Combiners...   Compiled by Mike Morris WA6ILQ   (callsign) /at/ repeater-builder /dot/ com

A Combiner is a system of cavities and optionally isolators (or cavities and optionally circulators paired with external loads) that allows multiple transmitters to share one transmitting antenna, but at a cost. Some combiner systems can cost you from 50% to 75% of your transmit power... i.e. that 100 watt repeater transmitter that gave you N miles radius coverage on a stand-alone antenna may only have the performace of a 50 watt or 25 watt system once the combiner is in line. Also don't forget that the antenna the combiner is feeding has a finite power limit. Some are rated at 200 watts, and by the time you combine 5 transmitters, each with 100 watts out, through a 3db loss combiner, that's still 250 watts that's going up the hose to the antenna, and (poof) goes the antenna (and the combiner needs dummy loads that can handle 250w continuous duty, and appropriate ventilation to get rid of the heat). Note that systems that use combiners usually have a separate receiving antenna that is multicoupled to each receiver.

Combiners are expensive not only in RF energy but also in money - a 2 port UHF combiner will set you back about US$4,600, a 4 port about US$8,400, an 8 port about US$16,000, and that's plus shipping. See http://www.telewave.com/pricelist/106-450combiners.html.

This web page split from the main page 12-Nov-2011.