Dudley, I actually use the configuration you mentioned for my current feedline. It allows me to run balanced transmission line from my balanced tuner, out the house (passing nearby metal) and underground for about 50 ft or so. This "coax as balanced line" configuration then feeds a long run of low loss 450 ohm open-wire line to my multi-band antenna.
The trick with lashing two pieces of coax together to achieve a balance line boils down to two best practices - use the highest impedance and lowest loss cable available and keep the coax run as short as possible. This will minimalize feedline losses as they are considerable in the coax segment compared to traditional openwire line. Overall, the coax to 450 ohm ladder line feed should have much less loss (in a high SWR multiband environment) compared to a full run with plain RG-8 transmission line. My balanced configuration uses a dual, low loss 75 ohm cable configured as you described feeding the RF out of the tuner into both center conductors with the shield boded together. The two cables are wiretied together and cut to be the same length. I use this system with a center fed 160 through 10 meter flatop 250 ft long and 70ft in the air. I have no issues with RF in the shack at all with my SDR-1000 and Edirol FA-66 sound card. Carmine W1EQX --- On Fri, 1/30/09, Dudley Hurry <jhu...@austin.rr.com> wrote: From: Dudley Hurry <jhu...@austin.rr.com> Subject: Re: [Flexradio] Balanced vs. unbalanced microphone inputs To: "Chris seeber" <ctsee...@cox.net> Cc: mindaugas2...@yahoo.com, flexradio@flex-radio.biz Date: Friday, January 30, 2009, 1:32 PM 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 Chris seeber wrote: > Dudley, > > Thanks. Yes, there is no doubt an "out of balance" situation going on > here. The lines are the same length, but they do come very close to the > PC (tower) case and are also routed too close to the ground wires in the > shack. There's no other way to route them in here. That's why I need > to get them outside and run coax in. I am hoping that will solve most > of the trouble. > > Chris, > KA1GEU > > -----Original Message----- > From: Dudley Hurry [mailto:jhu...@austin.rr.com] Sent: Thursday, January 29, 2009 4:51 PM > To: Chris seeber > Cc: mindaugas2...@yahoo.com; flexradio@flex-radio.biz > Subject: Re: [Flexradio] Balanced vs. unbalanced microphone inputs > > Chris, > > If you are using balanced line and getting RFI, something is out of balanced, most likely the latter line. You must be careful that the lengths of both lines are exactly the same, and that includes the antenna. And ANY metal objects close to either side will throw it out of balance. The whole ideal of balance lines is the word balanced, exactly the same and the RF will be canceled out. These things have to be planned very carefully. I have run balanced here and had no RF showing on my field strength meter, if it does, there is a problem. > 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/
