Is that good SWR really good Part 2

 If you read part 1 you saw that the reflected power from the antenna was attenuated by the inherent loss of the coax. This loss reduces the reflected power seen by any SWR meter at the transmitter. At the antenna in our previous example only 50 watts arrived but we started with 100 watts. The SWR meter thinks the forward power is 100 watts. It does not know that only 50 get to the antenna. If the true SWR at the antenna is 3:1 we will see 12.5 watts reflected and of that only 6.25 arrives back at the SWR meter.

So the SWR meter thinks the forward power is 100 and the reflected power is 6.25. That is a SWR of 1.67.

In reality the SWR is 3:1. The coax loss causes us to see a better SWR than we really have. 

When checking SWR at the transmitter we need to be careful and not accept that 1.67 SWR until we look further. For example we need to check our antennas when we first put them up to see what the SWR curve looks like. On my 80 meter dipole I get a good SWR on the low end but it rapidly rises as I move to the top. I check where my 2:1 SWR points are. They may be at 3.5 and 3.6 MHz. If at any time I find that the SWR up on 3.6 is only 1.5 I immediately know I have a problem with loss. Know where your SWR should be low and remember it should be high very much off frequency UNLESS there is excessive coax loss. I am always suspicious of any antenna that has a “flat “ SWR over the whole band. Typically antennas from 160 through 20 meters will have sharper (less flat) SWR curves than antennas on 15 and 10 meters. It all depends on the size of the band and the frequency. 

Some manufacturers actually make their antennas have loss so they can say it is a wide band antenna! If your SWR is too good you probably have a lot of loss in your cable or balun.

This chart shows the SWR differences with feedline loss. Note a 10:1 SWR looks like a 2:1 SWR with 4dB line loss!