Tunable active magnetic loop antenna
Anyone know of a good site offering build plans. Prefer plans from someone
who has built and used same. I need a quiet antenna like this and Wellbrook is just too expensive! http://www.wellbrook.uk.com/index.html |
Tunable active magnetic loop antenna
"Justtis" wrote in
: Anyone know of a good site offering build plans. Prefer plans from someone who has built and used same. I need a quiet antenna like this and Wellbrook is just too expensive! http://www.wellbrook.uk.com/index.html Here's a simple one: http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=10174 I had links to 2 Radio-Electronics projects on building a very nice small amplified antenna, one for BCB, the other for shortwave, but typically, I can't find them. |
Active magnetic loop antenna
Can be just an "active magnetic loop" design as the Wellbrook is. Doesn't
necessarily have to be tunable. I know what it's like to misplace things. I had a plan for a Wellbrook 1530 clone including the balanced broadband rf amp/control box but it's nowhere to be found. Probably ended up in the shredder. About 40 feet back from the house I'm running into all kinds of interference from Bell and Cable wires running at right angles across the back. I'll have to mount the unit somewhere between 20 and 35 feet away from the house for the best quiet spot. Then with the new rotor I purchased for the project, I can hopefully null out most of the rest of the interfering garbage. The MFJ-1026 should remove near all of what's left. 'Got everything ready for the build except the main part. "elaich" wrote in message ... "Justtis" wrote in : Anyone know of a good site offering build plans. Prefer plans from someone who has built and used same. I need a quiet antenna like this and Wellbrook is just too expensive! http://www.wellbrook.uk.com/index.html Here's a simple one: http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=10174 I had links to 2 Radio-Electronics projects on building a very nice small amplified antenna, one for BCB, the other for shortwave, but typically, I can't find them. |
Active magnetic loop antenna
How would a bicycle wheel work for an antenna? What if it was spinning
around and around like a windmill? cuhulin |
Tunable active magnetic loop antenna
Justtis wrote:
Anyone know of a good site offering build plans. Prefer plans from someone who has built and used same. I need a quiet antenna like this and Wellbrook is just too expensive! http://www.wellbrook.uk.com/index.html I have a 86cm tuned loop, that is better than the ALA1530 on an Akai tuner, cause it mixes up radios stations with the ala.. here a calculator. http://users.fulladsl.be/spb13810/ a wire of 15m will do for the 1500khz, but for 540Khz, you might need up to 20meter. I have used hula-hoops, and think that is the most efficient loop, ... -- -- 700+ Radio Stations on SW http://swstations.tk/ Shortwave transmissions in English, Francais, Nederlands, Deutsch, Suid-Afrikaans, Chinese, Dansk, Urdu, Cantonese, Greek, Spanish, Portuguese, ... http://radiolanguages.tk Updated every month or so .... |
Tunable active magnetic loop antenna
On 26 jun, 02:29, "Justtis" wrote:
Anyone know of a good site offering build plans. *Prefer plans from someone who has built and used same. I need a quiet antenna like this and Wellbrook is just too expensive!http://www.wellbrook.uk.com/index.html Hello Justtis, When you want to make a tunable loop (so tuning at the loop, or very close to it), you don't need an amplifier in most cases. Tuning (with reasonable match) has the advantage of large signal output for relative small loops and rejection of strong out of band signals. Also it is easier to get a good balance to avoid conducted interference traveling via the coaxial feeder to the loop antenna. Disadvantage is that you have to tune when changing band or frequency and the tuning unit is outdoors. Active loops save you from tuning, but may result in inter-modulation products due to strong signals. Also your receiver may suffer from this (in that case you need some form of preselection). From my own experience, loops do best up to the low HF. Above about 5 MHz, the performance difference between a loop and a vertical capacitive antenna (stick) is minimal. Of course when mounted at a rotor, the loop has the advantage of directivity for low elevation signals. Before buying any loop (or spending a lot of money on parts), first try one to make sure it solves your problem. When you are interested in one band only, you can make a provisional tuned loop yourself to see the improvement over your existing antenna. Try to get in contact with a radio amateur (HAM) group. Almost sure people over there will share their knowledge. You may also post in rec.radio.amateur.antenna Another less known method is to make a thick single-turn un-tuned loop with natural balun function in it (that are loops where the tubing is cut at the top of the loop). An example of a small strip-ype loop is given he http://www.tetech.nl/divers/small_H_FieldLoop2.jpg . Go the shack with low loss cable and do the tuning (and matching) in the shack. For transmitting this is no good option, but for reception only, this gives good results and you have the tuning/matching unit indoors adjacent to your receiver. Best regards, Wim PA3DJS www.tetech.nl Remove the obvious three characters in case of PM. |
Tunable active magnetic loop antenna
In article ,
"Justtis" wrote: Anyone know of a good site offering build plans. Prefer plans from someone who has built and used same. I need a quiet antenna like this and Wellbrook is just too expensive! http://www.wellbrook.uk.com/index.html Why don't you build a passive loop antenna? A loop antenna around 50 foot circumference will not need amplification. You can build it out of coax cable and split the shield halfway around the loop so it is shield balanced. A loop this size as a square is only about 12 foot a side. It's cheap and easy to build. -- Telamon Ventura, California |
Tunable active magnetic loop antenna
I actually meant to indicate a broadband active loop as the Wellbrook
model, mistakingly I chose to include "tuned". Very good advice! Thanks for pointing me in the right direction. My main receivers a Icom R71A(Kiwa memory board installed), Icom R-75, Kenwood TS-140(receive only), Kenwood R-1000, Drake R8. Portables: Grundig Satellit E1, Grundig Satellit 800, Sony SW-55, Sony ICF-2010, Sony ICF 5900W & 6500W. Many others waiting for a quiet antenna. Main listening interests: Ham 80/40 metre and utility stations(military, gov't, marine, air etc.). With the current lack of strong signals I'm trying to supply as near a noise free signal as possible. Thus the magnetic loop design. "Wimpie" wrote in message ... On 26 jun, 02:29, "Justtis" wrote: Anyone know of a good site offering build plans. Prefer plans from someone who has built and used same. I need a quiet antenna like this and Wellbrook is just too expensive!http://www.wellbrook.uk.com/index.html Hello Justtis, When you want to make a tunable loop (so tuning at the loop, or very close to it), you don't need an amplifier in most cases. Tuning (with reasonable match) has the advantage of large signal output for relative small loops and rejection of strong out of band signals. Also it is easier to get a good balance to avoid conducted interference traveling via the coaxial feeder to the loop antenna. Disadvantage is that you have to tune when changing band or frequency and the tuning unit is outdoors. Active loops save you from tuning, but may result in inter-modulation products due to strong signals. Also your receiver may suffer from this (in that case you need some form of preselection). From my own experience, loops do best up to the low HF. Above about 5 MHz, the performance difference between a loop and a vertical capacitive antenna (stick) is minimal. Of course when mounted at a rotor, the loop has the advantage of directivity for low elevation signals. Before buying any loop (or spending a lot of money on parts), first try one to make sure it solves your problem. When you are interested in one band only, you can make a provisional tuned loop yourself to see the improvement over your existing antenna. Try to get in contact with a radio amateur (HAM) group. Almost sure people over there will share their knowledge. You may also post in rec.radio.amateur.antenna Another less known method is to make a thick single-turn un-tuned loop with natural balun function in it (that are loops where the tubing is cut at the top of the loop). An example of a small strip-ype loop is given he http://www.tetech.nl/divers/small_H_FieldLoop2.jpg . Go the shack with low loss cable and do the tuning (and matching) in the shack. For transmitting this is no good option, but for reception only, this gives good results and you have the tuning/matching unit indoors adjacent to your receiver. Best regards, Wim PA3DJS www.tetech.nl Remove the obvious three characters in case of PM. |
Tunable active magnetic loop antenna
One inch by two inch strip of wood (for an antenna frame) is dirt cheap
at building supply stores.Wire is cheap too. cuhulin |
Tunable active magnetic loop antenna
On Jun 25, 5:29*pm, "Justtis" wrote:
Anyone know of a good site offering build plans. *Prefer plans from someone who has built and used same. I need a quiet antenna like this and Wellbrook is just too expensive!http://www.wellbrook.uk.com/index.html I use the ALA100 with home brew loops. Damn good, but you are right that it is expensive. The ALA100 is the cheapest of the Wellbrook products. They have some variants of it now. You need a good radio to use an untuned loop since it delivers a huge amount of RF. I suspect the ALA100 is just a wideband transformer and a common gate amp. You can get North Hills wideband transformers on ebay. I have a few of these transformers, but haven't got around to trying to make a home brew wellbrook. I found half a dozen North Hills 1301LB transformers in a surplus shop and wiped out their stock at $6 a pop. Oh, and I'm being a jerk and hoarding them. If you don't want to pay for a North Hills transformer, I suspect any passive video over twisted pair transformer will do the trick. I was thinking of using one unbal to bal to feed the source of a depletion mode JFET, ground the gate, then use the balanced end of another transformer as the load, tying the free end to the power supply, bypassed to ground, and of course the other end in series with the drain. Then feed the unbalanced side to the radio. If you had enough of these transformers, you could probably make a multicoupler using the same dcheme. Instead of one transformer in the path of the source, use several. There is some misconception that the Wellbrook loops are shielded. the pipe that you see is the loop itself. |
Tunable active magnetic loop antenna
In article
, " wrote: On Jun 25, 5:29*pm, "Justtis" wrote: Anyone know of a good site offering build plans. *Prefer plans from someone who has built and used same. I need a quiet antenna like this and Wellbrook is just too expensive!http://www.wellbrook.uk.com/index.html I use the ALA100 with home brew loops. Damn good, but you are right that it is expensive. The ALA100 is the cheapest of the Wellbrook products. They have some variants of it now. You need a good radio to use an untuned loop since it delivers a huge amount of RF. SNIP So stop whining about the cost and build a low cost passive loop. It if works well but you still need further improvement it will at least tide you over. All the amplification does for you is allow the loop to be smaller, which may mostly be a convenience depending on the environment. Be sure to build a balanced loop that only responds to the magnetic field. -- Telamon Ventura, California |
Tunable active magnetic loop antenna
I'm not whining about the cost of a homemade
loop! Where did you get that from? Please re read the messages! You seem to have run them together!! "Telamon" wrote in message ... In article , " wrote: On Jun 25, 5:29 pm, "Justtis" wrote: Anyone know of a good site offering build plans. Prefer plans from someone who has built and used same. I need a quiet antenna like this and Wellbrook is just too expensive!http://www.wellbrook.uk.com/index.html I use the ALA100 with home brew loops. Damn good, but you are right that it is expensive. The ALA100 is the cheapest of the Wellbrook products. They have some variants of it now. You need a good radio to use an untuned loop since it delivers a huge amount of RF. SNIP So stop whining about the cost and build a low cost passive loop. It if works well but you still need further improvement it will at least tide you over. All the amplification does for you is allow the loop to be smaller, which may mostly be a convenience depending on the environment. Be sure to build a balanced loop that only responds to the magnetic field. -- Telamon Ventura, California |
Tunable active magnetic loop antenna
On Jun 28, 6:17*pm, Telamon
wrote: In article , " wrote: On Jun 25, 5:29*pm, "Justtis" wrote: Anyone know of a good site offering build plans. *Prefer plans from someone who has built and used same. I need a quiet antenna like this and Wellbrook is just too expensive!http://www.wellbrook.uk.com/index.html I use the ALA100 with home brew loops. Damn good, but you are right that it is expensive. The ALA100 is the cheapest of the Wellbrook products. They have some variants of it now. You need a good radio to use an untuned loop since it delivers a huge amount of RF. SNIP So stop whining about the cost and build a low cost passive loop. It if works well but you still need further improvement it will at least tide you over. All the amplification does for you is allow the loop to be smaller, which may mostly be a convenience depending on the environment. Be sure to build a balanced loop that only responds to the magnetic field. -- Telamon Ventura, California I saw your other post on the subject. Feeding a loop to a 50 ohm input of a radio will not work well since once side of the loop will be at ground. This is where the wideband transformer comes into play. You can float the loop above ground if you have the transformer. It is possible to do the same with a differential amp, but good transformer would be lower noise. |
Tunable active magnetic loop antenna
On Jun 28, 4:10*pm, " wrote:
On Jun 25, 5:29*pm, "Justtis" wrote: Anyone know of a good site offering build plans. *Prefer plans from someone who has built and used same. I need a quiet antenna like this and Wellbrook is just too expensive!http://www.wellbrook.uk.com/index.html I use the ALA100 with home brew loops. Damn good, but you are right that it is expensive. The ALA100 is the cheapest of the Wellbrook products. They have some variants of it now. You need a good radio to use an untuned loop since it delivers a huge amount of RF. I suspect the ALA100 is just a wideband transformer and a common gate amp. You can get North Hills wideband transformers on ebay. I have a few of these transformers, but haven't got around to trying to make a home brew wellbrook. I found half a dozen North Hills 1301LB transformers in a surplus shop and wiped out their stock at $6 a pop. Oh, and I'm being a jerk and hoarding them. If you don't want to pay for a North Hills transformer, I suspect any passive video over twisted pair transformer will do the trick. I was thinking of using one unbal to bal to feed the source of a depletion mode JFET, ground the gate, then use the balanced end of another transformer as the load, tying the free end to the power supply, bypassed to ground, and of course the other end in series with the drain. Then feed the unbalanced side to the radio. If you had enough of these transformers, you could probably make a multicoupler using the same dcheme. Instead of one transformer in the path of the source, use several. There is some misconception that the Wellbrook loops are shielded. - the pipe that you see is the loop itself. Greater Surface {Effect} Area and Relative Greater Signal Capture Area over a single strand of Wire. ~ RHF |
Tunable active magnetic loop antenna
In article
, " wrote: On Jun 28, 6:17*pm, Telamon wrote: In article , " wrote: On Jun 25, 5:29*pm, "Justtis" wrote: Anyone know of a good site offering build plans. *Prefer plans from someone who has built and used same. I need a quiet antenna like this and Wellbrook is just too expensive!http://www.wellbrook.uk.com/index.html I use the ALA100 with home brew loops. Damn good, but you are right that it is expensive. The ALA100 is the cheapest of the Wellbrook products. They have some variants of it now. You need a good radio to use an untuned loop since it delivers a huge amount of RF. SNIP So stop whining about the cost and build a low cost passive loop. It if works well but you still need further improvement it will at least tide you over. All the amplification does for you is allow the loop to be smaller, which may mostly be a convenience depending on the environment. Be sure to build a balanced loop that only responds to the magnetic field. I saw your other post on the subject. Feeding a loop to a 50 ohm input of a radio will not work well since once side of the loop will be at ground. It works very well. I have several loop antennas. This is where the wideband transformer comes into play. You can float the loop above ground if you have the transformer. It is possible to do the same with a differential amp, but good transformer would be lower noise. The transformer is not necessary for a connection to the coax or a balanced amplifier input. You could clamp a few ferrite cores around the coax lead-in to the radio at the antenna connection to block noise coming from the radio if you don't already have the radio plugged into a EMI noise suppression power strip. -- Telamon Ventura, California |
Tunable active magnetic loop antenna
On Jun 29, 7:25*pm, Telamon
wrote: In article , " wrote: On Jun 28, 6:17*pm, Telamon wrote: In article , " wrote: On Jun 25, 5:29*pm, "Justtis" wrote: Anyone know of a good site offering build plans. *Prefer plans from someone who has built and used same. I need a quiet antenna like this and Wellbrook is just too expensive!http://www.wellbrook.uk.com/index.html I use the ALA100 with home brew loops. Damn good, but you are right that it is expensive. The ALA100 is the cheapest of the Wellbrook products. They have some variants of it now. You need a good radio to use an untuned loop since it delivers a huge amount of RF. SNIP So stop whining about the cost and build a low cost passive loop. It if works well but you still need further improvement it will at least tide you over. All the amplification does for you is allow the loop to be smaller, which may mostly be a convenience depending on the environment. Be sure to build a balanced loop that only responds to the magnetic field. I saw your other post on the subject. Feeding a loop to a 50 ohm input of a radio will not work well since once side of the loop will be at ground. It works very well. I have several loop antennas. This is where the wideband transformer comes into play. You can float the loop above ground if you have the transformer. It is possible to do the same with a differential amp, but *good transformer would be lower noise. The transformer is not necessary for a connection to the coax or a balanced amplifier input. You could clamp a few ferrite cores around the coax lead-in to the radio at the antenna connection to block noise coming from the radio if you don't already have the radio plugged into a EMI noise suppression power strip. -- Telamon Ventura, California Er, is there a reason you don't want to do this correctly? The thing with shortwave is you can toss out a piece of wire and get something. It is all a matter of digging the signal out of the noise. In any event, the transformers are easily purchased on ebay. Or in surplus shops if I don't beat you to them. |
Tunable active magnetic loop antenna
In article
, " wrote: On Jun 29, 7:25*pm, Telamon wrote: In article , " wrote: On Jun 28, 6:17*pm, Telamon wrote: In article , " wrote: On Jun 25, 5:29*pm, "Justtis" wrote: Anyone know of a good site offering build plans. *Prefer plans from someone who has built and used same. I need a quiet antenna like this and Wellbrook is just too expensive!http://www.wellbrook.uk.com/index.html I use the ALA100 with home brew loops. Damn good, but you are right that it is expensive. The ALA100 is the cheapest of the Wellbrook products. They have some variants of it now. You need a good radio to use an untuned loop since it delivers a huge amount of RF. SNIP So stop whining about the cost and build a low cost passive loop. It if works well but you still need further improvement it will at least tide you over. All the amplification does for you is allow the loop to be smaller, which may mostly be a convenience depending on the environment. Be sure to build a balanced loop that only responds to the magnetic field. I saw your other post on the subject. Feeding a loop to a 50 ohm input of a radio will not work well since once side of the loop will be at ground. It works very well. I have several loop antennas. This is where the wideband transformer comes into play. You can float the loop above ground if you have the transformer. It is possible to do the same with a differential amp, but *good transformer would be lower noise. The transformer is not necessary for a connection to the coax or a balanced amplifier input. You could clamp a few ferrite cores around the coax lead-in to the radio at the antenna connection to block noise coming from the radio if you don't already have the radio plugged into a EMI noise suppression power strip. Er, is there a reason you don't want to do this correctly? You don't need a transformer to "do it" correctly. The thing with shortwave is you can toss out a piece of wire and get something. It is all a matter of digging the signal out of the noise. In any event, the transformers are easily purchased on ebay. Or in surplus shops if I don't beat you to them. Yeah, that's what people do and then post complaints here. I'll let you in on a little secret. In order to be successful you have to remove obstacles not create them. You don't need to transform an impedance that close to the coax impedance. -- Telamon Ventura, California |
Tunable active magnetic loop antenna
In article ,
dave wrote: Telamon wrote: In article , " wrote: On Jun 29, 7:25 pm, Telamon wrote: In article , " wrote: On Jun 28, 6:17 pm, Telamon wrote: In article , " wrote: On Jun 25, 5:29 pm, "Justtis" wrote: Anyone know of a good site offering build plans. Prefer plans from someone who has built and used same. I need a quiet antenna like this and Wellbrook is just too expensive!http://www.wellbrook.uk.com/index.html I use the ALA100 with home brew loops. Damn good, but you are right that it is expensive. The ALA100 is the cheapest of the Wellbrook products. They have some variants of it now. You need a good radio to use an untuned loop since it delivers a huge amount of RF. SNIP So stop whining about the cost and build a low cost passive loop. It if works well but you still need further improvement it will at least tide you over. All the amplification does for you is allow the loop to be smaller, which may mostly be a convenience depending on the environment. Be sure to build a balanced loop that only responds to the magnetic field. I saw your other post on the subject. Feeding a loop to a 50 ohm input of a radio will not work well since once side of the loop will be at ground. It works very well. I have several loop antennas. This is where the wideband transformer comes into play. You can float the loop above ground if you have the transformer. It is possible to do the same with a differential amp, but good transformer would be lower noise. The transformer is not necessary for a connection to the coax or a balanced amplifier input. You could clamp a few ferrite cores around the coax lead-in to the radio at the antenna connection to block noise coming from the radio if you don't already have the radio plugged into a EMI noise suppression power strip. Er, is there a reason you don't want to do this correctly? You don't need a transformer to "do it" correctly. The thing with shortwave is you can toss out a piece of wire and get something. It is all a matter of digging the signal out of the noise. In any event, the transformers are easily purchased on ebay. Or in surplus shops if I don't beat you to them. Yeah, that's what people do and then post complaints here. I'll let you in on a little secret. In order to be successful you have to remove obstacles not create them. You don't need to transform an impedance that close to the coax impedance. BalUn? The transformer type would be a BALUN but it is not needed. The loop and lead in are all made of the same 50 ohm coax. The shield of the lead in and both sides of the loop are all connected together. The shield is opened halfway around the loop so the shield is balanced around the loop. One side of the loop center conductor is connected to the lead in center conductor. The other side of the loop center conductor is connected to the joined shield connection. The split shield picks up the far electric field equally and at opposite polarity so it is canceled. The coax center conductor has current induced in it from the magnetic field since it is shielded from the electric field. For the size of the loop the output will be less compared to an antenna that uses both fields to generate a signal to the radio but it also does a better job of canceling local noise sources provided the noise source is far enough from the antenna that its electric field will be canceled by the balanced shield. The result is a generally lower noise floor. Since I live in suburbia noise is a bigger issue than picking up the signal. In reverse order of preference: 1. Common mode antennas are near worthless around here. 2. Hertzian voltage antennas perform a little better than common mode. 3. Any type of hertzian closed loop antenna performs better than the voltage type. 4. The hertzian balanced shield loop antenna works better than 1 thru 3 above. You will notice a trend in a certain antenna parameter in the order of preference above. I'll leave it as an exercise for the reader to discover it. -- Telamon Ventura, California |
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