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Repeater antenna

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WelshCymru

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Dec 30, 2012
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Tenby, UK
Can anyone recommend an antenna for a repeater setup on a duplexer?

Frequency is on the VHF 169.0000 / 174.0000 range.

Thanks,
HF20
 

WA0CBW

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Shawnee Kansas (Kansas City)
There are many antennas that would cover that range. A little more information might help us determine which one would be best for your application like gain, power, directional, omni, etc.
BB
 

n5ims

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There's nothing really special antenna wise for a repeater so anything that works well on the frequency of operation will work well. One caveat to that is that you may wish to have a high quality antenna on your repeater. Not because it will work better, but simply since the cost of installation and cost of any down-time will generally offset the additional cost of the antenna. Your site may require a commercial quality antenna be installed, which pretty much solidifies the need for the high quality antenna.

Many commercial sites as well as non-commercial repeaters use a multi-element folded-dipole such as this one https://www.tessco.com/products/displayProductInfo.do?sku=75660&eventPage=1. It will give you long life, good gain numbers, and satisfy any "commercial antenna" requirements. While the cost isn't cheap, if you factor in the replacement cost of cheaper antennas (plus the tower crew needed to do the replacement) you'll actually save money over the life of the antenna.

One thing you fail to mention is that is important on a repeater that uses a duplexer is you must use some good quality coax. At a minimum you should use something like LDF4-50A (https://www.tessco.com/products/displayProductInfo.do?sku=429150&eventPage=1) and get larger diameter variants for longer runs. You should especially avoid the LMR style coax. While it may look good due to the cost and low loss, it won't work in a full-duplex environment due to passive intermod distortion (they do make a special version of LMR coax with low PID, but it isn't easy to find and costs more than regular LMR coax).
 

12dbsinad

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There's nothing really special antenna wise for a repeater so anything that works well on the frequency of operation will work well. One caveat to that is that you may wish to have a high quality antenna on your repeater..
Actually, this isn't always the case. Remember, an antenna for a repeater application runs full duplex if using a duplexer. Which means you need to recieve thru the antenna while applying RF power at the same time. A really cheap antenna will not do the job. It will create so much noise from loose joints and solder connections etc, that you will want to scrap the project. You just can't throw " any ol' antenna" on a repeater, if you want it to work as it should. More details would be helpful.
 

SCPD

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DB224-B

These are hard to beat. They have various freq ranges available from Ham on up to 174. Their UHF version is equally as good. I've installed several.
For around $900.00 they better be. Talk about sticker shock but as the saying goes you get what you pay for. If your antenna will be in an area that is not easy to access or have a failure at the worst possible time, then by all means spend the money!.
 

n5ims

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Actually, this isn't always the case. Remember, an antenna for a repeater application runs full duplex if using a duplexer. Which means you need to recieve thru the antenna while applying RF power at the same time. A really cheap antenna will not do the job. It will create so much noise from loose joints and solder connections etc, that you will want to scrap the project. You just can't throw " any ol' antenna" on a repeater, if you want it to work as it should. More details would be helpful.
While this is true, the same thing can be said about the repeater itself. Ideally, you should use a good, commercial grade repeater, but folks are always posting about building a repeater using two low end radios, including two cheap Chinese handhelds. If you want a quality repeater, use quality components combined properly. If you want a junk repeater, use junk components. You'll end up with only as good as you put into it.
 

DisasterGuy

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Maryland Shore
What is your licensed ERP? Achieving your ERP is a combination of your antenna, feedline, duplexer and PA output. Many station PAs can become unstable when operating at less than 50-75% of full power so your required loss (or gain) has to come from the remaining components. I agree that the DB224 is hard to beat (and yeas $900 is pretty middle of the road when it comes to commercial antenna costs) but with 6/9dBd you may find yourself needing to induce additional loss to meet your licensed ERP.
 

jim202

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New Orleans region
The other issue that hasn't been mentioned here is the location this antenna will be installed at. The first question to ask is this antenna to be top mounted or side mounted on the tower? Reason for the question is for lightning. A top mounted antenna is subjected to direct hits. A side mounted antenna below the top of the tower is protected in most cases from a direct hit.

With a top mounted antenna, I would stay away from a fiberglass stick antenna. They have a tendency to blow open from a strike and the remains look like a pealed banana. Use of a folded metal dipole antenna construction tends to fair much better in this application.

Side mounted antennas are not at that great of a risk from a direct strike. The tower serves as a big lightning rod and takes the blow normally before lower antennas have any damage. This is not to say you wont take some damage from a streamer strike off of the main bolt hitting the top of the tower.

The next question is are you in a dry climate location? Do you have a high sand content in the air from blowing wind? If so, you need to consider an antenna that is directly grounded and not an open center element like a ground plane or coaxial vertical. These antennas are prone to wind, snow and sand static. They are not a DC grounded antenna. As a result they build up static and it's the antenna input of the radio that has to dissipate all that static buildup.

So the bottom line is pick your antenna carefully. Base it on what your license limit may be on the ERP authorized. As another poster mentioned, the ERP is the transmitter output plus the antenna gain, less the coax cable loss. There are some web sites that can calculate the ERP for you so you don't go crazy trying to use a hand calculator.
 

teufler

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ST PETERS, MISSOURI
I use a G7-144. There are models that go higher in frequency. Its been on a water tower for 8 years, subject to ice and high winds in thunderstorms and its still as straight and swr wise , as good as when it was put up. I am using lmr 600 cable. Could be better but didn't have the man power for hard line erection. Using GM-300 repeater with a RIK 1 controller. Pretty low cost but effective. Antenna should cost about $195.00 dollars US. Gain ,the book says 7dbd, our club has several located on remote sites and all have held up. After 20 yrs or so, they get weak at the joints and have failed at that point. Fiberglass, Phelps Dodge and others, yes they have had a lighting strike and what was left was not pretty. Those have been replaced by 4 bay dipoles.
 
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If your service of operation allows the erp, I'd top mount with a db224 or side mount with a station/channel master.

They can often be found for next to nothing on the surplus market if you look closely.


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DisasterGuy

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The remains of a fiberglass antenna post lightning strike. Note how it was blown apart and the peeled banana look at the base previously described. The rest was never found.



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