Coaxial Cable Characteristics and Data
Used in Amateur Radio Stations

It is of importance when making decisions about getting the right coax for your Ham Station to understand that there are trade-offs that have to be considered between transmitter power, antenna gain, coax loss, erp, and your total Ham Station system performance.
Your bank account may also enter into the equation like most Hams.

The db differences in gains or losses on transmit and receive between the choices available to you are the important issue.

A difference of 3 db either way will not be apparent to the stations that you are communicating with on the other end; around the block or around the world. They won't hear or see (on the S meter) any difference if you run your transmitter at 50 watts instead of its maximum 100 watt output power as an example.
This is a difference of about 3db! The same ratio holds true comparing 500 watts with 1000 watts!
Now take this same analogy and apply it to coax.
Here is an example:
Your present coax is 100 feet long and has a loss of 3db per 100 feet.You change it to the same length, 100 feet, using a more expensive coax that has only about .1db loss per 100 feet.
(Very Expensive Stuff!)
This is about a 3db increase in signal strength to the antenna that you were loosing in the old coax.
The station on the other end usually won't know the difference, and usually, neither will your receiver!
A difference of 3 db or less between two antennas, two types of coax, or two station configurations is usually not sufficient to justify the higher costs of the more expensive, lower loss, coaxial cable unless you are a perfectionist with lots of money.
 
However, a difference of 6 db may well justify the more expensive approach with the higher quality coax or antenna setup.
Remember, if you can't increase your transmit or receive signal by at least 5 or 6 db or more, if may not be worth the effort and expense.

The tables below should help you decide what if any coax changes you need to make.
Color Key:
Green shade 50 - 52 ohm

Coax dB Loss per 100 Feet using common coax types:

Note: These tables are typical specifications for comparison only.
Values may not be exactly as quoted by a specific mfg.

Remember, you have to achieve about 6db gain or loss to to make much difference on the air to the other station on receive.

Using this table, you should see that with every 3db increase or decrease, your effectively doubling the ERP or cutting it in half.
Your feedline will always have some loss so in calculating your total antenna system loss, always subtract the total loss of your feedline from your antenna gain.

Example:

Your antenna gain is 6dbd.

Your coax loss is 2 db per 100 feet as stated by the mfg. You use 50 feet.

Your total system gain or loss would be:

Antenna gain 6dbd - loss of 1db(50 feet) = total gain (or loss) = 6 - 1 = 5 db

Another example:

You add 100 feet of coax with 3 db loss at your operating frequency to an antenna with 0 dbd gain.

So 0db - 3db = -3db loss in signal strength...you just cut your signal in half.

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