Antennetuner

En antennetuner eller ATU (fra engelsk antenna tuning unit omtrent dansk "antennetilpasningsenhed") er en enhed, som kan kobles mellem en radiosender, radiotransceiver eller/og sjældnere radiomodtager - og transmissionslinjen, eller bedre mellem transmissionslinjen og radioantennen.

En antennetuner kaldes også: Antenna Matching Unit, Aerial Matching Unit (AMU), matchbox, transmatch, antenna coupler, Antenna Coupling Unit (ACU), Antenna System Tuning Unit (ASTU), Antenna System Correction & Tuning Unit (ASCTU).

Formål og placering

En antennetuners formål er impedanstilpasning af antennens impedans til radiosenderens ønskede belastningsmodstand. I langt de fleste tilfælde er transmissionslinjens karakteristiske impedans lig radiosenderens ønskede belastningsmodstand. Hvis antennetuneren sættes mellem radiosenderen og transmissionslinjen, vil mistilpasningen mellem transmissionslinjen og antennen skabe stående bølger i transmissionslinjen og resultatet er øget effekttab i denne og i radiosenderen. Derfor er det bedst at sætte antennetuneren mellem transmissionslinjen og antennen (udendørs).

Hvis transmissionslinjen var tabsfri og kan tåle de højere strømme og spændinger, ville det være lige meget hvor antennetuneren blev isat. Formålet med antennetuneren er, at forbedre tilpasningen mellem radio og transmissionslinjen og/eller radioantenne. Antennens virkningsgrad eller udstrålingsdiagram bliver ikke ændret (fx forbedret) af antennetuneren.^[1] Dog vil fraværet af en balun typisk kunne ændre udstrålingsdiagrammet til det værre. Men systemet bestående af radiosender, transmissionslinje og en utilpasset radioantenne, bliver forbedret af en antennetuner, da radiosenderens miljø kan blive optimal, hvilket betyder, at radiosenderen kan aflevere langt det meste af den ønskede sendeeffekt til radioantennen.

En kommunikationsradio og transmissionslinje har sædvanligvis en fast impedans (typisk 50 ohm), som gælder et stort spektre af frekvenser, men antenner har kun den bestemte ønskede impedans ved resonansfrekvensen og typisk helt andre impedanser ved andre frekvenser. En antennetuner kan omdanne impedansen sådan at kommunikationsradioen "oplever", at impedansen er rigtig for et større frekvensspektre, sådan at samme antenne kan benyttes for et større spektre af frekvenser. Antennetuneren skal typisk justeres hver gang frekvensen ændres noget.

Simpel bredbåndstilpasning

Radiofrekvens transformatorer og autotransformatorer bliver nogle gange indlejret i design af smalbåndsantennetunere og antennekabelforbindelser. Transformatorer har typisk kun lille effekt på en antennes eller en smalbåndssenders kredsløb, men de kan gøre at antennetuneren bedre kan tilpasse impedanser.

Baluner har typisk også kun lille effekt på antennens eller en smalbåndssenders kredsløb, men de kan gøre at antennetuneren kan omforme mellem balanceret og ubalanceret kabling når nødvendig. En balun (eller fraværet af denne) vil påvirke antennens virkningsgrad eller udstrålingsdiagram.

Antennetilpasningsmetoder, som anvender transformatorer, kan typisk dække flere oktaver af frekvenser. En kommerciel kortbølge balun kan fx dække 3,5–30 MHz - dvs næsten hele kortbølgebåndet.

Smalbåndstilpasning

"Smalbånd" metoderne beskrevet herefter favner kun et mindre frekvensinterval (for hver justering), i modsætning til bredbåndsmetoderne beskrevet ovenfor.

Tilpasning med L-netværk

Et elektrisk netværk bestående af input, output - og en serie reaktiv komponent mellem input og output - og en parallel reaktiv komponent over enten input og output - kaldes et "L"-netværk. De to reaktive komponenter udgøres af kondensatorer og spoler (to i alt). Dette kredsløb er vigtigt, da mange automatiske antennetunere anvender det.

Dette kaldes et "L"-netværk fordi de to reaktive komponenter former et "L" roteret og/eller spejlet.

Typer af L-netværk og deres brug

L-netværk kan have otte forskellige konfigurationer, seks af dem er vist her.

En generel regel (med nogle undtagelser) er at L-serieelementets enlige ende går til siden med den laveste impedans.^[2]^[3]^[4]^[5]

Denne generelle regel gælder kun for resistive belastninger, med kun lidt reaktans. I de tilfælde hvor belastningen er overvejende reaktiv, såsom en antenne tilført et signal med frekvenser langt fra enhver antenneresonans, kan en anden konfiguration være nødvendig.^[6]

Et (evt. roteret og/eller spejlet) L-LC-netværk (fire styk ialt) er det simpleste kredsløb, hvormed man kan tilpasse en belastning med reaktans og resistanstransformation. Desuden kan man analytisk beregne eller måle sig frem til den mest effektive L-LC-netværkskonfiguration. Derfor er et (evt. roteret og/eller spejlet) L-LC-netværk bedre egnet til automatiske (og manuelle) antennetunere, når anvendt med R (resistans), jX (fase eller reaktans) og G (ledningsevne) nul-visere.^[7]^[8]

En antennetuner baseret på L-LC-netværk er mest effektiv i langt de fleste tilfælde.^[9]

Tilpasning med transmissionslinje

En antennetuner kan udgøres af en serie (typisk balanceret) transmissionslinje længder mellem input og output - og en mængde firedobbelpolede omskiftere som skifter en given transmissionslinje længde ind eller ud af signalvejen. For en given signalfrekvens vil antennetuner kunne tilpasse en antennes impedans til fx 50 ohm. En separat balun anvendes til at omsætte fra fx 50 ohm ubalanceret - og 50 ohm balanceret.^[10]

Andre tilpasningsnetværk

Der findes mange andre (meget kendte) antennetuner tilpasningsnetværk som kan anvendes, men de fleste af dem har ikke analytiske eller entydige løsninger og er derfor ikke specielt egnet til automatiske antennetunere - og giver hermed mulighed for ineffektive (ikke-optimale) tilpasninger ved automatisk og manuel justering. Eksempler på andre tilpasningsnetværk: π-netværk, L-match, T-match, reciprok L-netværk, differentiel-T-match, "Ultimate"-Transmatch, SPC-Transmatch.^[11]

Som nævnt ovenfor er et (evt. roteret og/eller spejlet) L-LC-netværk bedre egnet til automatiske og manuelle antennetunere, når anvendt med R (resistans), jX (reaktans) og G (ledningsevne) nul-visere.^[8]

Avanceret engangsbredbåndstilpasning

Det kan lade sig gøre at måle en antennes impedans som funktion af frekvensen - og så designe en bredbåndsantennetuner som kobles til antennen. Dette system af antenne og bredbåndsantennetuner behøver ingen efterfølgende justering og systemet er hermed gjort bredbåndet.^[12]^[13] Via systemet kan man sende kanaler med stor båndbredde eller springe mellem mange frekvenser uden genjustering.

Kilder/referencer

^ Old Wives' Tales In Amateur Radio. Chapter I: "An Antenna Tuner Does Absolutely Nothing Except Make The Transmitter Happy." by Cecil Moore, www.W5DXP.com, Rev. 1.5, Jan 9, 2014 Citat: "... The maximum power transfer theorem was first used with DC circuits. Given a source and a load, the theorem says that: Maximum power transfer will occur if the source resistance is equal to the load resistance. This is probably the origin of the myth that, for maximum power transfer to occur, an antenna must present a purely resistive, e.g. 50 ohm impedance, i.e. must be resonant... It seems to this author that since a tuner has the SAME effect no matter where it is located in a lossless system, and since a tuner must therefore necessarily have at least SOME effect no matter where it is located in a low-loss system, that an old wives' tale has bit the dust. In a low-loss antenna system, an antenna tuner in the shack indeed does have an effect on the power radiated by the antenna at the antenna..."
^ Silver, H.L. (Ed.) (2011). The ARRL Handbook for Radio Communications, 88th ed. Newington, CT: American Radio Relay League.
^ engr.sjsu.edu: Impedance Matching and Matching Networks. Valentin Todorow, December, 2009
^ rfic.eecs.berkeley.edu: U.C. Berkeley, Prof. Ali M. Niknejad: Matching Networks Arkiveret 18. april 2017 hos Wayback Machine Citat: "...Consider the L-Matching networks, named due to the topology of the network. We shall see that one direction of the L-match boosts the load impedance (in series with load) whereas the other lowers the load impedance (in shunt with the load)..."
^ Tast eksempel input (Rsource) og output (Rload) ind og en frekvens på 1e7 (10MHz) - de kredsløb, som ikke understøtter impedans omsætning, skriver NaN (not a number); dvs ingen løsning: John Wetherell: Impedance Matching Network Designer. (Now with 16 networks!), backup
^ Smith, Philip H. (1969). Electronic applications of the Smith Chart, p. 121. Tucker, GA: Nobel Publishing. ISBN 1-884932-39-8
^ g3ynh.info: Impedance Matching. Part 1: Basic Principles. By David Knight G3YNH and Nigel Williams G3GFC Citat: "...The first point to note is that the target impedance, 50+j0 Ω, lies on the 50Ω constant resistance line. An initial impedance Z that does not lie on this line can always be brought on to it by moving it around a circle of constant conductance, i.e., by placing a reactance in parallel with it. An intermediate impedance that lies on this line can always be brought to 50+j0 by placing a reactance in series with it. Therefore impedance matching can always (in principle) be carried out in a two-step operation...If an initial impedance has a resistive component of less than 50Ω, it can always be manipulated onto the 20mS constant conductance circle by placing a reactance in series with it. An intermediate impedance that lies on the 20mS circle can then always be brought to 50+j0 by placing a reactance in parallel with it..."
^ ^a ^b g3ynh.info: Impedance Matching. Part 3: L-Network Solutions. By David Knight G3YNH Citat: "...The antenna (or arbitrary load) impedance matching problem can be solved (at least in principle) using only L-networks. Such networks naturally give rise to solutions that avoid excessive excursions in the Z-plane; which means that they are likely to be efficient in terms of power transfer. The L-network approach also involves only two variables for two unknowns. This means that it can be implemented in simple algorithms that are guaranteed to terminate; the termination criterion being obtained by using null-indicators for resistance [R], conductance [G] and phase (or reactance) [jX] [see 6.5]..."
^ 14 January 2022, practicalantennas.com: antenna tuner efficiency and ratings Citat: "...First, the Unique Wire Tuner (the green Xs on the plot) almost always had the lowest losses of the group. For one thing, it is uses an “L” network, which theoretically will be the lowest loss configuration. But it also is configurable: I used 3 different arrangements of the components in matching this antenna, and two of them were the reverse of how it was designed to be used (due to the low impedances to be matched). Usually I was able to make a good guess what configuration to use based on the measured impedance, but swapping cables when changing bands is not particularly convenient...so, which tuner am I going to use? For the moment, probably the Unique Wire Tuner, and I’ll see if there is another configuration that does better on 30m....", backup
^ w5dxp.com: W5DXP's No-Tuner, All-HF-Band, Horizontal, Center-Fed Antenna Citat: "...The Ladder-Line Length Selector actually does tune the antenna system so no conventional "antenna tuner" is needed - no coils and no capacitors. Switches or relays (remote control) can be used for the switching function and should be sized according to the RF power levels involved...As one can see, the feedline losses average around one dB and the tuner losses are too small to matter..."
^ g3ynh.info: Impedance Matching. Part 2: Popular Matching Networks. By David Knight G3YNH and Nigel Williams G3GFC Citat: "...In the following sections we show what happens in impedance space (i.e., in the Z-plane) when the various popular matching networks (antenna tuners) are adjusted...Many articles have appeared in the amateur radio press over the years alluding, without proper analysis, to the superiority of the π-match over other types of AMU, on account of its similarity to a low-pass filter...The foregoing hopefully illustrates the point that a π-match network should never be used without some kind of output indicator. Output level measurement moreover, will indicate maximum efficiency when the least possible amount of inductance is used consistent with keeping as far away as possible from the R=0 line...It should be stressed here, that the L-match is not a cut-down or restricted range version of the π-match. It is simply a better circuit, which is more difficult to mis-adjust, does not suffer from the unwanted residual capacitance of an unused capacitor, and is cheaper to build...T-match is a widely used network, favoured because it can match a given range of load impedances using smaller values of capacitance than are required for a π or L network. Detailed modelling of the circuit however shows that the price paid for using smaller components is a reduction in efficiency...The SPC transmatch remained the ARRL standard for many years after its introduction in 1981. The design was dropped by the 19th edition of the ARRL Antenna Book (2000) however, as a result of efficiency calculations...Ambiguity in the adjustment of an antenna tuner can be eliminated by the use of an RF measuring bridge giving null indications of R, jX, and G, provided that the matching network does not contain ganged matching elements...", backup
^ semanticscholar.org: Wideband Tuning of Impedance Matching Networks using Hierarchical Genetic Algorithms for Multistandard Mobile Communications, backup
^ Design of a Broadband Electrical Impedance Matching Network for Piezoelectric Ultrasound Transducers Based on a Genetic Algorithm, backup Citat: "...transducer. A key feature of the new method is that it can optimize both the topology of the matching network and perform optimization on the components..."

[1] Old Wives' Tales In Amateur Radio. Chapter I: "An Antenna Tuner Does Absolutely Nothing Except Make The Transmitter Happy." by Cecil Moore, www.W5DXP.com, Rev. 1.5, Jan 9, 2014 Citat: "... The maximum power transfer theorem was first used with DC circuits. Given a source and a load, the theorem says that: Maximum power transfer will occur if the source resistance is equal to the load resistance. This is probably the origin of the myth that, for maximum power transfer to occur, an antenna must present a purely resistive, e.g. 50 ohm impedance, i.e. must be resonant... It seems to this author that since a tuner has the SAME effect no matter where it is located in a lossless system, and since a tuner must therefore necessarily have at least SOME effect no matter where it is located in a low-loss system, that an old wives' tale has bit the dust. In a low-loss antenna system, an antenna tuner in the shack indeed does have an effect on the power radiated by the antenna at the antenna..."

[2] Silver, H.L. (Ed.) (2011). The ARRL Handbook for Radio Communications, 88th ed. Newington, CT: American Radio Relay League.

[3] r.sjsu.edu: Impedance Matching and Matching Networks. Valentin Todorow, December, 2009

[4] rfic.eecs.berkeley.edu: U.C. Berkeley, Prof. Ali M. Niknejad: Matching Networks Arkiveret 18. april 2017 hos Wayback Machine Citat: "...Consider the L-Matching networks, named due to the topology of the network. We shall see that one direction of the L-match boosts the load impedance (in series with load) whereas the other lowers the load impedance (in shunt with the load)..."

[5] Tast eksempel input (Rsource) og output (Rload) ind og en frekvens på 1e7 (10MHz) - de kredsløb, som ikke understøtter impedans omsætning, skriver NaN (not a number); dvs ingen løsning: John Wetherell: Impedance Matching Network Designer. (Now with 16 networks!), backup

[6] Smith, Philip H. (1969). Electronic applications of the Smith Chart, p. 121. Tucker, GA: Nobel Publishing. ISBN 1-884932-39-8

[7] 3ynh.info: Impedance Matching. Part 1: Basic Principles. By David Knight G3YNH and Nigel Williams G3GFC Citat: "...The first point to note is that the target impedance, 50+j0 Ω, lies on the 50Ω constant resistance line. An initial impedance Z that does not lie on this line can always be brought on to it by moving it around a circle of constant conductance, i.e., by placing a reactance in parallel with it. An intermediate impedance that lies on this line can always be brought to 50+j0 by placing a reactance in series with it. Therefore impedance matching can always (in principle) be carried out in a two-step operation...If an initial impedance has a resistive component of less than 50Ω, it can always be manipulated onto the 20mS constant conductance circle by placing a reactance in series with it. An intermediate impedance that lies on the 20mS circle can then always be brought to 50+j0 by placing a reactance in parallel with it..."

[g3ynh3-8] 3ynh.info: Impedance Matching. Part 3: L-Network Solutions. By David Knight G3YNH Citat: "...The antenna (or arbitrary load) impedance matching problem can be solved (at least in principle) using only L-networks. Such networks naturally give rise to solutions that avoid excessive excursions in the Z-plane; which means that they are likely to be efficient in terms of power transfer. The L-network approach also involves only two variables for two unknowns. This means that it can be implemented in simple algorithms that are guaranteed to terminate; the termination criterion being obtained by using null-indicators for resistance [R], conductance [G] and phase (or reactance) [jX] [see 6.5]..."

[9] 14 January 2022, practicalantennas.com: antenna tuner efficiency and ratings Citat: "...First, the Unique Wire Tuner (the green Xs on the plot) almost always had the lowest losses of the group. For one thing, it is uses an “L” network, which theoretically will be the lowest loss configuration. But it also is configurable: I used 3 different arrangements of the components in matching this antenna, and two of them were the reverse of how it was designed to be used (due to the low impedances to be matched). Usually I was able to make a good guess what configuration to use based on the measured impedance, but swapping cables when changing bands is not particularly convenient...so, which tuner am I going to use? For the moment, probably the Unique Wire Tuner, and I’ll see if there is another configuration that does better on 30m....", backup

[10] w5dxp.com: W5DXP's No-Tuner, All-HF-Band, Horizontal, Center-Fed Antenna Citat: "...The Ladder-Line Length Selector actually does tune the antenna system so no conventional "antenna tuner" is needed - no coils and no capacitors. Switches or relays (remote control) can be used for the switching function and should be sized according to the RF power levels involved...As one can see, the feedline losses average around one dB and the tuner losses are too small to matter..."

[g3ynh2-11] 3ynh.info: Impedance Matching. Part 2: Popular Matching Networks. By David Knight G3YNH and Nigel Williams G3GFC Citat: "...In the following sections we show what happens in impedance space (i.e., in the Z-plane) when the various popular matching networks (antenna tuners) are adjusted...Many articles have appeared in the amateur radio press over the years alluding, without proper analysis, to the superiority of the π-match over other types of AMU, on account of its similarity to a low-pass filter...The foregoing hopefully illustrates the point that a π-match network should never be used without some kind of output indicator. Output level measurement moreover, will indicate maximum efficiency when the least possible amount of inductance is used consistent with keeping as far away as possible from the R=0 line...It should be stressed here, that the L-match is not a cut-down or restricted range version of the π-match. It is simply a better circuit, which is more difficult to mis-adjust, does not suffer from the unwanted residual capacitance of an unused capacitor, and is cheaper to build...T-match is a widely used network, favoured because it can match a given range of load impedances using smaller values of capacitance than are required for a π or L network. Detailed modelling of the circuit however shows that the price paid for using smaller components is a reduction in efficiency...The SPC transmatch remained the ARRL standard for many years after its introduction in 1981. The design was dropped by the 19th edition of the ARRL Antenna Book (2000) however, as a result of efficiency calculations...Ambiguity in the adjustment of an antenna tuner can be eliminated by the use of an RF measuring bridge giving null indications of R, jX, and G, provided that the matching network does not contain ganged matching elements...", backup

[12] semanticscholar.org: Wideband Tuning of Impedance Matching Networks using Hierarchical Genetic Algorithms for Multistandard Mobile Communications, backup

[13] Design of a Broadband Electrical Impedance Matching Network for Piezoelectric Ultrasound Transducers Based on a Genetic Algorithm, backup Citat: "...transducer. A key feature of the new method is that it can optimize both the topology of the matching network and perform optimization on the components..."

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