Hacksaw, Hope your still a member of the board. I know it's an old posting, but I'm new here and have a few explanations for you and others that were posting, and there were a lot of myths and misconceptions going on that need to be corrected. First off I AM an Electronics Engineer, and an Extra Class Ham. Been around the block quite a few times, and seen this before. What you experienced is the result of a floating ground. In short, the radio itself has (or had) an issue and needed to be sent in for repairs. This caused a DC voltage to show up on the output of the the radios RF connector that your SWR meter was reading, even though the radio was not transmitting. In audio circles this is often known as a ground loop. Now on to some of the errors I saw posted.
First: Grounding the base of a trunklip antenna mount... ALWAYS a must do to maintain a good SWR. Even if the trunk deck isnt plastic. the mount can develop rust between the set screws that clamp it in place, or even at the hinges.
Second: SWR does NOT change between radios or power levels if properly adjusted at the antenna. The Standing Wave Ratio is determined by transmitted power vs reflected power and is caused by one thing- the resonance of the antenna. When you tune the antenna you are setting the resonant frequency. Since the antenna is affected by capacitance and inductance of the antenna, the mount and all structures around it, it must be adjusted for resonance with these variables in place. Radios and power are not part of that equation. Remember when the power level changes the set point changes, but this does not mean the swr changes. Most SWR meters available to the end user are not sensitive enough for true readings of this fact, when ever possible use a cross needle meter. low level meter movement is less accurate than movement at higher levels which is why lab grade meters are always cross needle.
Third: this one confuses people a lot- noise in a receiver that can be eliminated or reduced by filtering the power supply is not the result of a noisy receiver, it's the result of an improperly bypassed receiver. Noisey receivers pick up the noise through the antennan not the power supply. Automotive power systems are some of the noiseist on the planet, and for giggles you should throw an oscilloscope on one some time.
These were the biggest misconceptions I noticed and were the primary reason I am posting on a three year old thread. I hope that it helps others with situations that they have been having problems with. These are not based on theory, but are proven fact, time and time again. If you are experiencing otherwise, then look for a problem in your installation, that needs to be corrected. With antennas look for grounds that should or should not exist. With radios acting odd, look for that missing RF ground. With Antennas that wont tune, (they get close but then the SWR shoots up suddenly) its more than likely incompatable for the frequency range, but believe it or not a simple match box MAY fix the issue IF it allows sufficient operating band width... but more often than not it's a matter of too thin of a conductor in the antenna itself. None of this is really magic. it's just the laws of physics being applied properly and understanding it's limits, and how to use them to your advantage.
