On Sun,2/14/2016 11:20 PM, bernhard.ho...@bmw.de wrote:
just an update..the Microham Microkeyer II has definitely a problem with RF!
Without diving into the details, I helped W6OAT chase down RFI issues in his station. He had a MicroHam box with an "interface" to the radio that was a jumble of wires. Virtually NO attention had been paid to the fundamental concept of a transmission line in the interface between it and the radio. While that is acceptable at baseband (audio), it is monumentally foolish when RF is present (i.e. an antenna on the roof).
Current flows in loops, whether at DC or at RF, and the loops form both antennas and magnetic loops whose coupling is proportional to the loop area. In the near field, magnetic coupling dominates, so the loop area can be a VERY big deal. EVERY signal path between devices must be treated as a transmission line of RFI is a potential issue. That means EVERY signal path should be a twisted pair or a coaxial pair, so that the path forms a transmission line. Any interface that does not do this is an invitation to RFI if the antenna is close enough, or if the power is high enough, or both.
This is NOT an indictment of Microham -- at a CQP expedition a few years ago, a team member showed up with an interface betweeen is radio and his amp to key the amp that was an RCA to RCA cable with a single wire, no shield. Chassis to chassis was depended on for the return. That works fine at DC to key the amp, but the resulting current loop area gives that circuit VERY STRONG coupling to an RF field, both as a magnetic circuit and as an antenna.
Noted RFI guru Henry Ott talks about understanding where ALL the current flows, which is revealed by "the hidden schematic lurking behind the ground symbol" that causes most issues with RFI and crosstalk.
73, Jim 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 Message delivered to arch...@mail-archive.com
