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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 |
#2
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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. |
#3
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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 |
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