G4HDU    20 Apr 2014 : 11:00

Hole free car mount

How I solved the problem of not making holes in the car!

Back in December 2011 Sue, my XYL, and I decided that we no longer needed the Kia Sedona as there was now only two of us at home, number one daughter, Jane, having left for university. A trip to Thorntrees Garage up in Leyland resulted in us purchasing an adapted wheelchair accessible VW Caddy. As an aside I can thoroughly recommend Glen and his team up at Thorntree's, friendly, knowledgeable and not pushy.

Obviously I wanted to continue to have my mobile operation with my FT-8900 but didn't want to drill holes in the vehicle. I also wanted to add the provision for HF mobile operation with my FT-897D and therefore wanted two antenna fixings. Due to the modifications to the vehicle I didn't think that a hatch back mount would work or indeed any of the other similar mounts. A mag mount for HF is too cumbersome and so I had a look at the roof.

So, how do I go about mounting the rig, a quad band antenna and, for occasional use, a Yaesu FT897 along with the screwdriver antenna from the same stable as the rig, the ATAS 120A?

Ready made fixing points


To my surprise I found that there were four screws strategically placed for mounting roof bars and roof racks on the vehicle in each of the four corners of the Caddy's roof. Removing one of the screws proved that a secure fixing could be made to these mounting holes and so I went in and started to check out ebay for antenna mounts. I found an antenna mount from Truck King Radio (who are now sadly defunct) which was both strong and stable. It being designed to take big CB aerials it was made from thick mild steel and had adjustable angle for fixing at different locations on a vehicle.

Assembly of the Mount

Also from the same place I picked up a matching SO239 cable assembly. This is a single hole mount with a length of coax connected to it and a PL 259 on the end. The quality is not over marvelous, crimped connection at the SO239 end and will allow water ingress. Some clear sealant soon put a stop to that problem. The order was duly placed and the goods arrived two days later courtesy of Her Majesty's mail.

239 Mount

Naturally, as is always the case, the bracket was the wrong shape to just go straight on to the roof, the plates have ridges in them for mounting on roof bars and so a short period in the garage with a blowtorch and a lump hammer straightened out one plate. An anvil would have been useful for this part, not being in possession of one, the concrete garage floor was employed. An extra hole to clear an M8 threaded machine screw was drilled into the plate and a small piece of plastic cut out to go between the bracket and vehicle roof, this was to prevent damage to the paintwork when the mount was fastened on. This formed an insulating layer between the mount and the car hence the use of the copper braid and an earthing point. The ATAS120 aerial really does need good bonding to the vehicle.

mounted 1060x650
Painted and Mounted

So that the brackets look more aesthetically pleasing I painted them with some silver Hammerite paint which, fortuitously, both matches the car and just happened to be lying around in the garage on a shelf from a previous job. The SO239 mount was mounted on the bracket along with a short length of braided wire  (stripped from an old length of coax) to go under some penny washers for the mounting screw to give a good earth connection.

The original screws provided by VW are made from a softish material and are not very long. Exploring the Screwfix website I tracked down some hex socket set screws which were the correct length and made from stainless steel.

The complete bracket was then mounted on the car ready for the installation of the 4 band whip (covering 10m, 6m, 2m and 70cms) and a matching bracket was mounted on the near side ready for the HF aerial. Originally it was intended to be just a simple multiband whip but a lovely treat by the XYL has now seen it upgraded to the ATAS 120A.

car front 1060x650
car rear 1060x650 IMAG0204
The Mountings from the Front The Mountings from the Rear Quad band Antenna