As W1SUJ recently demonstrated, a low SWR is not an indication of antenna performance. Richard got a 1.2:1 SWR on 2 meters with his new antenna, but could just about make the club repeater. SWR is supposed to tell you if the antenna is matched to the feed line, but the SWR meter is at the transmitter end of the line, so it measures the forward power coming out of the radio, but the reflected power is that that goes from the radio up the transmission line to the antenna, and is reflected back towards the transmitter, and goes down the transmission line again, so if there is loss in the transmission line (and all lines have loss) the reflected power at the SWR meter is way less than the real value.
For example, lets say we have 100′ of RG-8X. At 144 MHz this has 4 dB loss. The balun, antenna switches, and connectors may add another 2 dB. So we have 6 dB loss and therefore only 25% of our power gets to the antenna. Lets say because the antenna is defective or out of resonance, the SWR, at the antenna, is 10:1. So the antenna only accepts 18% of the 25%, or 4% of the transmitter power. The rest of the power is reflected back down the line. So the line loses 75% of the reflected power. This means that the SWR meter sees a reflected power of 25% of 82% of 25%, or 4.5% of the original power. Therefore, the SWR meter sees 100% forward power and 4.5% reflected power and reads 1.1:1. With this SWR you would expect everything to be great, but using a 25 watt transmitter you would be getting only 1 watt into the antenna.
At the same time, the antenna may receive great, as the SWR (and loss) when receiving is determined by the match between the transmission line and the receiver, and will be entirely different from the transmitting SWR. So, as Larson E. Rapp (WIOU), would say, “in hock vertis” and build or buy a field strength meter and find out what is really going out…