Topband: Zo of an individual CAT5 twisted pair

[James Rodenkirch]

Well, I have the wiring scheme all written out and plan on labeling each connection and checking twice and three times b4 soldering up the connection boxes and then connecting to the loop itself.....great dialogue, fellas.  Thank you ALL so much!!!
 
Great learning experience, trust me -- especially for being an 'ol fart!
 
72, Jim Rodenkirch K9JWV
 



> From: n4is at comcast.net
> To: rodenkirch_llc at msn.com; jim at audiosystemsgroup.com; topband at contesting.com
> Date: Mon, 12 Aug 2013 17:10:18 -0400
> 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
> > Yes, but there's a bit more to it. Twisted pair, by its nature, 
> > minimizes noise pickup.  That rejection is maximized if the 
> > terminations at both ends of the line are balanced -- that is, each 
> > side of the line has equal impedance to ground -- and if there is 
> > minimal common mode coupling at each end
> 
> 
> Hi guys
> 
> Jim is 100% right, balancing both ends is a MUST. But there is more. I would
> like to share what happened few month ago with a WF project. Peter N8PR
> built a beautiful WF with a polarization rotator. Peter can turn his WF
> horizontal or vertical. Very nice project. We decided to check the phase
> when the WF was about to go up. I measured the phase using a oscilloscope
> driving the feed line input with 5W to measure the phase at the loops. First
> at the 9:1 BALUN that feed the loops, the phase was correct and near 180
> degree, but the amplitude was not the same between the two loops, let's say
> 10% different from each other. Then when I measured the phase at the
> resistors, the phase was very different between them, near 50 degree and the
> amplitude way off, like 50% difference. It was hard to understand why such
> difference between the two loops and even harder to understand the phase
> difference between the transformer  and the resistor in the same loop. After
> removing all BALUNS and measuring them at the bench with a VNA we found one
> isolation BALUN inverted. Peter was feeding his WF with 75 ohm, and the
> BALUN had 4 turns on the 50ohms side and 5 turns on 75 ohms, and it was
> connected backward, 4 turns to the 75 ohms and 5 turns to the 50 ohm point,
> where the two 100 ohms line are connected 180 degree. After connecting the
> BALUN the way it should be, the phase measured at the transformer and the
> resistor become equal in both loops, and the amplitude also was equal as
> expected, the difference in phase or amplitude was not detectable anymore.
> 
> It was the first time I faced this situation. The FLAG antenna, or EWE, K9AY
> , pennant and WF are actually a loaded loop. Adding one resistor inside the
> loop the gain drops but you  get a cardioid pattern, good front back and
> good RDF. The signal when reach the first vertical wire is reflected to the
> second wire, and the signal when reach the second wire the signal is
> reflected to the first wire. When the signal reach the resistor it is
> dissipated, and when the second signal reach the transformer it goes to the
> feed line. The combination of these two currents give us the cardioid
> pattern. In the WF there is a combination of two cardioids to get side nulls
> and higher RDF. All this work fine "IF" there is no mismatch when the signal
> current reach the resistor and the BALUN, any mismatch impedance inside the
> loop will change the phase, and as a result, a deterioration in directivity.
> The value of the resistor should be very close to the impedance at the
> transformer, Example, for a FLAG feed with100 ohm line and 9:1 BALUM giving
> 900 ohms impedance,  the resistor should be near 900 ohms to avoid SWR
> inside the loops. This is necessary to keep the right phase to form a
> cardioid pattern. The FLAG is no resonant an can be used from 1Mhz to 10
> MHz, BUT it is very sensitive to impedance mismatch.
> 
> Before correcting the 50/75 BALUN the SWR measured with a MFJ was near
> 1;1,8. After correcting the BALUN it was 1:1,5. Measuring only the SWR does
> not tell much about the antenna. The FLAG wants to work, like Luis once
> said. However if there is a mismatch anywhere the results won't be good. It
> is complicated to measure impedance on 160m, near AM signals around.
> 
> The FLAG or dual FLAG like the WF require a perfect match to provide the
> expected performance, and any common mode current can compromise the RDF and
> the overall performance. 
> 
> Do It right at the first time, don't change anything in the project! Use
> what was recommended.
> 
> Regards
> JCarlos
> N4IS
> 
> _________________
> Topband Reflector