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I just bought a Diamond CP-5NMO hatch/lip mount and intend to put it on the hatchback lip of our 2018 Subaru Forester and, if it will fit, another one on our 2019 Kia Niro EV. I understand that hatch mounts typically present terrible ground planes - which makes sense - but that some types of antennas are more or less sensitive to this.

Question: What (amateur dual-band) antennas are a better or worse fit for this kind of installation?

My point of comparison is a dual-band 5/8 wave (Comet SBB-5) that I previously had roof mounted on my truck before an unfortunate incident involving a tree branch. I've installed this and, for what it's worth, it gets an SWR of ~1.3 on 146MHz.

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  • $\begingroup$ I have a lip mount base on my Crosstrek. I wanted to mount it on the top center of the hatch, but the antenna gets in the way. I wound up putting it part way down the side of the hatch. Definitely a compromise, but the only way I could do it. And even there if I open the hatch while parked under the open garage door, I have to push the whip out of the way so it doesn't get stuck in the cracks. The moral of the story: Many times physical restrictions outweigh RF performance. $\endgroup$
    – Duston
    Commented Oct 22, 2020 at 14:13
  • $\begingroup$ @Duston - I just got done installing the lip mount a half-dozen times and ended up in basically the same spot. I brought the cable forward by shoving it in various cracks around the seat, but the 5/8-wave antenna I have on there now has an SWR of 1.3 at 146MHz. I'd love to know (and maybe even get pictures of?) where you put the radio, the radio's controls, and how you brought power to it. $\endgroup$
    – William
    Commented Oct 22, 2020 at 20:28
  • $\begingroup$ There are two radios, the main one is an Icom IC-208H a Bendix-King EPH handheld. The main unit of the Icom and the amplifier for the BK are mounted to a strip of aluminum bar which fits over exposed bolt ends under the front passenger seat. The BK and the TinyTrak are just sitting on the floor. The remote cable for the 208H front panel goes under the carpet and up through the center arm rest (along with the power from the battery) up around and behind the storage cubby just in front of the gear shift. The coax is routed under the carpet and under the back seat to the back of the car. $\endgroup$
    – Duston
    Commented Oct 23, 2020 at 16:15

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Some (in fact quite a few) mobile antennas are effectively an "end-fed" design rather than a "ground-plane" design. One way to identify them is that they will generally have a noticeable transformer coil at the bottom (usually enclosed) to transform the impedance. If an antenna's description includes the words "ground-independent" or "radialless", or specifically mentions being suitable for pipe mount or luggage-rack mount, then there's a good chance it's this type. If the literature says it's a half-wave for 2m, then there's a good chance it's this type. If it has an element sticking straight out of the top of an NMO connector with no room for a coil, it's not that type.

There's a lot of misleading and confusing information out there when it comes to mobile antennas, both from manufacturers and from hams, so unfortunately the best solution is just to try it out, but at least hopefully you can find some likely suspects.

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  • $\begingroup$ I just discovered that Comet markets the SBB-5 that I have as ground independent, so it's accidentally a perfect choice for this install, it sounds like. Thanks! $\endgroup$
    – William
    Commented Oct 23, 2020 at 19:00
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    $\begingroup$ @William yeah, it should do :) $\endgroup$
    – hobbs - KC2G
    Commented Oct 23, 2020 at 19:56

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