Yep, you just made a good RF choke. Using ferrite cores that just slip over a cable doesn't give you much inductance. You need one that like the rod, lets you put multiple windings on it. You would need several 'beads' like 10 or 20 to get a similar effect.
FWIW, in my opinion, dipoles fed directly by coax, are nothing but a dipole fed by open wire. Both the shield and center conductor carry equal parts of the RF signal. The RF is supposed to stay on the inside of the shield, but that seldom happens, especially with broadbanded use of one dipole. Consequently, you need a way to stop the RF from flowing on the outside of the shield. Either a simple balun consisting of 6 to 10 turns of coax or a 1:1 balanced to unbalanced transformer at the feedpoint can work to stop this. Jim WA0LYK --- In digitalradio@yahoogroups.com, KV9U <[EMAIL PROTECTED]> wrote: > > I had asked a question recently about have ALC problems with digital > modes and did receive some suggestions privately. I had a slow > "oscillation" of the ALC over several seconds per oscillation with the > ALC peaking and then dropping back to zero and then going up to maximum > again. > > Initially I had thought this was only on 80 meters, but as it turned > out, I was also present whenever I was using my multiband dipole which > is directly overhead. My ground mounted vertical, which is 150 feet out > from the shack, caused no noticeable problem. > > As I had a fairly long shielded cable (6 feet) running from the sound > card to the ACC1 socket on the ICOM 756 Pro II, I decided to try some > toroid cores. No noticeable change. I did notice that I could reduce the > noise if the cables just happened to go over the top of the rig's > cabinet. Probably a capacitance to ground effect? > > I then took an Amidon rod and wrapped a few turns around it and did > notice a reduction in the problem. So I wrapped about 20 turns on the > core and the RFI appears to be completely gone. > > 73, > > Rick, KV9U > > > > > > Andrew O'Brien wrote: > > > Interesting. Anyone care to explain why RF would cause this ALC issue? > > > > On 2/13/06, *Mel* <[EMAIL PROTECTED] > > <mailto:[EMAIL PROTECTED]>> wrote: > > > > Hello Tim, TG6124, > > > > I solved the problem and I think it may have been RF. The day before > > the antenna had been playing up and I moved the coax cables and in > > doing so placed the cables from the ACC1 to the ISO box in a place > > where they seem to have caused this trouble. I separated them and the > > problem seems to have gone away. > > > > Many thanks for your response, I was surprised to have one as most of > > the correspondence seems to be involved with only one subject. > > > > Kind regards, Mel G0GQK > > > > > > > Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Other areas of interest: The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/digitalradio/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
