Patrick Martin wrote: > Since I use plastic boxes for my matching transformers, I only fitted > those with banana jaxs, so I use banana plugs on the end of the coax. > That would be hard to terminate those.
That's why you have ingress. Using banana jacks on the coax does not isolate the inner and outer surfaces of the coaxial cable shield. Either you need to put the matching transformers inside a metal box, with a coax jack mounted to the box, and the antenna input through small holes in the box with the transformer inside the box, this will create the isolated condition on the shield surfaces, or else add a really high impedance choke-type balun sleeve over the antenna end of the coax. The balun sleeve won't work as well as a shielded metal box. The sleeve choke and metal box would work better together than either one alone. > I have a regular coax fitting on > the receiver end screwed into a shilded SO239 to the back of the > receiver. This end is good. > By the way, isn't the matching transformer supposed to isolate the > antenna from the coax anyway? Nope. It will perform impedance and balanced to unbalanced transformation, but without the shielded box, it won't isolate the inner and outer coax shield surfaces. A sleeve-type choke balun places a high impedance on the outer surface of the shield of the coax, making it hard for the currents on the rest of the coax shield from making the transition to the inner surface. > So does a stray signal on the coax really > make any difference with a load on it? Yes. The outer surface of the shield becomes a part of the antenna. Rick Kunath _______________________________________________ IRCA mailing list [email protected] http://montreal.kotalampi.com/mailman/listinfo/irca Opinions expressed in messages on this mailing list are those of the original contributors and do not necessarily reflect the opinion of the IRCA, its editors, publishing staff, or officers For more information: http://www.ircaonline.org To Post a message: [email protected]
