Antenna spacing adding a second repeater

[emtprt]

We are in the process of adding a 150 watt analog 858.xxxx repeater with a 5dBi omni antenna to our radio system on an 85 foot tower. The 85 foot Rohn tower currently has 3 UHF antennas and a VHF antenna. The problem we are trying to avoid is interference with the 100 watt analog 852.xxxx repeater at the same site. The 100 watt 852.xxxx repeater has a sector antenna (unknown gain) mounted at 65 feet pointing Southwest.

We also have the option of mounting the antenna to a 50 foot monopole which is 40feet NNW of the tower or on a roof top tripod with a mast behind the Rohn tower (on the backside of the sector antenna).

I have researched the topic and have found conflicting information from a variety of sources. The mounting of the antenna on the backside of the tower above the sector antenna was advised by 1 vendor and another suggested the rooftop tripod behind and below the sector antenna.

If anyone could point me in the right direction I would be greatful.

Mark

[Jim202]

We are in the process of adding a 150 watt analog 858.xxxx repeater with a 5dBi omni antenna to our radio system on an 85 foot tower. The 85 foot Rohn tower currently has 3 UHF antennas and a VHF antenna. The problem we are trying to avoid is interference with the 100 watt analog 852.xxxx repeater at the same site. The 100 watt 852.xxxx repeater has a sector antenna (unknown gain) mounted at 65 feet pointing Southwest.

We also have the option of mounting the antenna to a 50 foot monopole which is 40feet NNW of the tower or on a roof top tripod with a mast behind the Rohn tower (on the backside of the sector antenna).

I have researched the topic and have found conflicting information from a variety of sources. The mounting of the antenna on the backside of the tower above the sector antenna was advised by 1 vendor and another suggested the rooftop tripod behind and below the sector antenna.

If anyone could point me in the right direction I would be greatful.

Mark

Welcome to the world of site planning. The big point to remember is the more money you have the easier your task is. The best way to do this is to combine both systems into one antenna system. To do that will require a combiner system to be installed. That is where the cost comes in.

What you haven't told us is what type or kind of duplexors are being used on both of the 800 repeaters. It will make a difference because of the rejection on the receive side of both of the repeaters. The intent here is to limit the TX power from getting to both of the receiver radio ports. This may or may not be a simple matter of placement of the antennas. With the wrong duplexors, it may not make a difference where the 2 antennas are. It may require adding a pass and notch filter to each of the receiver sides of the existing duplexors.

You need to do some more homework before anyone is going to give you some solid technical advice on this one.

Jim

[Bill_G]

You should run an intermod study to see if any of the freqs of interest will cause problems no matter where you place the antenna. There is a recent thread here discussing the interactions of 800 and UHF.

http://www3.telus.net/PassiveRF/

[emtprt]

The new repeater needs an omni-directional antenna for wide area coverage and has a 4 cavity pass-reject duplexer. This will be the only transmitter for the system.
The repeater that is already at the site has a sector antenna that covers a specific area of town and has gps timing with a comparitor for simulcasting. I am not sure what type of a duplexer is in the cabinet.

A combiner is financially out of the question due to budget restrictions and cuts.

[Will]

A separate omni antenna and feed line. 3 or 4 feet above the panel/sector antenna.

[emtprt]

Will give it a shot

Thanks