crisp@uncecs.edu (Russ Crisp) (01/30/91)
Hello. I'm interested in either building or buying a very low noise, high gain wide band preamplifier to use with my scanner. I have a Monitenna up about 40 feet, and I'm currently using a plain ole' tv booster with fair results. I'm interested in frequencies from around 30Mhz to around 512Mhz. If anyone has information on a source, or plans, for somthing like this I'd appreciate hearing from you. Thanks, Russ Crisp KA4UXZ CRISP@WCUVAX3.WCU.EDU
whit@milton.u.washington.edu (John Whitmore) (01/30/91)
In article <1991Jan29.185705.26404@uncecs.edu> crisp@uncecs.edu (Russ Crisp) writes: > >Hello. >I'm interested in either building or buying a very low noise, >high gain wide band preamplifier to use with my scanner. I have >a Monitenna up about 40 feet, and I'm currently using a plain ole' >tv booster with fair results. I'm interested in frequencies >from around 30Mhz to around 512Mhz. Avantek and Mini-circuits and Signetics all have VHF/UHF amplifiers with moderate gain and low noise at low cost, BUT you will want to limit the bandwidth on input to prevent front-end overload. The 60 Hz pickup on an antenna can easily be a few dozen volts, and that will saturate almost ANY amplifier you can name. That said, just use an IC integrated amp (these are typically four-pin pillbox package devices) or a good low-noise FET biased for 50 Ohm input impedance (U310 is recommended for this). If you use the FET, you'll get slightly better noise figure, but the output of the monolithics is 50 Ohms; the FET will require some matching. The capacitance of the FET is ignored if you use grounded-gate configuration, but can be part of your matching network in a grounded-source design (for highest gain). Posting your query on rec.ham-radio might be productive... John Whitmore