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[About Coaxial Cables]
DO YOU NEED NEW COAXIAL CABLE?

Here is a guide for those wanting to use old or second
hand coaxial cable of unknown quality. This proceedure
will make you aware of the losses that the cable will add
to your antenna system.

  1. Firstly make yourself a low power dummy load with
    a resistance of 150 ohms. This will represent a VSWR
    of 3:1 on a perfect feed line.

  2. Next fit the load to the antenna end of the coax and
    the other to your transmitter via a VSWR meter.

  3. Now all that remains is to measure the VSWR at the
    desired frequency of operation. Rember the loss will get
    higher as the frequency is increased.

  4. The closer your VSWR is to 3 the lower the loss . If
    you get a good VSWR then its time to toss the coax. Refer
    to the chart below for a guide.

SWR at TX <-----------> Cable attenuation

2.6:1 <-------------------> 0.5db
2.3:1 <-------------------> 1.0db
1.9:1 <-------------------> 2.0db
1.7:1 <-------------------> 3.0db
1.5:1 <-------------------> 4.0db

Remember that 3db means half your power is being lost in your
feed line. That means incoming as well as out going.

It should be noted that the dummy load can also be used to
check your VSWR meter reading. Simply put the dummy load
directly onto your meter and measure the VSWR, it should
read 3:1. It may be a good idea to check this before testing
your feed line.

Look for new tips as this site is developed.

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