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Real Hams Drill Holes

Written by admin on August 19th, 2013

You all know “that guy” – The one with the car or truck with the UHF/VHF antenna (or antennas) stuck to the roof or trunk lid and wires trailing off to the side that go through a trunk or door gap. The antenna maintains its death grip on the outside of the vehicle with the mysterious forces of magnetism, via a lip or edge clamp, or something that bolts to your roof rack. You wash your own car and drive a couple extra blocks to avoid parking garages. It’s all for the better you tell yourself. It is how you “suffer” for your art.  It is also why your significant other won’t let you touch their car.

I was “that guy”.  I also remember when I knew that it was time to no longer be “that guy”.

We all have that moment of clarity when we face a problem or challenge and know exactly what to do. My moment came to me right after finding dry clothes for my 10 year old.  We had just gone through a carwash and the water had run down the antenna feed wire, past the door gasket, and landed right in his lap.  Before we had entered the carwash I had tipped the mag mount antenna down and tucked it in along the roof rack so it would not get “stripped” off the roof as we went through the car wash.  This was the usual practice because to unscrew the antenna from the radio, pull the wire back under the floor mats, and through and under the roof rack rail was too much of a hassle.

I had just purchased this truck a few months ago – a nice, tuxedo black, 2010, Ford Expedition. It has a moonroof, and DVD player for the kids. The moonroof is for me as it is the closest thing I will be getting to a convertable for the foreseeable future. All that stuff on the headliner of the truck made me wonder how I was going to solve the challenge of mounting an antenna. To make matters even more complicated, many newer cars and trucks have roof pillar mounted “curtain” airbags.  So poking cables under trim panels with a screwdriver was not really an option either.  So I came up with a list of criteria.

  1. I wanted to be able to take the truck through a carwash without also washing the passengers.
  2. I wanted to be able to go into an underground parking garage.
  3. I wanted to be able to do 1 & 2 without taking the antenna off the roof.
  4. I wanted a stealthy/clean installation.  I was not looking to necessarily hide that I had a radio in the truck, but I did not want to advertise it either.
  5. I still needed it to be efficient and actually do the work of a proper antenna.

In other words, I want my cake and to be able to eat it too.

I spent the better part of a month reading articles on QST, searching forums, reading search engine hits, and speaking to my local Elmers. (Elmers are awesome.  I aspire to be one someday.)  I was able to break the solution down to the following…

  1. Choose a mount.
  2. Find an antenna that would be flexible enough to bend in a car wash or parking garage.
  3. As part of #2, possibly come to terms with putting extra holes in the shiny new truck.
  4. Install the solution without destroying my vehicle.

There are many, really great web sites that discuss all the do’s and don’ts of mounting a mobile antenna for UHF/VHF and HF.  NMO or through hole mounted antennas are typically considered the best, and everything else is a compromise. The true non-believers avoid the NMO, mag mounts, and lip or edge mounts and use glass mounts on passivated glass to achieve the goal of something is better than nothing.  None of these options were appealing. They were still going to damage the finish of the vehicle and/or be too much of a compromise on performance. So after this soul searching, it became clear that the best way to protect my vehicle and still be enjoy my hobby was to drill holes. NMO was the only option that made sense.

To find a subtable antenna I did have to look further than I thought – and it came from outside the normal amateur radio circles.  Nothing seemed to be what I wanted. I was looking at all the dual band NMO antennas. The issue was that dual band antennas were all going to be too tall and/or too stiff for my project. Spring mounts were no good. The springs added height and/or were too stiff.  Collar sprung antennas would still require me to get out of the truck, un-collar the aerial and fold it over. Motorized mounts were too much of a compromise on performance and still had wires on the outside of the vehicle to deal with.

I finally found what I was looking for from a company that markets to public safety, not the amateur radio market. Sti-Co makes an antenna called a Flexi-Whip. It is very low profile in the NMO mount, guaranteed not to break, is extremely flexible, and is tunable with a pair of diagonal cutters. The “gotcha” was it is not dual band. This is where that second NMO mount came into play.  I purchased 2 of the Flexi-Whip (ROOF-FT-NITIantennas, and a Comet duplexer (CF-4160J). By adding the duplexer I was able to take the output of the FT-8800 into the duplexer and out to the pair of 1/4 wave antennas, one for each band (2M and 440).  The flexible nature of the antenna, no dual band load coils or springs keeps the length of the 2M antenna just under 20 inches.  The 440 antenna is about 6.5 inches. It is barely even noticeable on top of the truck.

Know your limits. I knew right from the get-go that if I were to tackle the headliner in my vehicle it would have been an hours long, brutal, exercise in frustration, and potential damage, to either the headliner, the moonroof mechanism, the DVD player, or any combination of the above. I did not have the experience or the right tools to accomplish this.  So I started making some calls.  I found a really great, local, car stereo place.  With Navigation systems, DVD players, and satellite radios regularly a part of in-dash entertainment units now it is completely normal for them to go into headliners in a wide variety of vehicles to install GPS or Satellite radio antennas. For the pre-negotiated price of $100 they would install my antenna mounts. I was very pleased with the work they did. It was done in a couple of hours. The holes were lined up perfectly and centered along the top of the truck and the coax was run down the side pillars, under the flooring, and up into a space in the center console where I was going to mount the radio control unit.

To complete this project successfully I needed one more very important component… an Elmer (K7DAA) with an antenna analyzer. I had purchased a short jumper to connect the radio to the duplexer. When my Elmer put the analyzer on the antennas we discovered the jumper was a “magic length” that was resonant on 2M.  So I chopped off a couple inches, soldered on a new connector and we checked it again. To tune the antennas I read the instructions that came with the antennas and cut the 2 antennas a little longer than stated for each of the 2 bands. The analyzer was attached and I started snipping off 1/4″ at a time until the SWR was where it needed to be.

Ultimately this project came down to drill vs no drill. Making the decision to go NMO was one of the best I have made in my short ham career. Over the useful life of this vehicle I will have paint scratches, dings, and dents way worse than what was ever caused by the 3/4″ holes drilled for the 2 antennas. Every ham that has seen the install comments on how pro it looks. It has been through several car washes and there are no leaks or other problems to report. It has also been in parking garages without incident and without me having to remove them. I was able to meet all my original design criteria for roof clearance and system performance and ended up with a sharp looking vehicle to boot. If there was one regret I would have to say it was not installing a 3rd NMO at the same time I did the other 2.  I am KJ6VTP, and I am a Ham.  I drill holes.

 

 

 

 

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