Re: Topband: In search of resonance
On 1/30/2014 11:03 PM, Carl Braun wrote: If I can't get the antenna to resonate using the L I'd say that I'd consider shunt feeding the tower and work out an (omega) matching scheme to match the tower to my target freq. If that's the case, do I mount my upper shunt arm on the tower at 67' or at 90'? Can I run a single drop wire into my panel and then switch the feed between two matching networks? One for 160 and one for 80? Please advise Thanks Carl AG6X Carl, Why not just run a slant wire to your shack and feed the bottom against a ground system through an ATU. Don't expect any real drama on 80 meters as the tower is probably to long electrically. ut a slant on any frequency could be modeled to see what you choices are. The only way this could change if you made a decoupling sleeve on the tower so the radiator appear to be between 1/4 and 3/8 wave length. It can work as a duo bander but it will require some extra work and a good vacuum switch since the voltages may be high at the in/out switch point. Some directive in the direction of the slant may occur but it should be be slight. As far as a drop wire shunt is concerned: There should not be any advantage of having the drop wire shunt arm much higher than the approximated sweet point for you tower. Herb Schoenbohm, KV4FZ _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: In search of resonance
Herb, you can feed any number of bands through one gamma arm or wire as long as the highest frequency to be used is less than 1/4 wave length on the gamma arm or wire. The appropriate matching is still required for each band. I fed my 70ft grounded tower for 160, 80 and 40 meters with a gamma of 27ft length...de gary -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Herbert Schonbohm Sent: Tuesday, February 25, 2014 11:52 AM To: topband@contesting.com Subject: Re: Topband: In search of resonance On 1/30/2014 11:03 PM, Carl Braun wrote: If I can't get the antenna to resonate using the L I'd say that I'd consider shunt feeding the tower and work out an (omega) matching scheme to match the tower to my target freq. If that's the case, do I mount my upper shunt arm on the tower at 67' or at 90'? Can I run a single drop wire into my panel and then switch the feed between two matching networks? One for 160 and one for 80? Please advise Thanks Carl AG6X Carl, Why not just run a slant wire to your shack and feed the bottom against a ground system through an ATU. Don't expect any real drama on 80 meters as the tower is probably to long electrically. ut a slant on any frequency could be modeled to see what you choices are. The only way this could change if you made a decoupling sleeve on the tower so the radiator appear to be between 1/4 and 3/8 wave length. It can work as a duo bander but it will require some extra work and a good vacuum switch since the voltages may be high at the in/out switch point. Some directive in the direction of the slant may occur but it should be be slight. As far as a drop wire shunt is concerned: There should not be any advantage of having the drop wire shunt arm much higher than the approximated sweet point for you tower. Herb Schoenbohm, KV4FZ _ Topband Reflector Archives - http://www.contesting.com/_topband --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: In search of resonance
Thanks to all who responded to my post I will consider all of the ideas that were presented including improving the ground radials. That's a given. I have an ICE broadcast filter for RX...can this be of any use with the MFJ for analyzing the antenna? Shall I drop the 40m verticals or open them at the base to see if any readings change? The good news is the end of the L is run through a pulley attached to a 70' palm tree. I'll lower the end of the wire down and fold it back a few feet until I can get something to resonate. Stay tuned (pun intended). What's strange is that I had a version of this L up before with 2 temp radials lying on the ground. I used a REYCO trap at 67' and ran the rest of the L up 20' to the top of the tower and then out 15 to 20 ft. The REYCO trap has some inductance but the whole 160 portion wasn't much over 100' and the thing resonated on 80 too. The vertical portion was much closer to the tower than it is now...maybe 15-18 instead of 36 now. My Reyco trap has since bit the dust and Unadilla isn't making any more for at least another month. I'll post some results later after folding back some wire. Tnx again Carl AG6X From: donov...@starpower.net [mailto:donov...@starpower.net] Sent: Thursday, January 30, 2014 7:59 AM To: topband@contesting.com Subject: Re: Topband: In search of resonance Carl, Are you sure your MFJ meter isn't being overloaded by a broadcast station? Thats a very common problem especially on 160 meters. 73 Frank W3LPL From: Carl Braun carl.br...@lairdtech.com To: topband@contesting.com Sent: Thursday, January 30, 2014 4:16:53 AM Subject: Topband: In search of resonance Hello to the group I'm a newbie to 160 having only participated in various contests over the course of the last two years. I used an 80 meter aluminum tube vertical with a Reyco trap affixed to the top with a horizontal L: wire heading over to the palm tree. I've since converted that antenna into a pair of 40M verticals so I'm focusing my efforts on getting a resonant antenna on 60 and especially 160. Here's the hardware I'm working with... 90' Tri Ex Skyneedle tower with a Telrex 20 meter 5-element yagi on a 45' boom at 94'. Inverted L wire runs parallel to the tower and is spaced at 36 up to 85' and then out approx 60' or so. The tower is grounded via copper strap to three ground rods that are bonded to 1 ½ copper pipe that circles the perimeter of my tower and control panel base. The perimeter copper pipe is a 4' x 8' rectangle that currently has 16 radials screwed to it. Three of those radials are tied into my 40M phased array ground radial system with some of the radials as short as 30' and others as long as 100'. The ground screen for my 40M array uses 100 radials each 60-90' long. I'm adding radials as I have time. Half of the 16 radials are multi conductor rotor control cable that fans out to affix to the radial ring then converge back together for 10' across the driveway and then fan out. I do this to eliminate a lot of individual wires crossing my secondary driveway. I cannot get the inverted L to provide a dip on my MFJ 259 analyzer anywhere in the 160 meter band. I get dips at 8.2 MHz (R=36 ohms X=0) with reactance on each side of X=0. At 5 MHz R=40 ohms X=0 with reactance on each side of X=0. I cant get any significant dips neat the 80 or 160 band. However, when I approach 1.750MHz the resistance drops to 6 ohms and X is off the scale...at 1.825 I'm at 10 ohms and X is off the scale. Its as if my 140+ feet of wire is resonant on 8MHz. Also, I've experimented with shunt feeding the tower to see where the thing would resonate but got similar results. ON4UN says my 90' tower and 5 ele yagi should yield an antenna that is 110 to 115 degrees in total length so I followed his guidelines and tapped the tower at 67' with a gamma wire spaced at 36 . The tower had multiple dips at 27 MHz, 20 MHz, 14 MHz and at 7.5 MHz the resistance dropped to 6 ohms...the same low resistance I' m now seeing on the L at 1.750 or so. No dips were observed at 3.5 or 1.8 MHz. I plan to experiment with a gamma wire that goes all the way to the top of the tower to see where it resonates...if its still high in freq maybe I should consider an Omega match So all of that being said...why cant I find a resonant frequency on 160 with this L? Am I still too long? Is the tower causing that much interaction? I'd rather not cut the L long and insert a variable cap...I want it resonant at 1820 so I can use an unun to match the impedance and then run it into the shack. Any suggestions on getting the antenna to work? Thanks in advance for any help Carl AG6X _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: In search of resonance
To my amazement, a 5000-watt AM station on 1550 KHz 5 miles away is enough to clobber my MFJ-259's usefulness during the day. Fortunately they drop to 6 watts at local sundown (what do you suppose that is, a single 6L6?) 73, Pete N4ZR Check out the Reverse Beacon Network at http://reversebeacon.net, blog at reversebeacon.blogspot.com. For spots, please go to your favorite ARC V6 or VE7CC DX cluster node. On 1/30/2014 9:22 PM, chetmoore wrote: Thanks for this tidbit of information. As soon as this white manure melts (some people call it snow) I will do a re-check on my shunt fed tower. I think I did have at least one dip to zero and never did find a resonance point. Thanks Chet N4FX -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Tom W8JI Sent: Thursday, January 30, 2014 1:34 PM To: Tree Cc: 160; Carl Braun Subject: Re: Topband: In search of resonance You might be dealing with AM BCB being detected by the meter - and masking what you are looking for. No, because he gets a dip to zero reactance. If that happens anywhere, there is no BCI. 73 Tom _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: In search of resonance
On 160, that is. 73, Pete N4ZR Check out the Reverse Beacon Network at http://reversebeacon.net, blog at reversebeacon.blogspot.com. For spots, please go to your favorite ARC V6 or VE7CC DX cluster node. On 1/31/2014 6:27 AM, Pete Smith N4ZR wrote: To my amazement, a 5000-watt AM station on 1550 KHz 5 miles away is enough to clobber my MFJ-259's usefulness during the day. Fortunately they drop to 6 watts at local sundown (what do you suppose that is, a single 6L6?) 73, Pete N4ZR Check out the Reverse Beacon Network at http://reversebeacon.net, blog at reversebeacon.blogspot.com. For spots, please go to your favorite ARC V6 or VE7CC DX cluster node. On 1/30/2014 9:22 PM, chetmoore wrote: Thanks for this tidbit of information. As soon as this white manure melts (some people call it snow) I will do a re-check on my shunt fed tower. I think I did have at least one dip to zero and never did find a resonance point. Thanks Chet N4FX -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Tom W8JI Sent: Thursday, January 30, 2014 1:34 PM To: Tree Cc: 160; Carl Braun Subject: Re: Topband: In search of resonance You might be dealing with AM BCB being detected by the meter - and masking what you are looking for. No, because he gets a dip to zero reactance. If that happens anywhere, there is no BCI. 73 Tom _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: In search of resonance
You might be dealing with AM BCB being detected by the meter - and masking what you are looking for. No, because he gets a dip to zero reactance. If that happens anywhere, there is no BCI. 73 Tom _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: In search of resonance
Thanks for this tidbit of information. As soon as this white manure melts (some people call it snow) I will do a re-check on my shunt fed tower. I think I did have at least one dip to zero and never did find a resonance point. Thanks Chet N4FX -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Tom W8JI Sent: Thursday, January 30, 2014 1:34 PM To: Tree Cc: 160; Carl Braun Subject: Re: Topband: In search of resonance You might be dealing with AM BCB being detected by the meter - and masking what you are looking for. No, because he gets a dip to zero reactance. If that happens anywhere, there is no BCI. 73 Tom _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: In search of resonance
Tom Maybe you saw my post where I stated that the MFJ plunged to a minimum reading of 4 0hms at 1825? Does this reading mean that the L is near ground potential and 'in union' with the grounded Skyneedle at that freq? It could be from a few things, but two closely spaced conductors, with the parasitic conductor resonant near the target band of the fed conductor, commonly behaves this way. You might never be able to get Inverted L real part (resistance part) high at that spacing and length. If I can't get the antenna to resonate using the L I'd say that I'd consider shunt feeding the tower and work out an (omega) matching scheme to match the tower to my target freq. If that's the case, do I mount my upper shunt arm on the tower at 67' or at 90'? There is probably some ideal point where the shunt capacitance is minimized, and that would be best. There are hundreds of points that will work, but they will have higher Q. Can I run a single drop wire into my panel and then switch the feed between two matching networks? One for 160 and one for 80? I don't know. I've never looked at doing that. 73 Tom _ Topband Reflector Archives - http://www.contesting.com/_topband
