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Receiving Loop Antenna Question
If i were to construct a square receiving loop antenna for the am bcb that
is 24" or more per side..... how important would the guage of the wire be & also solid versus stranded wire? Antenna would be used indoors. |
Receiving Loop Antenna Question
"Spin" wrote in message ... If i were to construct a square receiving loop antenna for the am bcb that is 24" or more per side..... how important would the guage of the wire be & also solid versus stranded wire? Antenna would be used indoors. Hi Spin Have you seen this site? http://www.mindspring.com/~loop_antenna/ Jerry KD6JDJ |
Receiving Loop Antenna Question
Spin wrote:
If i were to construct a square receiving loop antenna for the am bcb that is 24" or more per side..... how important would the guage of the wire be & also solid versus stranded wire? Antenna would be used indoors. Any wire you can comfortably work with is fine. |
Receiving Loop Antenna Question
On Jan 21, 9:57*pm, "Spin" wrote:
If i were to construct a square receiving loop antenna for the am bcb that is 24" or more per side..... how important would the guage of the wire be & also solid versus stranded wire? Antenna would be used indoors. Doesn't matter much. Maybe a slight difference in Q with thin vs fat wire, but overall no big deal. I've got loops made from thin copper motor wire, and also one from insulated #14 gauge stranded house wire. They all work. From a mechanical standpoint I think a diamond is easier to deal with.. Here is one of my favorite designs for a cheap simple PVC loop. You can slap one together pretty fast. Kind of like PVC tinker toys.. :/ You do have to drill the holes, but that's easy. http://home.comcast.net/~nm5k/loop5.jpg |
Receiving Loop Antenna Question
Ian Jackson wrote:
In message , writes On Jan 21, 9:57 pm, "Spin" wrote: If i were to construct a square receiving loop antenna for the am bcb that is 24" or more per side..... how important would the guage of the wire be & also solid versus stranded wire? Antenna would be used indoors. Doesn't matter much. Maybe a slight difference in Q with thin vs fat wire, but overall no big deal. I've got loops made from thin copper motor wire, and also one from insulated #14 gauge stranded house wire. They all work. From a mechanical standpoint I think a diamond is easier to deal with.. Here is one of my favorite designs for a cheap simple PVC loop. You can slap one together pretty fast. Kind of like PVC tinker toys.. :/ You do have to drill the holes, but that's easy. http://home.comcast.net/~nm5k/loop5.jpg What about ribbon cable? I've got a fair length of ribbon cable (something like 25 wires - the sort used in PCs to connect hard drives and the like) put away for a rainy-day loop antenna project. While I could make one large loop using all 25 wires for the really low frequencies, I'll almost certainly cut it up and make several smaller loops with fewer wires for the higher frequencies. Or put some taps on it,say every 2 turns? each one connected to a pole of a large 12 position rotary switch.. then you can select a small loop,or a really large one,for the low stuff. :-) Tuneable! |
Receiving Loop Antenna Question
Ian Jackson wrote:
In message , writes On Jan 21, 9:57 pm, "Spin" wrote: If i were to construct a square receiving loop antenna for the am bcb that is 24" or more per side..... how important would the guage of the wire be & also solid versus stranded wire? Antenna would be used indoors. Doesn't matter much. Maybe a slight difference in Q with thin vs fat wire, but overall no big deal. I've got loops made from thin copper motor wire, and also one from insulated #14 gauge stranded house wire. They all work. From a mechanical standpoint I think a diamond is easier to deal with.. Here is one of my favorite designs for a cheap simple PVC loop. You can slap one together pretty fast. Kind of like PVC tinker toys.. :/ You do have to drill the holes, but that's easy. http://home.comcast.net/~nm5k/loop5.jpg What about ribbon cable? I've got a fair length of ribbon cable (something like 25 wires - the sort used in PCs to connect hard drives and the like) put away for a rainy-day loop antenna project. While I could make one large loop using all 25 wires for the really low frequencies, I'll almost certainly cut it up and make several smaller loops with fewer wires for the higher frequencies. Stick with a single wire and relatively few loops. More wire won't make the loop bigger, just harder to tune. |
Receiving Loop Antenna Question
On Fri, 23 Jan 2009 13:57:40 +0000, dave wrote:
Ian Jackson wrote: What about ribbon cable? I've got a fair length of ribbon cable (something like 25 wires - the sort used in PCs to connect hard drives and the like) put away for a rainy-day loop antenna project. While I could make one large loop using all 25 wires for the really low frequencies, I'll almost certainly cut it up and make several smaller loops with fewer wires for the higher frequencies. Stick with a single wire and relatively few loops. More wire won't make the loop bigger, just harder to tune. I don't think he meant to connect all those wires in parallel. But, it would be a little tedious to connect each wire at one end to its neighbor at the other end (of the loop), and _not_ create an ugly bird's nest at the 'joint'. Jonesy -- Marvin L Jones | jonz | W3DHJ | linux 38.24N 104.55W | @ config.com | Jonesy | OS/2 * Killfiling google & XXXXbanter.com: jonz.net/ng.htm |
Receiving Loop Antenna Question
Allodoxaphobia wrote:
I don't think he meant to connect all those wires in parallel. I thought he was talking about a tapped coil with the unused parts floating. Might result in a new Tesla coil design. :-) -- 73, Cecil http://www.w5dxp.com |
Receiving Loop Antenna Question
"Allodoxaphobia" wrote in message ... On Fri, 23 Jan 2009 13:57:40 +0000, dave wrote: Ian Jackson wrote: What about ribbon cable? I've got a fair length of ribbon cable (something like 25 wires - the sort used in PCs to connect hard drives and the like) put away for a rainy-day loop antenna project. While I could make one large loop using all 25 wires for the really low frequencies, I'll almost certainly cut it up and make several smaller loops with fewer wires for the higher frequencies. Stick with a single wire and relatively few loops. More wire won't make the loop bigger, just harder to tune. I don't think he meant to connect all those wires in parallel. But, it would be a little tedious to connect each wire at one end to its neighbor at the other end (of the loop), and _not_ create an ugly bird's nest at the 'joint'. Jonesy Hi Jonesy For what Its Worth, I tried making a big AM reception loop using some big ribbon cable, and it didnt work. The cable was/is color coded so it was easy to connect the ends so the input to output is a series connection of the wires. The antenna didnt work. I assummed it was due to excessive 'distributed capacity' between windings. I had no interest in researching the reason for ribbon cable use for AM loop antennas. Besides, it got Very difficult to assemble the loop onto the mounting frame and have it look presentable. " Stick with a single wire and relatively few loops. More wire won't make the loop bigger, just harder to tune." Jerry KD6JDJ |
Receiving Loop Antenna Question
In message , Allodoxaphobia
writes On Fri, 23 Jan 2009 13:57:40 +0000, dave wrote: Ian Jackson wrote: What about ribbon cable? I've got a fair length of ribbon cable (something like 25 wires - the sort used in PCs to connect hard drives and the like) put away for a rainy-day loop antenna project. While I could make one large loop using all 25 wires for the really low frequencies, I'll almost certainly cut it up and make several smaller loops with fewer wires for the higher frequencies. Stick with a single wire and relatively few loops. More wire won't make the loop bigger, just harder to tune. I don't think he meant to connect all those wires in parallel. But, it would be a little tedious to connect each wire at one end to its neighbor at the other end (of the loop), and _not_ create an ugly bird's nest at the 'joint'. I think that you underestimate my constructional abilities! I'm not sure how many turns would be needed. 4, 5 or 6 at the most (depending on frequency)? I'd certainly study the available information before I started. Of course, before I started, any superfluous wires would be stripped from the ribbon - it's just that the ribbon I've got has a lot wires. I really can't see any problem with cutting the ribbon, and then re-joining it with the end of each wire being connected to its neighbour This technique MUST have been used before by someone. -- Ian |
Receiving Loop Antenna Question
In message , Jerry
writes "Allodoxaphobia" wrote in message ... On Fri, 23 Jan 2009 13:57:40 +0000, dave wrote: Ian Jackson wrote: What about ribbon cable? I've got a fair length of ribbon cable (something like 25 wires - the sort used in PCs to connect hard drives and the like) put away for a rainy-day loop antenna project. While I could make one large loop using all 25 wires for the really low frequencies, I'll almost certainly cut it up and make several smaller loops with fewer wires for the higher frequencies. Stick with a single wire and relatively few loops. More wire won't make the loop bigger, just harder to tune. I don't think he meant to connect all those wires in parallel. But, it would be a little tedious to connect each wire at one end to its neighbor at the other end (of the loop), and _not_ create an ugly bird's nest at the 'joint'. Jonesy Hi Jonesy For what Its Worth, I tried making a big AM reception loop using some big ribbon cable, and it didnt work. The cable was/is color coded so it was easy to connect the ends so the input to output is a series connection of the wires. The antenna didnt work. I assummed it was due to excessive 'distributed capacity' between windings. I had no interest in researching the reason for ribbon cable use for AM loop antennas. Besides, it got Very difficult to assemble the loop onto the mounting frame and have it look presentable. Your findings are noted. I did wonder about the effects of distributed capacity between the windings. It looks like it's back to the drawing board! " Stick with a single wire and relatively few loops. More wire won't make the loop bigger, just harder to tune." Jerry KD6JDJ -- Ian |
Receiving Loop Antenna Question
On Jan 23, 8:45*am, Allodoxaphobia wrote:
On Fri, 23 Jan 2009 13:57:40 +0000, dave wrote: Ian Jackson wrote: What about ribbon cable? I've got a fair length of ribbon cable (something like 25 wires - the sort used in PCs to connect hard drives and the like) put away for a rainy-day loop antenna project. While I could make one large loop using all 25 wires for the really low frequencies, I'll almost certainly cut it up and make several smaller loops with fewer wires for the higher frequencies. Stick with a single wire and relatively few loops. More wire won't make the loop bigger, just harder to tune. I don't think he meant to connect all those wires in parallel. But, it would be a little tedious to connect each wire at one end to its neighbor at the other end (of the loop), and _not_ create an ugly bird's nest at the 'joint'. Jonesy Yep, it's a continuous single wire. If you used ribbon cable, you would have to put a cut, and the jumper to jump over to the next wire on each turn.. Would be a pain. You just take a single length of wire and thread it around through the holes until you have the number of turns you need. You are moving over a row of holes on each turn. The main thing to consider is you end up building the loop and deciding the proper number of turns around the capacitor you have, not the other way around. A double 365pf cap "730 pf total if jumped together" will let you be able to tune the whole AM-BC band with most loops. My 44 inch per side diamond loop for MW has five turns. My 16 inch diameter circle loop for MW uses 12 turns. Both are using basically the same cap values. I also use a single turn coupling loop that is inside and slightly smaller than the main loop. But it does not effect tuning, and it's size and spacing from the main loop is fairly uncritical. The cap is in parallel with the main loop winding. If you use a portable with a built in loop stick antenna, you can just couple the radio to the loop and it will work. But all my radios require a feed line to the antenna. |
Receiving Loop Antenna Question
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Receiving Loop Antenna Question
On Jan 25, 3:51*am, wrote:
On Jan 23, 8:45*am, Allodoxaphobia wrote: On Fri, 23 Jan 2009 13:57:40 +0000, dave wrote: Ian Jackson wrote: What about ribbon cable? I've got a fair length of ribbon cable (something like 25 wires - the sort used in PCs to connect hard drives and the like) put away for a rainy-day loop antenna project. While I could make one large loop using all 25 wires for the really low frequencies, I'll almost certainly cut it up and make several smaller loops with fewer wires for the higher frequencies. Stick with a single wire and relatively few loops. More wire won't make the loop bigger, just harder to tune. I don't think he meant to connect all those wires in parallel. But, it would be a little tedious to connect each wire at one end to its neighbor at the other end (of the loop), and _not_ create an ugly bird's nest at the 'joint'. Jonesy Yep, it's a continuous single wire. If you used ribbon cable, you would have to put a cut, and the jumper to jump over to the next wire on each turn.. Would be a pain. You just take a single length of wire and thread it around through the holes until you have the number of turns you need. You are moving over a row of holes on each turn. The main thing to consider is you end up building the loop and deciding the proper number of turns around the capacitor you have, not the other way around. A double 365pf cap "730 pf total if jumped together" will let you be able to tune the whole AM-BC band with most loops. My 44 inch per side diamond loop for MW has five turns. My 16 inch diameter circle loop for MW uses 12 turns. Both are using basically the same cap values. I also use a single turn coupling loop that is inside and slightly smaller than the main loop. But it does not effect tuning, and it's size and spacing from the main loop is fairly uncritical. The cap is in parallel with the main loop winding. If you use a portable with a built in loop stick antenna, you can just couple the radio to the loop and it will work. But all my radios require a feed line to the antenna. I would not be so quick to dismiss the ribbon wire on the basis of capacitance build up ! If you start from the middle of one end by joining the two center wires together and from then on joining the end to end wires moving outwards what you have then done is to cancel not only the capacitance build up but also the inductance build up. You can then unfasten the first step on the center winding and feed it from that point i.e. center fed Art |
Receiving Loop Antenna Question
"Art Unwin" wrote in message ... On Jan 25, 3:51 am, wrote: On Jan 23, 8:45 am, Allodoxaphobia wrote: On Fri, 23 Jan 2009 13:57:40 +0000, dave wrote: Ian Jackson wrote: What about ribbon cable? I've got a fair length of ribbon cable (something like 25 wires - the sort used in PCs to connect hard drives and the like) put away for a rainy-day loop antenna project. While I could make one large loop using all 25 wires for the really low frequencies, I'll almost certainly cut it up and make several smaller loops with fewer wires for the higher frequencies. Stick with a single wire and relatively few loops. More wire won't make the loop bigger, just harder to tune. I don't think he meant to connect all those wires in parallel. But, it would be a little tedious to connect each wire at one end to its neighbor at the other end (of the loop), and _not_ create an ugly bird's nest at the 'joint'. Jonesy Yep, it's a continuous single wire. If you used ribbon cable, you would have to put a cut, and the jumper to jump over to the next wire on each turn.. Would be a pain. You just take a single length of wire and thread it around through the holes until you have the number of turns you need. You are moving over a row of holes on each turn. The main thing to consider is you end up building the loop and deciding the proper number of turns around the capacitor you have, not the other way around. A double 365pf cap "730 pf total if jumped together" will let you be able to tune the whole AM-BC band with most loops. My 44 inch per side diamond loop for MW has five turns. My 16 inch diameter circle loop for MW uses 12 turns. Both are using basically the same cap values. I also use a single turn coupling loop that is inside and slightly smaller than the main loop. But it does not effect tuning, and it's size and spacing from the main loop is fairly uncritical. The cap is in parallel with the main loop winding. If you use a portable with a built in loop stick antenna, you can just couple the radio to the loop and it will work. But all my radios require a feed line to the antenna. I would not be so quick to dismiss the ribbon wire on the basis of capacitance build up ! If you start from the middle of one end by joining the two center wires together and from then on joining the end to end wires moving outwards what you have then done is to cancel not only the capacitance build up but also the inductance build up. You can then unfasten the first step on the center winding and feed it from that point i.e. center fed Art .... but a multi-turn loop in which the self-inductance cancelled wouldn't be much of a receiving antenna! Production of EMF from the magnetic field caused by current flowing in the adjacent turns and production of EMF from the magnetic field component of an incident radio wave rely on the same principle. Chris |
Receiving Loop Antenna Question
On Sun, 25 Jan 2009 09:11:19 -0800 (PST), Art Unwin
wrote: what you have then done is to cancel not only the capacitance build up but also the inductance build up AKA Resistor |
Receiving Loop Antenna Question
"christofire" wrote in message ... "Art Unwin" wrote in message ... On Jan 25, 3:51 am, wrote: On Jan 23, 8:45 am, Allodoxaphobia wrote: On Fri, 23 Jan 2009 13:57:40 +0000, dave wrote: Ian Jackson wrote: What about ribbon cable? I've got a fair length of ribbon cable (something like 25 wires - the sort used in PCs to connect hard drives and the like) put away for a rainy-day loop antenna project. While I could make one large loop using all 25 wires for the really low frequencies, I'll almost certainly cut it up and make several smaller loops with fewer wires for the higher frequencies. Stick with a single wire and relatively few loops. More wire won't make the loop bigger, just harder to tune. I don't think he meant to connect all those wires in parallel. But, it would be a little tedious to connect each wire at one end to its neighbor at the other end (of the loop), and _not_ create an ugly bird's nest at the 'joint'. Jonesy Yep, it's a continuous single wire. If you used ribbon cable, you would have to put a cut, and the jumper to jump over to the next wire on each turn.. Would be a pain. You just take a single length of wire and thread it around through the holes until you have the number of turns you need. You are moving over a row of holes on each turn. The main thing to consider is you end up building the loop and deciding the proper number of turns around the capacitor you have, not the other way around. A double 365pf cap "730 pf total if jumped together" will let you be able to tune the whole AM-BC band with most loops. My 44 inch per side diamond loop for MW has five turns. My 16 inch diameter circle loop for MW uses 12 turns. Both are using basically the same cap values. I also use a single turn coupling loop that is inside and slightly smaller than the main loop. But it does not effect tuning, and it's size and spacing from the main loop is fairly uncritical. The cap is in parallel with the main loop winding. If you use a portable with a built in loop stick antenna, you can just couple the radio to the loop and it will work. But all my radios require a feed line to the antenna. I would not be so quick to dismiss the ribbon wire on the basis of capacitance build up ! If you start from the middle of one end by joining the two center wires together and from then on joining the end to end wires moving outwards what you have then done is to cancel not only the capacitance build up but also the inductance build up. You can then unfasten the first step on the center winding and feed it from that point i.e. center fed Art ... but a multi-turn loop in which the self-inductance cancelled wouldn't be much of a receiving antenna! Production of EMF from the magnetic field caused by current flowing in the adjacent turns and production of EMF from the magnetic field component of an incident radio wave rely on the same principle. Chris but thats they master theory behind art's antennas, they are self destructive. |
Receiving Loop Antenna Question
On Jan 25, 12:11*pm, "christofire" wrote:
"Art Unwin" wrote in message ... On Jan 25, 3:51 am, wrote: On Jan 23, 8:45 am, Allodoxaphobia wrote: On Fri, 23 Jan 2009 13:57:40 +0000, dave wrote: Ian Jackson wrote: What about ribbon cable? I've got a fair length of ribbon cable (something like 25 wires - the sort used in PCs to connect hard drives and the like) put away for a rainy-day loop antenna project. While I could make one large loop using all 25 wires for the really low frequencies, I'll almost certainly cut it up and make several smaller loops with fewer wires for the higher frequencies. Stick with a single wire and relatively few loops. More wire won't make the loop bigger, just harder to tune. I don't think he meant to connect all those wires in parallel. But, it would be a little tedious to connect each wire at one end to its neighbor at the other end (of the loop), and _not_ create an ugly bird's nest at the 'joint'. Jonesy Yep, it's a continuous single wire. If you used ribbon cable, you would have to put a cut, and the jumper to jump over to the next wire on each turn.. Would be a pain. You just take a single length of wire and thread it around through the holes until you have the number of turns you need. You are moving over a row of holes on each turn. The main thing to consider is you end up building the loop and deciding the proper number of turns around the capacitor you have, not the other way around. A double 365pf cap "730 pf total if jumped together" will let you be able to tune the whole AM-BC band with most loops. My 44 inch per side diamond loop for MW has five turns. My 16 inch diameter circle loop for MW uses 12 turns. Both are using basically the same cap values. I also use a single turn coupling loop that is inside and slightly smaller than the main loop. But it does not effect tuning, and it's size and spacing from the main loop is fairly uncritical. The cap is in parallel with the main loop winding. If you use a portable with a built in loop stick antenna, you can just couple the radio to the loop and it will work. But all my radios require a feed line to the antenna. I would not be so quick to dismiss the ribbon wire on *the basis of capacitance build up ! If you start from the middle of one end by joining the two center wires together and from then on joining the end to end wires moving outwards what you have then done is to cancel not only the capacitance build up but also the inductance build up. You can then unfasten the first step on the center winding and feed it from that point i.e. center fed Art ... but a multi-turn loop in which the self-inductance cancelled wouldn't be much of a receiving antenna! *Production of EMF from the magnetic field caused by current flowing in the adjacent turns and production of EMF from the magnetic field component of an incident radio wave rely on the same principle. Chris As an experimenter I am inclined to give things a try. If everything can be solved by the brain while sitting on the sofa then it would be a waste of time! As a recieving antenna all you would need is wire that has distributed loads and ZERO lumped loads, so why not just get rid of the lumped loads via cancellation? The complications that you bring up, I suggest, would be applicable to transmitting antennas only thus I feel experimentation is required before looking for a reason to discard. Sometimes an innocent experiment provides a long looked for answer to the most complicated question |
Receiving Loop Antenna Question
"Art Unwin" wrote in message ... snip As an experimenter I am inclined to give things a try. If everything can be solved by the brain while sitting on the sofa then it would be a waste of time! As a recieving antenna all you would need is wire that has distributed loads and ZERO lumped loads, so why not just get rid of the lumped loads via cancellation? Resonance? I think we already invented that. |
Receiving Loop Antenna Question
On Jan 25, 9:52*am, Cecil Moore wrote:
wrote: My 16 inch diameter circle loop for MW uses 12 turns. I know multiple loop antennas are lossy for transmitting. Are they adequate for receiving because of the AGC dynamic range in the receiver? -- 73, Cecil *http://www.w5dxp.com I'm not sure how the AGC comes into play here.. The 16 inch antenna provides plenty enough signal, even with no preamp used. You could turn the AGC on or off, wouldn't really matter. No different than any other antenna you might connect in that regard. They are lossy for transmitting, but on the MW bands you have so much excess signal level it's not an issue as far as receiving. Note the ferrite bar antenna, which is even more lossy than the open loops I use. It has no problem providing enough signal for a cheap portable radio. You might be surprised just how much level you can get from a tuned small loop on the low bands. As an example, that 16 inch loop provides more signal than the whip on a car. I once tried it with a delco radio in my truck. I hooked the loop up to it, and it was as hot as a firecracker vs the standard whip. The catch is the system is very high Q, and requires constant tuning of the cap as you change frequency. |
Receiving Loop Antenna Question
On Jan 25, 11:11*am, Art Unwin wrote:
I would not be so quick to dismiss the ribbon wire on *the basis of capacitance build up ! I would not be so quick to assume I dismissed ribbon wire on the basis of capacitance buildup. Where do you read any such thing in what I posted? Has nothing to do with why I wouldn't use ribbon cable. Using a ribbon cable would be a pain in the arse. You would have to cut and jumper each turn to the next turn. Makes more sense just to use a single wire and thread it through the holes, row by row if multiple turns are needed. |
Receiving Loop Antenna Question
On Jan 25, 5:37*pm, wrote:
On Jan 25, 11:11*am, Art Unwin wrote: I would not be so quick to dismiss the ribbon wire on *the basis of capacitance build up ! I would not be so quick to assume I dismissed ribbon wire on the basis of capacitance buildup. Where do you read any such thing in what I posted? Has nothing to do with why I wouldn't use ribbon cable. Using a ribbon cable would be a pain in the arse. You would have to cut and jumper each turn to the next turn. Makes more sense just to use a single wire and thread it through the holes, row by row if multiple turns are needed. I did this with ribbon cable once and it is actually pretty easy to do. I couldnt have taken more than 15 minutes to fabticate an 8 turn coil. Jimmie |
Receiving Loop Antenna Question
"Art Unwin" wrote in message ... On Jan 25, 12:11 pm, "christofire" wrote: "Art Unwin" wrote in message 8 I would not be so quick to dismiss the ribbon wire on the basis of capacitance build up ! If you start from the middle of one end by joining the two center wires together and from then on joining the end to end wires moving outwards what you have then done is to cancel not only the capacitance build up but also the inductance build up. You can then unfasten the first step on the center winding and feed it from that point i.e. center fed Art ... but a multi-turn loop in which the self-inductance cancelled wouldn't be much of a receiving antenna! Production of EMF from the magnetic field caused by current flowing in the adjacent turns and production of EMF from the magnetic field component of an incident radio wave rely on the same principle. Chris As an experimenter I am inclined to give things a try. If everything can be solved by the brain while sitting on the sofa then it would be a waste of time! As a recieving antenna all you would need is wire that has distributed loads and ZERO lumped loads, so why not just get rid of the lumped loads via cancellation? The complications that you bring up, I suggest, would be applicable to transmitting antennas only That principle is Faraday's Law which is fully reciprocal, so no, this is equally applicable to receiving and transmitting antennas. I hope 'EMF' isn't being misread as anything other than its original meaning in this context, that is, electro-motive force (the non-ambiguous form of 'voltage'). Chris |
Receiving Loop Antenna Question
On Jan 26, 8:38*am, "christofire" wrote:
"Art Unwin" wrote in message ... On Jan 25, 12:11 pm, "christofire" wrote: "Art Unwin" wrote in message 8 I would not be so quick to dismiss the ribbon wire on the basis of capacitance build up ! If you start from the middle of one end by joining the two center wires together and from then on joining the end to end wires moving outwards what you have then done is to cancel not only the capacitance build up but also the inductance build up. You can then unfasten the first step on the center winding and feed it from that point i.e. center fed Art ... but a multi-turn loop in which the self-inductance cancelled wouldn't be much of a receiving antenna! Production of EMF from the magnetic field caused by current flowing in the adjacent turns and production of EMF from the magnetic field component of an incident radio wave rely on the same principle. Chris As an experimenter I am inclined to give things a try. If everything can be solved by the brain while sitting on the sofa then it would be a waste of time! As a recieving antenna all you would need is wire that has distributed loads and ZERO lumped loads, so why not just get rid of the lumped loads via cancellation? The complications that you bring up, I suggest, would be applicable to transmitting antennas only That principle is Faraday's Law which is fully reciprocal, so no, this is equally applicable to receiving and transmitting antennas. I hope 'EMF' isn't being misread as anything other than its original meaning in this context, that is, electro-motive force (the non-ambiguous form of 'voltage'). Chris Hi Chris, I need a bit more with respect to your response in more layman terms When a multi turn helix is generated it can be used for both transmitting and receiving. When generating two helix antennas where one is contra wound and both are connected at the top you are saying that it will NOT be suitable for receiving ! We know by common use that the single helix is good for transmitt and receive . So what exactly does the addition of the contra winding do to prevent the combination from receiving? Looking forward to your take on the question. Best regards Art |
Receiving Loop Antenna Question
"Art Unwin" wrote in message ... On Jan 26, 8:38 am, "christofire" wrote: "Art Unwin" wrote in message 8 Hi Chris, I need a bit more with respect to your response in more layman terms When a multi turn helix is generated it can be used for both transmitting and receiving. When generating two helix antennas where one is contra wound and both are connected at the top you are saying that it will NOT be suitable for receiving ! We know by common use that the single helix is good for transmitt and receive . So what exactly does the addition of the contra winding do to prevent the combination from receiving? Looking forward to your take on the question. Best regards Art OK. The term 'helix' is most often applied to the travelling-wave antenna invented by John Kraus, often used at VHF and above, which generates or receives a circularly-polarised wave predominantly in the direction of its axis. It is also used in 'normal-mode helix' for the type of monopole element often found on walkie talkies, that generates and receives a linearly-polarised wave. Both of these are connected to electronics at one end only. The discussion was about loop antennas having one or more turns, with both ends of the winding connected to electronics. This construction can also be called a solenoid, but it would provoke confusion to call it a 'helix'. When an alternating current is passed through a solenoid it generates a magnetic field, H, through its centre and around it - the transmitting case. When a solenoid is placed in an alternating magnetic field, if any lines of magnetic force pass through its winding it will generate an electro-motive force (EMF) from which current can be drawn to operate a receiver - the receiving case. In the transmitting case the physical characteristics (described by the intrinsic impedance) of 'space' - the air surrounding the solenoid - cause an electric field, E, to be generated from the alternating magnetic field, in phase with the H field that caused it (viz. the intrinsic impedance of space is real not complex) and together these in-phase E and H components give rise to an electromagnetic wave. A fraction of the input power will be radiated away from the solenoid in that wave, in directions where their vector cross-product ExH is not zero. The field strength of either the E or H component of the radiated wave will decay linearly with increasing distance. You can find a good account of this process in books like 'Antennas' by the late John Kraus but it isn't possible to get very far without use of mathematics. Chapter 7 of 'Antennas for all applications' by Kraus and Marhefka, the 2002 edition, covers all this in greater detail and would be worth obtaining if you're interested. The 'sense' (i.e. clockwise/anticlockwise with respect to some datum) of the winding of a solenoid, and the direction of the current applied, affect the polarity of the magnetic field it produces, and vice versa for the receiving case. Consequently, the phase with respect to time of the alternating H field (and the alternating E-field component of the radiated electromagnetic wave) depend on the 'sense' of the winding, but the polarisation of the radiated wave depends on the alignment of the axis of the solenoid. By convention, 'polarisation' is the angular direction of the E field in the outgoing wave, which is perpendicular to the H-field component, and both are perpendicular to the direction of propagation, so solenoid with a horizontal axis radiates a vertically-polarised (VP) radio wave - and receives best from a VP wave; the ferrite-rod-in-a-broadcast-receiver case. Back to my original point: if part of the winding of the solenoid is wound in the opposite sense to the rest of the winding then its contribution to the generated H field, or the EMF on receiving, will oppose the contribution from the other part of the winding. If the winding has half in each 'sense', connected in series (like a non-inductive wire-wound resistor), then it will not generate an H field or develop an EMF from an incident H field, so it will not work as a transmitting or receiving antenna ... for the reasons outlined above. Enough? Chris |
Receiving Loop Antenna Question
On Jan 26, 12:16*pm, "christofire" wrote:
"Art Unwin" wrote in message ... On Jan 26, 8:38 am, "christofire" wrote: "Art Unwin" wrote in message 8 Hi Chris, I need a bit more with respect to your response in more layman terms When a multi turn helix is generated *it can be used for both transmitting and receiving. When generating two helix antennas where one is contra wound and both are connected at the top you are saying that it will NOT be suitable for receiving ! We know by common use that the single helix is good for transmitt and receive . So what exactly does the addition of the contra winding do to prevent the combination from receiving? Looking forward to your take on the question. Best regards Art OK. *The term 'helix' is most often applied to the travelling-wave antenna invented by John Kraus, often used at VHF and above, which generates or receives a circularly-polarised wave predominantly in the direction of its axis. *It is also used in 'normal-mode helix' for the type of monopole element often found on walkie talkies, that generates and receives a linearly-polarised wave. *Both of these are connected to electronics at one end only. The discussion was about loop antennas having one or more turns, with both ends of the winding connected to electronics. *This construction can also be called a solenoid, but it would provoke confusion to call it a 'helix'. When an alternating current is passed through a solenoid it generates a magnetic field, H, through its centre and around it - the transmitting case. When a solenoid is placed in an alternating magnetic field, if any lines of magnetic force pass through its winding it will generate an electro-motive force (EMF) from which current can be drawn to operate a receiver - the receiving case. In the transmitting case the physical characteristics (described by the intrinsic impedance) of 'space' - the air surrounding the solenoid - cause an electric field, E, to be generated from the alternating magnetic field, in phase with the H field that caused it (viz. the intrinsic impedance of space is real not complex) and together these in-phase E and H components give rise to an electromagnetic wave. *A fraction of the input power will be radiated away from the solenoid in that wave, in directions where their vector cross-product ExH is not zero. *The field strength of either the E or H component of the radiated wave will decay linearly with increasing distance. You can find a good account of this process in books like 'Antennas' by the late John Kraus but it isn't possible to get very far without use of mathematics. *Chapter 7 of 'Antennas for all applications' by Kraus and Marhefka, the 2002 edition, covers all this in greater detail and would be worth obtaining if you're interested. The 'sense' (i.e. clockwise/anticlockwise with respect to some datum) of the winding of a solenoid, and the direction of the current applied, affect the polarity of the magnetic field it produces, and vice versa for the receiving case. *Consequently, the phase with respect to time of the alternating H field (and the alternating E-field component of the radiated electromagnetic wave) depend on the 'sense' of the winding, but the polarisation of the radiated wave depends on the alignment of the axis of the solenoid. *By convention, 'polarisation' is the angular direction of the E field in the outgoing wave, which is perpendicular to the H-field component, and both are perpendicular to the direction of propagation, so solenoid with a horizontal axis radiates a vertically-polarised (VP) radio wave - and receives best from a VP wave; the ferrite-rod-in-a-broadcast-receiver case. Back to my original point: if part of the winding of the solenoid is wound in the opposite sense to the rest of the winding then its contribution to the generated H field, or the EMF on receiving, will oppose the contribution from the other part of the winding. *If the winding has half in each 'sense', connected in series (like a non-inductive wire-wound resistor), then it will not generate an H field or develop an EMF from an incident H field, so it will not work as a transmitting or receiving antenna ... for the reasons outlined above. Enough? Chris Chris First of all thank you very much for the effort that you placed in your response. It really what I expected from you after reading your profile ie the anbsence of derision. Now I am not fully convinced with your response as the rest of the newsgroup already suspect Coming from a different direction with respect to mathematics, when adding a timevarying field to a Gaussian field it equates in every way to the laws of Maxwell. Both of these laws I consider as an absolute truth. The above therefore states that the presence of particles is undeniable in the generation of RF communication. Because of the specificity of a state of equilibrium in a Gaussian field the following can be stated. A radiator or array can be any size, shape or varied elevation ...............AS LONG AS IT IS IN A STATE OF EQUILIBRIUM From the above ground rules which is confirmed by Maxwells laws the single winding of a wire is NOT in equilibrium unless the lumped properties are cancelled which leaves a structure that is in equilibrium ala wire that is conductive and with no other properties other that he addition of distributed loads that are common from a conductor. Your response is based on the generation of fields without which the radiator cannot receive by incoming waves from a transmitter, Where as my response is based on the basis of particles impinging on a receive antenna to create oscillation. The biggest difference is the interpretation of a tank circuit( a circuit in equilibrium) where in the perfect case of zero friction your aproach would define this operation as a zero tx/rc element My interpretation is that it cannot be zero friction even if the distributed components were friction free because of the presence of particles, which must be impelled by force to another radiator to create oscillation. So to sum up Your aproach is from dissipating fields to provide communication and mine is from non dissipating fields that dislodge particles as it rotates to and from the distributed loads using both as energy retainers.. As I have stated before, this is a presently a widely known method in a macro re enactment of salvage processes that sorts materials by directional magnetic field thrusts provided by eddy fields I do need more time to study your response to see the difference between the field aproach and the particle aproach tho with my present circumstances I may not be able to determine. Again, thankyou for your gentlemanly response, a rarity in this particular newsgroup. Regards Art |
Receiving Loop Antenna Question
"Art Unwin" wrote in message ... On Jan 26, 12:16 pm, "christofire" wrote: "Art Unwin" wrote in message 8 Chris First of all thank you very much for the effort that you placed in your response. It really what I expected from you after reading your profile ie the anbsence of derision. Now I am not fully convinced with your response as the rest of the newsgroup already suspect Coming from a different direction with respect to mathematics, when adding a timevarying field to a Gaussian field it equates in every way to the laws of Maxwell. Both of these laws I consider as an absolute truth. The above therefore states that the presence of particles is undeniable in the generation of RF communication. Because of the specificity of a state of equilibrium in a Gaussian field the following can be stated. A radiator or array can be any size, shape or varied elevation ...............AS LONG AS IT IS IN A STATE OF EQUILIBRIUM From the above ground rules which is confirmed by Maxwells laws the single winding of a wire is NOT in equilibrium unless the lumped properties are cancelled which leaves a structure that is in equilibrium ala wire that is conductive and with no other properties other that he addition of distributed loads that are common from a conductor. Your response is based on the generation of fields without which the radiator cannot receive by incoming waves from a transmitter, Where as my response is based on the basis of particles impinging on a receive antenna to create oscillation. The biggest difference is the interpretation of a tank circuit( a circuit in equilibrium) where in the perfect case of zero friction your aproach would define this operation as a zero tx/rc element My interpretation is that it cannot be zero friction even if the distributed components were friction free because of the presence of particles, which must be impelled by force to another radiator to create oscillation. So to sum up Your aproach is from dissipating fields to provide communication and mine is from non dissipating fields that dislodge particles as it rotates to and from the distributed loads using both as energy retainers.. As I have stated before, this is a presently a widely known method in a macro re enactment of salvage processes that sorts materials by directional magnetic field thrusts provided by eddy fields I do need more time to study your response to see the difference between the field aproach and the particle aproach tho with my present circumstances I may not be able to determine. Again, thankyou for your gentlemanly response, a rarity in this particular newsgroup. Regards Art You're welcome. I can't say I understand much of what you've written above but I'm sure there are often many ways to visualise the same physical process; the wave/particle duality of EM radiation being one often spoken about. For this case, I wrote from the viewpoint of the work reported in a large number of text books: the set of principles that's passed on at universities and has been used to design the vast majority of antennas that have been used since the discovery of radio. I'm not aware of any successful antenna designs, operating lower than EHF, based on a particle theory of electromagnetic radiation. However I am aware of a few unsuccessful designs (e.g. the 'crossed-field antenna') for which the creators have purported to re-write the known (wave) theory of radiation. I know it's generally bad to generalise (!) but it seems clear to me, and probably many others, that antennas based on well-documented, well-understood, theory are always a safer bet! They certainly are in (most lines of) business where cost matters - but perhaps not in amateur circles where different motives apply. Chris |
Receiving Loop Antenna Question
On Jan 26, 1:59*pm, "christofire" wrote:
"Art Unwin" wrote in message ... On Jan 26, 12:16 pm, "christofire" wrote: "Art Unwin" wrote in message 8 Chris First of all thank you very much for the effort that you placed in your response. It really what I expected from you after reading your profile ie the anbsence of derision. Now I am not fully convinced with your response as the rest of the newsgroup already suspect Coming from a different direction with respect to mathematics, when adding a timevarying field to a Gaussian field it equates in every way to the laws of Maxwell. Both of these laws I consider as an absolute truth. The above therefore states that the presence of particles is undeniable in the generation of RF communication. Because of the specificity of a state of equilibrium in a Gaussian field the following can be stated. A radiator or array can be any size, shape or varied elevation ..............AS LONG AS IT IS IN A STATE OF EQUILIBRIUM From the above ground rules which is confirmed by Maxwells laws the single winding of a wire is NOT in equilibrium unless the lumped properties are cancelled which leaves a structure that is in equilibrium ala wire that is conductive and with no other properties other that he addition of distributed loads that are common from a conductor. Your response is based on the generation of fields without which the radiator cannot receive by incoming waves from a transmitter, Where as my response is based on the basis of particles impinging on a receive antenna to create oscillation. The biggest difference is the interpretation of a tank circuit( a circuit in equilibrium) where in *the perfect case of zero friction your aproach would define this operation as a zero tx/rc element My interpretation is that it cannot be zero friction even if the distributed components were friction free because of the presence of particles, which must be impelled by force to another radiator to create oscillation. So to sum up *Your aproach is from dissipating fields to provide communication and mine is from non dissipating fields that dislodge particles as it rotates to and from the distributed loads using both as energy retainers.. As I have stated before, this is a presently a widely known method in a macro *re enactment of salvage processes *that sorts materials by directional magnetic field thrusts provided by eddy fields I do need more time to study your response to see the difference between the field aproach and the particle aproach tho with my present circumstances I may not be able to determine. Again, thankyou for your gentlemanly response, a rarity in this particular newsgroup. Regards Art You're welcome. I can't say I understand much of what you've written above but I'm sure there are often many ways to visualise the same physical process; the wave/particle duality of EM radiation being one often spoken about. *For this case, I wrote from the viewpoint of the work reported in a large number of text books: the set of principles that's passed on at universities and has been used to design the vast majority of antennas that have been used since the discovery of radio. *I'm not aware of any successful antenna designs, operating lower than EHF, based on a particle theory of electromagnetic radiation. *However I am aware of a few unsuccessful designs (e.g. the 'crossed-field antenna') for which the creators have purported to re-write the known (wave) theory of radiation. I know it's generally bad to generalise (!) but it seems clear to me, and probably many others, that antennas based on well-documented, well-understood, theory are always a safer bet! *They certainly are in (most lines of) business where cost matters - but perhaps not in amateur circles where different motives apply. Chris Understood I have an applied patent that is on the net somewhere that goes thru these same motions to obtain an array inequilibrim whbich are then displayed via the AO pro program whiuch confirms the equilibrium theoryn that is obtained by the Gaussian field aproach on Maxwells laws. On the same patent request I provided an analysis of a verticle dipole which for maximum gain is tipped with reference to earth. The tipping force is the weak force or the eddy field I spoke of which is not included in programs associated with planar forms that are based on intercoupling coupling. The same aproach can also be applied using the equilibrium requirement as I proposed earlier. The only problem I can see in using MOM programs is the validity of close spaced conduntors where it is possible to conceive of interfering eddy currents not impinging upon particles, but it terms of receiving there is nothing to prevent the impact of particles on the radiator. At present my tower antenna is made of circularly wound wires in both the cw and ccw direction, again based on the equilibrium finding, where the antenna is a travelling wave form that is end fed which allows for smaller volume antennas to those presently known. Everything revolves around the extended Gaussion theorem which equates to Maxwell's laws with the addition of particles within a boundary in equilibrium. Break that association down then all of mine falls apart. I will place a dual wound helix on my page in the next couple of days that is produced via the AOP Minninec program for antennas by Beasely so that you can see it for your self. It will not be completely accurate as such an arrangement requires many more point calculations than I have available to me. Will be at hospital all day tomorrow so please be patient on my page issue. Best regards Art |
Receiving Loop Antenna Question
"christofire" wrote in message ... I can't say I understand much of what you've written above but I'm sure there are often many ways to visualise the same physical process; and be glad that you don't understand it! its pure bafflegab, unless you really like magical levitating diamagnetic neutrinos that hop off the antenna to make em waves. |
Receiving Loop Antenna Question
On Jan 26, 5:22*pm, "Dave" wrote:
"christofire" wrote in message ... I can't say I understand much of what you've written above but I'm sure there are often many ways to visualise the same physical process; and be glad that you don't understand it! *its pure bafflegab, unless you really like magical levitating diamagnetic neutrinos that hop off the antenna to make em waves. David Your accusations doesn't bother me. After all, you got a degree by memorising the books without checking from first principles for yourself. Choosing from a,b,c or d is a similar short cut for education without the application of personal intelligence It would be suicidal for any student to not parrot phrases and teachings ennunciated by their professor. He is the one who reads your work and determines whether you have earned a degree or not, thus conformity is a requirement. When you stated that statics has no place with respect to radiation or words to that effect it was understandable for me as the aproach that I ventured is not covered in any of the books presently being published. The point that all should know is that you cannot build a castle on sand, or in other words, all theories must rest on a sound foundation or findings and since your degree was obtained by being a follower your reaction to that which is not in compliance with the books of the day is perfectly understandable Take care Art Unwin KB9MZ.......xg (uk) |
Receiving Loop Antenna Question
On Jan 26, 2:40*pm, Art Unwin wrote:
On Jan 26, 1:59*pm, "christofire" wrote: "Art Unwin" wrote in message .... On Jan 26, 12:16 pm, "christofire" wrote: "Art Unwin" wrote in message 8 Chris First of all thank you very much for the effort that you placed in your response. It really what I expected from you after reading your profile ie the anbsence of derision. Now I am not fully convinced with your response as the rest of the newsgroup already suspect Coming from a different direction with respect to mathematics, when adding a timevarying field to a Gaussian field it equates in every way to the laws of Maxwell. Both of these laws I consider as an absolute truth. The above therefore states that the presence of particles is undeniable in the generation of RF communication. Because of the specificity of a state of equilibrium in a Gaussian field the following can be stated. A radiator or array can be any size, shape or varied elevation ..............AS LONG AS IT IS IN A STATE OF EQUILIBRIUM From the above ground rules which is confirmed by Maxwells laws the single winding of a wire is NOT in equilibrium unless the lumped properties are cancelled which leaves a structure that is in equilibrium ala wire that is conductive and with no other properties other that he addition of distributed loads that are common from a conductor. Your response is based on the generation of fields without which the radiator cannot receive by incoming waves from a transmitter, Where as my response is based on the basis of particles impinging on a receive antenna to create oscillation. The biggest difference is the interpretation of a tank circuit( a circuit in equilibrium) where in *the perfect case of zero friction your aproach would define this operation as a zero tx/rc element My interpretation is that it cannot be zero friction even if the distributed components were friction free because of the presence of particles, which must be impelled by force to another radiator to create oscillation. So to sum up *Your aproach is from dissipating fields to provide communication and mine is from non dissipating fields that dislodge particles as it rotates to and from the distributed loads using both as energy retainers.. As I have stated before, this is a presently a widely known method in a macro *re enactment of salvage processes *that sorts materials by directional magnetic field thrusts provided by eddy fields I do need more time to study your response to see the difference between the field aproach and the particle aproach tho with my present circumstances I may not be able to determine. Again, thankyou for your gentlemanly response, a rarity in this particular newsgroup. Regards Art You're welcome. I can't say I understand much of what you've written above but I'm sure there are often many ways to visualise the same physical process; the wave/particle duality of EM radiation being one often spoken about. *For this case, I wrote from the viewpoint of the work reported in a large number of text books: the set of principles that's passed on at universities and has been used to design the vast majority of antennas that have been used since the discovery of radio. *I'm not aware of any successful antenna designs, operating lower than EHF, based on a particle theory of electromagnetic radiation. *However I am aware of a few unsuccessful designs (e.g. the 'crossed-field antenna') for which the creators have purported to re-write the known (wave) theory of radiation. I know it's generally bad to generalise (!) but it seems clear to me, and probably many others, that antennas based on well-documented, well-understood, theory are always a safer bet! *They certainly are in (most lines of) business where cost matters - but perhaps not in amateur circles where different motives apply. Chris Understood I have an applied patent that is on the net somewhere that goes thru these same motions to obtain an array inequilibrim whbich are then displayed via the AO pro program whiuch confirms the equilibrium theoryn that is obtained by the Gaussian field aproach on Maxwells laws. On the same patent request I provided an analysis of a verticle dipole which for maximum gain is tipped with reference to earth. The tipping force is the weak force or the eddy field I spoke of which is not included in programs associated with planar forms that are based on intercoupling coupling. The same aproach can also be applied using the equilibrium requirement as I proposed earlier. The only problem I can see in using MOM programs is the validity of close spaced conduntors where it is possible to conceive of interfering eddy currents not impinging upon particles, but it terms of receiving there is nothing to prevent the impact of particles on the radiator. At present my tower antenna is made of circularly wound wires in both the cw and ccw direction, again based on the equilibrium finding, where the antenna is a travelling wave form that is end fed which allows for smaller volume antennas to those presently known. Everything revolves around the extended Gaussion theorem which equates to Maxwell's laws with the addition of particles within a boundary in equilibrium. Break that association down then all of mine falls apart. I will place a dual wound helix on my page in the next couple of days that is produced via the AOP Minninec program for antennas by Beasely so that you can see it for your self. It will not be completely accurate as such an arrangement requires many more point calculations than I have available to me. Will be at hospital all day tomorrow so please be patient on my page issue. Best regards Art ok Chris I have to get ready for an operation early tomorrow so I collected some stuff from the past and just put it into a package for my son to post for me. It will at least give you some stuff to look at until I get back. The important thing to remember is all other polarizations are always 3db down from 'max gain' and with only one circular direction with horiz and vert. The object is to choose the polarization required which you are aiming for to get the purest of radiation which helps in the reflected signal when searching for weather abnormalities at airports such as wind shear with minimum distortion. Sorry I could not plan the offering so I have not vetted what is posted See....,. http://users.sdsc.edu/~unwin/ Best regards Art unwin KB9MZ.......xg (uk) |
Receiving Loop Antenna Question
What about ribbon cable? I've got a fair length of ribbon cable
(something like 25 wires - the sort used in PCs to connect hard drives and the like) put away for a rainy-day loop antenna project. While I could make one large loop using all 25 wires for the really low frequencies, I'll almost certainly cut it up and make several smaller loops with fewer wires for the higher frequencies. -- Ian- Hide quoted text - Hello Ian, I have used 16 core ribbon cable, with each core connected in series for an AM broadcast band loop antenna. It was about 1 metre long in circumference which gave me a total length of 16 metres. I used a cheap tuning variable capacitor with a switch which connected another capacitor to increase the total capacitance so I could tune down to the bottom of the AM band. It is coupled through the internal ferrite antenna in the radio. On my main tuner in the house, it has connections for an antenna on the back, so I made another ribbon cable loop antenna and put a single wire with it as a pick up wire. Each end of the pick up wire is connected to the antenna inputs on the tuner. I have made four of them. They are easily made, not too fiddly and they work well. Cheers Max |
Receiving Loop Antenna Question
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Receiving Loop Antenna Question
"Ian Jackson" wrote in message ... In message , writes What about ribbon cable? I've got a fair length of ribbon cable (something like 25 wires - the sort used in PCs to connect hard drives and the like) put away for a rainy-day loop antenna project. While I could make one large loop using all 25 wires for the really low frequencies, I'll almost certainly cut it up and make several smaller loops with fewer wires for the higher frequencies. -- Ian- Hide quoted text - Hello Ian, I have used 16 core ribbon cable, with each core connected in series for an AM broadcast band loop antenna. It was about 1 metre long in circumference which gave me a total length of 16 metres. I used a cheap tuning variable capacitor with a switch which connected another capacitor to increase the total capacitance so I could tune down to the bottom of the AM band. It is coupled through the internal ferrite antenna in the radio. On my main tuner in the house, it has connections for an antenna on the back, so I made another ribbon cable loop antenna and put a single wire with it as a pick up wire. Each end of the pick up wire is connected to the antenna inputs on the tuner. I have made four of them. They are easily made, not too fiddly and they work well. Cheers Max Ah! Thanks for that info. It does seem to conflict with the previous advice. I was thinking about a somewhat larger loop - maybe using 2 or 3m of ribbon, but with fewer turns - but I can't see why 'working well' should no longer apply. I have no preference for using ribbon - it's just that is seems like a simple way of getting several turns 'in one go' (if you know what I mean). Obviously, you will reduce the self capacity (and have a greater potential tuning range) by using a loop with the turns well spaced - although the inductance will probably be a bit less, and you'll need to add a turn or two to compensate. My next question is about using varicap diodes to tune the loop. Most designs use a conventional capacitor, but a varicap would enable the loop to be located (say) in the loft, and the tuning varied from the shack downstairs. Is this technology worth perusing (ie Googling)? Or has it been found to be a waste of time? Thanks again. -- ian Varicaps are fine and you will find devices containing pairs like the BB212, specifically intended for tuning domestic receivers. They're used in all the modern radios that are digitally controlled. The trick is to use them in balanced pairs so strong signals don't push a single diode into conduction. Chris |
Receiving Loop Antenna Question
On Wed, 28 Jan 2009 13:03:45 -0000, "christofire"
wrote: My next question is about using varicap diodes to tune the loop. Most designs use a conventional capacitor, but a varicap would enable the loop to be located (say) in the loft, and the tuning varied from the shack downstairs. Is this technology worth perusing (ie Googling)? Or has it been found to be a waste of time? Varicaps are fine and you will find devices containing pairs like the BB212, specifically intended for tuning domestic receivers. They're used in all the modern radios that are digitally controlled. The trick is to use them in balanced pairs so strong signals don't push a single diode into conduction. Hi All, The strong signal issue goes well beyond the possibility of conduction. When you think about a voltage controlled capacitor, you have to account for the effects of the voltage of the signal you are tuning (and those you are not tuning). The BB212 application is found characterized for signal levels less than 100mV (typically far less). Why? A half volt signal level at the terminals of the device (taking the BB212 for example) biased at 1V will swing the capacitance 100pF above and below where it would be thought to be tuned. Of course, correspondingly smaller signals have correspondingly smaller swings - it all depends on how much you can tolerate. This swing is also a problem for PIN diodes used as voltage variable attenuators. 73's Richard Clark, KB7QHC |
Receiving Loop Antenna Question
In message , Richard Clark
writes On Wed, 28 Jan 2009 13:03:45 -0000, "christofire" wrote: My next question is about using varicap diodes to tune the loop. Most designs use a conventional capacitor, but a varicap would enable the loop to be located (say) in the loft, and the tuning varied from the shack downstairs. Is this technology worth perusing (ie Googling)? Or has it been found to be a waste of time? Varicaps are fine and you will find devices containing pairs like the BB212, specifically intended for tuning domestic receivers. They're used in all the modern radios that are digitally controlled. The trick is to use them in balanced pairs so strong signals don't push a single diode into conduction. Thanks for the advice, however...... Hi All, The strong signal issue goes well beyond the possibility of conduction. When you think about a voltage controlled capacitor, you have to account for the effects of the voltage of the signal you are tuning (and those you are not tuning). The BB212 application is found characterized for signal levels less than 100mV (typically far less). Why? A half volt signal level (that's surely one hell of an RF signal?) at the terminals of the device (taking the BB212 for example) biased at 1V will swing the capacitance 100pF above and below where it would be thought to be tuned. Of course, correspondingly smaller signals have correspondingly smaller swings - it all depends on how much you can tolerate. Varicap diodes will always suffer from having their capacitance modulated by an RF signal impressed upon them. However, they do seem to work well enough - even when the RF level is pretty high (which must be the case especially with varicap-tuned oscillators - ie most VCOs and PLL systems). Presumably, the effect of this modulation will be to generate intermodulation products. In VCOs, this will simply appear as harmonics of the oscillator signal (which you would get anyway - even with a conventional tuning capacitor). Where multiple-frequency signals are present (like you have with the receiving loop), the most apparent effect of the modulation of the diode capacity will appear as crossmodulation and other nasties on the other signals in the passband. However, as varicaps ARE used for the tuning of the input of receiver RF stages, how do they 'get away with it'? This swing is also a problem for PIN diodes used as voltage variable attenuators. My understanding of things is that the effectiveness of PIN diodes relies on them having a very poor performance at RF (especially at VHF and UHF). In attenuator circuits, they are forward biassed, and the DC current passing through them varies their RF resistance. However, the charges flowing through the junction are so 'sluggish' that they don't react to the rapidly-changing RF voltages. There is therefore negligible modulation of the RF resistance by the RF signals passing though them. -- Ian |
Receiving Loop Antenna Question
"Richard Clark" wrote in message ... On Wed, 28 Jan 2009 13:03:45 -0000, "christofire" wrote: My next question is about using varicap diodes to tune the loop. Most designs use a conventional capacitor, but a varicap would enable the loop to be located (say) in the loft, and the tuning varied from the shack downstairs. Is this technology worth perusing (ie Googling)? Or has it been found to be a waste of time? Varicaps are fine and you will find devices containing pairs like the BB212, specifically intended for tuning domestic receivers. They're used in all the modern radios that are digitally controlled. The trick is to use them in balanced pairs so strong signals don't push a single diode into conduction. Hi All, The strong signal issue goes well beyond the possibility of conduction. When you think about a voltage controlled capacitor, you have to account for the effects of the voltage of the signal you are tuning (and those you are not tuning). The BB212 application is found characterized for signal levels less than 100mV (typically far less). Why? A half volt signal level at the terminals of the device (taking the BB212 for example) biased at 1V will swing the capacitance 100pF above and below where it would be thought to be tuned. Of course, correspondingly smaller signals have correspondingly smaller swings - it all depends on how much you can tolerate. This swing is also a problem for PIN diodes used as voltage variable attenuators. 73's Richard Clark, KB7QHC Hi Richard I made a capacitator rotator for my 6 foot AM loop using a hobby shop servo to rotate the air variable cap. It works quite well and the components are affordable. The 3 section air capacitor allowed the use of each section by switching to the appropriate section with a TO-5 relay. That is Brute Force to tune an AM loop, but sure makes sense and uses affordable parts. Jerry KD6JDJ |
Receiving Loop Antenna Question
On Wed, 28 Jan 2009 20:12:15 +0000, Ian Jackson
wrote: Thanks for the advice, however...... Why? A half volt signal level (that's surely one hell of an RF signal?) I can see you don't know what environment you are living in. That, or you live out in a pastoral setting and the house has no significant RF contribution. Most of the world is urbanized and folks live within short distances of large transmitters. Varicap diodes will always suffer from having their capacitance modulated by an RF signal impressed upon them. However, they do seem to work well enough - even when the RF level is pretty high (which must be the case especially with varicap-tuned oscillators - ie most VCOs and PLL systems). You don't put the Varicap into the high level part of the circuit. This is obvious from the outset. Presumably, the effect of this modulation will be to generate intermodulation products. In VCOs, this will simply appear as harmonics of the oscillator signal (which you would get anyway - even with a conventional tuning capacitor). A conventional cap (and a conventional inductor, much less) will not contribute harmonics because it is linear. Harmonics comes from nonlinear components added by the circuit (partial conduction of an active component that aids in the oscillation). Where multiple-frequency signals are present (like you have with the receiving loop), the most apparent effect of the modulation of the diode capacity will appear as crossmodulation and other nasties on the other signals in the passband. However, as varicaps ARE used for the tuning of the input of receiver RF stages, how do they 'get away with it'? They don't if you are in such an environment. Again, if you don't know your environment, then it's all a crap shoot. There is no "getting away with it." The alternative is that the designer of a product fully anticipated these issues and purposely chose a design that minimized the effect of accidental contributions. Not all designers are up to speed on the topic. The web is full of reported failed projects that do not take bias Z and filtering into consideration. This swing is also a problem for PIN diodes used as voltage variable attenuators. My understanding of things is that the effectiveness of PIN diodes relies on them having a very poor performance at RF (especially at VHF and UHF). In attenuator circuits, they are forward biassed, and the DC current passing through them varies their RF resistance. However, the charges flowing through the junction are so 'sluggish' that they don't react to the rapidly-changing RF voltages. There is therefore negligible modulation of the RF resistance by the RF signals passing though them. Poor performance when a PIN diode is first and foremost a diode for RF and microwave applications? Only if you are using it for the wrong reason (like using a 1N23 for 120V 60HZ power rectification). PIN diodes are used as resistors and switches, not rectifiers. Further, don't confuse the switch application as meaning fast turn-off in the pico-to-subnanoseconds. Speed is relative to the application of signal path steering where 100s of nanoseconds is more than adequate. Consult: http://www.ieee.li/pdf/pin_diode_handbook.pdf 73's Richard Clark, KB7QHC |
Receiving Loop Antenna Question
On Wed, 28 Jan 2009 20:19:20 GMT, "Jerry"
wrote: Hi Richard I made a capacitator rotator for my 6 foot AM loop using a hobby shop servo to rotate the air variable cap. It works quite well and the components are affordable. The 3 section air capacitor allowed the use of each section by switching to the appropriate section with a TO-5 relay. That is Brute Force to tune an AM loop, but sure makes sense and uses affordable parts. Jerry KD6JDJ Hi Jerry, You have certain advantages over most of the correspondents here. You are something of a gear head, you know where to find things, you know how to put them together, and you actually do it. When I was a kid, I had the same bent, but my resources were from government surplus when you needed 400Hz 26V supplies (or other such oddities). It was back in the 60s when I started experimenting with Varicaps except they were 1N23 style diodes sold for their Varicap properties (which comes free with almost any diode); the real Varicaps sold for far too much for my allowance. Wasn't much tuning ratio back then either - about 3:1 to 5:1 - today's have more range than most air caps. 73's Richard Clark, KB7QHC |
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