Most of my long runs are Heliax, 3/8" to 7/8" depending on which runs (most of mine are 3/4" and 7/8"). I don't run LMR 600 anyplace, and I only use a couple of long runs of LMR 400. N type and SMA I see those kinds of losses well above 1 GHz. So 0db - 3db = -3db loss in signal strength.you just cut your signal in half.How sure are you of that 1 dB/connector and at what frequency? More typically I see 0.1 to 0.25 dB / connector up to about 1 GHz and depending on the connector type. You add 100 feet of coax with 3 db loss at your operating frequency to an antenna with 0 dbd gain.
You use 50 feet.Īntenna gain 6dbd - loss of 1db(50 feet) = total gain (or loss) = 6 - 1 = 5 db Your coax loss is 2 db per 100 feet as stated by the mfg. 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. Using this table, you should see that with every 3db increase or decrease, your effectively doubling the ERP or cutting it in half.
Remember, you have to achieve about 6db gain or loss to to make much difference on the air to the other station on receive. You use an antenna that has 6dbd gain vs the old one that had 0dbd gain.īy using the chart above, you will see that with 100 watts at the antenna feedpoint, your effective radiated power would be 398 watts! Values may not be exactly as quoted by a specific mfg. Note: These tables are typical specifications for comparison only. The tables below should help you decide what if any coax changes you need to make.Ĭoax dB Loss per 100 Feet using common coax types: 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. However, a difference of 6 db may well justify the more expensive approach with the higher quality coax or antenna setup. The station on the other end usually won't know the difference, and usually, neither will your receiver!Ī 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.
This is about a 3db increase in signal strength to the antenna that you were loosing in the old coax. You change it to the same length, 100 feet, using a more expensive coax that has only about. Your present coax is 100 feet long and has a loss of 3db per 100 feet. Now take this same analogy and apply it to coax. This is a difference of about 3db! The same ratio holds true comparing 500 watts with 1000 watts! 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. The db differences in gains or losses on transmit and receive between the choices available to you are the important issue.Ī 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. Your bank account may also enter into the equation like most Hams. 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.