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Repeater Bandwidth and Antenna gain


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#1 rareed63

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Posted 06 March 2019 - 09:36 AM

I'm getting ready to put a repeater on the air I have a Bridgecom I see that GMRS still uses wide bandwidth but also read its 20Khz as opposed to 25Khz? also on antenna gain, I've noticed a Midland GMRS bundle that sells a 10db gain antenna bundled with a 40 watt radio doesn't that yield an ERP of more than 50 watts?



#2 quarterwave

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Posted 06 March 2019 - 10:03 AM

Mains (462.550, 462.575...) are 25KHz spacing. Bandwidth is 20KHz (2.5kHz guard on either side). Just set it for Wideband and it will use 5KHz deviation and you'll be fine. 

 

ERP is not the concern, the FCC spec is a max of 50 watts at the connector, so any electrical gain in the antenna design is fine. I run a 1/4 wave (0 gain) on vehicle, but my repeater antenna is a ASP805 which is 10dB gain. My output is 50 watts, but my ERP is something like 300. Rule is 50 at the radio (or out of the Duplexor).

 

http://antennas.ca/calc_ERP.htm


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