Rochester VHF Group 12 December 2008 Preamps & Noise Figure Rochester VHF Group 12 December 2008

Preamps Most VHF/UHF receiving systems with nominal sensitivity can use some additional gain and improved noise figure. A Preamplifier if properly selected allows you to hear weak signals with improved Signal to Noise Ratio. A reasonable investment yields significant more DX at VHF/UHF Proper selection requires a “System Approach”… understanding total receiving system impact. Good Preamps are reasonably easy to homebrew. There are cost effective commercial solutions. Measurements are a little sophisticated, but expensive test equipment is not a necessity. 11/12/2018 Rochester VHF Group

Modern Preamps Bipolar Transistor Field Effect Transistor Dual Gate FET MOSFET – Metal Oxide Semiconductor FET MESFET – Metal Semiconductor FET HEMT High Electron Mobility Transistor (low resistivity, doped to achieve advanced results) PHEMT Pseudomorphic HEMT (small gate length FETs) 11/12/2018 Rochester VHF Group

Preamps 40’s Open Mixers, tubes, 15-25 dB NF 50’s Low noise tubes, nuvistors, first xstrs 3-6 dB NF 60’s Transistors, JFETs, Parametric Amps 2-3 dB NF 70’s Hot JFETs, Dual-Gate FETs, Bipolar Xstrs, MASERs 80’s GaAs FETs in TVRO industry 90’s Small gate length FETs, MMICs Today PHEMT, BJT, GaAs MMICs Future? 11/12/2018 Rochester VHF Group

Preamps Filtering/Z-Matching – Exclude unwanted signals to inconsequential levels (pre-selection filtering) and provide necessary impedance transformation Gain – Enough to determine system RX sensitivity (p/o overall amplification needed to detect signals and mask the effects of subsequent stages) Noise Figure – As low as can be obtained at good economy Linearity – Amplify without creating new spurious signals 11/12/2018 Rochester VHF Group

Effects of Filtering / Matching Improved rejection of unwanted signals – off channel Provide impedance transformation – matching input to output for best Gain or Noise performance (sometimes a controlled mis-match or “noise match”) Off-frequency complex impedances – maybe not unilaterally stable amplifier Filter elements don’t usually introduce additional IM but the net effect on the device is important to the amplifier performance Sharp filters may exclude wide band noise that the measuring instrument is including in calibration – adds uncertainty 11/12/2018 Rochester VHF Group

Typical Receive Chain 11/12/2018 Rochester VHF Group

Down East Preamp – 144 MHz 11/12/2018 Rochester VHF Group

Noise and Gain Noise is amplified along with the signal Both S + N eventually presented to the detector 11/12/2018 Rochester VHF Group

Noise Figure 11/12/2018 Rochester VHF Group

Thermal Noise Power Noise Power of a 3 dB NF preamp = 1.2E-17 Watts = -139.2 dBm 11/12/2018 Rochester VHF Group

Noise Figure vs Sensitivity 11/12/2018 Rochester VHF Group

Y-Factor NF Measurement 11/12/2018 Rochester VHF Group

Excess Noise Ratio 11/12/2018 Rochester VHF Group

Using a Noise Source 11/12/2018 Rochester VHF Group

Y-Factor 11/12/2018 Rochester VHF Group

Noise Figure Measurement 11/12/2018 Rochester VHF Group

Noise Figure Measurement 11/12/2018 Rochester VHF Group

Linearity 11/12/2018 Rochester VHF Group

Effects of Non-Linearity 11/12/2018 Rochester VHF Group

Intercept Point 11/12/2018 Rochester VHF Group

Intercept Point High IP3 and Low NF designs don’t usually coincide, but may overlap Best performance is lowest NF with acceptable IP3 1 dB Compression is typically easier to measure and shows trend 11/12/2018 Rochester VHF Group

Resources Other Interesting Resources To Know About: Noise Figure ; Microwaves 101 http://www.microwaves101.com/encyclopedia/noisefigure.cfm Principles of Semiconductor Devices – Bart Van Zeghbroeck http://ece-www.colorado.edu/~bart/book/contents.htm http://www.dxzone.com/catalog/Technical_Reference/Preamplifiers/ Tommy Henderson - wd5ago@hotmail.com http://www.g0mrf.freeserve.co.uk/432LNA.htm http://www.frenning.dk/OZ1PIF_HOMEPAGE/144_and_432MHz-LNA.htm 11/12/2018 Rochester VHF Group

Extras 11/12/2018 Rochester VHF Group

432 Multimode With No Preamp 11/12/2018 Rochester VHF Group

432 Multimode With Preamp in Shack 11/12/2018 Rochester VHF Group

432 Multimode With Preamp at Antenna 11/12/2018 Rochester VHF Group

Noise Figure History 11/12/2018 Rochester VHF Group

Commercial Preamps 11/12/2018 Rochester VHF Group

Commercial Preamps 11/12/2018 Rochester VHF Group

Down East Preamp 10 GHz 11/12/2018 Rochester VHF Group

DB6NT Preamp 432 MHz 11/12/2018 Rochester VHF Group

Homebrew Designs 11/12/2018 Rochester VHF Group

Homebrew Designs 11/12/2018 Rochester VHF Group

Homebrew Designs 11/12/2018 Rochester VHF Group

Homebrew Designs 11/12/2018 Rochester VHF Group

Homebrew Designs 11/12/2018 Rochester VHF Group

Example Source of GaAs FETS 11/12/2018 Rochester VHF Group

416B Triode 11/12/2018 Rochester VHF Group

Parametric Amplifier Uses a diode pumped with microwave power in a “negative resistance” region of it’s transfer curve to amplify signal energy. 11/12/2018 Rochester VHF Group