In theory a 5/8 wave will put a little more signal at the horizon over a 1/2 wave, but when mounting with questionable ground plane all bets are off.
Does this mount attach with only the 2 visible screws or is there some other metal to metal contact to extend the ground plane? I believe the cowl piece it mounts on is plastic and the two long screws would not transfer the ground plane of the bracket very much leaving the antenna mostly floating in mid air with just the bracket as the ground plane.
I'd usually carry a 1/4 wave for the steep terrain and 5/8 for the flatter desert.
You won't have any problems with the CoolTech.... it is very sturdy, you're not going to bend it.... and it functions flawlessly. Don't be scared.... !
I do not know.... but, I am using the Laird Technologies - B4505CNS - 450-470 Antenna w/Spring, No Ground Plane, NMO mount, with a Midland MXT575 (50 watt) GMRS, the CoolTech cowl mount, and I trimmed the coax to the proper length ---- and I am very happy with the performace.
I have the Cooltech mount and decided on it to see how it will fair. I did a lot of research before I purchased it, I am just not sure which of my radios I am going to connect to it.
The antenna shown looks like a Larsen NMO 2/70B, same thing I run in post #26 in this thread. According to factory specs this antenna requires a ground plane which would not be sufficiently supplied on this particular mount. However my hood mounted trunk lip mount with the underside of the plastic cowl pieces covered with conductive aluminum tape provides an adequate ground plane even at CB frequencies.With some or all of an antenna near vertical surfaces of metal, RF can tend to bounce right back at the antenna, causing impedance mismatch as well as indicate a high Standing Wave Ratio. For this reason, I am not fond of the cowl, fender-hood and even rear spare tire mounts for antennas. That said, they do work. Just not optimal locations that result in reduced range.
Of course, Wranglers and Gladiators don't have a metal roof where we can ideally mount an antenna dead center, to achieve an optimal omni-directional signal for reception and transmission. Even if we did have a metal roof or a roof rack ground strap-bonded to the JEEP's body, then our taller vehicle height lends itself to antenna damage with garage door openings and tree branches that the UPS truck hasn't taken care of yet. Even knowing the pros and cons of cowl & fender mounts or a mount between the rear door/window and spare wheel metal, most of us accept the compromise of these locations versus something that will work better but at some cost to custom make. Like say, a "Slot" antenna that pancakes t about 5 inches above a roof, including non-metal roofs but are a bit involved to design, make and particularly, optimize.
I did make my own cowl mounts a number of years ago to fit my JK Jeep. The primary mount is simply off the shelf, after market Mirror brackets. With the factory JK mirrors still inserted in the original door mounts, these extra mounts that bolt on the cowl bolts, allowed me to make step washer inserts out of aluminum for mouhnting and electrical conductivity with a 6 inch SO-239 feed thru. A little bit of hardware allows me to install an NMO mount antenna or an SO-239 based antenna.
The end result is aesthetically pleasing, super strong and works -- but even with the roughly 6 inches of outward extended location of the antenna vs windshield pillar, cowl and hood, it still has invisible RF signal bounce from these vertical surfaces. Which means the antennna performance is still compromised in this location. Just a bit less than the body attached, closer mounts being marketed today.
If my rugged mount achieved a better receive and especially transmitted signal over the close-in mounts, I would have looked into whether this met the requirements to process a Patent Application. Fun fact, since the antenna is closer to the metal parts of the door mirror, you can see the Standing Wave Ratio (SWR) vary slightly by swinging the door open, thus mirror metal/metalized parts affect the SWR. Since this mount is no more ideal than the close to hood or cowl sheet metal mounts offered commercially, I chose not to consider if my design could be Patented. However, if you would like to do this for your own JK to have heavy duty antenna mounts, then take a look at the attached pictures. 6 inch SO-239 feed thru, nuts, spacers, and SO-239 to NMO adapters to aseemble on the Step Spacer can be found through some Amateur Radio Suppliers.
Gene / K7TXO
Not sure about others, but, I can tell you that I found the Laird Technologies - B4505CNS much better reception and transmission than the Midland MXTA26 with the Cool Tech cowl mount, and the spring it has -- is basically required for 4wheeling.
