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#11
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Flex dryer vent hose loop antenna
On Mon, 2 Nov 2015 09:13:38 -0600, amdx wrote:
Below some pressure level, it will probably flop over if mounted vertically. That's why I mumbled that I wasn't sure if it should be mounted vertically with a support pole, or horizontally on a flat sheet of plywood. Both will work, but I'm not sure which is better. Hang it upside down. Mikek But, all the photons will fall out of the loop that way. Actually, there's a problem. It doesn't work as well upside down. The magnetic loop has a rather directional field and takeoff angle and does NOT have a constant current around the loop: http://www.nonstopsystems.com/radio/vids-ant/antenna-Mag-Loop-Demo1.wmv https://www.youtube.com/watch?v=SUYI81dkEMA I suspect that an inverted loop will send most of the RF into the ground. I should probably test this. http://www.nonstopsystems.com/radio/img-ant/antenna-magloop-rad-angle.gif You might find this interesting on designing the 50 ohm matching network to the loop, where the impedance varies by where it's fed: http://www.g0cwt.co.uk/magloops/new_page_6.htm -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#12
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Flex dryer vent hose loop antenna
On Mon, 02 Nov 2015 16:39:09 -0800, Jeff Liebermann
wrote: You might find this interesting on designing the 50 ohm matching network to the loop, where the impedance varies by where it's fed: http://www.g0cwt.co.uk/magloops/new_page_6.htm Mo https://www.youtube.com/watch?v=NdofH6R22Dg Skip forward to 12:03 for an interesting comment: "Commercial loops are usually radiating towards the ground and a lot of the signal is warming the snails. I don't know how so many people could have got it so wrong for so long". -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#13
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Flex dryer vent hose loop antenna
On 11/1/2015 6:42 PM, Jeff Liebermann wrote:
On Sun, 1 Nov 2015 18:10:56 -0800, Paul Drahn wrote: Probable should clear the lint out first! Paul, KD7HB I know that hams are cheap, but I didn't realize that extended to stealing the neighbors dryer vent hose in order to build an antenna. I highly recommend purchasing a new hose, which comes pre-cleaned: http://www.acehardware.com/family/index.jsp?categoryId=2627981 Incidentally, there's no requirement that the entire loop be made from expandable hose. The loop could be in the form of a square loop, where the flat base and flat top are rigid aluminum structures, and the two vertical sections are flexible dryer vent hose. The weight of the flat top would help collapse the antenna although I suspect that springs or weights would work better. It's not like inflatable antennas and structures are a new thing: http://ltaprojects.com/towers/inflatable-antenna-video-towers/ham I am looking at the vent pipe from our reflow oven. We made it up from 4", 4' long vent pipe pieces, including "T" and "EL" pieces. That should work better than the expandable dryer vent hose. Paul, KD7HB |
#14
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Flex dryer vent hose loop antenna
On 11/3/2015 11:59 AM, Paul Drahn wrote:
On 11/1/2015 6:42 PM, Jeff Liebermann wrote: On Sun, 1 Nov 2015 18:10:56 -0800, Paul Drahn wrote: Probable should clear the lint out first! Paul, KD7HB I know that hams are cheap, but I didn't realize that extended to stealing the neighbors dryer vent hose in order to build an antenna. I highly recommend purchasing a new hose, which comes pre-cleaned: http://www.acehardware.com/family/index.jsp?categoryId=2627981 Incidentally, there's no requirement that the entire loop be made from expandable hose. The loop could be in the form of a square loop, where the flat base and flat top are rigid aluminum structures, and the two vertical sections are flexible dryer vent hose. The weight of the flat top would help collapse the antenna although I suspect that springs or weights would work better. It's not like inflatable antennas and structures are a new thing: http://ltaprojects.com/towers/inflatable-antenna-video-towers/ham I am looking at the vent pipe from our reflow oven. We made it up from 4", 4' long vent pipe pieces, including "T" and "EL" pieces. That should work better than the expandable dryer vent hose. I think the point is that the flex tubing antenna can be tuned by adjusting the loop rather than the capacitor. Interesting idea although it may not prove practical in the end. -- Rick |
#15
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Flex dryer vent hose loop antenna
On 11/2/2015 2:49 PM, Jeff Liebermann wrote:
On Mon, 2 Nov 2015 00:28:03 -0500, rickman wrote: You are assuming it will maintain something remotely like a circle. I don't see that happening. Have you worked with this stuff? Maybe what you have is more pliable than the stuff I used. I've worked with the vinyl dryer hose, but not the aluminum foil variety. With the vinyl, I was using the helical "Slinky" part of the hose as an HF antenna. As I mentioned, the steel spring got hot and melted the vinyl. Sure, there is nothing good about the slinky dryer tube you mention. Steel has horrible conductivity with its high resistance *and* very shallow skin effect. But even a copper wire of that small gauge would not be effective in a transmitter loop antenna. The actual inflatable antenna was a vertical monopole, so I never even tried to make a loop, and am not sure it will work. That's why I'm trying to recruit someone else to do the dirty work. I guess I could go shopping and do it myself, but I'm kinda busy this week (mostly recovering from the last 3 week of overwork). I suspect that there might be problems if I use too much air pressure. With the monopole, the hose would handle about 30 psi before producing a leak. It thinks that's more than enough to inflate the loop, but might not be enough to be self supporting, especially with a capacitor at the top. I bought a piece of dryer aluminum to use in another experiment (btw, a four foot column does not create much chimney effect over a 100 W light bulb) and they are stiff, too stiff to be worked by a balloon. Also they bend by expanding one side and not the other. Once it is bent it is a bit hard to straighten out. I am not trying to dampen your spirits. I suggest you buy a short piece of this stuff and just bend it by hand. Get a feel for it and see if you think this type of tube can be manipulated by simple machinery. I think it will cost less than $10 to try this. I don't mean fall apart necessarily, but just not be much like a loop antenna. I think the hard part will be shrinking it back down and keeping its shape. Proof of the pudding... The optimum shape is a circle with square, hexagon and octagon shapes being a tolerable facsimile. I guess the question is whether a random pretzel shape will work. Dunno, difficult to simulate, but easy to try. The prevailing wisdom is the area is what matters. Given what I saw in those videos which seem to show directionality in the plane of the loop, I'm not so sure. That and the results people seem to get with helical loop antennas make me think we don't really "get" loop antennas. There are helically wound antennas that have a similar issue. I have yet to see any equations to model them. I wonder if they work or not, in the sense of any better than a simple loop. One of the local club members build a 160 meter vertical rubber ducky (helical antenna) with ground radials and ended up with a usable bandwidth of about 2KHz. Keeping it tuned on frequency was a challenge. I think it was only about 10ft high and reportedly worked fairly well. I tried to model it with 4NEC2 but gave up for some forgotten reason. I think it was my inability to model the ground characteristics. Based on this example, I would say a loop would be better because the grounding isn't part of the puzzle. I don't have any equipment to date. I have a couple of projects ahead of this if I decide to build something. No test equipment? It's difficult to build anything without some basic RF equipment. I can provide a basic shopping list if you would like. My shop, which I've been told should be repurposed a museum. http://802.11junk.com/jeffl/pics/home/slides/lab.html You clearly have much more experience than I do. I wold barely know how to use a SWR meter and don't have an LRC meter... I can't remember what a grid dip meter is. Sigh. I have 4 assorted grid dip meters. I can mail you one if you would like to play. It's very handy for measuring the resonant frequencies of any LC circuit or antenna. It's not very accurate but will get you in the ballpark or at least tell you if you're too high or too low in frequency. Like this, but with more paint chipped off and the case missing. At least all the coils are there. http://www.universal-radio.com/used/W483lrg.jpg Note that it won't go down to 60 KHz although I tried making a coil that covered the range. Thanks for the offer. Let me get my other stuff out of the way and maybe I'll take you up on this. -- Rick |
#16
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Flex dryer vent hose loop antenna
On 11/2/2015 6:39 PM, Jeff Liebermann wrote:
On Mon, 2 Nov 2015 09:13:38 -0600, amdx wrote: Below some pressure level, it will probably flop over if mounted vertically. That's why I mumbled that I wasn't sure if it should be mounted vertically with a support pole, or horizontally on a flat sheet of plywood. Both will work, but I'm not sure which is better. Hang it upside down. Mikek But, all the photons will fall out of the loop that way. Actually, there's a problem. It doesn't work as well upside down. The magnetic loop has a rather directional field and takeoff angle and does NOT have a constant current around the loop: http://www.nonstopsystems.com/radio/vids-ant/antenna-Mag-Loop-Demo1.wmv https://www.youtube.com/watch?v=SUYI81dkEMA I suspect that an inverted loop will send most of the RF into the ground. I should probably test this. http://www.nonstopsystems.com/radio/img-ant/antenna-magloop-rad-angle.gif You might find this interesting on designing the 50 ohm matching network to the loop, where the impedance varies by where it's fed: http://www.g0cwt.co.uk/magloops/new_page_6.htm Sorry Jeff, When my post didn't show up, I noticed I sent it to you. Here it is for the rest. Just to add to the confusion, Helically Loaded You might glean info from here, or at the least admire all the work put into the projects. http://theradioboard.com/rb/viewtopic.php?f=10&t=4399 Copper doughnut with lots of solder connections http://www.aa5tb.com/jl1boh_03.jpg http://www.hlmagneticloopantennas.com/ Hmm, I read a few comments, maybe not the way to go. Mikek |
#17
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Flex dryer vent hose loop antenna
On 11/2/2015 7:39 PM, Jeff Liebermann wrote:
On Mon, 2 Nov 2015 09:13:38 -0600, amdx wrote: Below some pressure level, it will probably flop over if mounted vertically. That's why I mumbled that I wasn't sure if it should be mounted vertically with a support pole, or horizontally on a flat sheet of plywood. Both will work, but I'm not sure which is better. Hang it upside down. Mikek But, all the photons will fall out of the loop that way. Actually, there's a problem. It doesn't work as well upside down. The magnetic loop has a rather directional field and takeoff angle and does NOT have a constant current around the loop: http://www.nonstopsystems.com/radio/vids-ant/antenna-Mag-Loop-Demo1.wmv I don't get this video. I can't really hear what he is saying so when he says at the end, "this is not what you would expect" I don't get it. https://www.youtube.com/watch?v=SUYI81dkEMA This video is about the voltage and current around a loop, but he says it is a 1/10 wave loop, but I can't tell that. He has another video showing the directionality of a 1/4 wave delta antenna. I'm wondering if this is also a 1/4 wave antenna. I suspect that an inverted loop will send most of the RF into the ground. I should probably test this. http://www.nonstopsystems.com/radio/img-ant/antenna-magloop-rad-angle.gif Which type of loop antenna are you talking about, 1/4 wave, or 1/10 wave (small, magnetic)? I can't tell anything about this antenna and it seems to contradict the other video. You might find this interesting on designing the 50 ohm matching network to the loop, where the impedance varies by where it's fed: http://www.g0cwt.co.uk/magloops/new_page_6.htm -- Rick |
#18
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Flex dryer vent hose loop antenna
In message , rickman
writes https://www.youtube.com/watch?v=SUYI81dkEMA When he's measuring towards the capacitor, won't the presence of his hand be causing the loop to de-tune - hence less current? -- Ian |
#19
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Flex dryer vent hose loop antenna
On 11/4/2015 6:49 AM, Ian Jackson wrote:
In message , rickman writes https://www.youtube.com/watch?v=SUYI81dkEMA When he's measuring towards the capacitor, won't the presence of his hand be causing the loop to de-tune - hence less current? Yes. But, is it measurable? |
#20
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Flex dryer vent hose loop antenna
In message , John S
writes On 11/4/2015 6:49 AM, Ian Jackson wrote: In message , rickman writes https://www.youtube.com/watch?v=SUYI81dkEMA When he's measuring towards the capacitor, won't the presence of his hand be causing the loop to de-tune - hence less current? Yes. But, is it measurable? Being a high-Q circuit, I would think that a small amount of additional C would cause considerable de-tuning. -- Ian |
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