Re: Topband: Modeling Transmit Antenna Affect on Rx Antenna Performance?
Your feedline is about 350 feet. That is (with RG213 -velocity 0,66-) close to 1 wavelength. With 1 wavelength feedline, the TX antenna is floating when the feedline is open in the shack. Just wrong once more. !! _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Modeling Transmit Antenna Affect on Rx Antenna Performance?
Your feedline is about 350 feet. That is (with RG213 -velocity 0,66-) close to 1 wavelength. With 1 wavelength feedline, the TX antenna is floating when the feedline is open in the shack. I'm sorry to say that , but the concept is wrong, the TX antenna resonance as structure has nothing to do with the impedance. Floating the element makes it 1/4 element, keeping it connect it works like a 1/2 wave resonant antenna. I presemted some solutions on my Webnair at wwwrof, still available and you can download the slides with extra information. Like PY2XB inverted V when disconnected from the feed line drops the noise 2 S units on the RX antenna. Changing the impedance you can notice a change in the noise but only few dbs. JC N4IS _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Modeling Transmit Antenna Affect on Rx Antenna Performance?
Paul, Your feedline is about 350 feet. That is (with RG213 -velocity 0,66-) close to 1 wavelength. With 1 wavelength feedline, the TX antenna is floating when the feedline is open in the shack. Depending on your transceiver configuration (if the TX antenna is completely decoupled when using the RX antenna input) you may not even need a special relay. I did it this way during many years with a TX antenna 5 meters away from my K9AY loops. Kees, PE5T -- From: "Paul Ferguson" Sent: Friday, September 30, 2016 9:10 PM To: Subject: Topband: Modeling Transmit Antenna Affect on Rx Antenna Performance? For transmit I use a 160M T antenna with on ground radials. I am considering installing a Circle-8 receiving array such as one made by Hi-Z. The receive array would be very close to the T, maybe within 100 feet. I am using EZNEC to see how the transmit antenna proximity affects the pattern of the Rx array. I have a simple EZNEC model of a 4 square Rx array. The model uses a source on each 20-foot Rx vertical, with the pattern determined by the phase of each source. I put models of the T and the Rx array in the same EZNEC model. With the source removed from the T, the radials are connected to the T portion of the antenna. This configuration shows a big degradation in Rx front to back ratio. If I open the T at the feed-point by either putting in a source with zero current or simply breaking the connection between the T and its radials, running the model shows little to no affect on the Rx pattern. I could use a relay at the antenna to disconnect the feed line near the feed-point when not transmitting, but I would rather avoid the relay because of running QSK and wanting to avoid the wiring run. My modeling runs, using either an effectively open or shorted feed line at the T, do not represent my real system because it is not open or shorted. The feed is about 350 feet of coax to a K9YC-designed common-mode choke and a 1:1.56 unun. I am wondering if there might be value in disconnecting the feed line from the antenna and measuring the impedance looking back into the unun/choke/coax string. Take this impedance and add it as an RLC network connected across the feed-point of the T antenna. My thought is this would be close to what the Rx array is really seeing when I look for the affect of the nearby T in the EZNEC run. Am I on a decent path or lost in the woods? 73, Paul, K5ESW _ Topband Reflector Archives - http://www.contesting.com/_topband - Geen virus gevonden in dit bericht. Gecontroleerd door AVG - www.avg.com Versie: 2016.0.7797 / Virusdatabase: 4656/13119 - datum van uitgifte: 09/30/16 _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Modeling Transmit Antenna Affect on Rx Antenna Performance?
Hi Paul, Modeling the effect of the feedline and the receiver terminating the feedline is tricky. Some are able to short or open the TX feedline in the shack due to a "favorable" length from the antenna to the shack. The brute force method is to install a vacuum relay at the feedpoint which leaves the feedpoint hanging on RX. That's tough for QSK, but can be done based on a microHam or WinKey box, used as keyer both to paddle and contest software. You also need to consult the mfr of the RX array which may have limits to the amount of induced voltage to the Hi-Z. So until determined otherwise, you have a TX bothering RX on TX issue in addition to a TX bothering RX on RX issue. 73, Guy. On Fri, Sep 30, 2016 at 3:20 PM, JC wrote: > My TX antenna is 60ft from my vertical WF and my horizontal WF is at the > top > of my TX antenna. I am using a Folded Unipole configuration, it is a > skirt > with 3 wires forming a cage. The skirt detune the tower during RX and help > the TX with a huge broad band. > > In your case, just open the T disconnecting it from the coaxial cable using > a fast vacuum relay. This will to the same as my UNIPOLE. Just keep the T > floating during RX. > > 73 > JC > N4IS > > > _ > Topband Reflector Archives - http://www.contesting.com/_topband > _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Modeling Transmit Antenna Affect on Rx Antenna Performance?
Paul, I suggest you talk to Gary KD9SV as he built a Hi-Z around his TX antenna. Incidentally the ground radials under the Hi-Z is not a good idea. I suspect you would have to use NEC4 to see the real effect of the radials. I have not made a test myself to see how close radials could be. Disconnecting the T element on one band like 160 will work for that band but likely will not work the same on 80 meters. Leaving it connected might be better. Same situation with the feedline impedance looking back toward the radio. That may change with band as well. Lee K7TJR -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Paul Ferguson Sent: Friday, September 30, 2016 12:10 PM To: topband@contesting.com Subject: Topband: Modeling Transmit Antenna Affect on Rx Antenna Performance? For transmit I use a 160M T antenna with on ground radials. I am considering installing a Circle-8 receiving array such as one made by Hi-Z. The receive array would be very close to the T, maybe within 100 feet. I am using EZNEC to see how the transmit antenna proximity affects the pattern of the Rx array. I have a simple EZNEC model of a 4 square Rx array. The model uses a source on each 20-foot Rx vertical, with the pattern determined by the phase of each source. I put models of the T and the Rx array in the same EZNEC model. With the source removed from the T, the radials are connected to the T portion of the antenna. This configuration shows a big degradation in Rx front to back ratio. If I open the T at the feed-point by either putting in a source with zero current or simply breaking the connection between the T and its radials, running the model shows little to no affect on the Rx pattern. I could use a relay at the antenna to disconnect the feed line near the feed-point when not transmitting, but I would rather avoid the relay because of running QSK and wanting to avoid the wiring run. My modeling runs, using either an effectively open or shorted feed line at the T, do not represent my real system because it is not open or shorted. The feed is about 350 feet of coax to a K9YC-designed common-mode choke and a 1:1.56 unun. I am wondering if there might be value in disconnecting the feed line from the antenna and measuring the impedance looking back into the unun/choke/coax string. Take this impedance and add it as an RLC network connected across the feed-point of the T antenna. My thought is this would be close to what the Rx array is really seeing when I look for the affect of the nearby T in the EZNEC run. Am I on a decent path or lost in the woods? 73, Paul, K5ESW _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Modeling Transmit Antenna Affect on Rx Antenna Performance?
My TX antenna is 60ft from my vertical WF and my horizontal WF is at the top of my TX antenna. I am using a Folded Unipole configuration, it is a skirt with 3 wires forming a cage. The skirt detune the tower during RX and help the TX with a huge broad band. In your case, just open the T disconnecting it from the coaxial cable using a fast vacuum relay. This will to the same as my UNIPOLE. Just keep the T floating during RX. 73 JC N4IS _ Topband Reflector Archives - http://www.contesting.com/_topband