#50 OHM HARDLINE COAX FOR FREE#
#50 OHM HARDLINE COAX SERIES#
#50 OHM HARDLINE COAX TV#
#50 OHM HARDLINE COAX FREE#

To start out, lay out your coax to the proposed length but make it longer than it needs to be to reach your destination. This will only happen on one frequency, but will be close enough to cover most of a ham band. Thus our 50 ohm antenna at the other end of the 75 ohm will appear as 50 ohms to the transmitter. The impedance of the far end will be reflected on the near end. The special case where the feed line is a multiple of a half wavelength can be used to advantage when the antenna and feed line are of different impedances.

#50 OHM HARDLINE COAX FREE#

A quarter wave of coax will be physically shorter than a quarter wavelength in free space. Second, by wave length we mean electrical wavelength. Changing frequency will change the wavelength. First the same frequency is used for all tests. Two assumptions are made for the experiments above. If the coax is an odd multiple of a quarter wave, you will see 25 ohms resistive and no reactive component. When the coax length is a multiple of a half wave length, you will see 100 ohms resistive and no reactive component. The reactance will be either inductive or capacitive depending on the length. You will get 100 ohms right? Wrong!ĭepending on the length of the coax you will get a complex impedance with resistive and reactive components. Now suppose you get out your antenna analyzer and repeat the experiment.

What will the SWR be for each length of coax? It will always be 2:1 for every coax, again assuming your coax has no losses. You put your resistor on one end of each coax and the SWR bridge on the other end. Suppose you have a 100 ohm resistor and an assortment of 50 ohm coax lengths. Transmission lines have a wonderful property in that they act as impedance transformers.

#50 OHM HARDLINE COAX FOR FREE#

Members can down load PDF’s of Maxwell’s articles for free from the ARRL web site.

#50 OHM HARDLINE COAX SERIES#

The 1973 QST series Another Look at Reflections by Walter Maxwell, W2DU, is also well worth reading. Read the appropriate sections in the ARRL Antenna Book. Many hams don’t understand basic transmission like theory. Losses increase with higher SWR, but using low loss coax to begin with reduces this problem. This is more of a problem with solid state rigs than tube rigs or amplifiers that are have variable output tuning networks.Ģ. Your rig can’t match to the impedance presented. There are only two reasons you need low SWR.ġ. You will not get a perfect SWR with this method, but perfect SWR is not necessary. I do this with one run that connects to a pair of triband Yagis. The easiest way is to just not worry about the mismatch and just hook up with the 75 ohm line. I adapt PL-259 connectors with brass tubing.

A number of ways to make connectors have been devised. Connectors can be purchased that will work, but they tend to be very expensive and difficult to find. The standard PL-259 connectors we use with our rigs and antennas do not fit on the 75 ohm hard line cable. Can we use 75 ohm coax with our 50 ham systems? Of course we can! We just have to convert 75 ohms to 50 ohms – or maybe not.īefore getting into impedance considerations of the CATV cable, there is the other catch. So, there has to be a catch, right? Actually there are two. They will often give away or sell these lengths for very low prices. Cable companies consider 100’ or more as short lengths. It is cheaper to throw the roll ends out than splice them together. What is even better, cable companies don’t like to mess with short lengths. Because they use thousands of miles of this cable every year the production costs are low. The industry uses cable with low loss dielectric and a solid aluminum cover.

#50 OHM HARDLINE COAX TV#

TV frequencies are in the VHF and UHF range, compounding the problem. They have to run very long runs of coaxial cable. Unfortunately low loss coax is more expensive than the garden variety types.Ĭable TV companies have the same problem. The solution of course is to use low loss coax. Losses increase as the length of the coax increase and as frequency increases. Losses waste power from your transmitter and limit the ability to copy weak signals. LMR-400 has lower losses than the others listed. The easiest way to connect your rig to your antennas is to use 50 ohm coax such as RG-8, RG213, RG-58, or my favorite, LMR-400. Most transceivers and antennas designed for ham use are based on 50 ohm impedance.

50 ohm hardline coax