UHF base antenna with gain?

plectron25

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#1
I am experimenting with SDR, and also have a couple of Trunktracker series scanners monitoring area systems. Most of what I am interested in is between 453 and 508 Mhz. Reception distances are short- say a ten mile radius, minimal hills, lots of bandwidth competition in the area (central NJ). One APCO25 system (500-503 Mhz), one Motorola Type 2 Smartnet (506-508Mhz).

I am looking for a relatively subtle antenna for chimney mounting. Running through a splitter to the variety of receivers is going to take my signal down 7dB minimum, so I would like to put up an antenna with some gain. I plan to use LMR400 down from the roof.

Would the Tram 1486 Fiberglass 6.5db antenna make sense?
http://www.trambrowning.com/page-15.pdf

Other suggestions?

I am willing to pay up to $175 or so.

Thanks!
 
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#2
Should be fine

I've had one up for several years, I use it for GMRS and 70cm ham. Works great as far as I'm concerned,
no problems with 5 years or so of out outdoor use. Bear in mind, you will, if my memory serves,
need to trim the elements on the inside for your frequency range of choice.


Regards

JB
 
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#3
Tuning isn't as critical when you are receiving only.

If I was in your place, I'd take a look at one of the Diamond X- series antennas. They are dual band, VHF and UHF, so you could use it for receiving on the VHF band too.

If you ever decide to get your amateur radio license, which often happens when people get bitten by the "bug", you'll have a suitable antenna ready to go.
Diamond® Antenna ~ X50NA Dualband Base/Repeater Antenna
Diamond® Antenna ~ X200A Radiation Pattern

If possible, and when you have the option, choose the antenna with the N connector over the ones with the UHF connectors. The N connectors have a bit better performance, and are better sealed.
 
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#4
tuning

Given that the antenna can go as low as 406 or so, and op wants 453 up to 508mhz, tuning may not be critical,
but it might not be irrelevant either.

But the previous poster makes a good point about considering a dual bander. For example, I have also
a comet gp-15 which is a triband. Does well on lowband, vhf air, high band, and uhf.
 
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#5
If you use a splitter and would like to have a broad bandwidth from the antenna I would suggest to use an antenna amplifier inserted between coax and antenna. It would compensate for the splitter loss, as well as coax, and work as a buffer between the antenna and coax so that the impedance will be constant to the coax regardless of what the antenna have when you use it outside of its bandwidth.

My experiance is that antenna amplifiers are a big improvement when the antenna isn't perfectly matched, like it is for wideband scanner antennas or a tuned antenna used outside of its frequency range.

/Ubbe
 
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#6
I would not recommend Diamond amateur antennas for the OPs frequency range. These antennas are designed and tuned for roughly 440-450Mhz and to use them to 508MHz is operating 58MHz out of band, or many times their specified range.

When doing this the antenna will have far less gain if any and the radiation pattern can skew way above or below the horizon further degrading out of band operation. There are commercial antennas that have consistent performance across the entire range and they show up used for reasonable prices if you shop around.
prcguy
 
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#7
The dual band antennas all exhibit their gain in a very narrow band, centred on the ham bands - moving even 5MHz away reduces their efficiency below that of a dipole - so a properly designed antenna for the desired band is always a sensible move, even if expensive.
 

plectron25

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#8
I would not recommend Diamond amateur antennas for the OPs frequency range. These antennas are designed and tuned for roughly 440-450Mhz and to use them to 508MHz is operating 58MHz out of band, or many times their specified range.

When doing this the antenna will have far less gain if any and the radiation pattern can skew way above or below the horizon further degrading out of band operation. There are commercial antennas that have consistent performance across the entire range and they show up used for reasonable prices if you shop around.
prcguy
Can you suggest any specific models to look for that have wide band consistent performance? I have looked for performance plots for the various antennae I have looked at without much luck.
 
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#9
Before you decide on an antenna, how much signal do you have to work with at your location?

You said 10 mile radius, minimum hills. If the signal is strong, even having an off frequency antenna will work. If you need the antenna gain to overcome splitter losses, then that's a good point, but there are ways to address that.

While I like frequency specific antennas for what I do, a dual band antenna might be a good option if your needs ever steer towards amateur radio and budget gets in the way.
 

plectron25

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#10
To help me understand the options better: the recently installed local system (RR sid=4774) is a Project 25 Phase I trunked system. I am interested in being able to hear the fireground activity that used to be on point to point talkaround frequencies. Now that they have migrated to this trunked system how are these former talkaround communications typically handled? Do fire trucks have mobile repeaters to assure solid on-site communications?

Obviously there are many ways to provide this sort of short range communications. My antenna choice would be best if it is optimized for directly receiving these low powered transmissions if they presumably bypass the repeater.

If newer system designs route ALL communications through the trunking system then it should not be as difficult to receive.
 

plectron25

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#11
Tuning isn't as critical when you are receiving only.

...
If you ever decide to get your amateur radio license, which often happens when people get bitten by the "bug", you'll have a suitable antenna ready to go.
...

I have a valid FCC Technician license, but have yet to transmit in the Amateur bands during the 18 years I have had it, so I don't think I will be moving in that direction.

I built the attic mounted ground plane antenna I have used with my home scanner over 40 years ago out of aluminum #6 solid wire, a little ceramic insulator and some RG58 with assistance from my 1974 ARRL handbook. It has worked adequately from 47mhz up to 800 Mhz for decades, but now I think it is time to implement something a bit more appropriate.

And yes, I prefer N connectors- as long as someone else is attaching them. I plan to purchase pre-terminated cables.
 
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#13
I have several GP-9s both amateur and commercial and they are around 7dBd gain on UHF.
prcguy


It's not subtle but it's smokin hot. I love my Comet GP9. UHF lists almost 12db gain. I have LMR400 to. I can talk mobile about 40 miles vhf. Hear ambulances all over. Dual-Band | Comet Antenna I don't know what it will do at your frequencies but maybe you can google that.
 
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#14
I have a valid FCC Technician license, but have yet to transmit in the Amateur bands during the 18 years I have had it, so I don't think I will be moving in that direction.
Good plan.
Then I'd agree with the others, get a frequency specific antenna.

The specifics of the system that you want to listen to will need to come from someone with more knowledge of the system.
Unfortunately many fire departments will put their fire ground operations on a trunked system. That can be good for scanner listeners, but not always good for fire fighters.
Ideally, fire ground would be a simplex channel, in which case you'll need a good antenna to hear a few watt radio 10 miles out.
In fact, you might need more than a good antenna, you might need a bit of altitude. The height of your antenna will impact what you hear. If your antenna is down low on your chimney, you are likely going to have issues hearing simplex communications from far off.
 
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#15
...Most of what I am interested in is between 453 and 508 Mhz...

I am looking for a relatively subtle antenna for chimney mounting...

Other suggestions?...
Antenna Specialists used to manufacture (MANY years ago) a UHF GAIN ground-plane monitor antenna. The model number was the MONR20 (see attached picture below) and if you keep an eye out you can find them occasionally showing up on eBay or elsewhere. The MONR20 was terminated in an SO-239 connector which would mate with a PL-259.

You could accomplish the same thing today (and maybe even better with an N connector) by purchasing a 5 dB gain UHF mobile antenna (for the frequencies you want to monitor) with an NMO mounting base and mate it with an NMO ground-plane kit with an N connector. The Laird MBCN ground-plane kit ($29.95) would be a good choice: https://www.theantennafarm.com/catalog/laird-technologies-mbcn-7531.
 

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#17
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#19
You go me curious, so I looked it up.. It's quite a bit north of $1000.. The Sinclair 2015 Price catalog shows the antenna listing for $3670

Damn. You can probably source it for much less at retail. But it would be the last antenna you buy for a repeater. Heck, you would likely replace the repeater before the antenna. I have repeaters operating on 30+ year old Sinclair 310-C4 antennas with 30+ year old Alucel feed line and you would never know it. ROI is like a $122/yr. pretty cheap investment when you don’t have to replace a garbage antenna every couple of years due to water/wind/corrosion damage.

These were installed by old school techs working for telco’s. back when things were done right as a matter of keeping your job. NO short cuts.


Sent from my iPhone using Tapatalk
 
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#20
You go me curious, so I looked it up.. It's quite a bit north of $1000.. The Sinclair 2015 Price catalog shows the antenna listing for $3670
Current list price on Tessco is $3870.00. With an account, you can get it for $3028.96
Not unreasonable for a good base antenna.
 
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