Hybrid transformer

<h2 id="motivation">Motivation</h2>
<p>The primary use of a <a href="/facts/Voiceband/XTQ6l9zo">voiceband</a> hybrid transformer is to convert between <a href="/facts/Two-wire_circuit/j0hbjBtD">2-wire</a> and <a href="/facts/Four-wire_circuit/C3InvEMe">4-wire</a> operation in sequential sections of a <a href="/facts/Information_transfer/cDXdYmhQ">communications</a> circuit, for example in a <a href="/facts/Four-wire_terminating_set/XvVzhwLX">four-wire terminating set</a>.  Such conversion was necessary when <a href="/facts/Repeater/JTkWvTEP">repeaters</a> were introduced in a 2-wire circuit, a frequent practice at early 20th century <a href="/facts/Telephony/2GwTTepw">telephony</a>.  Without hybrids, the output of one amplifier feeds directly into the input of the other, resulting in uncontrollable <a href="/facts/Feedback/XnuWH3zp">feedback oscillation</a> (upper diagram). By using hybrids, the outputs and inputs are isolated, resulting in correct 2-wire repeater operation. Late in the century, this practice became rare but hybrids continued in use in <a href="/facts/Line_card/0DvMWFhf">line cards</a>.
</p><h2 id="implementations">Implementations</h2>
<p>Hybrids are realized using <a href="/facts/Transformer/EYYfXWrF">transformers</a>. Two versions of transformer hybrids were used, the single transformer version providing unbalanced outputs with one end <a href="/facts/Ground_(electricity)/F6TEMIVv">grounded</a>, and the double transformer version providing <a href="/facts/Balanced_circuit/sMCd065d">balanced ports</a>. 
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<h3>Single transformer</h3>
<p>For use in <a href="/facts/Two-wire_circuit/j0hbjBtD">2-wire</a> <a href="/facts/Repeater/JTkWvTEP">repeaters</a>, the single transformer version suffices, since amplifiers in the repeaters have grounded inputs and outputs. X, Y, and Z share a <a href="/facts/Ground_(electricity)/F6TEMIVv">common ground</a>. As shown at left, signal into W, the 2-wire port, will appear at X and Z. But since Y is bridged from center of coil to center of X and Z, no signal appears. Signal into X will appear at W and Y. But signal at Z is the difference of what appears at Y and, through the transformer coil, at W, which is zero. Similar reasoning proves both pairs, W & Y, X & Z, are conjugates.
</p><h3>Double transformer</h3>

<p>When both the <a href="/facts/Two-wire_circuit/j0hbjBtD">2-wire</a> and the <a href="/facts/Four-wire_circuit/C3InvEMe">4-wire circuits</a> must be <a href="/facts/Balanced_circuit/sMCd065d">balanced</a>, double transformer hybrids are used, as shown at right. Signal into port W splits between X and Z, but due to reversed connection to the windings, cancel at port Y. Signal into port X goes to W and Y. But due to reversed connection to ports W and Y, Z gets no signal. Thus the pairs, W & Y, X & Z, are conjugates.
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<h2 id="applications">Applications</h2>
<p><a href="/facts/Telephone_hybrid/4goz8rw8">Telephone hybrids</a> are used in <a href="/facts/Telephone_exchange/PaRpGm8I">telephone exchanges</a> to convert the 4-wire appearance to the 2-wire <a href="/facts/Last_mile_(telecommunications)/8TkkKm8e">last mile</a> connection to the subscriber's <a href="/facts/Telephone/P7uEgWQX">telephone</a>.  A different kind of hybrid is used in telephone <a href="/facts/Handset/2qH0y5MT">handsets</a> to convert the four wires of the transmitter (earpiece) and receiver (microphone) to the 2-wire line connection.  This kind of hybrid is more commonly called an "induction coil" due to its derivation from high-voltage <a href="/facts/Induction_coil/vyAFgQsU">induction coils</a>.  It does not produce a high voltage, but like the high-voltage variety, it is a <a href="/facts/Step-up_transformer/EYYfXWrF">step-up transformer</a> in order to <a href="/facts/Impedance_matching/0mdy9TAp">impedance match</a> the low-impedance <a href="/facts/Carbon_microphone/tx24LyHA">carbon button transmitter</a> to the higher impedance parts of the system.  The simple induction coil later evolved into a form of hybrid as a <a href="/facts/Sidetone/tVnJaEVN">sidetone</a> reduction measure, or volume of microphone output that was fed back to the earpiece. Without this, the phone user's own voice would be louder in the earpiece than the other party's.<a class="footnote-ref" id="fnref:1" href="#fn:1"><sup>1</sup></a><a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a>  Today, the transformer version of the hybrid has been replaced by <a href="/facts/Power_dividers_and_directional_couplers/4LNPkdnN">resistor networks</a> and compact IC versions, which use <a href="/facts/Integrated_circuit/fjn6vg7C">integrated circuit</a> electronics to do the job of the hybrid coil.
</p><p>Radio-frequency hybrids are used to split radio signals, including television.  The splitter divides the <a href="/facts/Antenna_(radio)/pGlcXBvc">antenna</a> signal to feed multiple receivers.
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<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/Magic_tee/3NjnXVzg">Magic tee</a></li>
<li><a href="/facts/Rat-race_coupler/TnxaGISt">Rat-race coupler</a></li></ul>

<h2 id="external-links">External links</h2>
<ul><li>Douglas Rice (2008) <a href="http://www.dougrice.plus.com/dougnapTheory/index.htm">Modelling Telephony Hybrids as 2 × 2 Matrices</a></li></ul>

<p> This article incorporates <a href="/facts/Copyright_status_of_works_by_the_federal_government_of_the_United_States/Q1jvr96g">public domain material</a> from <a href="https://web.archive.org/web/20220122224547/https://www.its.bldrdoc.gov/fs-1037/fs-1037c.htm"><i>Federal Standard 1037C</i></a>. <a href="/facts/General_Services_Administration/Np3opv9x">General Services Administration</a>. Archived from <a href="https://www.its.bldrdoc.gov/fs-1037/fs-1037c.htm">the original</a> on 2022-01-22. (in support of <a href="/facts/MIL-STD-188/D5rsvdsW">MIL-STD-188</a>).
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<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>Joseph Carr, Steve Winder, Stephen Bigelow, Understanding Telephone Electronics, pp. 68-70, Newnes, 2001 ISBN 0080520030. <a href="/wiki/ISBN_(identifier)" target="_blank">/wiki/ISBN_(identifier)</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>Lewis Coe, The Telephone and Its Several Inventors: A History, pp. 124, 173, McFarland, 2006 ISBN 0786426098. <a href="/wiki/ISBN_(identifier)" target="_blank">/wiki/ISBN_(identifier)</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
</ol>

Hybrid transformer open-in-new

Hybrid transformer