Receive antenna height for translator

FM does it with frequency!
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Receive antenna height for translator

Post by musiconradio.com » Wed Sep 28, 2016 1:50 pm

We are having some ducting issues receiving a primary for a translator. The antenna is currently indoors. We would like to put it on the tower. We are looking at at about 160 feet. The antenna is tuned to the receive the exact frequency (a Samco) and directional. Any tips to maximize reception. Thanks.

Lee_Wheeler
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Re: Receive antenna height for translator

Post by Lee_Wheeler » Wed Sep 28, 2016 4:54 pm

Without specifics it is difficult to give a good answer. The variables are distance, terrain, and interference from other stations. In general, you want to go at the lowest height that will reliably get the job done. More height, beyond what gets (more or less) line of sight, just results in more line loss and a higher probability of co or adjacent channel interference.

Just getting it out of the building may be enough to get the job done.

...Lee

w9wi
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Re: Receive antenna height for translator

Post by w9wi » Wed Sep 28, 2016 6:19 pm

If the problem truly is ducting then more height might *hurt*.

Is there a single interfering station responsible? What direction is it relative to the desired station? Is the Samco the same antenna you're already using?
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Doug Smith W9WI
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Re: Receive antenna height for translator

Post by musiconradio.com » Wed Sep 28, 2016 6:46 pm

No. We are currently using a outdoor TV antenna propped against a wall (go figure). The station interfering is west of us about 90 miles. It is a C1. We are a Class A.

We tried the Samco outside mounted at about 15 feet with no results. The primary is about 25 miles. So we looking at height to get line of sight.

w9wi
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Re: Receive antenna height for translator

Post by w9wi » Wed Sep 28, 2016 6:57 pm

What direction is the desired signal?

When there is no ducting, how is the signal from the desired station?
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Doug Smith W9WI
Pleasant View, TN EM66

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Re: Receive antenna height for translator

Post by musiconradio.com » Thu Sep 29, 2016 8:05 am

East. No issues on car radio, and comes in fair on the current unusual setup we now have. (TV antenna in concrete building).

w9wi
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Re: Receive antenna height for translator

Post by w9wi » Thu Sep 29, 2016 10:49 am

So it's exactly the opposite direction from the interfering signal.

I think I'd try... *lowering* the antenna... and putting it on the east side of the building. So the building (and the transmitter, and whatever other metal stuff is in there) is between the antenna and the interference.

When you say "no results" with the Samco, you do mean it works as well as the TV antenna but not any better, right?

I would try using the Samco (in that east-of-the-building location) and rotating it very slowly. Don't just point it at the desired signal. You might find a position where you lose a little bit of the desired signal -- and a LOT of the interference.
--
Doug Smith W9WI
Pleasant View, TN EM66

rich wood
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Re: Receive antenna height for translator

Post by rich wood » Fri Oct 14, 2016 2:15 pm

It sounds like you need an antenna with a better front to back ratio, so the gain is towards the front of the antenna. A Scala antenna may serve you well. See:
http://www.kathrein-scala.com/catalog/CL-FMRX.pdf

TPT
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Re: Receive antenna height for translator

Post by TPT » Fri Oct 14, 2016 5:59 pm

We used this with success for a translator. The station we were relaying was a class A with a low antenna site, some 38 miles away. There was a first adjacent, at about 100 degrees off the path from that station, only 31 miles away. Worked reasonably well.

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Re: Receive antenna height for translator

Post by musiconradio.com » Tue Nov 15, 2016 11:09 am

Thanks everyone for the information. Someone suggested lining the back of the wall where the antenna is sitting (opposite side of receive signal) with tin or metal to deflect the encroaching signal. Any ideas or thoughts on that theory.

TPT
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Re: Receive antenna height for translator

Post by TPT » Tue Nov 15, 2016 11:26 am

Hardware cloth (similar to window screen material but metal-folks use it to keep rabbits out of the garden).

Not that expensive but not sure it will work. We've used it to screen the back of a C-Band dish to block out a telco microwave site, but that's a lot higher in frequency!

W2XJ
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Re: Receive antenna height for translator

Post by W2XJ » Tue Nov 15, 2016 7:24 pm

A few points:

Under ideal conditions the undesired signal is within about 10 DB of the desired station in a theoretical world. Actually those levels fluctuate. This is not ducting but the typical variation in propagation found at FM frequencies.

160 feet is too high, that favors the path to the undesired station.

I would try a better antenna at about 30 feet. Wade antenna is the best for this kind of application.

http://wadeantenna.com/product/channel- ... dic-array/

They have extensive experience in designing custom offset arrays which puts deep nulls where you need them. A typical arrangement is 90 degree offset in the horizontal plane. That greatly enhances the front to back ratio. Other offsets move the deepest nulls elsewhere, depending on the direction of the interference. They can do a survey and develop the optimal pattern for your location.

I, too, am skeptical that screening the building will solve the problem but it is cheap enough to try.

I think, after looking at theoretical signal levels of the two stations, this could be a receiver issue as well. Since, as I mentioed previously, the desired and undesired signals are so close in level the receiver's capture ratio is critical. You want one with a capture ratio as close to zero as practical. Inovonics Aaron 650 is one. You can also look at Deva. There are demo possibilities so you might be able to try a receiver first without paying any money.

The distance from the desired station to the translator makes me suspect this might be a non-comm. If that is the case, investigate an alternate means of feeding it.

TPT
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Re: Receive antenna height for translator

Post by TPT » Wed Nov 16, 2016 11:53 am

We used a Sony HD tuner for a translator because of a spur at the stie on an adjacent channel. Worked well, where an Inovonics composite receiver was useless.

W2XJ
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Re: Receive antenna height for translator

Post by W2XJ » Wed Nov 16, 2016 3:49 pm

But which model?

PaulBWalkerJr
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Re: Receive antenna height for translator

Post by PaulBWalkerJr » Wed Nov 16, 2016 6:20 pm

W263CF 100.5 Meridian, MS picking up WLYB 96.3 Livingston, AL

I hear that translator gets out real well for 10 watts, about as well as a translator running 75 watts on the same tower

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