Topband: Zo of an individual CAT5 twisted pair

[Jim Garland]

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:rodenkirch_llc at msn.com] 
Sent: Monday, August 12, 2013 10:47 AM
To: Jim Garland; topband at contesting.com
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: 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