)
HZWKLQJVDUHPRUHLUULWDWLQJWRPH
WKDQ OLVWHQLQJ WR DQ DQDORJ UH
SHDWHUZLWKORZGHYLDWLRQDQGORZ
DXGLREDQGZLGWK LW¶VMXVWJUDWLQJRQWKH
HDUVDOOPLGUDQJHDQGQRILGHOLW\/RZ
GHYLDWLRQDOVRPDNHV\RXFRQVWDQWO\
DGMXVW\RXUUDGLR¶VYROXPHIRUGLIIHUHQW
XVHUV7KLVDUWLFOHGHVFULEHVDUHSHDWHU
DXGLR DFFHVVRU\ WKDW DOORZV \RX WR
LQFUHDVHWKHEDQGZLGWKRIDQDQDORJ)0
UHSHDWHUWR+]ZKLOHDGGLQJDQ
H[WUDOD\HURISURWHFWLRQDJDLQVWRYHU
GHYLDWLRQ,WDOVRHOLPLQDWHVDQ\UHVLG
XDO&7&66 3/ WRQHV
7KHGXDOILOWHUIHDWXUHVDSROHORZ
SDVV ILOWHU VHW WR +] VWURQJO\
DWWHQXDWLQJDXGLRDERYH+]7KH
VORSHRIWKHILOWHULVVXFKWKDWLWSURYLGHV
DQDGGLWLRQDOG%RIUHMHFWLRQDW
+]WKH)&&DOORZDEOHOLPLWIRUQDUURZ
EDQG)0GHYLDWLRQ7KH+]IUH
TXHQF\ ZLOO JLYH UHSHDWHU RSHUDWRUV
URRPWRDGMXVWWKHGHYLDWLRQVRPHZKDW
KLJKHUDVZHOODVLQFUHDVHWKHDXGLR
TXDOLW\RIWKHUHSHDWHU
7KHVHFRQGILOWHULVDSROHKLJKSDVV
ILOWHUVHWWR+]7KLVILOWHUUHPRYHV
DQ\UHVLGXDO&7&66WRQHVWKDWPD\EH
SUHVHQWLQWKHVLJQDO7KHSROHILOWHU
ZLOOUHGXFHDQ\WRQHVLQWKHVWDQGDUG
WR+]VXEWRQHEDQG
7KHHQGUHVXOWLVDKLJKSHUIRUPDQFH
DXGLRILOWHULQJV\VWHPWKDWSURYLGHVD
FOHDQVLJQDOIURPWR+]LQD
VPDOOLQFKE\LQFK3&ERDUGDQG
JLYHV+]RIDYDLODEOHEDQGZLGWK
IRUWKH³.)0VWDQGDUG ́
Why Do We Need It?
7RGD\¶VUHSHDWHUV\VWHPVDUHPDU
YHOVRIDPDWHXUUDGLRHQJLQHHULQJ
:KRZRXOGKDYHWKRXJKWMXVWDIHZ
VKRUW \HDUV DJR WKDW WKHUH HYHU
ZRXOGEHDWLPHZKHQDFOXEFRXOG
RSHUDWHDILUVWFODVVUHSHDWHUV\VWHP
ZLWKRXW D UHVLGHQW UHSHDWHU JXUX"
(YHU\WKLQJ KDV EHFRPH SOXJDQG
SOD\OLNHWKH%ULGJH&RPVHULHVDQG
<DHVX¶V)XVLRQUHSHDWHUV
7KHEDQGZLGWKVWDQGDUGVRIWRGD\¶V
UHSHDWHUVDUHH[FHOOHQW1HDUO\DOORI
WKHPKDYHJRRGIUHTXHQF\DQGGHYLD
WLRQUHVSRQVHXSWRDERXW+]WKH
)&&OLPLW2IWHQSUREOHPVDUHFDXVHG
E\WKHXVHUV7RGD\¶VLQH[SHQVLYH9+)
KDQGKHOGVKDYHLQFRQVLVWHQWGHYLDWLRQ
WKH\¶UHDOORYHUWKHSODFH0DQ\FOXEV
KDYH D ³GHYLDWLRQ DGMXVWPHQW QLJKW ́
HYHU\\HDURUVRWRJHWXVHUV¶UDGLRVVHW
FRUUHFWO\
8QIRUWXQDWHO\ WKHUH LV QR PRGHUQ
VSHFLILFDWLRQWRGHILQHZKDW³+L)L ́9+)
LVRUFRXOGEH7KHROGKDPUDGLRVSHF
LILFDWLRQIRUWKHDXGLREDQGZLGWKZDV
WR+]OHIWRYHUIURPWKHODQG
OLQHWHOHSKRQHV\VWHPGD\V2YHUWKH
\HDUV UDGLR HTXLSPHQW KDV FRQWLQX
RXVO\LPSURYHGDQGPRVWRIWRGD\¶V
UHSHDWHUV\VWHPVFDQHDVLO\WUDQVPLW
+]WR+]ZLWKN+]GHYLDWLRQ
7KHH[WUDEDQGZLGWKLVHVVHQWLDOWR
3DUUDQ5G
6W/HRQDUG0'
HPDLO ZGR\J#DUUOQHW!
Enjoy wideband audio on your analog FM repeater with this
simple-to-build op-amp filter system!
The 4KFM Audio Filter
BY DWAYNE KINCAID,* WD8OYG
)LJXUH%ORFNGLDJUDPRIWKHDXGLRILOWHU
3KRWR$7KHFLUFXLWERDUGIRUWKHILOWHULVWLQ\²MXVWE\LQFKHV
5HFHLYHU'LVFULPLQDWRU
WR+]9SS
5HFHLYHU'LVFULPLQDWRU
WR+]9SS
2XW
2XW
&4$XJXVW 9LVLW2XU:HE6LWH