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Has anyone built one of these:
http://members.cox.net/rwagoner/columns/am_antenna.html??
Has anyone built one of these:
http://members.cox.net/rwagoner/columns/am_antenna.html??
It seems to me that 4 turns is not nearly enough, at least not with 22 gauge wire. What about tuning? An air cap?
Total posts : 45366Ken,
No, I have not built this specific antenna but when new to radio I built one similar. Mine was also untuned, it had about 10 turns if I recall right, and it didn’t perform very well. This is not a fair critique because I had available a long wire antenna which outperformed the loop. At the time I concluded that the loop wasn’t worth the effort.
In those days the radios were larger than those today and the built in loop and rod antennas were larger and seemed to perform better than the small ones in today’s portables and table tops.
This is a case of trying it to find if it works in your situation. It does seem that more than four turns will be needed if a parallel cap. is used to tune it. An air variable cap would be my choice.
Neil
Total posts : 45366The description of this loop seems clear enough, but “seems” is not a precise word, and I’d also like to see a schematic drawing as a kind of 2nd proof of the design.
Although it’s been established that loops are respected antennas, what seems hard to comprehend for me is the fact that a loop is so similar to a coil, which of course is not a type of antenna, but is capable of providing “loading” at a local level of design, with no expected radiation or reception in and of itself.
Also I wonder why the signal is not canceled to the same degree it is enhanced by the fact that phasing is shifted 360-degrees by every turn.
Total posts : 45366The loop antenna responds to the magnetic RF field rather than the electric field. The induced voltage depends on the area of the loop with each turn of the coil producing a voltage. A typical coil with a long length compared to the diameter has very little area with which to capture the magnetic field.
Also I wonder why the signal is not canceled to the same degree it is enhanced by the fact that phasing is shifted 360-degrees by every turn.
The dimensions involved are small compared to the RF wavelength so the phase shift in the coils is negligible and the voltage induced in each turn adds to the total. So more turns means more voltage up to the point where the inductance becomes a limiting factor.
Neil
Total posts : 45366I built one after conversations here.
My loop is wound on two cross arms about 20″ each at right angles. There are about 12 to 15 turns, don’t remember exactly. The two ends of these turns are connected to a typical AM radio air variable tuning capacitor.
Then, a 2 turn loop on the same cross arms is the link which connects to the antenna terminals on my receiver. Although, just placing a typical portable radio near the loop enhances the received signals.
The tuning cap forms a fairly sharp peak in signal strength and rotating the loop shows a fair amount of directional capability.
The final number of turns for the main loop was determined by the range of tuning capable with the capacitor. To tune lower frequencies I added a couple more turns to the main loop.
Total posts : 45366I counted the number of turns and find 15 turns for the tuned loop and 1 turn for the pickup loop. As stated before I played with the number of turns to adjust the tuning range as it wouldn’t quite cover the whole AM band.
The pickup loop goes directly to the antenna input terminals. The tuning cap connects the 15 turn loop. Both sections of the tuning cap are paralled so the equivalant value is probably around 400 to 500 uuf.
Just tinker until it works!
The loops are #18 insulated hookup wire.
Total posts : 45366Ken was not able to post on this thread. For several days I was not able to respond to any forum topic. I wrote an e-mail to the administrator, and he must have fixed the problem. Thanks.
Total posts : 45366Although I am able to post here, I was blocked from posting on a 2009 thread that I wanted to add to.
Total posts : 45366There’s been no changes to anyone’s user status, both of you are registered and active on the user control panel.
Which 2009 thread?
Can you start a new thread?
Thank you, btw 🙂
Total posts : 45366No problem starting a thread here … Ken N.
Total posts : 45366Hmmm … seems I can post to this one now.
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