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Radioguy7268, I'm in Brooklyn very south and east, no buildings just houses, by the water... Very little rf interference. The only uhf rf 70cm is the nypd / fire / ems repeaters on a couple of telephone poles and vhf from Airplanes, Kennedy Airport and marine channels. People don't even have driveway door remotes.... Nearest cell tower is 1 mile. But lots of above the ground electrical wire on telephone poles.... We have about 3 gmrs repeaters and 5 ham 70cm repeaters. But Brooklyn is huge... We can fit 2 1/2 London's or Berlin and France together inside Brooklyn..The repeaters are all spaced far apart. It's not like Manhattan at all. We have a saying in Brooklyn - Keep Brooklyn low and local.... No tall buildings and no Wal-Mart. My antenna is 45ft high. which is 20 ft over my house. Only a couple of drive thru about 3 miles away that broadcast on .5 watts murs. Just mom and pop stores that most don't even take debit card..... I'm in the sticks of Jamaica Bay...I'm by a 25 square mile national park made up of wetlands sparse trees. I work in Manhattan and can hit my repeater 20 air miles from the 28 floor roof deck my friend is the super of...5 watt hand held.

Also to add: I see by the callsign that the OP is located in NYC, and I'll assume that the repeater is on the rooftop of a building in the NYC area. There's a ton of RF energy in and around NYC. A Notch style duplexer is designed to be decent protection against the repeater's own frequencies. An inexpensive Notch style duplexer is NOT good at high concentrations of RF - such as at a mountaintop repeater site, or at a downtown urban area with tons of transmitters and intermod. A duplexer should absolutely be tuned to a specific pair of frequencies. I'll avoid arguing over how some people try to cover the entire GMRS range with one single duplexer. If they're doing it, they're not doing it very well. Putting a UHF cavity filter on the receive side of the duplexer (between the high side duplexer connection and the actual receiver) would help to deaden down some of the RF noise that might otherwise overload the front end of the receiver. I would also avoid putting a pre-amp on a setup like this. You're probably just going to be amplifying noise - as much or more than your desired signal. I have bought (and tested) a few of the Chinese duplexers off eBay. The quality of equipment and tuning varies. Generally, you're getting what you pay for. The better units from China tested out as good as most compact notch style duplexers I've seen from Sinclair or Celwave. I would not recommend using a notch style duplexer at a High RF site location - as mentioned. If you can't afford the real deal Bandpass/Bandreject Duplexer, then try to get some tuned bandpass cavities/cans.

All duplexers require tuning; the range just says where the notch and/or pass frequency can be set within. The pass is tuned to your repeater's receive frequency (467.xxx), and the notch is tuned to the transmit frequency (462.xxx). The pass filter attenuates out-of-band signals; the notch attenuates the repeater's own transmission. Both characteristics are frequency-dependeny, and since the duplexer filters both the received signal and the repeater's transmitted signal, there's two different frequencies to take into account. I wouldn't run any receive preamp without bandpass cavities in front of it; it'd be very sensitive to desensitization and intermod otherwise.