ARLA/CLUSTER: O que é melhor, a linha paralela ou o cabo coaxial.?
João Costa > CT1FBF
Quinta-Feira, 15 de Dezembro de 2016 - 13:47:27 WET
Ham Radio - Which Is Best, Twin Feeder or Coaxial Cable?
Coaxial cables are used by many radio hams due to the fact that it is
a very convenient way to put power in to your aerial and receiving
signals from it, coax is easily terminated with 50 ohm plugs called
PL-259 connectors, but there are many coaxial types of cables and new
radio Hams often wonder which one to use a and why. Do you use coax at
HF or is there a better way?
Coaxial cable is used mainly because of its inherent impedance and
matching convenience, coax is easy to work with and matches your
transceiver correctly; most VHF and UHF aerials are 50 ohm impedance,
coax is designed for the same impedance and will match your aerial
correctly and give you a good S.W.R. reading close to one to one.
Depending on how far your aerial is located from your operating desk
R-G-58 coaxial cable will suffice; it has a diameter of about .194
inches. All coaxial cable has loss over measured lengths and I would
check with manufactures data before buying cable. For mobile
installation R-G-58 is a good choice. R-G-8U is a good general purpose
coax and suitable for long runs.
For UHF and VHF use with high power in the region of 100 watts, use
R-G-213, it is very low loss cable and built to last. If you are
running coax from your aerial back to your shack over a long distance
always use heavy low loss coax because the loss in signal both
outgoing and incoming will be affected by cheaper coax.
Coaxial cables are the most popular form of transmission line for
getting your signals to and from your aerials. There are many types of
cable to choose from and it can be confusing to choose the best one.
In this article, I have highlighted the most common types of coax to
use for VHF and UHF transmissions, R-G-43 and R-G-58 are also good for
making up patch leads need to connect S.W.R. metres or aerial matching
system to your transmitter.
But what about HF, do you use coaxial cable or something different? My
choice at HF is to use twin feeder, you will probably know that a half
wave dipole aerial is approximately 73 ohms impedance at the centre,
twin feeder is an alternative matching feeder to use other than coax
and it does have advantages over coaxial cable. 75 ohm twin is quieter
than coax, a great benefit to the HF operator. Twin can be stapled to
outside brick work and does not radiate in the way coax does from its
Braid, Twin Feeder is balanced and will connect directly to your
aerial matching unit, or directly to your transceiver with the aid of
a simple matching transformer.
John Allsopp G4YDM
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