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1-5 of 5 messages
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NMO at microwave bands
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by N7MSD on October 15, 2009
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I've been trying to find an answer for this by Googling and searching here in EHam, but keep coming up empty. Since there's no dedicated microwave forum, I guess this is the best place to post this (too many DC people in the MobileHam one).
Companies like MP/Niljon and others offering up antennas that work at the 13cm amateur/ISM bands and above yet using apparently standard NMO mounts. Now one look at that mount tells me it won't work in the microwave spectrum: maybe cell/SMR is as high as it will go, and that's pushing it. A few hits on literature said 1 GHz tops.
Larsen created a new mount they call NMOHF, which I've heard described (but haven't seen myself) as NMO with the center replaced with the inside of a N/TNC-style connector, thus dramatically raising the cutoff frequency and lowering the potential loss/SWR.
The trouble is that I don't see much info out there about people using this new mount, much less if anyone other than Larsen makes it.
So, for you microwave elmers that know way more than I do, what would be your opinion of these omni antennas that come with NMO? Or should I just make a point of sticking to using bulkhead-N mounts like the Japanese have done and seems to be gaining some adoption elsewhere as well?
For the record, I just bought a Comet SB-97 tribander which uses said N mount; I've owned a Diamond NR2000NA in the past that I was very happy with. Previous to that I owned an Austin Pentenna which didn't work very well even on lower bands. I've been thinking of the MP/Niljon Mobile Ultra as a do-everything antenna (cell phone, wardriving, every amateur band from VHF to H-microwave), but am very leery it only comes in NMO (the spec sheet doesn't say if it's the microwave version).
Also, if you have a better place I should post this question, please let me know.
Thanks, Mike
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RE: NMO at microwave bands
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by KZ1X on October 17, 2009
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There are indeed specially designed versions of the NMO idealized for north of 1 GHz - and I've used them before, if only to play with (they didn't make much difference to me). All the ones I tested with were from Austin Antennas (se below). Using some decent feedline and a network analyzer, you could see how they would work better. Dielectrics were machined Delrin, all the contact pieces were engineered metals/platings, and clearly paid attention to, and so forth. Dick isn't involved in the day-to-day there anymore so I don't know what's what these days since the company was sold, but it does seem they don't sell their specialty mounts the way they used to. Note that the mounts may still be available but most of the business there is for the FBI/CIA/NSA/BATF/Treasury these days. I too had a Austin Triune once and it wasn't my cup of tea but their 500C is a barn-burner for its size, and other accessories they make have been simply superb in execution. FWIW.
I see now that Radiall makes these north-of-1-GHz NMO mounts:
http://www.tessco.com/products/displayProductInfo.do?sku=436486
so there you go.
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RE: NMO at microwave bands
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by WB6BYU on October 17, 2009
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Larsen antennas also offer special high frequency NMO
mounts for their antennas:
http://www.larsen-antennas.com/mobile.shtml
They actually have a new mount type that can be converted
between low (< 1.7 GHz) or high (up to 6 GHz) quite easily.
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RE: NMO at microwave bands
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by KO1D on October 19, 2009
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I had an ID 1 in the car and used an NMO. The microwave guys I know all told me that was the wrong path. That there were N connectors you could use for mobile applications.
I'd toss this one to your local Microwave society and see what they say or drop W1GHZ a note at the league for some feedback.
GL ES 73
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RE: NMO at microwave bands
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by CLEARSIGNAL on October 27, 2009
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Hi Mike,
Every component in the RF pathway exiting the radio plays a role independently as well as in harmony with each other.
The coaxial cable is essentially a series of tuned L-C (inductance-capacitance) circuits with a resistance component.
Such is also the case with the NMO (e.g. roof) mount, the NMO portion above, and the antenna itself.
The higher frequency NMO lower portion mounts as you noted and such as from LAIRD tune better across microwave frequencies with a dummy load attached.
What’s important, yet often forgotten, is that the upper NMO component is also made for higher frequencies.
That said, all components interact such that the lower NMO part, upper NMO part, and antenna can actually tune together to give SWR and performance desired at higher frequencies even with some older style NMO’s.
Such becomes even more difficult and less optimal when attempting wide-band/UWB designs in this way.
MPantenna does produce antennas with VHF/UHF/SHF-Microwave UWB performance such as with the SUPER-M ULTRA Base Station and Mobile Antennas but even this company will use N and even SMA connectors for optimum performance for such as UWB cell-microwave specific designs (pending release).
Dr. Jack Nilsson, N8NDL
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