Impedance matching Antenna (radio)

-


maximum power transfer requires matching impedance of antenna system (as seen looking transmission line) complex conjugate of impedance of receiver or transmitter. in case of transmitter, however, desired matching impedance might not correspond dynamic output impedance of transmitter analyzed source impedance rather design value (typically 50 ohms) required efficient , safe operation of transmitting circuitry. intended impedance resistive transmitter (and receivers) may have additional adjustments cancel amount of reactance in order tweak match. when transmission line used in between antenna , transmitter (or receiver) 1 antenna system impedance resistive , near characteristic impedance of transmission line in order minimize standing wave ratio (swr) , increase in transmission line losses entails, in addition supplying match @ transmitter or receiver itself.


antenna tuning refers cancellation of reactance seen @ antenna terminals, leaving resistive impedance might or might not desired impedance (that of transmission line). although antenna may designed have purely resistive feedpoint impedance (such dipole 97% of half wavelength long) might not true @ frequency used at. in cases physical length of antenna can trimmed obtain pure resistance. on other hand, addition of series inductance or parallel capacitance can used cancel residual capacitative or inductive reactance, respectively.


in cases done in more extreme manner, not cancel small amount of residual reactance, resonate antenna resonance frequency quite different intended frequency of operation. instance, whip antenna can made shorter 1/4 wavelength long, practical reasons, , resonated using so-called loading coil. physically large inductor @ base of antenna has inductive reactance opposite of capacitative reactance such vertical antenna has @ desired operating frequency. result pure resistance seen @ feedpoint of loading coil; resistance lower desired match commercial coax.


so additional problem beyond canceling unwanted reactance of matching remaining resistive impedance characteristic impedance of transmission line. in principle can done transformer, turns ratio of transformer not adjustable. general matching network @ least 2 adjustments can made correct both components of impedance. matching networks using discrete inductors , capacitors have losses associated components, , have power restrictions when used transmitting. avoiding these difficulties, commercial antennas designed fixed matching elements or feeding strategies approximate match standard coax, such 50 or 75 ohms. antennas based on dipole (rather vertical antennas) may include balun between transmission line , antenna element, may integrated such matching network.


another extreme case of impedance matching occurs when using small loop antenna (usually, not always, receiving) @ relatively low frequency appears pure inductor. resonating such inductor capacitor @ frequency of operation not cancels reactance magnifies small radiation resistance of such loop. implemented in broadcast receivers, small ferrite loop antenna resonated capacitor varied along receiver tuning in order maintain resonance on broadcast band







Comments

Post a Comment

Popular posts from this blog

Life and work Ustad Mansur

-
tulip kashmir (c. 1610) mansur naqqash the year of mansur s birth unknown. name suffixed in miniatures naqqash, can refer artist, painter, or carver, indicating came family in artistic profession. single miniature showing babur meeting sister (folio 8, national museum) attributed mansur otherwise finds no mention in babur s memoirs (baburnama). associated other artists of period including basawan, miskina , nanha. during akbar s reign appears have been involved colourist in plates book of akbar (akbarnama) , name not mentioned abu l-fazl among list of artists. akbar followed principle artwork should include name of artist on margin. british museum s copy of akbarnama (1604) includes folios (35,110a,110b , 112a) name prefixed ustad (=master), indicating rise excellence. early works included parts of portraits , other scenes. earliest works made part of baburnama (1590–95) , of these assistant or colourist. veena-player (c. 1595) , coronation portrait of jahangir (c. 1605, made along
Read more

Kiev 35 mm cameras Kiev (brand)

-
kiev 4a rangefinder camera kiev 4 jupiter-8m lens , original camera case kiev produced several 35 mm film rangefinder cameras clones of pre-war contax ii , contax iii cameras, , range of 35mm slr cameras. after war had ended, soviet union demanded new sets of contax tools original toolmaker in dresden , ordered fair number of trial cameras made zeiss trademarks , coated lenses these 1946 in postwar east germany. successful, german instructors transferred kiev. missing specialists in few cases recruited in west germany. still available parts went in same direction. in fact, removing front of kiev ii cameras, 1 see metal stamped contax name, pressed out , re-stamped kiev. kiev 15 tee kiev 19 body kiev rangefinders retained same lens mount prewar contax rangefinders , lenses can interchanged. cameras went through few minor modifications become kiev iii , kiev 4. there kiev 5 modernized upper part integrated meter. attractive, though poorly made , unreliable, production terminated. other m
Read more

Types Stern

-
1 types 1.1 transom 1.2 elliptical 1.3 cruiser 1.4 others types transom 1. keel (light peach) 2. skeg (dark purple) 3. deadwood (olive drab) 4. stern post (forest green) 5. filling chock (bright yellow) 6. filling transoms (pale yellow-green) 7. wing transom (turquoise) 8. helm port (orange) 9. counter timbers (pale violet) 10. margin (indigo) 11. horn timber (green) 12. stern timbers (apricot) 13. side-counter timbers (pale yellow) 14. quarter-timbers (red) 15. fashion timber (fuchsia) 16. cant frames (blue) 17. square body frames (uncolored) in naval architecture, term transom has 2 meanings. first, transom can refer of individual beams run side-to-side or athwart hull @ point abaft fashion timber; second, transom can refer flat or curved surface panel of transom stern. in sense, transom stern product of use of series of transoms, , hence 2 terms have blended. the stern of classical sailing ship housed captain s quarters , became increasingly large , elaborate between 15th , 18th
Read more