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Exposed dipole array reliability

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LakeMan2

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I am running a low power UHF repeater (MTR2000) for private use. Over the past 4-5 months the performance has been degrading in terms or receiving more noise and static even in fairly near by transmissions. I am pretty sure it is antenna. Although it could be a number of things in the transmission line which I will have to check.

Regardless, I am running a Comet GP-6NC and have had it up for a couple of years now. It is at the top of the tower, but it is only a 50' tower. We get a fair amount of wind in terms of frequency but not strong winds, but the antenna moves a fair amount.

I know the GP-6 is not a particularly good repeater antenna for a number of reasons and my performance degradation matches what I have read about these types of antenna over time.

I was strongly considering the move to a DB-408-B. I have read a lot of good things about them based on historical performance and robustness. The problem is I have now read how the new ones may not be quite as good as they used to be, as well as you apparently can't buy replacement phase harnesses etc.

My first question is has the reliability of the NEW DB-408's really sunk that low or are they still robust antenna? I like the omni coverage of the dual 4 dipole of the DB-408. I am in the south (little to no ice) and not near the coast. So an external harness is not the end of the world. But for what they cost I don't want to mess with the harness going bad in a year or two and then having to buy a whole new antenna. They are not exactly that cheap.

I looked at Sinclar. While I don't mind paying a decent price for a quality long term solution they are about 2x the DB-408, single 4 dipole with somewhat poorer coverage. They might be a bit more than I need given the fairly mild conditions of the location.

So if the DB-408 are not what they used to be, what would be an equivalent/good (in terms of performance) dipole manufacturer?

Thanks
 

brushfire21

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I have used a few Commscope DB-222A 2-element antennas with good success and I used good high quality zip-ties to secure the wiring harness to the mast. My last repeater project has an RFS 340-1 VHF 4-bay dipole with internal wiring harness. It's tall but it's a really nice antenna for the money in my opinion.

However I would suggest getting someone in with a service monitor and antenna analyzer to look the whole system over. It could be an issue with the antenna, cable, connector, duplexer etc. Would hate to see you spend a lot of money on an antenna and it turns out it was something else.
 

LakeMan2

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I have used a few Commscope DB-222A 2-element antennas with good success and I used good high quality zip-ties to secure the wiring harness to the mast. My last repeater project has an RFS 340-1 VHF 4-bay dipole with internal wiring harness. It's tall but it's a really nice antenna for the money in my opinion.

However I would suggest getting someone in with a service monitor and antenna analyzer to look the whole system over. It could be an issue with the antenna, cable, connector, duplexer etc. Would hate to see you spend a lot of money on an antenna and it turns out it was something else.
Thanks for the input. I have a service monitor and antenna analyzer so I will be looking things over before I do anything. I have always known that the Comet was not exactly a quality repeater antenna, but it is what I had at the time so I used it. It worked well enough initially but was always a little "noisy". I thought trying a exposed dipole might quiet things up some. The DB-408 was attractive because it had a good pattern, reasonable gain, and was fairly light at 17ibs. My antenna is at the top of a 10' mast on the tower, so weight is somewhat of a factor. The Sinclairs, and even your RFS looks lo be around 40lbs. I don't know that I need something quite that stout.

On the other hand I don't want to pay for a new DB-408 if the quality has gone down and the harness takes in water in a year or two. If that is the case, I might as well just buy the Comet every three years or so and live with that. I can buy a lot of Comets for the price of even a DB-408.

The antenna is on a small tower on our property so, while a pain, it is relatively easy to change out the antenna. I don't have to pay someone to climb a tower.

If the DB-408 were still good quality and I had a chance of getting 10 years out of it, I would likely go for it just to have a quality repeater antenna.
 

lmrtek

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If you are on TOP of a tower, then dipoles are the only way to go due to their strike survival compared to fiberglass antennas.

And the db408 is a very good antenna and I've used them on many repeaters over the years.

The static you hear is likely duplex noise due to bad connections either in the feedline connector or more likely the antenna.

Comet and diamond antennas are really not reliable in repeater service and won't last long in the severe service that's needed.

The ONLY low cost fiberglass antenna I use is the Hustler G6 -450 series.

They are true commercial grade REPEATER service antennas and I've had several In service now for more than 25 years without any issues.
 

gmt0000

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Apr 23, 2005
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The DB line is not what it once was for sure, but sill probably one of the better commercial antennas available. I was on a tower recently and noticed a DB-224 (VHF) side mounted on the tower with a date code of 4/77. It's still in service connected to a back-up system. It sweeps out good on the Anritsu Site Master. On the other hand, I have replaced 4 DB-224's in the last 5 years that had only been up 5-10 years. All of these had water intrusion in the harness where they join together. When installing new units, we go ahead and seal all of the potential "problem areas" with a liquid sealer prior to installation now. Time will tell if this works, but I would recommend if you go with an open dipole, you do the same.

Dale
 

brushfire21

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If your antenna is easy to get to and change, then that gives you options. But having swapped out several cheap antennas that people have used (Diamond, Comet or anything less then a $250 antenna in my opinion) and seeing the difference in coverage, build and longevity, I will never use one for a permanent repeater operation. Pay once, hurt once and smile all the way to bank when you don't have to touch it for a long time.

Even using the less expensive exposed dipoles and DYI cheap upgrades (extra water proofing of the phasing connection and zip tie holding the cabling to the mast) will be an excellent choice! The DB series antenna are not bad for the cost (low end of the exposed dipole options) but in my opinion are waaay better then any cheapy vertical on the market.
 

kayn1n32008

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I looked at Sinclar. While I don't mind paying a decent price for a quality long term solution they are about 2x the DB-408, single 4 dipole with somewhat poorer coverage. They might be a bit more than I need given the fairly mild conditions of the location.



So if the DB-408 are not what they used to be, what would be an equivalent/good (in terms of performance) dipole manufacturer?



Thanks

If you are looking for an antenna that is built better than a DB408, your options are limited.

Sinclair, Commprod and Bluewave are the only three companies I would recommend.

A Sinclair equivalent would be SD3352-HF1PASNM(D00B), the Sinclair antenna can be either a omni or bi-directional pattern. It is also a higher gain antenna than the DB408. The Sinclair also is a higher gain antenna (DB408- 8.7dBi vs. SD3352-8.5dBd)

IMHO, the Sinclair antenna is far superior in build quality, and the coax harness is also internal, not on the outside exposed to the elements. You may pay more for it, but you won't likely need to replace it. Unfortunately if you operate a repeater, you need a quality antenna, having said that Comet and Diamond are cheap for a reason. They are junk.



Sent from my iPad using Tapatalk
 

LakeMan2

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If you are looking for an antenna that is built better than a DB408, your options are limited.

Sinclair, Commprod and Bluewave are the only three companies I would recommend.

A Sinclair equivalent would be SD3352-HF1PASNM(D00B), the Sinclair antenna can be either a omni or bi-directional pattern. It is also a higher gain antenna than the DB408. The Sinclair also is a higher gain antenna (DB408- 8.7dBi vs. SD3352-8.5dBd)

IMHO, the Sinclair antenna is far superior in build quality, and the coax harness is also internal, not on the outside exposed to the elements. You may pay more for it, but you won't likely need to replace it. Unfortunately if you operate a repeater, you need a quality antenna, having said that Comet and Diamond are cheap for a reason. They are junk.
Thanks for pointing out the dBi vs dBd I missed that when I was looking at the specs. I looked at the Sinclair and it does look nice. No doubt the build quality and internal harness is better, and any additional gain is nice too. It is a tough call. I would have to get actual quotes, but looking online the DB-408 is around $1000 and the SD3352 around $2300 or more. The question I will have to decide on is if the difference in build/performance is enough to be worth the cost in my case. Given my use case (private, non-critical, fairly ease to replace, mild environment) the DB-408 build and external harness is probably fine, although the Sinclair would be better. The SD3352 ~2dB higher gain would always be nice too, but again is it worth it, that is always the question.

Anyways, with the info in this thread I feel I can make a more informed decision.

Thanks
 

kayn1n32008

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Thanks for pointing out the dBi vs dBd I missed that when I was looking at the specs. I looked at the Sinclair and it does look nice. No doubt the build quality and internal harness is better, and any additional gain is nice too. It is a tough call. I would have to get actual quotes, but looking online the DB-408 is around $1000 and the SD3352 around $2300 or more. The question I will have to decide on is if the difference in build/performance is enough to be worth the cost in my case. Given my use case (private, non-critical, fairly ease to replace, mild environment) the DB-408 build and external harness is probably fine, although the Sinclair would be better. The SD3352 ~2dB higher gain would always be nice too, but again is it worth it, that is always the question.



Anyways, with the info in this thread I feel I can make a more informed decision.



Thanks


To give you an idea, there are dozens of repeater sites in Alberta that used to support a commercial wide area network, this system was decommissioned somewhere around 20+ years ago. The network operated for 15 odd years.

An amateur radio organization I belong to has reused some of these antennas and feed lines on these sites and have had remarkable results.

One site in particular, (100m tower plus an extra 10-15m of 7/8" feedline into the shack) had a solid 80+ km radius of usable coverage with only 12w at the antenna port on the duplexer.

A 30+ year old antenna, with 30+ year old feed line. While the initial cost is significant, you will not be replacing the antenna.

Yes it is at least $1300 more, but it is not made of cheap, TV antenna grade thin aluminum. It is thick walled aluminum, designed to be deployed in the absolute worst environment, and just simply work. That is not something I would subject a DB408 to, between the materials and the external harness, as I just do not believe it would last.

The other nice feature of the Sinclair antenna is that it is VERY broadband, with low PIM. You do not need to tune the antenna, and could have ham gear anywhere between 420-450MHz, GMRS, and even T-band equipment with out issue. That is something the DB408 simply can not do this.
 
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