RE: [Repeater-Builder] UHF Repeater Preamp

[Steve S. Bosshard \(NU5D\)]

Howdy Dino regarding the preamp and filter.   First thing that sticks out is sweeping the line.  This is a good figure of merit for an antenna system and cable.  The process involves running a sweep across the band and a graphical representation of VSWR across the band.  The unit of measure is called rho, or return loss, Measured in dB.  There is a direct relation between return loss and VSWR, where a 25 dB return loss represents a very low standing wave ratio, and ideal was 28 to 30 db on microwave antennas.   A good return loss or low standing wave is an indication of a good antenna and feedline, needed for good duplex operation.   Noise figure is a measure of the inherent noise generated in an amplifier, and the result of several stages in cascade.  Each stage contributes gain and noise.  A low noise high gain amplifier ahead of several noisy stages can dramatically improve the overall noise figure of a receiver, and is one of the benefits of a low noise preamp.   At UHF the most common filter would be either a cavity or else a helical resonator.  A good quality BpBr duplexer ahead of the preamp might be just AOK, or else an additional cavity ahead of the preamp might be needed if there is much receiver desense.   A lot depends on other transmitters at the same or near by locations, and lots of cut and try is needed.   Regards,   Steve NU5D   Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service.