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Author Topic: Amateur Grade Antennas for Repeater Service  (Read 74388 times)
AF6D
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« on: March 18, 2015, 09:57:19 AM »

This goes completely against my wishes. But I need a dual band solution for a 2 meter and 440 repeater in a limited space insulation. It has been suggested that we use a comment GP 9 or a Diamond X 510 fed with 7/8 inch hardline into a high quality diplexer and then routed to the duplexers of the 2 meter and 440 repeaters. I know of a fixed repeater insulation that does is with exceptional performance and reliability. Our installation will be mobile using a trailer mounted hydraulic antenna mast at the scene of disasters.

with this said, which antenna would prove to be the most reliable?
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K4JJL
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« Reply #1 on: March 19, 2015, 07:56:47 AM »

Either of those should be fine in a temporary situation.  However, if it's mounted on a tall tower or at a high elevation, you're gonna have a bad time.  Those antennas don't survive wind for long.  The outside will be fine, but the inside will break from repeated stress of vibration.

https://farm5.staticflickr.com/4086/5018618600_e4eb9c3945_o.jpg

https://farm5.staticflickr.com/4148/5018617224_8e6773e1d5_o.jpg
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AF6D
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« Reply #2 on: March 19, 2015, 08:41:50 AM »

In addition to the Diamond and Comet I too use the Tram antennas. I can't tell the difference except their price.

The proposed site has a 200 foot tower that has limited space just as our budget is limited. Our thought was to side mount the GP-9 and use a stand-off at the middle and top. There is another ham on the same tower doing the same thing. He hasn't said how many times he has replaced the antenna. It is a desert site with very, very little rain and low winds -- most of the time.

With this said I live at 6,300 feet with a Hustler G7-144 30 feet above my house that has long been exposed to high winds and rime ice without detriment. I submit that in comparison an aluminum antenna doesn't compare to a Tram / Diamond / Comet. But then again I don't know of an aluminum dual band base antenna. In essence I agree with you.
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K4JJL
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« Reply #3 on: March 20, 2015, 07:20:45 AM »

You could go the 2-antenna route and use a diplexer.  My repeaters all have Andrew antennas.  DB-224 for V and DB-420 for U.
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AF6D
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« Reply #4 on: March 20, 2015, 07:44:10 AM »

Hey, thanks for the reply. The issue isn't a lack of antennas. It is a lack of tower space "due to current loading..." We also use the DB224 and love it. We need a one antenna solution to feed two repeaters and not two antennas to feed one radio. A diplexer can do that but ruggedness and reliability are a concern of a Tram / Diamond / Comet antenna. The repeater site is in the desert and seldom sees rain or snow. Wind does occur but even that is mild. When rain does occur it is pretty severe t-storms and I don't think we're gonna be able to do the one antenna approach.

Begging may follow...  Grin
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WB6BYU
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« Reply #5 on: March 20, 2015, 09:12:30 AM »

The problem with many amateur-grade antennas is the joints:  any stray resistance there causes a
voltage drop on transmit that causes noise on receive.  This becomes more of a problem with two
repeaters on a common antenna.  The result is that weak stations may be able to bring up the
repeater, but once the transmitter turns on the resulting noise generated in the antenna can cover
them up.  Commercial antennas for this purpose are typically welded to eliminate any potential
induced voltage across joints, and even when are often discarded when they become noisy even
though they are still quite adequate for simplex operation (where one doesn't need to receive
while transmitting.)

So I'd think the critical factor is the quality of the internal joints in the antenna rather than the
physical survivability of the antenna itself.  Any flexing due to wind will often make matters worse
as it stresses and loosens the joints.  You may need to open up the antenna and braze/weld the
joints in the sections to improve performance.
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AF6D
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« Reply #6 on: March 20, 2015, 09:17:47 AM »

So braze/weld the joints. Can do. We also said that we'd side-mount the antenna and use a stand-off in the middle and at the top. Not much flexing I'd think. But I was wrong yesterday, I think...
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WB8VLC
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« Reply #7 on: March 21, 2015, 09:31:43 AM »

As BYU  mentions the internal connections of the comet and diamond antennas are an issue.

 Several years ago at a low level location on a 35 foot building our club used a dual band diamond 2/440 antenna and after one week we were experiencing issues with a 3rd Fo of the repeater output at 146.88 MHZ being heard by another clubs input of a 445.65/-440.650 repeater.

The filters all checked fine, an isolator and a duplexer were swapped the antenna swapped with a same model replacement with no resolution.

Only when that style dual band  antenna was removed and replaced with a Phelps Dodge single band model did the 3rd Fo issue go away.

A club member discovered that simply shaking the antennas resulted in rattling internally and cutting the radome apart on the first one showed that most internal connections were questionable and some actually fractured.
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AF6D
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« Reply #8 on: March 21, 2015, 02:30:56 PM »

I understand and agree. I'd like to know how another repeater in the building has survived.
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K1ZJH
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« Reply #9 on: March 24, 2015, 11:16:28 AM »

I started playing with repeaters in the late 1960's. One thing I learned is that if the repeater is going to be located on a remote, mountain top location, and exposed to extreme weather conditions, Amateur Grade is not going to fly. The ONLY exception was when we used a few Isopoles as temporary replacements when a Stationmaster or other similar commercial antenna failed--and they did fail. Eventually we went over to exposed dipole arrays, and they have seemed to work the best for longevity and noise problems.  I gave up taking care of several club machines some time back, and put my own private machine on the air about 15 years ago. It is using a DB-224 mounted on a commercial site,  and has been running flawlessly, with no required site visits since it was installed. Your antenna and duplexers are the heart of the system. No place to cut corners, in my opinion.

Pete
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WR2I
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« Reply #10 on: April 01, 2015, 07:57:45 AM »

The Hustler fiberglass antennas like the G6-440 and G6-270 used coax cable elements, that were soldered. I did use them in temporary repeater application and encountered no problems. I have not used on in over 20 years, so you may want to contact them regarding construction of the current antennas they manufacturer. I had nothing but problems with Diamond, Comet type antennas. All of the previous comments regarding duplex noise and PIM issues I confirmed when tested. I would avoid using those antennas in repeater applications.

Marc
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ON7WP
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« Reply #11 on: April 06, 2015, 01:29:54 AM »

I used Diamond X-510 antennas on the Brussels repeater.  I had 5 of them...   

The antenna typically lasted for 3 months, then noise due to passive intermodulation killed all the weak signals.  Transmit performance of the antenna was outstanding however, and no external signs of degradation even at 100 m elevation.

When dismantling such an antenna after a year outside the top section was completely filled with water, while the two bottom parts were still dry.  The foam used to center the element causes the condensed water to be trapped due to lack of ventilation.

If you want to use X-510 for a low power repeater, OK.  With 1 watt no issues with passive intermod, but replace all the foam with plastic center spreaders.

Do not use the antenna for duplex with more than 10 watts.  The antenna is PIM-paradise.

I was able to find a NOS Jaybeam C5-2M of over 25 years old.  Almost the same gain and no intermod.

Kathrein (germany) and Procom (Danmark) sell nice monoband antennas.

There are currently NO gain dual band repeater antennas on the market, unfortunately....

Pedro M.J. WYNS
ON7WP-AA9HX-C5WP
repeater guru serving the Brussels, Antwerp, Averbode and Botrange multinamd repeater systems
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AF6D
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« Reply #12 on: April 06, 2015, 02:23:09 AM »

Your personal experience is invaluable. I discarded the thought of an amateur grade antenna some time ago. Your comments echo why. I am still curious how another 2m repeater on the same tower is using an amateur grade antenna with such success. I questioned it when I saw the diplexer.
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W8RED
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« Reply #13 on: May 13, 2015, 12:46:15 PM »

Not Cheap but if you need/want a real dual band antenna and built like a tank for repeater use:
Comprod F-3676
http://www.comprodcom.com/Products/Exposed%20Dipole%20Antennas/antennas-dual-antenna-array_16__34/

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N0XAX
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« Reply #14 on: June 08, 2015, 10:04:15 PM »

Spectral still makes the Isopole if you want to go with a two antenna solution? Very robust antenna! I have one here that is 20 years or older. Good antennas for a hostile enviroment.

www.isopole.com
« Last Edit: June 08, 2015, 10:06:31 PM by N0XAX » Logged
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