View Full Version : Starting Work on a Big Vertical for 40/75

12-11-2015, 05:27 PM
I am working on a vertical that will be a full 1/4 wave on 40, which will also have a center load coil for use on 75. I am going to shunt the coil for use on 40, and add a capacity hat when used on 75.

The RV is a 36' 92 Nu-Wa Snowbird 5th wheel. This trailer is constructed of a fiberglass outer layer, with hard blueboard insulation and an inner plywood covering. SO... no metal in the body or on the roof.

My idea is to fabricate a custom antenna mount on the pinbox, where the HF antenna will mount. VHF and AM, etc. will go on the roof with an artificial groundplane.

I have lots of old scrap aluminum tubing of different lengths on hand to build with, thinking about using 2" tubing for the first 15 feet, with a 5" copper coil for loading, then a telescoping whip about 17' long from a salvaged CB 5/8 groundplane.

I am getting ready to assemble it and test away from the RV with radials to see how it plays! Of course, it will be huge and not meant for any kind of mobile ops. The coil is optimized for high Q, 5" in diameter and 5" long and about 33 uh, it should be close to correct...

Any other experimenters out there?

12-13-2015, 12:02 PM
With the vertical mounted on the pin box, I will deploy temporary radials in several directions from the pinbox to improve the counterpoise. Since there is no metal in the body or roof, I think the pin box will be an excellent place to mount the antenna. The frame should make a good counterpoise. When I don't want to unhook the tow rig, a couple large heavy grounding straps will attach to the truck to use it as well.

12-13-2015, 05:19 PM
Dale, are you joshin' us? Looks to me like you're actually building a moonshine still. :whistle:

12-13-2015, 11:23 PM
Now you're talking! How about a combination still/vertical antenna? Very low loss, very high Q, but very narrow bandwidth. I will be parked on nets mostly. Santa may be bringing me that antenna analyzer to fine tune with.

12-14-2015, 05:14 PM
So what did you use for a coil forming tool?

12-29-2015, 12:54 AM
So what did you use for a coil forming tool?

Yah... that thar is one purdy coil :-)