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Author Topic: Antennas - Getting Creative  (Read 5704 times)

Posts: 378


« on: January 01, 2014, 12:38:29 AM »

Our repeater is located at 6,389 feet and uses a DB224e that is side-mounted 2 feet off of a Rohn 25. We had no choice and the tower space is free. But I mounted the antenna with all elements pointing out to my detriment. Although we enough excellent 270° coverage I lose the north where there is a growing ham community. We're about to go live (finally) with our 2nd MSF 5000 but it has me wondering about our current location. The 2nd location misses a key area and its antenna will also be side-mounted and missing key spots.

If I rotate the elements to omni on such a small tower face is it worth it to the extent of getting more coverage to the north? There is a mountain 100 feet taller than ground level and my 85 foot tower almost gets me over it. We tested from my driveway on simplex and a station in a fringe area could communicate using a Station Master on a 30 foot mast. This tells me that the repeater antenna just needs help.

Besides putting the elements into omni positioning I thought of using a low-loss power divider and putting a low 6dB gain yagi on the tower facing the northern area. Would it be worth it? As a true ECOMM repeater there is a major recreational area frequented by hams that we really want to put a signal into.

Thank you in advance and HAPPY NEW YEAR!!!

Posts: 21760

« Reply #1 on: January 03, 2014, 10:34:08 AM »

Hard to say if the addition of the yagi will help.

Using a power divider, the 6 dB gain yagi becomes a 3 dB gain yagi, and the DB224e loses 3 dB of its gain as well, since power dividers split power on both TX and RX.

Might be worth a try to see what happens, it's kind of unpredictable.

Posts: 680

« Reply #2 on: January 04, 2014, 03:46:07 PM »

and you potentially will get oddly shaped nulls where the relative phase of the signal from the Yagi happens to be 180 degrees out from the original omni and at just the wrong amplitude.

This kind of thing is hard to predict, maybe try it and see is the best approach.

There are clever designs for multiple omnis around a tower that minimize the nulls. Imagine 3 120 degree sector antennas one on each side of a triangular tower, the trick is in getting the relative phasing right.


Posts: 378


« Reply #3 on: January 04, 2014, 09:39:53 PM »

I changed the game. I signed a contract to put another repeater up on Quartzite (Sol. Calif.) that will entirely cover the high desert. It will be linked to Wild Oak Ridge repeater (So. Calif.) for nearly 360° coverage using Allstar with a RF link as a backup. Allstar will allow them to be voted/simulcast with an unvoted / unsimulcast RF link in case of a major disruption of the internet.

This is the best solution that I can come up with. We were trying to work with a vendor for the mountain that is blocking us without success. Too many changing agreements and no contract.

I thought that this might be a workable solution even if using a phasing harness.

Thank you all so much for your ideas.
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