Theem modulator yog ib lub voj voog nyob rau hauv uas theem ntawm cov cab kuj yoj tswj los ntawm lub teeb liab modulating. Muaj ob hom sine yoj theem kev hloov pauv: ncaj qha theem kev hloov pauv thiab tsis ncaj theem hloov kho. Lub hauv paus ntsiab lus ntawm kev hloov kho theem ncaj qha yog siv cov teeb liab modulating ncaj qha hloov qhov tsis sib xws ntawm lub voj voog resonant, kom cov teeb liab nqa los ntawm lub voj resonant los tsim cov theem hloov thiab tsim cov theem hloov kho yoj; Lub indirect theem modulation txoj kev ua ntej modulates lub amplitude ntawm lub modulated yoj, thiab ces transforms lub amplitude hloov mus rau hauv lub theem hloov, thiaj li mus cuag cov theem modulation. Txoj kev no tau tsim los ntawm Armstrong hauv xyoo 1933, hu ua Armstrong modulation method
Lub tshuab hluav taws xob tswj microwave theem hloov hluav taws xob yog ob lub chaw nres nkoj siv los muab cov theem sib txawv ntawm cov zis thiab cov khoom siv hluav taws xob uas tuaj yeem tswj tau los ntawm lub teeb liab tswj (feem ntau yog DC bias voltage). Tus nqi ntawm cov theem hloov pauv tuaj yeem sib txawv tsis tu ncua nrog cov teeb liab tswj lossis ntawm tus nqi txiav txim ua ntej. Lawv hu ua analog phase shifters thiab digital phase shifters feem. Theem modulator yog binary theem hloov keying modulator nyob rau hauv microwave kev sib txuas lus system, uas siv nruam square nthwv dej los hloov cov teeb liab cov cab kuj. Sine yoj theem kev hloov pauv tuaj yeem muab faib ua theem ncaj qha kev hloov pauv thiab theem tsis ncaj qha kev hloov pauv. Los ntawm kev siv cov kev sib raug zoo uas sine yoj amplitude lub kaum sab xis yog ib feem ntawm instantaneous zaus, zaus modulated yoj yuav hloov mus rau theem modulated yoj (los yog vice versa). Feem ntau siv ncaj qha theem modulator Circuit Court yog varactor diode theem modulator. Lub indirect phase modulation circuit yog qhov nyuaj tshaj li qhov ncaj qha theem hloov hluav taws xob Circuit Court. Nws lub hauv paus ntsiab lus yog tias ib txoj hauv kev ntawm tus neeg nqa khoom teeb liab tau hloov pauv los ntawm 90 ° theem hloov pauv thiab nkag mus rau qhov sib npaug amplitude-modulator txhawm rau txhawm rau amplitude modulation ntawm tus cab kuj. Tom qab tsim nyog attenuation, lub teeb liab tau ntxiv rau lwm txoj hauv kev ntawm tus cab kuj kom tso tawm cov teeb liab amplitude-modulating. Qhov Circuit Court no yog tus cwj pwm los ntawm kev ruaj ntseg siab, tab sis lub sij hawm hloov tsis tuaj yeem loj dhau (feem ntau tsawg dua 15 °) lossis muaj kev cuam tshuam loj heev. Cov theem yooj yim modulator feem ntau yog siv hauv FM transmitters.
