Re: [Elecraft] magnetic loop antennas
Hi I live in an apartment (temporary) and built a 36 diameter magnetic loop with a vacuum variable capacitor bought off eBay, tuned by a motor drive. It is optimized for 20 and 17 meters, but works well on all bands from 40 to 10 meters (this really depends on the capacitance range) It tunes to a low SWR on my KX3 and works very well outside, clear of the building. But on the apartment balcony the performance is poor, as it is too close to rebar in the concrete framing and the steel mesh in the stucco walls Roger NZ6RQ / ZL2BHW -Original Message- From: Bill Blomgren [mailto:billb...@nc.rr.com] Sent: Monday, May 20, 2013 6:43 PM To: elecraft@mailman.qth.net Subject: [Elecraft] magnetic loop antennas I saw the great writeup on the magnetic loop antenna and the inventive High Voltage capacitor for tuning the thing. I'm looking at one of them strictly because I'm stuck in an apartment. The fact it should be good for 100 watts is perfect for what I'm looking at buying. I'm just wondering about the copper pipe used for the outer loop... I spotted some very reasonably priced flexible conduit that could be used for the loop proper. Do what is necessary to bond the capacitor into the rig, and it would appear to be a reasonable alternative to the rather pricy copper pipe. (They want your first born here for that, and the thieves are busy collecting anything that isn't nailed down. Thoughts on that for its larger diameter, which should help with the coupling to the rest of the world... __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] magnetic loop antennas
An alternative is to use a length of 1/2-inch Heliax using only the outer shield. This stuff it pretty easy to find at hamfests and much cheaper than the copper in it. I plan to make a 6-foot loop with some (someday). I have an old U100 rotator that could rotate it on a ten foot pole. 73, Ed - KL7UW __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] magnetic loop antennas
I googled 'flexible conduit' and what I see looks like BX cable -- made out of a single flat piece of metal wrapped in a spiral shape. If this is what you are talking about, it would be AWFUL for this purpose -- it would have a very high RF resistance and so be very inefficient. There are very high currents in the loop and you have to keep the resistance at RF as low as possible -- that's why large-diameter copper tubing is good. Do you have a link to a picture of the stuff you are looking at? On 5/20/2013 6:43 PM, Bill Blomgren wrote: I saw the great writeup on the magnetic loop antenna and the inventive High Voltage capacitor for tuning the thing. I'm looking at one of them strictly because I'm stuck in an apartment. The fact it should be good for 100 watts is perfect for what I'm looking at buying. I'm just wondering about the copper pipe used for the outer loop... I spotted some very reasonably priced flexible conduit that could be used for the loop proper. Do what is necessary to bond the capacitor into the rig, and it would appear to be a reasonable alternative to the rather pricy copper pipe. (They want your first born here for that, and the thieves are busy collecting anything that isn't nailed down. Thoughts on that for its larger diameter, which should help with the coupling to the rest of the world... -- Vic, K2VCO Fresno CA http://www.qsl.net/k2vco/ __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] magnetic loop antennas
Loop can work well in an apartment. Good to know what is in/behind walls if possible. Voltages and field strengths can be very high so care is in order. Resistance in loop increases losses. With respect to copper versus less expansive materials. You get what you pay for. 73 es GL KL7JT On May 20, 2013, at 9:43 PM, Bill Blomgren billb...@nc.rr.com wrote: I saw the great writeup on the magnetic loop antenna and the inventive High Voltage capacitor for tuning the thing. I'm looking at one of them strictly because I'm stuck in an apartment. The fact it should be good for 100 watts is perfect for what I'm looking at buying. I'm just wondering about the copper pipe used for the outer loop... I spotted some very reasonably priced flexible conduit that could be used for the loop proper. Do what is necessary to bond the capacitor into the rig, and it would appear to be a reasonable alternative to the rather pricy copper pipe. (They want your first born here for that, and the thieves are busy collecting anything that isn't nailed down. Thoughts on that for its larger diameter, which should help with the coupling to the rest of the world... __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] magnetic loop antennas
As an alternative to copper pipe, you might consider copper foil. RF flows along the surface of the conductor so it matters little how thick it is. You might take something like PVC tubing, form it into the required loop, and cover it with copper foil. Just be sure you use a single piece so you don't have to splice it anywhere around the loop that would require the RF currents to cross the splice. You might get away with a soldered seam running all the way around the loop but I suspect the solder wouldn't do anything. Just be sure the copper overlaps along the edge. Use tape or ty-wraps to secure the copper. Next to the ohmic losses in the loop itself, the majority of losses in loops is in the junctions connecting the loop to the capacitor and in the capacitor itself if it has a sliding contact to the rotor. 73, Ron AC7AC -Original Message- From: elecraft-boun...@mailman.qth.net [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Vic K2VCO Sent: Monday, May 20, 2013 7:07 PM To: elecraft@mailman.qth.net Subject: Re: [Elecraft] magnetic loop antennas I googled 'flexible conduit' and what I see looks like BX cable -- made out of a single flat piece of metal wrapped in a spiral shape. If this is what you are talking about, it would be AWFUL for this purpose -- it would have a very high RF resistance and so be very inefficient. There are very high currents in the loop and you have to keep the resistance at RF as low as possible -- that's why large-diameter copper tubing is good. Do you have a link to a picture of the stuff you are looking at? On 5/20/2013 6:43 PM, Bill Blomgren wrote: I saw the great writeup on the magnetic loop antenna and the inventive High Voltage capacitor for tuning the thing. I'm looking at one of them strictly because I'm stuck in an apartment. The fact it should be good for 100 watts is perfect for what I'm looking at buying. I'm just wondering about the copper pipe used for the outer loop... I spotted some very reasonably priced flexible conduit that could be used for the loop proper. Do what is necessary to bond the capacitor into the rig, and it would appear to be a reasonable alternative to the rather pricy copper pipe. (They want your first born here for that, and the thieves are busy collecting anything that isn't nailed down. Thoughts on that for its larger diameter, which should help with the coupling to the rest of the world... -- Vic, K2VCO Fresno CA http://www.qsl.net/k2vco/ __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] magnetic loop antennas
Hello, I built one that works great for 40 30m: http://radiopreppers.com/index.php/topic,180.0.html Gil. -- PGP Key: http://keskydee.com/gil.asc On May 20, 2013, at 9:43 PM, Bill Blomgren wrote: I saw the great writeup on the magnetic loop antenna and the inventive High Voltage capacitor for tuning the thing. I'm looking at one of them strictly because I'm stuck in an apartment. __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] magnetic loop antennas
Some people use 1/4 inch flexible copper tubing, the kind you use to hook up the icemaker on a refrigerator. You can hammer the ends flat, drill a hole, and connect them. It is about $1/foot and reasonably self-supporting. This appnote at MFJ has some good information on DIY loops: http://www.mfjenterprises.com/antennatalk6.php wunder K6WRU On May 20, 2013, at 7:31 PM, Ron D'Eau Claire wrote: As an alternative to copper pipe, you might consider copper foil. RF flows along the surface of the conductor so it matters little how thick it is. You might take something like PVC tubing, form it into the required loop, and cover it with copper foil. Just be sure you use a single piece so you don't have to splice it anywhere around the loop that would require the RF currents to cross the splice. You might get away with a soldered seam running all the way around the loop but I suspect the solder wouldn't do anything. Just be sure the copper overlaps along the edge. Use tape or ty-wraps to secure the copper. Next to the ohmic losses in the loop itself, the majority of losses in loops is in the junctions connecting the loop to the capacitor and in the capacitor itself if it has a sliding contact to the rotor. 73, Ron AC7AC -Original Message- From: elecraft-boun...@mailman.qth.net [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Vic K2VCO Sent: Monday, May 20, 2013 7:07 PM To: elecraft@mailman.qth.net Subject: Re: [Elecraft] magnetic loop antennas I googled 'flexible conduit' and what I see looks like BX cable -- made out of a single flat piece of metal wrapped in a spiral shape. If this is what you are talking about, it would be AWFUL for this purpose -- it would have a very high RF resistance and so be very inefficient. There are very high currents in the loop and you have to keep the resistance at RF as low as possible -- that's why large-diameter copper tubing is good. Do you have a link to a picture of the stuff you are looking at? On 5/20/2013 6:43 PM, Bill Blomgren wrote: I saw the great writeup on the magnetic loop antenna and the inventive High Voltage capacitor for tuning the thing. I'm looking at one of them strictly because I'm stuck in an apartment. The fact it should be good for 100 watts is perfect for what I'm looking at buying. I'm just wondering about the copper pipe used for the outer loop... I spotted some very reasonably priced flexible conduit that could be used for the loop proper. Do what is necessary to bond the capacitor into the rig, and it would appear to be a reasonable alternative to the rather pricy copper pipe. (They want your first born here for that, and the thieves are busy collecting anything that isn't nailed down. Thoughts on that for its larger diameter, which should help with the coupling to the rest of the world... -- Vic, K2VCO Fresno CA http://www.qsl.net/k2vco/ __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] magnetic loop antennas
You can use thick coax with PL-159/SO-239 connectors… This way your loop is packable. Gil. -- PGP Key: http://keskydee.com/gil.asc On May 20, 2013, at 11:05 PM, Walter Underwood wrote: Some people use 1/4 inch flexible copper tubing __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] magnetic loop antennas
You can just use heliax. Works perfect. Dr. William J. Schmidt - K9HZ / J68HZ/ 8P6HK/ ZF2HZ Owner - Operator Big Signal Ranch Staunton, Illinois email: b...@wjschmidt.com -Original Message- From: elecraft-boun...@mailman.qth.net [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Vic K2VCO Sent: Monday, May 20, 2013 9:07 PM To: elecraft@mailman.qth.net Subject: Re: [Elecraft] magnetic loop antennas I googled 'flexible conduit' and what I see looks like BX cable -- made out of a single flat piece of metal wrapped in a spiral shape. If this is what you are talking about, it would be AWFUL for this purpose -- it would have a very high RF resistance and so be very inefficient. There are very high currents in the loop and you have to keep the resistance at RF as low as possible -- that's why large-diameter copper tubing is good. Do you have a link to a picture of the stuff you are looking at? On 5/20/2013 6:43 PM, Bill Blomgren wrote: I saw the great writeup on the magnetic loop antenna and the inventive High Voltage capacitor for tuning the thing. I'm looking at one of them strictly because I'm stuck in an apartment. The fact it should be good for 100 watts is perfect for what I'm looking at buying. I'm just wondering about the copper pipe used for the outer loop... I spotted some very reasonably priced flexible conduit that could be used for the loop proper. Do what is necessary to bond the capacitor into the rig, and it would appear to be a reasonable alternative to the rather pricy copper pipe. (They want your first born here for that, and the thieves are busy collecting anything that isn't nailed down. Thoughts on that for its larger diameter, which should help with the coupling to the rest of the world... -- Vic, K2VCO Fresno CA http://www.qsl.net/k2vco/ __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
