NMO Connector question

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dave3825

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I have a few nmo mount antennas laying around and looking to get an inexpensive NMO Mag mount for my truck and my wife's suv. Has anyone ever tried one of these out? If so, how does it perform?

Im going to contact the seller and ask if that is an actual nmo on the mag base that would take the standard nmo antenna, or just that one. I have some of these antennas that mount to whats shown in the pic and does not look like it will work. Hate asking these ebay sellers cause many of them have no clue what they are even selling.

The connector on the mag looks like it has a hole in the center where as what I have does not
 

mmckenna

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The e-Bay photo isn't an NMO, it's a "UHF" SO-239 connector.

That alone would be a red flag against purchasing.

There are adapters that will convert an SO-239 connector to an NMO, but why? SO-239's were never designed to be a mobile antenna mount. They are not waterproof and I wouldn't trust them to hold a large antenna at highway speeds or a tree branch strike.

I'd get a proper NMO mount, you'll be happier, it'll work better and you shouldn't have to worry about it. I'd also stick with the name brand stuff. While you might save a few bucks going with some cheap knock off (that includes Tram/Browning) you'll likely pay for it in the long run. I've got vehicles at work that are 20+ years old still running original NMO mounts and antennas.
 

dave3825

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mmckenna

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No, I haven't used one of those, and here's why I wouldn't….

A 1/4 wave antenna is a reasonable size antenna for VHF and UHF, and they work well. When they start getting crammed into smaller and smaller packages, they lose a LOT of efficiency.
On UHF, 1/4 wave is about 6 inches, depending where you are in the band. Stuffing 6 inches of antenna into a 3 inch tall can isn't going to work well, but it'll likely be "good enough" for short range use.
On VHF, 1/4 wave is about 18-19 inches, depending where your are in the band. Now, imagine trying to jam 19 inches of antenna into a 3" tall space. It won't work well.

I know a few people that have tried name brand "low profile" antennas, and here's their experiences:
UHF: they work well enough. Not great performers, but a good trade off between size and performance. Like I said above, putting a UHF antenna into 3 inch tall can is doable, as long as you don't expect miracles.
VHF: Everyone, and I do mean -everyone- that I know who has used one of the "low profile" VHF antennas has hated it. I think a week was the longest anyone lasted with one of them. I've been offered several of them for free, because it was either that or they'd take up valuable room in the dumpster. Seriously. I don't know anyone that is happy with those antennas. They are -very- narrow banded, maybe you'd be able to get 1MHz of acceptable VSWR out of the antenna. The other drawback is that if you run much more than about 50 watts, they start to melt. Yes, melt. All that RF energy being put onto a small circuit board trace doesn't work well. Something has to give.
Where the VHF do work is if you are limited to only one or a few closely spaced frequencies, run low power, and only want to talk short distances. Then, they work, but will never work as well as a "real" antenna.

Basically what these antennas are is a circuit board with a bunch of traces on it that look like a 1/4 wave antenna on VHF and on UHF. The traces just run back and forth on the circuit board to make it fit into the small space.

While the advertising will claim a lot, I doubt it's true. I'd love to waste some money, but one, and put it on my analyzer to see how they look.

Seriously, unless you really have to have that specific antenna and don't expect much performance or range, you can easily do better. And for about the same price.

A 1/4 wave antenna is going to work very well. Even at VHF, it's going to be less than 19 inches tall. The whip material is thin enough that they barely show up. And, they are cheap. You can easily find VHF 1/4 wave NMO whips for $10 or less, even brand new ones from reputable companies.

…and what about UHF?
Well, a 3/4 wave UHF antenna is nearly identical in length to a 1/4 wave VHF antenna. In fact, I ran a 1/4 wave VHF (19 inches tall) NMO antenna on my old truck for years connected to a dual band radio. VSWR was low on 2 meters, like 1.3:1 across the band. VSWR on UHF was even lower. The trade off is that the radiation patter on UHF is a bit funky, but it still worked well enough for me. Primary use was on VHF.

You can get dual band whips for a bit more money. They'll work the same as a 1/4 wave on VHF and a co-linear on UHF. You can also get higher gain antennas that will work well.

Personally, even for 4 weeks of use a year, I'd go with either a 1/4 wave VHF antenna, or get a "real" dual band whip antenna. It'll work way better.

Antennas are ruled by the laws of physics, and no one, not even the cheap Chinese manufacturers, have a bottle of magic pixy dust that will allow them to cheat those laws.

I think you'd be disappointed with that antenna.
 

cmdrwill

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Here is one very good NMO mag mount. Note Industry standard NMO mount and NO plastic spacer.
 

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kayn1n32008

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Thank you, I knew it did not look right. My use for the mag would be only for family trips so it would not be on a vehicle more than 4 weeks a year. I emailed the seller asking for anything that backs it as being NMO. Cant wait for the response.

Since your here, have you ever used one like this?
HH-N2RS Dual Band Antenna MOTOROLA CAR Mobile Radio UHF VHF 400-470 136-174 NMO

The gain claims are out to lunch. There is no way in hell that antenna has 3dB gain on VHF. even if the gain numbers were printed backwards, there is no way in hell that antenna has 2.5dB gain, even if it is dBi, it is still out to lunch on VHF. On VHF it likely has a negitive gain, probably around -18dB or worse.
 

cmdrwill

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My dummy load has -9DB gain.......

And did you read the comments for that Ebay item, antenna? Seems my dummy load works just as well..
 
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dave3825

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Thank you for the detailed responses.

I have a few what I believe to be 1/4 wave nmo mount antennas. 1 for 162 173 and 1 for 800MHz. I am looking to be slightly discrete, and my wife said she does not wanting her suv looking like a geek mobile. We mostly travel in her car. I will look for a good quality mag mount. I will need a good nmo multiband antenna as when we travel, there are many bands in use. Here at home, I mostly listen to UHf t band and 700/800 MHz

As far as the low profile antennas, if they suck, why are L E agencies starting to use them? Starting to see them more and more.

Thanks again.


Lol here is the email I sent them with their reply.

Can you provide any information backing the claim that this antenna is an NMO mount? It sure looks like "UHF" SO-239 on the magnet.

Thanks
Dave

New message from: cyber24hour_us (26,055TurquoiseShooting Star)
Hi friend,

Thank you for your inquiry. I am so sorry that I know all information is same as the listing. The item you receive will be exactly the same with the pictures show. You can visit our website about detailed information. Glad to help you. If you have any questions, please feel free to contact me.
 

kayn1n32008

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As far as the low profile antennas, if they suck, why are L E agencies starting to use them? Starting to see them more and more.


While low profile antennas will not give the performance say a ham operator is looking for, they are usually more than adequate for an agency that only operates in its system designed coverage area.

For instance where I live, the system is designed to cover the city of Edmonton, and the city police only operate with in the city(usually) while they may have to leave the jurisdiction in the case of a criminal flight, it is usually ended before they run out of coverage of the radio system. They don't need high gain antennas when in the city to use the system.

There is no need to have super high gain antennas to use the system with in the city boundaries and low profile antennas are more than adequate for their needs.



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crazyboy

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While low profile antennas will not give the performance say a ham operator is looking for, they are usually more than adequate for an agency that only operates in its system designed coverage area.

For instance where I live, the system is designed to cover the city of Edmonton, and the city police only operate with in the city(usually) while they may have to leave the jurisdiction in the case of a criminal flight, it is usually ended before they run out of coverage of the radio system. They don't need high gain antennas when in the city to use the system.

There is no need to have super high gain antennas to use the system with in the city boundaries and low profile antennas are more than adequate for their needs.



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This plus a benefit being low profile antennas are less susceptible to damage, especially when it comes to car washes.
 

mmckenna

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As far as the low profile antennas, if they suck, why are L E agencies starting to use them? Starting to see them more and more.

On 800MHz, they work just about as well as a 1/4 wave. In fact, I'm using some at work on my system.
On UHF, they work not quite as well as a 1/4 wave, but good enough for most.

I'd be very surprised if you are seeing VHF model low profile antennas used for public safety. There are some multiband/LTE type antennas that look similar to the VHF low profiles, but they are not VHF.

And my statement stands. The VHF low profile antennas suck bad.

It's also an "add on" item when doing installs. Some dealer convinces the department that these "new" antennas are better. Agency falls for it, because after all, it's just taxpayers money, and there's an endless supply of that.
 

chief21

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As far as the low profile antennas, if they suck, why are L E agencies starting to use them? Starting to see them more and more.


What you're seeing on public safety vehicles are more than likely either 800 MHz or GPS antennas... probably not VHF. As agencies modernize their equipment or transition to larger, multi-agency radio systems (many of which are 800 MHz trunked systems), such systems often include the use of mobile data terminals and automatic vehicle location (AVL). These smaller antennas work well enough at those higher frequencies and also help to minimize the 'porcupine' appearance.

John
 

Golay

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Up in frequency

As far as the low profile antennas, if they suck, why are L E agencies starting to use them? Starting to see them more and more.

To go along with what Chief21 and McKenna are saying:
Low profile antennas work well at UHF and above. VHF don't work well at all. It's all about length and frequency. Like McKenna said, as the physical length of the antenna becomes a fraction of the quarter wave of the operating frequency, antenna efficiency goes down.
 

Rred

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Law enforcement agencies have their own criteria. They typically will be using repeater-based systems, so there is more power in the system and they can get away with less power in the vehicle. And they have a "business" case for a clandestine antenna. Many of us knew how to spot a cop car by the hub caps, by the extra antenna whips, even by the way the suspension rode and the tail lights moved at night. If they are looking to make a surprise visit someplace--there's the need for a less noticeable antenna.

A bit more important compromise (perhaps) than whether a spouse has geek avoidance syndrome in mind.

Of course, considering how expensive these stubby antennas are...Doubting Thomases and hands-on learners can easily buy one anyway, and see for themselves if it is of any use. Lunch money, not rent money.
 
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