How to Choose a Ham Radio Antenna
It’s hard to say which is more important for a ham radio operator: the radio or the antenna. Making up for deficiencies in one by improving the other is difficult. A good antenna can make a weak radio sound better than the other way around. You need to give antenna selection at least as much consideration you do to radio selection.
Gee, how tough can picking a feed line be? It’s just coax, right? Not really, and you may be surprised by how much feed line can affect your signal, both on transmit and receive.
When one operator started hamming, he used 100 feet of RG-58 with a 66-foot dipole that he tuned on all bands. He didn’t know that on the higher bands, he was losing more than half of his transmitter output and received signals in the coax. The 50-foot piece he was using on his 2 meter antenna lost an even higher fraction of the signals.
Although losing 50 percent, or 3 dB (decibels), is only about half an S unit (S units measure signal strength; a change of 1 S unit represents a factor of 4 times higher or lower power), he lost a few contacts when signals were weak or the band was noisy.
Making up that loss with an amplifier costs hundreds of dollars. Changing antennas to a beam with 3 dB of gain costs at least that much, not counting the mast and rotator. That makes the extra $20 to $25 cost of lower-loss RG-213 cable look like a pretty good bargain.
Here is a comparison of several popular feed lines in terms of their relative cost (based on RG-58) and the loss for a 100-foot section at 30 MHz and 150 MHz. The loss is shown in dB and in S units on a typical receiver, assuming that one S unit is equivalent to 6 dB.
|Type of Line and Characteristic Impedance||Outside Diameter (Inches)||Cost Per Foot Relative to RG-58||Loss of 100′ at 30 MHz in dB and S Units||Loss of 100′ at 150 MHz in dB and S Units|
|RG-174A/U (50 ohms)||0.100||2/3||6.4 dB/1 S unit||>12 dB/>2 S units|
|RG-58C/U (50 ohms)||0.195||1||2.6 / 0.5||6.7 / 1.1|
|RG-8X (50 ohms)||0.242||1¼||2.0 / 0.3||4.6 / 0.7|
|RG-213/U (50 ohms)||0.405||3||1.2 / 0.2||3.1 / 0.5|
|1″ ladder line||½″ or 1″ width||1 to 2||0.1 / <0.1||0.4 / <0.1|