On Fri, 26 Mar 2010, James Adkins wrote: > We are considering installing a 2-meter repeater, standard 600 kHz > spacing, with separate antennas for transmit and receive, looking at > phasing together 2 DB-228's for RX and 2 DB-228's for TX and using a > high-power transmitter, such as a Motorola Nucleus at 250-300w or > other high-power transmitter. Does anyone have a formula or know what > formula would need to be used to determine the amount of vertical > separation needed to provide the isolation required for such a duplex > operation? > We are wanting separate TX and RX antennas because of plans to have the > repeater on a > platform located 1200' in the air, and heliax runs are not practicable.
There's a chart on the repeater-builder website from GE's older information. http://www.repeater-builder.com/antenna/thoughts-on-isolation.html http://www.repeater-builder.com/antenna/separation.html In short, you're going to have a lot of coax in use already with a DB-2216. You should still have cans on the receiver side, as well as a notch can (rated for the power level) on the transmit side. You may be able to locate the appropriate notch-type can from paging company surplus. Typically they have 7/16" DIN connectors and are aperture coupled between cans. The receive side will need a notch cavity for the transmitter frequency, and some form of a bandpass filter to prevent other signals from causing front-end overload. Just one DB-228 at 500+ ft HAAT will cover out to 100 miles. There's a repeater 35 miles northeast of my apartment that I can work on an HT in my living room. I sit at about 900 ft AGL; the repeater is at 1300 ft AGL. I can work the machine from the laundromat as well -- at 750 ft AGL. I wish you much luck in this endeavor. It's a big project indeed. -- Kris Kirby, KE4AHR Disinformation Analyst
