping under the washer and into the car. On the inside I also try to use a layer of mastic type sealant. DO NOT use a sealer that smells of vinegar.
Now that we have the antenna base mounted, it is time to run the coax to where you will have the radio. The route you run the coax will depend on several factors, such as where the radio is to be mounted, what access/trim panels be be removed and what space is behind them. I have a preference to use the door pillar, as most have plenty of room behind the seat belt to run a coax cable. Now the cable can either run under the kick strip by the door, or under the carpet to the center console and then under the console to the radio. Both methods work, and while I have used both, again MY preference is to run it under the kick strip, as it seems to have less chance of getting damaged there, than just laying under the carpet. Use the one that works best for where you intend to mount the radio
Tech237
N7AUS
Chipmonks roasting on an open fire
Hot sauce dripping from their toes.
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Tech237
Moderator
Username: Tech237
Post Number: 1302
Registered: 4-2004
| | Posted on Monday, February 15, 2010 - 7:17 am: |
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Installing Radios in Vehicles
PART #2
Now we start to look at the real important parts of installing a radio in any vehicle – that of location and power.
Location:
Some one once mentioned, about business', that the most important thing is location, location, location. The same can just about be said about installing a radio in a vehicle. Why install a radio if you cannot read the display, reach the control etc with ease, safety and comfort.
After all, what good is installing a radio BEHIND you, so that you need to turn round to reach any of the controls? Not only uncomfortable for you, but darn right dangerous. Yet people have done this in the past. I have also seen radios bolted to the plastic panel the has SRS engraved into it (image that hitting you if the trip the air bag), held in place with bungee cords and even with Velcro. One ham mounted his HF radio to a wooden frame (using heavy duty hardware) but left the frame to just sit over the transmission hump unsecured, while another ham bolted his IC-706 out of sight under the rear seat of his SUV, where it got little, if any ventilation. All of these, mentioned above, are basically accidents waiting to happen.
The best advise I can give is, take the time to play with different locations for the radio. Have somebody hold it in the possible location, while you sit strapped to in the drivers seat and see how easy the radio is to see (with out taking your eyes from the front of the vehicle for too long), how easy you can locate and adjust the desired control.
Now finding suitable locations in modern cars (small, little or no vacant areas) is getting harder, and I usually try to use places like the space dedicated to hold cassettes or cds, and even the location of the separate cassette deck. Heck for some radios, even the ashtray space maybe usable. Apart from being easier to cut these sections, you can cheaply replace the piece when it comes time to trade the car in.
In my wife's Blazer (not so small but still no spare places), I replaced the cassette deck (who uses cassettes?) and mounted the 2m/70cm in that space. This places it out of harms way, but easy access to the controls and the display. Earlier I had mounted this same radio under the drivers seat of the Grand Am
(here it could get cooling air flow), and just located the remote head on the dash.
Currently in the Hyundai, I have my 706 mounted in the trunk, with the remote cable and speaker wiring running forward under the kick strips. The head (removed when parked) sits on a bracket mounted just under the AM/FM radio and a small patch cable neatly brings a RJ-45 joiner to alongside the seat, where the mic now plugs in. If I really wanted to make my life easier, I could have run a cable back to the main body and used the mic socket there instead.
Bad Locations:
Earlier, I mentioned a couple of not so good places to mount a radio, but where else is a bad idea? How about on the side of the transmission tunnel? Or on an overhead shelf? Or under the dash near the driver or passenger? Or where it fouls an existing car control or door.
All of the above sound pretty obvious, except I have seen them all done in the past. For those not sure, why did I place the transmission tunnel and under dash in the bad list?
During some bad incidents, in rally cars, I have been amazed at places where I have left patches of helmet coloured paint – places that strapped in and sitting stationary were impossible to reach. It is simply amazing how much the human body stretches and distorts during a sudden change of direction or stop. A radio on the transmission tunnel, or dash may seem out of the way, but you could actually hit it – painfully.
For the same reasons, I have never been a fan of the bolt-in shelves that sit under the roof of trucks and SUVs Yes they work, but.... Now I am not going to tell you not to use any of these methods,as your choices maybe limited, but I strongly advise to try and find another method and location.
Over the years I have installed radios in to vehicles ranging from rally/race cars, to brand new BMWs up to tour buses costing hundreds of thousand dollars. All in cases safety and ease of use took precedence over esthetic's. This is not to say that didn't pay attention to looks,as I have done installs (Limo's and Hearses in particular) that you would swear were built into the car by the manufacturer.
Where I can get away with it, without it looking bad, I'll try to angle the radio slightly towards the driver to make it easier to see the display and controls. In most installs the location of the radio will be a compromise based on several of the above mentioned factors PLUS the wishes of SWMBO.
Tech237
N7AUS
Chipmonks roasting on an open fire
Hot sauce dripping from their toes.
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Tech237
Moderator
Username: Tech237
Post Number: 1304
Registered: 4-2004
| | Posted on Monday, February 15, 2010 - 5:19 pm: |
|
Installing Radios in Vehicles
PART #3
Running Power
Now this may sound simple, but you would be amazed at how often I have seen this part of an install messed up – powering 50W+ radios from cigarette lighter sockets, cable run in via the gap between the fender and the front door, run through holes drilled in the firewall with the wire rubbing against the bare metal, just to name a few poor installations issues.
I once had to troubleshoot the install of a 2m radio that worked great during the day, but blew fuses at night - if you transmitted. The gent concerned had wired the radio, with no fuses to the input side of his headlight switch. Headlights and radio in receive mode was under the headlight fuse rating, but transmit and BLAM there went the fuse. The guy just did not connect the two issues, and really had no idea where he was powering the radio from, did not mention losing headlights as well until queried it.
Over the years I have settle on the following method as working 9 out of 10 times, and that 10th time is usually and unusual installation.
1) Use shielded cable for both leads from battery to as close to the radio as possible. Add a toroid choke right at the radio. Often, for low power radios, I'll use coax. I use the inner conductor for the power and ground the shield at ONE END ONLY. I'll do this for both the positive and negative runs.
2) Fuse both leads as close to the battery as possible – even if the supplied harness has a fuse right near the radio. The fuse at the battery protects THE CAR from the power cables melting if something goes wrong, while the fuse at the radio ONLY protects the radio.
3) Keep radio power leads separated from other leads in the car to reduce chances of power lead induce RFI issues.
4) Use as thick as power lead as practicable for the radio(s) concerned. 20A on a 6ft length of power cord can cause a noticeable voltage drop on too thin a conductor, which not only may cause the radio problems, but could also cause the lead to over heat and become a fire hazard.
5) Support the power cabling as much as possible. Allowing a cable to flex excessively, will cause that cable to fail in time. This does not mean that it has to be cable tied ever 6 inches, but run it on flat surfaces, don't let it cross big gaps unsupported etc..
6) Anytime you must run a cable through a hole drilled in a panel, use a grommet and if possible add a couple of layers of heat-shrink tubing at that point on the cable as extra protection. One of my cars, had a double layered firewall, I ran the cabling inside a flexible tube as well.
The above will work for most installations, but what about non-standard type installation?
In my Hyundai, I have a 4 gauge cable that runs from the battery (via a LARGE Fuse) to the trunk of the car. There I have a separate fuse panel connected to this cable. At this junction is a 1M 1W resistor in series with a 1000uF 25VDC capacitor that runs from the power in terminal to ground. This filters out most pulse type noises. Varying the capacitor size may help in eliminating noise. The resistor is there to reduce current flow in the event the capacitor shorts out.
From the fusebox to the 706 I use the standard Icom power cable, figure 8 wrapped around a toroid, which blocks a lot of other noises. The radios negative lead is grounded to the chassis rail and the battery has a second ground strap going to the front end of the same rail. I have also connected the radios ground terminal to this same chassis rail.
Again, I would have prefered to use shielded cable, but for the length of the run and the gauge needed cost became a factor.
External Speakers and Other Options
Again, not much needs to be said about using an external speaker except place it where not only is is audible but also out of the way. Years back, when I first started in the trade and cars had soft vinyl roof linings, we use to place a speak again the vehicles roof under the lining about 6 inches behind the drivers ear, the wiring then ran down the door pillar to the radio. Even with modern roof linings this may still be an option in some cars.
Not matter where you mount the actual speaker make sure it is one designed for communications, as some music type speakers produce a muddy sounding signal when used with communications equipment. Also use a shielded speaker cabling to reduce chances of RF or RFI pick up by the cabling.
I have configured installations with hands-free microphones that use a push on/push off ptt (one of these for a handicapped ham in his van), ptt circuits that have a button the gear shift that if you push and release it (less than 5 secs) the radios drops out of transmit when you release the button, but if you hold it in for more than 5 seconds the radio stays in transmit until you push and release the button again. Mounted microphones on the visor (old in-car cell phone kits area great source of visor mics), microphones and headsets in bike helmets and even tried throat mics in a mobile installation.
The one thing I wont do, in a mobile installation is run VOX circuits.
Tech237
N7AUS
Chipmonks roasting on an open fire
Hot sauce dripping from their toes.
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