Recommendations for Feeder Line, ECO-4, Shivley 6813

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Recommendations for Feeder Line, ECO-4, Shivley 6813

Post by abwdvm »

We are abandoning the 3 1/8 line on the old tower. I think our antenna is a Shivley 6813 4 bay?

Nitrogen ran out months ago.

We will see the condition of the antenna tomorrow.

So, provided we can reuse (new o-rings, etc) the Shivley 6813, what line is recommended. We have found a spool of AVA-7 50($4 per foot), but it does not require nitrogen. But i think I read where people where using AVA7-50, installing a Gas manifold and running Nitrogen for Antennas that need it. I guess the foam allows 7 psi of Nitrogen to crawl up the line?

So for this plan, we would need two 1 5/8 EIA to 1 5/8 connectors, and the gas manifold.

Am I way off here? Anyone have an opinion?
technician at an 1000w AM station in Texas
Nathaniel Steele
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Re: Recommendations for Feeder Line, ECO-4, Shivley 6813

Post by Nathaniel Steele »

Lets get all the details we need here.
ERP; (you said 3500W in another post right?)
Antenna gain:from shively's website a 4bay 6813 has a power gain of 2.14if full wave spaced or 1.32 if half wave spaced. So we need to Know for sure the spacing.
Length of transmission line: Distance from tX to tower, Distance up the Tower.
Any additional losses from Filters, etc.

Then someone can do calculations. But at a casual glance yes it looks like AVA7-50 should be fine, if your ECO 4 can make anywhere near full power you Should have plenty of headroom.

AS for nitrogen you have two options. The AVA7-50 has a hollow center conductor, with the right connectors (possibly this wasa modification, I've only read about it) You can send the nitrogen up the center. Or, you can run the nitrogen line all the way up the tower.

Third option, get a non pressurized antenna and forget about nitrogen/dehydrators forever.
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Re: Recommendations for Feeder Line, ECO-4, Shivley 6813

Post by TPT »

Should have read this thread before the one about the output power. As I mentioned in the feedline thread--read the rules first about changes to the transmission plant to see if you might need to get a cp first.

I would add to this discussion that we should figure out the numbers you need at the new site to determine some other questions. For one--how old is the Shively antenna? It may make sense to figure out the TPO (Transmitter Power Out) you would need for a smaller antenna (fewer bays)--and go new.

Is this an existing tower or a new build? Lots of potential pit falls here. I went through a move 5 years ago--bought the land beside the original site & built a new tower, getting off a tower owned by Clear Channel. Good move--tower was sold to Vertical Bridge 2 years later. Had lots of fun navigating the environmental rules, paying off Indian tribes, etc.
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