When I did my test, I didn't use a balun - I just attached a coax connector to the CAT5e to get a rough check on the VSWR. The noise pickup was probably a result of not having a balanced feed. I made this test to see if CAT5 would be a suitable feedline for portable QRP operation, and it actually worked quite well. Running 100W into a dummy load, with about 50 ft of CAT5, showed no perceptable VSWR.
73, Jim W8ZR _____ From: James Rodenkirch [mailto:[email protected]] Sent: Monday, August 12, 2013 10:47 AM To: Jim Garland; [email protected] Subject: RE: Topband: Zo of an individual CAT5 twisted pair Well, Jim, here is what N4IS stated (bolded words my emphasis) - looks like he found the twisted pair to reduce the noise OR am I reading it incorrectly? Or are there two different noises being discussed??? <http://www.t6lg.com/> www.t6lg.com The noise level was unbearable for low bands, Ilian was not able to hear even the strong European station but Ilian had a good signal on low bands. I worked him on 80m back in October and start chatting with him on skype. I proposed a flag antenna to improve his RX capabilities. The problem with most field station is lack of good ground, this issue makes a very complicated situation with common mode noise everywhere, from the coax cable feeding the inverted V to the AC wire system and power generators, and other antenna cables. There is not a simple way to ground the receiver, every wire connected to the radio became part of the antenna system. The solution was a system , not only a simple flag antenna. Ilian radio is a FT897 that does not have a separated RX port. I send him a DX Engineering RTR-1 Receive Antenna Interfaces RTR-1, that switch was necessary to keep high isolation between the RX antenna and the TX antenna. The flag antenna has low gain and I sent Ilian a preamp made by Gary KD9SV, a FET follower design with high IP3. 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. > From: [email protected] > To: [email protected]; [email protected] > Date: Mon, 12 Aug 2013 10:38:57 -0600 > Subject: Re: Topband: Zo of an individual CAT5 twisted pair > > I believe that if you parallel two twisted pairs of a CAT5 cable, you'll > have a 50 ohm transmission line.(Each twisted pair is 100 ohms). I've tried > this with CAT5e cable and find it works well, even for transmitting, up to > about 100W. The VSWR match was very close to 50 ohms. The problem is that > there is very poor noise rejection. When I used it as transmission line for > a receive antenna I picked up all the computer hash, fluorescent lights, > etc. in the area. I quickly abandoned the experiment and went back to coax > cable. > 73, > Jim W8ZR > > > -----Original Message----- > > From: Topband [mailto:[email protected]] On Behalf Of James > > Rodenkirch > > Sent: Monday, August 12, 2013 10:32 AM > > To: [email protected] > > Subject: Topband: Zo of an individual CAT5 twisted pair > > Importance: High > > > > In an earlier post to this reflector, Carlos, N4IS, mentions using one > pair of twisted wires > > out of a CAT5 cable to feed the delta loop antenna used by T6LJ. > > > > I am assembling the pieces/components needed to put an "FO0AAA style" > delta loop > > receive antenna up and want to use the twisted pair cable as well., > > > > My question is: > > > > Does it matter which twisted pair of wires I use? > > > > Thanks, in advance, for any thoughts....72, Jim Rodenkirch K9JWV > > > > _________________ > > Topband Reflector > > _________________ > Topband Reflector _________________ Topband Reflector
