Topband: Zo of an individual CAT5 twisted pair

[James Rodenkirch]

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???
 
 

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: 4cx250b at miamioh.edu
> To: rodenkirch_llc at msn.com; topband at contesting.com
> 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:topband-bounces at contesting.com] On Behalf Of James
> > Rodenkirch
> > Sent: Monday, August 12, 2013 10:32 AM
> > To: topband at contesting.com
> > 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