- Cp RF ng trc (radio frequency, feeder, coaxial cable, rf
cable) c s dng nhiu trong cc trm thu pht sng v tuyn BTS (base
tranceiver station). bn cao (do cu to dng cp ng trc, cp cng nghip)
nn c th lp t trong cc mi trng lm vic khc nghit nh hm l, cng trnh
ngm.- Cp RF ng trc (radio frequency, feeder, coaxial cable, rf
cable) c ch to gm mt dy ng trung tm (inner conductor) c bao bc bi
mt vt liu cch li l cht in mi khng dn in (dieletric insulator),
chung quanh cht in mi c qun bng dy bn kim loi (outer conductor) va
dng lm dy dn va bo v khi s pht x nhim in t. Ngoi cng li l mt lp v
bc (jacket lm bng cht khng dn in thng l PVC, PE. Cp RF ng trc
(radio frequency, feeder, coaxial cable) c hai loi, loi nh (Thin) v
loi to (Thick).- Dy cp ng trc c thit k truyn tin cho bng tn c bn
(Base Band) hoc bng tn rng (broadband). Dy cp loi to dng cho ng xa,
dy cp nh dng cho ng gn, tc truyn tin qua cp ng trc c th t ti 35
Mbit/s.Ngoi ra dy cp ng trc cn chia lm 2 loi l loi cng v loi do.Loi
cng th c mt lp bo v dy c cn loi do th l mt vin bo v, thng l mt dy
ng. S suy gim v tr khng ca dung mi nh cng c nh hng quan trng n tnh
nng ca cp. Dung mi c th c hoc rng. Tn cng ca cp l mt u kt ni RF
(radio frequency). V trng in t mang tn hiu ch tn ti trong khong
khng gia bn trong v dy dn pha ngoi, nn n khng b suy gim hay chu nh
hng ca pht x nhim in t. Do cp ng trc c s dng nh mt ng truyn tn s
cao truyn ti nhng tn hiu cao tn hoc mt di rng tn hiu.
Mun bit v Feeder hoc cc thit b vin thng khc th cc bn nn xem
catalogue ca chng, trong rt c th v r rng!VD nh Feeder 7/8 nu sdng
tn s 1800Mhz th suy hao 5,75dB/100m.Feeder 1/2 nu sdng tn s 1800Mhz
th suy hao 10,1dB/100m.
Suy hao ca fi ph thuc vo rt nhiu yu t khi ch to nh ng knh li
trong, li ngoi, cht in mi gia hai lp li,....
Cp 7/8 tn s ti a 5000Mhz th suy hao l 10.40 dB/100m v nng lng
tiu th l 0.96 kw. Cn cp 1/2 tn s 5000Mhz suy hao l 18.00db/100m,
nng lng tiu th 0.476kw, cp 1/2' cn c th s dng tn s 8000Mhz vi tiu
hao l 23.91db/100m v nng lng tiu th 0.358kw.Vi so snh ny th ta thy
cp 7/8' lng suy hao thp hn nhng nng lng tiu th cng nhiu hn do c tnh
cu to cp 7/8 c li rng gia v 1/2 c li c
feeder 7/8 thng dng cho vic truyn dn vi khong xaloi 1/2 hay dung
cho vic truyn dn gn
Hin nay, tn s ct ca mt s loi nh Rosenberger Feeder (Germany) ln
n 11 Ghz. Andrew Feeder (USA) c tn s ct ln ti 18 Ghz.Ngoi ra, ngi
ta cn dng Feeder cc trm thu pht Viba Minilink hay Pasolink vi di tn
(7Ghz hay 15 Ghz)
