On Mon, Dec 24, 2012 at 8:22 AM, Gerald Capodieci <jcapodi...@gmail.com>wrote:
> Stray RF in the shack can damage other equipment such as wireless > Internet routers. It may be unhealthy to the operator and be the > source of RFI to neighbors. > Here are some ways to stop Stray RF. > 1. Use only balanced antenna with less than 1.5:1 SWR. > At the risk of offending, this is an old wives tale. SWR has nothing to do with SWR in the shack and what Tim said, RF on the outside of the coax has EVERYTHING to do with RF in the shack. RF current on the outside of the coax can come from two places. It can be conducted from the antenna or it can be picked up from being in the near-field. A current/common-mode choke at the feed point of the antenna will stop the former and current/common-mode chokes at the entry to the building and again just before the equipment in the shack will take care of near-field pick-up. > 2. If you have to use an antenna tuner use ladder line. > Note: Even if the tuner reads a 1:1 match to the radio, the SWR and > thus the reflected power could be very high between the tuner and the > antenna. The reflected power can radiated in many undesirable > directions or just become heat in the tuner, feed line and any loading > coils in the antenna. > Well, if the balanced line is truly balanced, the fields from the equal-but-opposite currents in the conductors will cancel out, eliminating radiation and/or pick-up. But that still won't deal with common mode currents and you still need the common-mode choke. It is just that building a common mode choke for balanced line is MUCH more difficult than building one for coax. In that case it is easier you put the common mode choke between the tuner and the rest of the station. BTW, you can also use a current choke/common-mode choke to turn an unbalanced tuner into a balanced tuner. That is how I get my SGC-239 to tune my loop without sending RF back down the outside of the coax to the shack. -- Brian Lloyd, WB6RQN/J79BPL 3191 Western Dr. Cameron Park, CA 95682 br...@lloyd.com +1.767.617.1365 (Dominica) +1.916.877.5067 (USA) _______________________________________________ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flexradio.com/ Homepage: http://www.flexradio.com/
