I have considered using a couple of short pieces of RG11 to get the balanced line out of the shack. I don't think the additional resistance would be that great, as the length would only be about 5 feet. However, I'm sure there are some pretty high SWR points on the transmission line, so I'm not sure how much loss that 5' would cause.
The major RFI problem I am having at the moment is with the Ethernet cable running to the PC in the shack. Unfortunately it is UTP, which runs through the walls from the second floor to the basement and back up to the first floor, where the router is. So it's a long (probably about 75'), unshielded cable. I also get some RFI into the computer speaker system, but I don't generally use them when I'm transmitting so I just turn them off. The speakers connected to the 5000A don't seem to have a problem, even though all the cabling is very close to each other. The reason I think the primary culprit is the balanced line coming into the shack is that when I first installed it, transmitting on 20 meters would cause so much RFI that it would cause the computer to reboot. By moving the transmission lines around, just a little bit (since there isn't very much else I can do with them), I was able to eliminate that problem. The space is very limited and there are a lot of ground wires and the computer itself which are all very close to the transmission lines. I'm sure the close proximity of all these things must be causing a problem. I am in the process of reading K9YC's article. I'm hoping to have it finished today. It is an excellent article. I am hoping the Ethernet problem is a pin 1 problem and can be eliminated with the use of some ferrite cores. Thanks to everybody for the suggestions. Chris KA1GEU -----Original Message----- From: Lux, James P [mailto:james.p....@jpl.nasa.gov] Sent: Friday, January 30, 2009 1:43 PM To: Dudley Hurry; Chris seeber Cc: flexradio@flex-radio.biz Subject: Re: [Flexradio] Balanced vs. unbalanced microphone inputs Except that the reason folks usually run balanced transmission lines is to have low loss, from the high Z of the line (high Z = low current = low IR losses, which dominate at HF over the dielectric loss). Two coaxes makes a 100 ohm line, so you don't get the low loss benefit from balanced openwire line. (8x also has tiny center conductors..) If you ran dual RG-11 sized wire, perhaps.. (RG-213/RG-8 sized wire has a AWG 13 center conductor.. Compare to openwire line with AWG14 or AWG16) Is the problem coupling "out of" a balanced openwire line? .. If you're having interference problems with balanced AUDIO cables, then something else is wrong. Twisted pair, unshielded, should have substantially better interference rejection than any sort of coax lashup, paired or otherwise. Look for a leakage capacitance problem at one end or the other. The audio circuit probably has different parasitic C from each side to ground, and while at audio frequencies this isn't a big deal, at RF, it could be a problem. Have you looked at K9YC's RFI-ham write up? It explains all sorts of stuff about running wires hither and yon, interference, filtering, etc. Pin 1 problems are a big issue, and he addresses how they can creep in. Jim, W6RMK On 1/30/09 10:32 AM, "Dudley Hurry" <jhu...@austin.rr.com> wrote: Chris, Here is another way to run the wires in, take two identical runs of coax, at least RG8x, tie the grounds together on the outside end, but this way you can run the twin lead inside without effecting near field.. This might solve your issue getting inside.. 73, Dudley WA5QPZ _______________________________________________ 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.flex-radio.com/ Homepage: http://www.flex-radio.com/
