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Commercial Radio Antennas - Please keep discussion related to professional, commercially used antennas and antenna systems for the two-way radio industry. Topics for the use of these antennas on amateur bands are accepted here.

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Old 06-03-2018, 3:09 AM
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Default Laird WPD136M6C-001 Performance Woes

Just purchased this antenna and it arrived bright and early this morning.

I haven't had the chance to test SWR extensively yet, but it seems good in most places, and it is being used on an existing installation, that works great with other antennas.

This antenna has gotten a couple rave reviews here, and other places as well. I'm using it mainly for business band stuff, but with its broadband capabilities figured it would be nice to have 1 antenna for that plus ham frequencies as well.

After hooking it up this morning, this antenna is being SEVERELY outperformed everywhere by even the 1/4 wave whip that it was meant to replace. The performance difference is 2, sometimes 3 bars lower (XPR5550) on this antenna vs. the 1/4 wave.

Anybody have any clue as to what might be going on? It was brand new from Laird, not used or anything.

Any help would be greatly appreciated, since I'm just lost.
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Old 06-03-2018, 5:56 AM
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It's a unity gain antenna to begin with. Looking at the vague specifications, it doesn't really indicate what it's tuned for. I would not expect great performance for amateur radio or scanner use.
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Old 06-03-2018, 1:24 PM
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Originally Posted by iMONITOR View Post
It's a unity gain antenna to begin with.
So is the 1/4 wave, so I wouldn't really expect such a drastic decrease in performance. And actually, it's only unity gain on VHF. They claim 6 dBi on UHF and 700/800.
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Old 06-03-2018, 2:24 PM
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I'd check to make sure the center pin of the antenna is making contact with the NMO mount. Some antennas can have a longer skirt on the base and prevent the center pin from making contact.

I'd also look at strong out of band signals. Could be the multiband antenna is picking up strong signals from nearby and impacting the receiver.
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Old 06-03-2018, 6:37 PM
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I had one of these briefly and returned it. It had issues mating up with the NMO mount.
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Old 06-03-2018, 7:24 PM
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I've used one as a temporary replacement when and dual band fell apart. It had a flat VSWR across 2m and 70cm. I didn't notice any reduced receive.
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Old 06-03-2018, 8:31 PM
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Quote:
Originally Posted by mmckenna View Post
I'd check to make sure the center pin of the antenna is making contact with the NMO mount. Some antennas can have a longer skirt on the base and prevent the center pin from making contact.

I just bought a Laird 760-870 base loaded antenna. It's very high quality. The center pin in the NMO connector is gold plated, and has a strong spring loaded plunger to assure good contact. Maybe there are some cheap Chinese copies out there.

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Old 06-04-2018, 12:03 AM
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Thanks guys,

I'll give a new mount a try. I have a few mag mounts laying around. I can least use that to make sure they are mating properly.



Quote:
Originally Posted by iMONITOR View Post
I just bought a Laird 760-870 base loaded antenna. It's very high quality. The center pin in the NMO connector is gold plated, and has a strong spring loaded plunger to assure good contact. Maybe there are some cheap Chinese copies out there.
Mine is exactly the same. I bought it from Tessco, so unless Tessco started marketing cheap Chinese knockoffs as Laird products lately, it's legit. I see what mmckenna is saying. Even with the spring-loaded pin, the pin is not very long at all.

My measurements say that it "should" be mating up with my mount, but it's probably a game of millimeters.
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Old 06-04-2018, 12:35 AM
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Not sure what's in the base of those, but checking for contact with a multimeter would tell you a lot.

I've found this on a few other antennas, where low NMO mounts don't make contact with some antenna bases.
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Old 06-04-2018, 1:42 AM
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Quote:
Originally Posted by mmckenna View Post
Not sure what's in the base of those, but checking for contact with a multimeter would tell you a lot.

I've found this on a few other antennas, where low NMO mounts don't make contact with some antenna bases.
That's definitely what I'm leaning toward. I found 2 magnet mounts laying around (one is even a Laird mount, which you would think would work with the Laird antenna), but to be honest, they all appear to have the same size mount portion.

I'll give these other mounts a try later today and see what I can come up with.
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Old 06-04-2018, 6:22 AM
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Quote:
Originally Posted by alcahuete View Post
Mine is exactly the same. I bought it from Tessco, so unless Tessco started marketing cheap Chinese knockoffs as Laird products lately, it's legit. I see what mmckenna is saying. Even with the spring-loaded pin, the pin is not very long at all.
My measurements say that it "should" be mating up with my mount, but it's probably a game of millimeters.

You're is nothing like mine. According to the model number in your OP, this is what you have:





Laird Technologies - 136-174/380-520/760-870 MHz Antenna w/ Spring TESSCO SKU : 368700 Mfg Part #: WPD136M6C-001 Qty/UOM : 1 EACH UPC: 888063687006
https://www.tessco.com/products/disp....do?sku=368700


Usually these 'one does all' wide band antennas to not perform anywhere as good as one that is tuned for a particular band.
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Old 06-04-2018, 10:14 AM
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Quote:
Originally Posted by iMONITOR View Post
You're is nothing like mine.
I was referring to the spring loaded center pin. Yes, it is exactly the same in that regard.

Quote:
Usually these 'one does all' wide band antennas to not perform anywhere as good as one that is tuned for a particular band.
That is generally true. But at the same time Laird is not one of the companies that usually lies about their gain. While I'm not necessarily expecting 6dBi on that broad of an antenna (though they do state that figure), I definitely expect it to perform better than a unity gain 1/4 wave, or at the very least, the same level.

I don't have the RSSI numbers in front of me right now, but 3 bars on the 5550 is a HUGE difference in signal.
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Old 06-04-2018, 12:40 PM
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Quote:
Originally Posted by alcahuete View Post
I was referring to the spring loaded center pin. Yes, it is exactly the same in that regard.

That is generally true. But at the same time Laird is not one of the companies that usually lies about their gain. While I'm not necessarily expecting 6dBi on that broad of an antenna (though they do state that figure), I definitely expect it to perform better than a unity gain 1/4 wave, or at the very least, the same level.

I don't have the RSSI numbers in front of me right now, but 3 bars on the 5550 is a HUGE difference in signal.
The XPR5550 is not a wide band antenna. It is tuned to perform between 450-470 MHz and has a gain of 5.5 dB.

At that frequency the specs for your WPD136M6C-001 shows a gain of only 2.1 dBi. around that same frequency band of 450-470. Even the claimed gain in the 700/800 band is still only 6 dBi. dBi is not the same as dB.

If you're going for maximum performance on both the scanner and the ham radio, I'd recommend installing a second antenna. The one-does-all approach is always a compromise.
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Old 06-04-2018, 5:47 PM
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Quote:
Originally Posted by iMONITOR View Post
The XPR5550 is not a wide band antenna. It is tuned to perform between 450-470 MHz and has a gain of 5.5 dB.
I'm not going to lie...I have absolutely NO idea what you're talking about. The XPR5550 is a Motorola radio, not an antenna.


Quote:
Originally Posted by iMONITOR View Post
dBi is not the same as dB.
Yes...I'm well aware of that. That's why I clearly put dBi in every single one of my posts.


Quote:
Originally Posted by iMONITOR View Post
If you're going for maximum performance on both the scanner and the ham radio, I'd recommend installing a second antenna. The one-does-all approach is always a compromise.
Not once in any of my posts did I mention a scanner...anywhere.



In any event, mmckenna and others, it does appear that the mount is not high enough to make contact with the pin on the antenna. I used a magnet mount today that perhaps was very slightly longer on the NMO screw part, and I really tightened the antenna.

It does appear to be performing really well now. I haven't been able to test it completely yet, since I just put it on the new mount about 10 minutes ago, but so far I'm pretty impressed. In my limited testing, it does seem to be handily beating the 1/4 wave.

Mmckenna, I know you deal with this stuff a lot for work...is there any way to find out how long the mounts are without just spending the money and testing? My exiting NMO punched through the roof is actually a Laird mount...which apparently isn't long enough to work with this Laird antenna. Very convenient.

Thanks again for the help!
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Old 06-04-2018, 7:51 PM
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Quote:
Originally Posted by alcahuete View Post
I'm not going to lie...I have absolutely NO idea what you're talking about. The XPR5550 is a Motorola radio, not an antenna.

Yes...I'm well aware of that. That's why I clearly put dBi in every single one of my posts.

Not once in any of my posts did I mention a scanner...anywhere.

In any event, mmckenna and others, it does appear that the mount is not high enough to make contact with the pin on the antenna. I used a magnet mount today that perhaps was very slightly longer on the NMO screw part, and I really tightened the antenna.

It does appear to be performing really well now. I haven't been able to test it completely yet, since I just put it on the new mount about 10 minutes ago, but so far I'm pretty impressed. In my limited testing, it does seem to be handily beating the 1/4 wave.

Mmckenna, I know you deal with this stuff a lot for work...is there any way to find out how long the mounts are without just spending the money and testing? My exiting NMO punched through the roof is actually a Laird mount...which apparently isn't long enough to work with this Laird antenna. Very convenient.

Thanks again for the help!
Well it may be hard to believe I was trying to help. I guess I got confused along the way.

I'm not familiar with Motorola radio models. When I did a Google search on XPR5550, this antenna came up:
https://www.amazon.com/Motorola-450-.../dp/B00UO1ET9I

When I did a Google search on Laird Technologies - 136-174/380-520/760-870, I found this:
https://www.zipscanners.com/vehicle-...a-package.html

You should have stopped me at my first reply where I said: "I would not expect great performance for amateur radio or scanner use." Sorry I cluttered up your thread.
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Old 06-04-2018, 8:05 PM
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Quote:
Originally Posted by alcahuete View Post
Mmckenna, I know you deal with this stuff a lot for work...is there any way to find out how long the mounts are without just spending the money and testing? My exiting NMO punched through the roof is actually a Laird mount...which apparently isn't long enough to work with this Laird antenna. Very convenient.
I don't know, but it would be helpful if the manufacturers would settle on something. I've run across this before.
I've never had this issue with any Larsen antennas, which is why I usually stick with them.
Also, making sure the mount is designed for the thickness of the material is important.
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Old 06-04-2018, 8:06 PM
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You should have stopped me at my first reply where I said: "I would not expect great performance for amateur radio or scanner use." Sorry I cluttered up your thread.

You didn't clutter up the thread at all, and I know you were trying to help. I was just SO confused by some of the stuff you were saying. I was at work for most of these posts just posting super fast during some breaks, so sorry if I sounded short. I REALLY appreciate you trying to help. No ill-will intended at all. Thank you for replying!

It seems to be figured out for the most part, though I'm going to head out in the car a little later and do some more very non-scientific signal tests. SWR tests will be done tommorrow across various frequencies. I think the mount fixed it.

Now I just wish there was some way of telling whether or not various NMO mounts will work with this antenna. If I do decide to go with this antenna vs. the 1/4 wave, my current NMO mount is going to have to be replaced, and there doesn't seem to be a way to measure the length of the damn things, without just buying them and trying them out.
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Old 06-04-2018, 8:14 PM
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Quote:
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I don't know, but it would be helpful if the manufacturers would settle on something. I've run across this before.
I've never had this issue with any Larsen antennas, which is why I usually stick with them.
Also, making sure the mount is designed for the thickness of the material is important.
Thank you Sir! Yeah, I have a bunch of Larsen stuff too, in fact the majority of my antennas. Unfortunately, they didn't really have anything comparable to this one that I could find.

Oh well...guess it will just be trial and error.
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Old 06-04-2018, 8:23 PM
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I own and use the multi-band WPD136M6C-001 (https://www.theantennafarm.com/catal...36m6c-001-4286) on a regular basis with excellent results on all my scanners. I use it with this mag mount: NMO 5" Mag Mount | Scanner Master
For 800MHz I like the Laird B8065C: https://www.theantennafarm.com/catal...ies-b8065c-905
I have a wide range of mobile antenna's and the above are my favorites at this time.
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Old 06-04-2018, 8:23 PM
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Quote:
Originally Posted by alcahuete View Post
Thank you Sir! Yeah, I have a bunch of Larsen stuff too, in fact the majority of my antennas. Unfortunately, they didn't really have anything comparable to this one that I could find.

Oh well...guess it will just be trial and error.
Yeah, trial and error, unfortunately…

I'm probably going to need to spec out some of these multiband antennas for work in a year or two. I've avoided buying one for myself for a few years, but work is going to force me.
I may need to purchase a few different ones and give them a try. If I do, I'll try to remember to measure the base.
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