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: [email protected] > To: [email protected]; [email protected]; [email protected]; > [email protected] > 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:[email protected]] On Behalf Of James > Rodenkirch > Sent: Monday, August 12, 2013 6:08 PM > To: JC N4IS; [email protected]; [email protected] > 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: [email protected] > > To: [email protected]; [email protected]; > [email protected] > > 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 > > _________________ > Topband Reflector > > _________________ > Topband Reflector _________________ Topband Reflector
