[AMRadio] Loop antenna feed question
Well - my Valiant is putting out stable rated power on all bands - this morning I'll suss out where the audio is disappearing to - should be ready for Air then... now to turn to the Radiator. I'm still in the 'steep' part of the EasyNEC learning curve - and I've gone through the several ARRL antenna books - so I'm properly confused. I have a loop of 14ga hard copper wire around the rear of my propery, attached (with insulators spaced at abt 8' apart) to the fence - of about 450 feet diameter, and nearly (but not quite) square. It is about 5' above the ground, except for one leg which is attached to the house, where it is about 7'. I am feeding it with 450-ohm ladder-line. My Question to the Antenna Gurus is this: At the feed-point, should I maintain the ladder-line spacing where it joins the loop ends, or should there be an angle, ie. should the loop ends be wider than the feedline pitch - and if so, what should the included angle of the feedline 'transistion' be...? I've approached this from two or three analytical directions, and of course have different (and somewhat exclusive) answers so I'm Learning, which is a good thing. Cheers John KB6SCO
Re: [AMRadio] Loop antenna feed question
John, I to am a novice at this stuff. I'm having trouble visualizing your antenna. You said, the fence - of about 450 feet diameter, and nearly (but not quite) square. Could you clarify this to me? I too have a horizontal loop. Mine is about 15' off the ground, and has about 240' of wire (roughly 4 X 60'). I feed it with 450 ohm ladder line to the ground. My antenna is resonant at about 3.9 Mhz, and the impedance at SWR minimum (1.5:1) is about 80 ohms. I measure this right on the ground between the ladder line and my DPDT knife switch (I ground it out when not in use). I then use a 1:1 current balun, and RG-8X coax to the shack. My first try was to convert from 450 to 300 ohm tv twin lead at the hole in the wall, and go straight to a Johnson 275 matchbox with 300 ohm twin lead. This was dismal since the Johnson matchbox doesn't seem to have a wide tuning range to feed 80 ohms balanced. It did work unbalanced however, but poorly. So I switched to coax after a 1:1 balun for the run inside. If I do it again, and intend to feed this antenna at resonance, 75 ohm coax straight all the way might be an option. This loop loads up like a SOB, and absolutely NO RF in the shack. The problem though is that my signal reports are usually poor (often) to great (once in a while). It seems that for this to work efficiently as a low horizontal loop (high angle radiator) for short skip, I need good soil conductivity, or counterpoise. Stations beyond 500 miles can hardly copy me, and yet I can sometimes be full scale at 150 to 200 miles out early in the evening. Regards, Jim WD5JKO --- John Lawson [EMAIL PROTECTED] wrote: Well - my Valiant is putting out stable rated power on all bands - this morning I'll suss out where the audio is disappearing to - should be ready for Air then... now to turn to the Radiator. I'm still in the 'steep' part of the EasyNEC learning curve - and I've gone through the several ARRL antenna books - so I'm properly confused. I have a loop of 14ga hard copper wire around the rear of my propery, attached (with insulators spaced at abt 8' apart) to the fence - of about 450 feet diameter, and nearly (but not quite) square. It is about 5' above the ground, except for one leg which is attached to the house, where it is about 7'. I am feeding it with 450-ohm ladder-line. My Question to the Antenna Gurus is this: At the feed-point, should I maintain the ladder-line spacing where it joins the loop ends, or should there be an angle, ie. should the loop ends be wider than the feedline pitch - and if so, what should the included angle of the feedline 'transistion' be...? I've approached this from two or three analytical directions, and of course have different (and somewhat exclusive) answers so I'm Learning, which is a good thing. Cheers John KB6SCO __ AMRadio mailing list Home: http://mailman.qth.net/mailman/listinfo/amradio Help: http://mailman.qth.net/mmfaq.html Post: mailto:AMRadio@mailman.qth.net AMfone Website: http://www.amfone.net AM List Admin: Brian Sherrod/w5ami
Re: [AMRadio] Loop antenna feed question
John, Hmmm 450 loop at 5'. Feedpoint impedance would vary all over the place depending on frequency. Do you transmitting on this setup, and if so, are you using some kind of an antenna tuner, balanced output or single ended, how long is the feedline, and what frequencies do you intend to use? In any case, can't see that fanning out at the feedpoint would be necessary or useful. Dennis D. W7QHO Glendale, CA
Re: [AMRadio] Loop antenna feed question
Getting up a bit higher would probably improve things. To get on the air I've used setups worse than I care to talk about. Anything works better than nothing. Right now I'm using a dipole thats about 54' each side, fed with a pair of 80' RG-59 coax cables to a 4:1 balun in the basement, with 3' of RG-58 to a tuner. Ladder line is useless in my situation. Its hanging off 30' of chain link fence top rail, swagged together, run vertical, and bolted to a 4x4 post. The 5100-b loads up anywhere from 80 to 10 meters. I have been told it can't work. Go figger. Good luck, George KB2Z At 05:43 PM 12/4/05, you wrote: John, I to am a novice at this stuff. I'm having trouble visualizing your antenna. You said, the fence - of about 450 feet diameter, and nearly (but not quite) square. Could you clarify this to me? I too have a horizontal loop. Mine is about 15' off the ground, and has about 240' of wire (roughly 4 X 60'). I feed it with 450 ohm ladder line to the ground. My antenna is resonant at about 3.9 Mhz, and the impedance at SWR minimum (1.5:1) is about 80 ohms. I measure this right on the ground between the ladder line and my DPDT knife switch (I ground it out when not in use). I then use a 1:1 current balun, and RG-8X coax to the shack. My first try was to convert from 450 to 300 ohm tv twin lead at the hole in the wall, and go straight to a Johnson 275 matchbox with 300 ohm twin lead. This was dismal since the Johnson matchbox doesn't seem to have a wide tuning range to feed 80 ohms balanced. It did work unbalanced however, but poorly. So I switched to coax after a 1:1 balun for the run inside. If I do it again, and intend to feed this antenna at resonance, 75 ohm coax straight all the way might be an option. This loop loads up like a SOB, and absolutely NO RF in the shack. The problem though is that my signal reports are usually poor (often) to great (once in a while). It seems that for this to work efficiently as a low horizontal loop (high angle radiator) for short skip, I need good soil conductivity, or counterpoise. Stations beyond 500 miles can hardly copy me, and yet I can sometimes be full scale at 150 to 200 miles out early in the evening. Regards, Jim WD5JKO --- John Lawson [EMAIL PROTECTED] wrote: Well - my Valiant is putting out stable rated power on all bands - this morning I'll suss out where the audio is disappearing to - should be ready for Air then... now to turn to the Radiator. I'm still in the 'steep' part of the EasyNEC learning curve - and I've gone through the several ARRL antenna books - so I'm properly confused. I have a loop of 14ga hard copper wire around the rear of my propery, attached (with insulators spaced at abt 8' apart) to the fence - of about 450 feet diameter, and nearly (but not quite) square. It is about 5' above the ground, except for one leg which is attached to the house, where it is about 7'. I am feeding it with 450-ohm ladder-line. My Question to the Antenna Gurus is this: At the feed-point, should I maintain the ladder-line spacing where it joins the loop ends, or should there be an angle, ie. should the loop ends be wider than the feedline pitch - and if so, what should the included angle of the feedline 'transistion' be...? I've approached this from two or three analytical directions, and of course have different (and somewhat exclusive) answers so I'm Learning, which is a good thing. Cheers John KB6SCO __ AMRadio mailing list Home: http://mailman.qth.net/mailman/listinfo/amradio Help: http://mailman.qth.net/mmfaq.html Post: mailto:AMRadio@mailman.qth.net AMfone Website: http://www.amfone.net AM List Admin: Brian Sherrod/w5ami __ AMRadio mailing list Home: http://mailman.qth.net/mailman/listinfo/amradio Help: http://mailman.qth.net/mmfaq.html Post: mailto:AMRadio@mailman.qth.net AMfone Website: http://www.amfone.net AM List Admin: Brian Sherrod/w5ami
Re: [AMRadio] Loop antenna feed question
LB Cebik, W4RNL, on his web site, talking about Cloud Warmers, indicates 35 feet as the accepted height for a 75m loop. I am planning a loop for 160m at just a little over that height. Joe W4AAB - Original Message - From: [EMAIL PROTECTED] To: [EMAIL PROTECTED]; amradio@mailman.qth.net Cc: [EMAIL PROTECTED] Sent: Sunday, December 04, 2005 4:53 PM Subject: Re: [AMRadio] Loop antenna feed question John, Hmmm 450 loop at 5'. Feedpoint impedance would vary all over the place depending on frequency. Do you transmitting on this setup, and if so, are you using some kind of an antenna tuner, balanced output or single ended, how long is the feedline, and what frequencies do you intend to use? In any case, can't see that fanning out at the feedpoint would be necessary or useful. Dennis D. W7QHO Glendale, CA __ AMRadio mailing list Home: http://mailman.qth.net/mailman/listinfo/amradio Help: http://mailman.qth.net/mmfaq.html Post: mailto:AMRadio@mailman.qth.net AMfone Website: http://www.amfone.net AM List Admin: Brian Sherrod/w5ami
Re: [AMRadio] Loop antenna feed question
crawfish wrote: LB Cebik, W4RNL, on his web site, talking about Cloud Warmers, indicates 35 feet as the accepted height for a 75m loop. I am planning a loop for 160m at just a little over that height. Joe W4AAB Does he say -why- having the antenna no more than 1/8th wave above ground is better than having it a quarter wave up? I had it explained to me one time like this (strictly dipole speaking) Picture in your mind, a conventional half-wave, center fed dipole. Using each end as the outside points, draw a circle around the antenna. The dipole ends make the width across the circle. The height of the circle, from ground, would be the same as the length - 1/2 wavelength long. In the neighborhood of 3.880, that length calculates out to 120' (468 / 3.9Mc = 120') So, with the picture of the circle around the dipole in your mind, mentally change the circle to a 'wheel', that is your signal. If your antenna isn't *at least* 1/4 wavelength above ground, your wheel is stuck in the dirt, trying to radiate freely. Makes sense to me, that way - and as long as any part of your antenna is up at 60' or above, you'll find you've got a better-than-average signal coming from the antenna with comparable power levels. So, I've said all that, to ask this question: What's the difference in half-wave dipoles and their height above ground, and a full wave loop ( L(ft) = 1005 / f(Mc) Using 75m as an example: L(ft) = 1005 / 3.9 L(ft) = 257.7ft ) operating at half-height, as a cloud warmer? I Have a loop up, except that this loop started life as an inverted Vee on 75m. The Apex of the antenna is around 60'. This is not where the feed point is. Because my 51' crankup Tri-Ex tower is buried in the ground in the -front- yard (I inheirited it from my dad, who set it up when I was still living on the Left coast) in order to fit the antenna in the lot, the feed point has to be pretty much over the house, and the antenna support off-center. After changing from coax to ladder line, it was just a matter of closing in the bottom of the 75m Inverted Vee. The rope that holds the apex of the antenna in the air (via a pulley attached to a 40' push-up mast, in the middle of the tower) angles down to the yard-separating fence, which pulls the bottom part of the antenna away from the tower by about 10'. Over all length of the antenna is somewhere around 240 and 260'. I didn't measure. 60' of open-wire feed-line forgives many measuring sins. I am using a Heathkit SA-2060A 2kW impedance matching device, which has a nice, -big- torroid balun that directly feeds the open-wire output. It is curious to note that I now find I don't need to run more than around 100w to be only 3db weaker than those stations running 500w or more, of carrier output. 200w of carrier from my rig into this antenna has me a bit better than equal signal strength in the Northeast (according to WA1HLR) as compared to the 'power-houses' on 3.885 in the EARLY mornings. Since I have a bad case of neighboritis, I keep the power down. This loop is known to be called a Delta loop (looks like a big triangle), with the apex of the antenna around 60', the southwest end supported about 20~25 off the ground, and the northeast end about 10~15 off of the ground, and it is a full-wave loop antenna for 75m, except that it's on a Vertical plane, as opposed to a big ol' square cloud-warmer. I like to describe it best, by saying If you've got room for a 75m Inverted vee, then you've got room for a delta loop antenna The angle of radiation is -much- lower, but theres still enough high-angle stuff to work the close-in stuff, and because it -is- a loop, it's quieter than a dipole. The futzing and fretting over whether or not the ladderline legs should be spread out or not? pshaw... it don't need to be perfect - it just needs to have power fed to it. What I'd -really- like to try, is to utilze my neigbors two 70' tall Pecan trees, run a straight line between them, then bring the two lines down in an inverted delta position, and feed it where the antenna points to the ground. But as I've stated... I have neighboritis. I can't convince them that by raising the lightbulb further away from the area that's being illuminated, the less light there will be to shine on the affected area. *shrug* The same argument could be used against Covenance cases... the higher the antenna, the less likely it will interfere with something, close-in. Another good argument for having your half-wave dipole at least 1/4w above ground... Try it. You might be surprised. --- 73 = Best Regards, -Geoff/W5OMR
Re: [AMRadio] Loop antenna feed question
Ask yourself, what do you gain by using a Loop? From a transmit perspective, not much, if anything. I have heard many people switch from loops to dipoles at the same power level and location and saw little difference. From a receive perspective, maybe something. You might reduce noise in your receiver. I can't speak to this since I have never used a Loop. So, you gain in your receiver, but that is all. What good is it to hear someone if you can't put a signal to him/her? Not only that, you use 2X the wire to build a loop which won't transmit any better than an inverted Vee at the same height. If you want close in communications out to 150 miles daytime and 300 or so nighttime (under current propagation conditions) on 75 use a low antenna. If you desire communications out further than that, get the antenna up over 40 ft and the ends more than 20 ft. off the ground. So long as the angle of the legs are more than 100 degrees. Where all this falls down is the ground. If the voltage points are near ground the worms will love you, if the current node is near ground, impedance problems. So you have a choice. In past years that I couldn't get my antenna up in the clear, I made lots of friends close in and always dropped out if someone couldn't hear me. Rememberthere are no short cuts on antennas. Proper installation equals good results for the desired coverage and design matters little. 73 Jim W5JO LB Cebik, W4RNL, on his web site, talking about Cloud Warmers, indicates 35 feet as the accepted height for a 75m loop. I am planning a loop for 160m at just a little over that height. Joe W4AAB John, Hmmm 450 loop at 5'. Feedpoint impedance would vary all over the place depending on frequency. Do you transmitting on this setup, and if so, are you using some kind of an antenna tuner, balanced output or single ended, how long is the feedline, and what frequencies do you intend to use? In any case, can't see that fanning out at the feedpoint would be necessary or useful. Dennis D. W7QHO Glendale, CA
