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Thread: NMO to SMA mount - why the specific frequency rating?

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    Default NMO to SMA mount - why the specific frequency rating?

    Found an interesting note while planning out a new antenna rack for my vehicle. I came across this NMO to SMA mount which would work perfectly with what I've got in mind, but for whatever reason PCTEL specifies a minimum frequency that the mount can operate on. They say that the mount is only for use above 800MHz, which in my mind doesn't make any sense at all. Power ratings, loss, etc all go down as frequency increases so I can't figure out why they'd limit the lower end of a recommended frequency.

    I'm planning on getting three of these for three antennas, V/U/800, and mounting them across some L-channel aluminum mounted to the rear of my vehicle. I have a similar setup now that works spectacularly but it's getting worn and was more of a test than anything - surprised it's lasted this long. Anyway these looked great for my idea but that lower frequency spec has me thrown off. I'm assuming it's just arbitrary and there's no real reason it can't be used for V/U, but I wanted to get a sanity check from the membership on here just in case something screwy was afoot.


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    The mistake is at Tessco. The OEM website says the MMF series works from 0-6ghz.
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    I have seen band ratings on some older NMO where the center connector head was a larger "circle". These mounts did not work well on 800mhz/900Mhz bands. The issue was that at those freq the capacitance started to change due to the larger relative surface areas between the center tab and the underlying ground plane of the NMO mount style. The solution was to reduce the mount head to a smaller diameter reducing the effect to a negligible level.

    large
    NMO large.jpg

    small
    NMO small.jpg

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    I still have a box of new mounts that have a removable disc that changed the diameter from the large type to the small one.
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