Topband: Zo of an individual CAT5 twisted pair

[James Rodenkirch]

When asked, these days, how my day is going, Charlie, I respond with, "Going great 'cuz I am on the green side of the grass"!

> From: charlie-cunningham at nc.rr.com
> To: rodenkirch_llc at msn.com; n4is at comcast.net; jim at audiosystemsgroup.com; topband at contesting.com
> Date: Mon, 12 Aug 2013 18:18:28 -0400
> Subject: Re: Topband: Zo of an individual CAT5 twisted pair
> 
> Well, we're mostly all " 'ol farts", Jim, but the alternative is GRIM!
> 
> 73,
> Charlie. K4OTV
> 
> -----Original Message-----
> From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of James
> Rodenkirch
> Sent: Monday, August 12, 2013 6:08 PM
> To: JC N4IS; jim at audiosystemsgroup.com; topband at contesting.com
> Subject: Re: Topband: Zo of an individual CAT5 twisted pair
> 
> 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
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> Topband Reflector
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