Basically, any vertical antenna needs a ground plane. For mobile VHF/UHF, there is often enought sheet metal to satisfy this, wherever you mount the antenna (as long as it is mounted properly!) For HF, there is pretty much never enough metal in the car to make a ground plane. The ground plane ends up being the ground under the car, and the car acts like a kind of capacitor between the antenna and the ground plane, so the more metal the better. Unfortunately, the way modern cars are built, all the metal parts aren't really connected together that well (as far as RF energy is concerned) so we have to help it out, by bonding the various metal parts of the car together. For my car this project was two straps between the hood and the front fenders, two straps across the trunk hinges, 1 strap on each of the 4 passenger doors, and a strap from the engine block to the frame. I also wanted to put straps on the exhaust, but I don't fit under this car like I did my last one! The exhaust straps will have to wait till I can borrow a jack and some jack stands from my buddy (or sneak my car onto the lift at his work - he's an auto mechanic).
Here are just a couple of the pictures of my bonding straps, and my fancy soldering method for putting these together. For soldering these I do a quick and dirty method. Since there is no insulation to worry about melting, I don't really to worry about getting the parts just a little too hot.....
- Getting the Bonding straps on the exhaust. The exhaust on cars can act like a giant antenna, and re-radiate noise. Bonding stops this. If I'm lucky, the noise I'm hearing is re-radiated from the exhaust, and will go away at that point.
- Playing around with my engine strap. The bonding strap on the engine is a bit longer than I would prefer, so there is a slight chance that it is causing more problems than it is solving. I might play around with taking it off, and/or finding a different place to put it so it can be much shorter.
- Finish the RF choke on my coax. When I installed the antenna, right where the antenna is mounted I put 6 turns of coax. I still need to add a ferrite bead or 2 in order to make this choke more effective at knocking down common mode currents, which can also cause some noise issues.
- A trip to HRO, or an online order to get a speaker (See my failed experiment post)
- A couple additional antenna toys that I plan to get and install (stay tuned for this)
- A CB radio & antenna install (because I spend a lot of time on the highway, a CB is still nice to have for talking to the truckers to find out whats up with weird traffic)
- "Phase 2" of the mobile install - plans to be revealed when I finish items 1, 2, and 3 above.
- The Home Shack - no actual physical progress here. My "home project" time has been used up on trying to button up the trim in the new master bedroom, and working on the new master bathroom (projects left over from the addition we did a while back.) Once those are done, my efforts will go back down to the concrete cube in my basement.