On Mon, 15 Mar 2010 19:44:31 -0400, Joe Subich, W4TV wrote: >This is a common problem with DXDoubler due to differences >in chassis potential between transceivers. TopTen Systems >have even published an application note concerning the issue: >http://www.qth.com/topten/apnote9.htm
>Their solution, as you have already discovered is to add >two transformers in the headphone line between one of the >transceivers and the DXDoubler. They also suggest a low resistance bond between one transceiver chassis and the other BEFORE resorting to transformers. That's my fundamental recommendation as well. It also helps to get power for both radios from the same AC outlet, or from outlets whose green wires are bonded together (for example, multiple outlets in the same steel backbox). There are two common causes of this problem. One is the potential difference between the two radios. Bonding and using the same outlet will fix that. The second common cause is a magnetic field that couples into the loop between the two radios and the DXDoubler. That field is most often is established by a big power transformer very close to the rig (either the linear supply for the rig(s) or the power transformer for the power amp. The field is coupled to the audio two ways. First as the induced voltage, and second as current flowing into a pin 1 problem at either (or both) end(s). Magnetic field coupling can be minimized by reducing the loop area. In this case, the loop consists of the audio cable shields and the radio bonding path. This may sound counter-intuitive, but that means making one of those cables longer so that the cable for radio two follows a path from the DXDoubler to radio one and then along the bonding conductor to radio two, and lacing the cables together with ty-wraps. Adding transformers can also break that magnetic loop, but if the transformers are unshielded (and most inexpensive transformers are unshielded) the transformers may pick up the magnetic field and couple it as a differential signal. 73, Jim Brown K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
