JC, Thanks for the info, much appreciated. I see that I need to go ahead and try CAT5 and see how it compares to coax for my flag feedline.
73, Bob K6UJ On Sep 9, 2013, at 5:08 PM, JC N4IS wrote: > Bob > > Here the missing part of my original post to motivate you to try a single > twisted pair. > > See bellow Ilian's comments about the performance of the RX antenna. Illian > was not detuning his TX antenna. > > Regards > JC > N4IS > > hi Jose > > [12:02:50 PM] Ilian: My log is already uploaded on LoTW and ClubLog > > [12:03:23 PM] Ilian: 1394 QSO on 160m > > [12:04:15 PM] Ilian: more than 1200 QSOs after RX antenna installing > > [12:05:02 PM] Ilian: about 150 QSOs without RX antenna for more than 2 > months on the air > > [12:05:57 PM] Ilian: 1200 QSOs made with RX antenna for 1 month and 10 days > > [12:06:49 PM] Ilian: 68 DXCC worked on 160m during the all operation > > [12:07:49 PM] Ilian: about 40 countries worked after RX antenna installing > within 1 month and 10 days > > [12:09:49 PM] Ilian: 3865 QSOs on 80m during the all operation, about 2500 > worked after RX antenna installing > > [12:10:24 PM] Ilian: 112 DXCC worked on 80m for whole period > > [12:11:54 PM] Ilian: about 50 new DXCC worked after RX antenna installing > for a month and 10 days > > [12:13:36 PM] Ilian: http://t6lg.com/?page_id=221 > > [12:14:05 PM] Ilian: you can see all statistics here > > [12:15:57 PM] Ilian: Thank you, Jose! > > -----Original Message----- > From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Bob K6UJ > Sent: Monday, September 09, 2013 10:20 AM > To: topband List List > Subject: Re: Topband: CAT5 for Flag Antenna Feedline ? > > Jim, > > Your hams guide to RFI is my bible for mitigating RFI issues. My feedline > chokes are all designed from this great article. I probably have optimized > my feedline to the flag in regards to common mode noise but after reading > the post I was curious about CAT5. Before possibly wasting my time > experimenting with CAT5 for feeding my flag I wanted to learn more about it. > Below is a paragraph from the Topband reflector thread titled "high > performance receive antenna at T6LG" that sparked my interest. They were > discussing the delta shaped flag they used which was used before on the > FO0AAA dxpedition. > > Bob > K6UJ > > The parts for the antenna was very simple, a 9"1 balun and a 910 ohms > resistor, and a 100 to 75 ohms BALUN to feed the preamp. The key component > here was the CAT 5 single twisted pair to feed the flag antenna without any > common mode noise pickup (it is necessary to strip the CAT5 and separate > each of the 4 pairs), a coax cable won't work in high noise environment, > even with a killer choke the ground does not help to stop the common node > noise. That was not the first time a twisted pair saved the day, two years > ago I suggested Rolf PY1RO a similar antenna fed with twisted pair that > worked very well, bringing the noise to zero in a s9+20 noise environment. > > On Sep 8, 2013, at 11:12 PM, Jim Brown wrote: > >> On 9/8/2013 10:30 PM, Bob K6UJ wrote: >>> I got the impression from the post >>> that CAT5 is immune to common mode noise. >> >> I've not heard that, nor can I think of a theoretical basis for saying so. > CAT5 is very good twisted pair, with a high twist ratio, Zo = 100 ohms, and > its loss is low enough to make it work fine on 160M. The primary advantage > of twisted pair is that it rejects DIFFERENTIAL mode noise. Rejection is > greatest when both ends of the line are balanced. >> >> One possible source of your confusion may be reading, but not fully > understanding, my work, and Neil Muncy's work, on SCIN, whereby certain > deficiencies in the construction of a cable shield convert common mode > current to a differential voltage on the signal pair. I have on several > occasions observed that high quality unshielded twisted pair, like CAT5/6/7, > would have much better noise rejection than that sort of cable. Read about > it in several tech papers and tutorials on my website. No need to burden the > list with it. >> >> 73, Jim K9YC >> >> _________________ >> Topband Reflector > > _________________ > Topband Reflector > _________________ Topband Reflector