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Locked Wellbrook construction
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Wellbrook antenna: is the loop shielded? I am guessing maybe not,
since its performance still seems to be good into the VHF range. IF not - will shielding such a loop, be worthwhile to diminish electrical field noise? I am thinking a "Hula Hoop" toy might be a basis for a homemade loop. Cut open the loop, feed wire thru it, and glue back together. Maybe with aluminum foil wrapped around the thing, for shielding, and amplifier module attached right to the loop. WL1030 page - i very much look forward to reading the material there. I just wonder why it is necessary to "register". What is the thinking behind that? -Hue Miller |
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In a message dated 14/05/2007 20:21:50 GMT Daylight Time,
rmoore5@... writes: You are wrong that the Aluminim is the actual antenna. There are wires inside of it and it is only there as a mechanical support. I know this because I've removed the potting material from one of these to find out. This can also be verified by examining the 5030. It is a semi-ridgid version of the ALA-1530. Rob ---------------------------------- Hi Rob Are you sure re the 1530? Certainly it's true for the 5030 as that's got a plastic tube, and I can hear the wire rattling around inside it as I'd expect, but I've never heard anything rattling inside the 1530. I would expect that you'd see wires going to the potted amp, even if the tube is the antenna, as the tube will likely mechanically terminate inside the plastic entry tubes on the electrical junction box used as a housing with perhaps a screw and solder tag connection at the ends. regards Nigel GM8PZR |
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In a message dated 14/05/2007 21:08:36 GMT Daylight Time,
christrask@... writes: Patrick is absolutely correct in stating that the aluminum shield (aka the outer conductor)is the actual antenna. This is the manner in which shielded loops function at their operating frequency. At very low frequencies where most electrical field noise exists, the currents and voltages of both arms of the outer conductor are equal in both potential and polarity (provided the gap is at the exact centre), with the currents being the same on both surfaces of the outer conductor material and zero at the gap. The currents that are coupled to the inner conductor(s) cancel so that there is no net noise current delivered to the receiver. ------------------------------------- Hi Chris The Wellbrook isn't a shielded loop antenna. There no gap in this loop, other than inside the housing at the bottom where it connects to the amp. regards Nigel GM8PZR |
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Patrick Reynaert
Hi,
the wellbrook is not a shielded antenna, the Aluminium tube is the actual antenna. Shielding (with a gap of course) a loop only shields it from electrical noise at very low frequecies, i.e. at frequencies where the shield thickness is less than the skin depth. At higher frequencies, where the shield is thicker than the skin depth, the shield only helps to get a better balance, and hence a better 'null' in the reception pattern. Patrick. Hue Miller <kargo_cult@...> wrote: Wellbrook antenna: is the loop shielded? I am guessing maybe not, since its performance still seems to be good into the VHF range. IF not - will shielding such a loop, be worthwhile to diminish electrical field noise? I am thinking a "Hula Hoop" toy might be a basis for a homemade loop. Cut open the loop, feed wire thru it, and glue back together. Maybe with aluminum foil wrapped around the thing, for shielding, and amplifier module attached right to the loop. WL1030 page - i very much look forward to reading the material there. I just wonder why it is necessary to "register". What is the thinking behind that? -Hue Miller If you've got links, post them in the Links section! Post files here. If the file comes from a website, please put it in the Links rather than uploading the file. You can now view images at higher resolution in Photos. Upload JPG and GIF into Photos. Please convert BMP or TIF to JPG or GIF before uploading. And please trim all this when replying! Yahoo! Groups Links --------------------------------- Food fight? Enjoy some healthy debate in the Yahoo! Answers Food & Drink Q&A. |
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In a message dated 14/05/2007 22:20:39 GMT Daylight Time,
davidgriffin@... writes: Does someone have a Wellbrook loop in a convenient enough location to ground the shield and see what happens? If it's the antenna, then it won't act like one when grounded. If it's not the antenna, would there be any noticeable effect of grounding it? Please don't make me got out and drive a stake in the ground...... Dave ------------------------------ Interesting question, but "no" Having said that, grounding the plastic loop on my 5030 probably wouldn't prove very much:-) Go on, go drive that stake...... it's the obvious way of proving it, one way or another, and...... since you thought of it first.............:-) regards Nigel GM8PZR |
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In a message dated 15/05/2007 00:04:14 GMT Daylight Time,
fraser.castle@... writes: Ref. Is it shoelded or not ? Didn't we read earlier in the groups messages that Patrick had been kind enough to dismantle an ALA1530 ? Surely if Patrick says his dismantled ALA1530 had connections from the amp input to the aluminium loop we can take it that the ALA1530 is not shielded ? ------------------------ I think that's a reasonable assumption:-) |
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Rob Moore
Patrick,
You are wrong that the Aluminim is the actual antenna. There are wires inside of it and it is only there as a mechanical support. I know this because I've removed the potting material from one of these to find out. This can also be verified by examining the 5030. It is a semi-ridgid version of the ALA-1530. Rob This--- In loopantennas@..., Patrick Reynaert <preynaert@...> wrote: actual antenna. electrical noise at very low frequecies, i.e. at frequencies where the shield thickness is less than the skin depth. At higher frequencies, where the shield is thicker than the skin depth, the shield only helps to get a better balance, and hence a better 'null' in the reception pattern. shielded? I am guessing maybe not, since its performance still seems to be good into the VHF range.the Links rather than uploading the file. and GIF into Photos. Please convert BMP or TIF to JPG or GIF before uploading.
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Patrick is absolutely correct in stating that the aluminum shield (aka
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the outer conductor)is the actual antenna. This is the manner in which shielded loops function at their operating frequency. At very low frequencies where most electrical field noise exists, the currents and voltages of both arms of the outer conductor are equal in both potential and polarity (provided the gap is at the exact centre), with the currents being the same on both surfaces of the outer conductor material and zero at the gap. The currents that are coupled to the inner conductor(s) cancel so that there is no net noise current delivered to the receiver. At operating frequencies, the potentials of the two arms of the outer conductor are equal and opposite (again provided that the gap is at the exact centre). The currents at the gap are equal and opposite. These currents flow around the end of the arms at the gap, resulting in no net current at the gap but at the same time resulting in equal and opposite currents on the inner surface of the shield. These then couple to the inner conductor(s) and subsequently couple to the receiver. The frequency at which the outer conductor goes from being an electrostatic shield to being the actual antenna depends on the conductivity and thickness of the material. In general, the point is somehwere in the vicinity of ten to twnety skin depths, depending on whose evaluation you are using. Chris ,----------------------. High Performance Mixers and / What's all this \ Amplifiers for RF Communications / extinct stuff, anyhow? / \ _______,--------------' Chris Trask / N7ZWY _ |/ Principal Engineer oo\ Sonoran Radio Research (__)\ _ P.O. Box 25240 \ \ .' `. Tempe, Arizona 85285-5240 \ \ / \ \ '" \ IEEE Senior Member #40274515 . ( ) \ '-| )__| :. \ Email: christrask@... | | | | \ '. c__; c__; '-..'>.__ Graphics by Loek Frederiks ----- Original Message -----
From: "Rob Moore" <rmoore5@...> To: <loopantennas@...> Sent: Monday, May 14, 2007 12:18 PM Subject: [loopantennas] Re: Wellbrook construction Patrick, You are wrong that the Aluminim is the actual antenna. There are wires inside of it and it is only there as a mechanical support. I know this because I've removed the potting material from one of these to find out. This can also be verified by examining the 5030. It is a semi-ridgid version of the ALA-1530. Rob This--- In loopantennas@..., Patrick Reynaert <preynaert@...> wrote:
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Patrick Reynaert
hi Rob,
regarding the ALA1530: there is indeed a wire that from the PCB into the Al tube, but this is connected with the tube by a small screw, about 2cm away from the plastic enclosure. So, in my opinion, the Al tube is the actual antenna. Best regards, Patrick Rob Moore <rmoore5@...> wrote: Patrick, You are wrong that the Aluminim is the actual antenna. There are wires inside of it and it is only there as a mechanical support. I know this because I've removed the potting material from one of these to find out. This can also be verified by examining the 5030. It is a semi-ridgid version of the ALA-1530. Rob This--- In loopantennas@..., Patrick Reynaert wrote: actual antenna. electrical noise at very low frequecies, i.e. at frequencies where the shield thickness is less than the skin depth. At higher frequencies, where the shield is thicker than the skin depth, the shield only helps to get a better balance, and hence a better 'null' in the reception pattern. shielded? I am guessing maybe not, since its performance still seems to be good into the VHF range.the Links rather than uploading the file. and GIF into Photos. Please convert BMP or TIF to JPG or GIF before uploading.
If you've got links, post them in the Links section! Post files here. If the file comes from a website, please put it in the Links rather than uploading the file. You can now view images at higher resolution in Photos. Upload JPG and GIF into Photos. Please convert BMP or TIF to JPG or GIF before uploading. And please trim all this when replying! Yahoo! Groups Links --------------------------------- Be a better Heartthrob. Get better relationship answers from someone who knows. Yahoo! Answers - Check it out. |
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Rob Moore
Nigel is correct. The Wellbrook isn't a shielded loop antenna.
There are actually two wires that run into each leg aluminum loop that provides structural support for the antenna and come out the other side of the loop. I believe (but haven't disassembled it this far because it wouldn't be of much use after that) that the entire loop is filled with the potting compound. That's why you don't hear any wires rattling. The Wellbrook is a very well constructed, fairly straightforward loop, which relies on an excellent balanced preamp design and careful construction to minimize noise pickup. Rob --- In loopantennas@..., gandalfg8@... wrote: potential and polarity (provided the gap is at the exact centre), with thecurrents being the same on both surfaces of the outer conductor material and zeroat the gap. The currents that are coupled to the inner conductor(s) cancelso that there is no net noise current delivered to the receiver.bottom where it connects to the amp. |
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n2chi
Does someone have a Wellbrook loop in a convenient enough location to
ground the shield and see what happens? If it's the antenna, then it won't act like one when grounded. If it's not the antenna, would there be any noticeable effect of grounding it? Please don't make me got out and drive a stake in the ground...... Dave --- In loopantennas@..., gandalfg8@... wrote: potential and polarity (provided the gap is at the exact centre), with the currentsbeing the same on both surfaces of the outer conductor material and zero atthe gap. The currents that are coupled to the inner conductor(s) cancelso that there is no net noise current delivered to the receiver.where it connects to the amp. |
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Rob Moore
I have one up a tree and can try that tonight. I assume that
grounding the aluminum loop to the shell of the BNC connector is what you're referring to? Rob --- In loopantennas@..., "n2chi" <davidgriffin@...> wrote: there be any noticeable effect of grounding it? Please don't make me got out(aka whichthe outer conductor)is the actual antenna. This is the manner in andshielded loops function at their operating frequency. At very low currentsvoltages of both arms of the outer conductor are equal in bothpotential andpolarity (provided the gap is at the exact centre), with the beingzero atthe same on both surfaces of the outer conductor material and thebottomgap. The currents that are coupled to the inner conductor(s) cancelso thatthere is no net noise current delivered to the receiver. whereit connects to the amp. |
where it connects to the amp.Oh. That's very different. Never mind. Chris ,----------------------. High Performance Mixers and / What's all this \ Amplifiers for RF Communications / extinct stuff, anyhow? / \ _______,--------------' Chris Trask / N7ZWY _ |/ Principal Engineer oo\ Sonoran Radio Research (__)\ _ P.O. Box 25240 \ \ .' `. Tempe, Arizona 85285-5240 \ \ / \ \ '" \ IEEE Senior Member #40274515 . ( ) \ '-| )__| :. \ Email: christrask@... | | | | \ '. c__; c__; '-..'>.__ Graphics by Loek Frederiks |
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n2chi
Hi Rob,
I think I'd try something I'm more sure is grounded. If I remember correctly, the coax shield between the loop and the electronics is NOT grounded. I seem to remember the installation materials saying NOT to ground that section of coax. So shorting the aluminmum of the loop to the shell of the BNC might not yield a ground. But then, that would probably short out the antenna? Dave --- In loopantennas@..., "Rob Moore" <rmoore5@...> wrote: it outwon't act like one when grounded. If it's not the antenna, wouldtherebe any noticeable effect of grounding it? Please don't make me got canceland drive a stake in the ground......(aka so thatbottomthere is no net noise current delivered to the receiver. |
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Rob Moore
Hi Dave,
Well the shield is grounded by the time it gets into the house but maybe I'll try it both ways. That may take a little longer. Rob --- In loopantennas@..., "n2chi" <davidgriffin@...> wrote: location to itground the shield and see what happens? If it's the antenna, thenoutwon't act like one when grounded. If it's not the antenna, wouldtherebe any noticeable effect of grounding it? Please don't make me gotcanceland drive a stake in the ground......(aka |
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n2chi
Rob,
I just found my 1530 instruction sheet and it reminded me that the coax has DC voltage on it (for the circuitry up at the loop base)so don't short it out. Also, it does say to NOT ground the coax between the loop and the downstream Antenna Interface box "as it may introduce noise." Nigel: Not to worry about my using a stake; my wife won't let me play with anything sharp any more. Dave --- In loopantennas@..., "Rob Moore" <rmoore5@...> wrote: NOT togrounded. I seem to remember the installation materials saying NOT toground that section of coax. So shorting the aluminmum of the loop whatthe shell of the BNC might not yield a ground. But then, that would thenlocation toyou're referring to? gotitwon't act like one when grounded. If it's not the antenna, wouldtherebe any noticeable effect of grounding it? Please don't make me shieldoutand drive a stake in the ground...... in(akathe outer conductor)is the actual antenna. This is the manner lowwhichshielded loops function at their operating frequency. At very currentsfrequencies where most electrical field noise exists, the andcancelcurrentsvoltages of both arms of the outer conductor are equal in bothpotential andpolarity (provided the gap is at the exact centre), with thebeingzero atthe same on both surfaces of the outer conductor material andthegap. The currents that are coupled to the inner conductor(s)so thatbottomthere is no net noise current delivered to the receiver. |
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Rob Moore
Hi Dave,
Just got home. I wasn't planning on shorting the aluminum tube to the center condicutor of the cable. Just to the shell of the BNC connector, which doesn't have any power on it. Thanks for the intruction information. I bought my ALA-1530 used and it didn't come with any instructions. Rob --- In loopantennas@..., "n2chi" <davidgriffin@...> wrote: coax has DC voltage on it (for the circuitry up at the loop base)sodon't short it out. Also, it does say to NOT ground the coax betweenthe loop and the downstream Antenna Interface box "as it may introducenoise." Nigel: Not to worry about my using a stake; my wife won't let meplay with anything sharp any more. |
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Hey Everyone;
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Newbie/first poster here. So 'hello'. Been following the Wellbrook saga with great interest. Warning: While not a hands-on expert, I have read enough about active loops to be concerned about shorting the Wellbrook's feed line to prove anything. Yes, the Wellbrook has DC running the coax to feed the active electronics at the loop base. IE, both sides of the coax are hot w/ respect to ground. If you want to prove/disprove whether the aluminum loop is the active element or an RF shield, why not clip the aluminum loop itself straight to earth ground? I beleive if the aluminum loop is shield, you will observe an increase in noise but little effect on gain. If the loop is the active element, you should notice a huge drop in gain/sensitivity. Hope that helps. Mark in Milwaukee x-WB9AQI --- In loopantennas@..., "Rob Moore" <rmoore5@...> wrote:
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Rob Moore
If you actually took a look at a Wellbrook, you would see that the
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design has the coax shield as a common gnd point. Unless the aluminim ring is "hot" with respect to common, it should not cause any power problems to connect them. Rob --- In loopantennas@..., "airchecklover" <mdh@...> wrote:
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