Roof-racking VHF antennas on SUV

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Here are various pictures of the options opened by adding Thule roof racks to my Subaru Forester.

Flat

Most cars’ “curves” include their roof line. The Forester is no exception. The Thule crossbars also have a slight curve being higher in the middle. Still this is much flatter than the leisurely curves of the SUV. The result is this antenna platform does a good job of keeping the antennas pointing straight up. This isn’t a big deal for 1/4 wave monopoles, but good collinear antennas can be quite sensitive to angles.

What about grounding?

My original Diamond Antenna end-fed dual band antenna requires no ground and even insists it shouldn’t be grounded as tests confirm. Not so with the 6m Diamond Antenna HF6FX 1/4 wave monopole and the Diamond Antenna NR22L monster. These models require radials, ground plane or some equivalent to function correctly. Fortunately for VHF the two brackets are both electrically connected to the Thule crossbars via solid bolt connections. However, the Thule crossbars and clamps are not electrically connected to the Forester’s raised roof rails. Tests suggest the brackets plus crossbars provide sufficient “counterpoise” for VHF work although the 6m wavelength is a bit of a stretch. For HF, something will need modification to unify this elevated system of conductors to the vehicle body, but that’s a project for another time.

Conclusion

Hey it works. The bends in the 2m collinear bracket ensure the top of this monster antenna remain below the legal height limit… or at least very close to it. Some preliminary testing shows the tall collinear bests the shorter end-fed antenna by about 2 dB for most signals heard.

Double collinear vs. EFHW in mobile test
Double collinear vs. EFHW in mobile test

Is 2 dB worth 97 inches? It was for me for the Virginia QSO Party, but I’m not sure it’s a keeper for daily driving. We will see.

The big bracket atop Thule roof racks is plenty sturdy enough to host a “shorty” Scorpion screwdriver or equivalent. I just need to solve the ground connection problem first… plus a lot more I’m sure.

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