Well I have heard this said before. My VSWR without any chokes is 1.3:1 at best. When I add a ferite isolator it goes up to 2.5:1 = unusable. So very obviously use it without.
There is no obvious reason for a high VSWR (i.e. no metallic objects around) 9M pole up with the IMAX on. The GM also reads a 1.2:1 SWR on the identical mount situation.
I am not categorically saying there is no CMC's on the Coax/Poles but neither am I clearly experiencing negative effects from any that are present. (other than the potential noise we are discussing) I am not going to use a choke because it makes the antenna unusable.
I wonder if the coil choke and or/ferite choke negatively interacts with the matching arrangement of the IMAX. Maybe it is a CMC on the feeder issue but in lieu of no known negative effects and no current clamp I cannot actually tell.
My radiation near field is empty of any noise sources as I am out in the country side. Only a car that is switched off. On occasion I hear crackling from spark plugs firing when a car goes past but I get that with every antenna I have ever installed. There must be a lot of EMF being produced and radiated. There is an old fashioned 1930's car that drives around and I can hear it coming from 300M away lol. Seems to have zero spark suppression.
"On another note the gm elements are completely encased in insulation and the imax had only about 2/3rds ( the top section being stainless steel) The gm also shows dc short across the coax and open circuit to the top radiator( being fed with a cap) these points alone might contribute to rx noise difference.
The top section on my IMAX is copper and the entire antenna is encased in fibreglass. In diagrams of the IMAX2000 I have seen a section referred to as a capacitor as well.
There are numerous holes to pick in this article but it seems like there is at least some kind of brass insert in the IMAX...
http://www.k3dav.com/solarconimax2000antenna.htm
To quote the relevant section:
"Near the inside middle of the center section, there is a high power capacitor-coupler (Shown below), and yes it radiates and couples the top half of the antenna. This allows the center section to radiate a larger pattern than most verticals do."
