Rap 'n Tap
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From: Garry Nichols
Date: 11/13/00
Time: 9:19:11 PM
Remote Name: 207.198.13.226
Hi Charlie,
I think it will work, but not sure of how well. Here are some ideas to kick around:
>At the top end of the band the total amount of wire will be longer than a half wave. Even without a capacitor it will unlikely tune above about 1000 kHz. You will have to play around with the number of turns and overall size. Keep the size as large as possible and adjust the turns count until the combination comes out right. Loop efficiency will be higher with greater amounts of square footage internal to the loop. >Having multiple turns will reduce the amount of wire it takes to bring about half wave resonance because of increased inductance from the turns and distributed capacity between the turns. >How did you plan on coupling it to the detector and phones, and to a tuning capacitor? Did you plan on bringing the two end leads down to the listening area? >The magnetic flux lines around a loop pass thru the center and then curve outward bending around gradually 180 deg to pass thru the plane of the loop outside the loop on their way back to the center where they started. I mention this because this loop will be "close to the ground" in relation to the size of the loop and a wavelength at the operating freq. This means that they will pass through the building and more importantly (I think) a lot of earth. This will cause losses. >Despite the previous point, I think that the large size may counter balance the earth losses. >Polarization will be horizontal. This may help to reduce sigs on any nearby interfering stations. More distant stations received via ground wave will be attenuated, perhaps greatly depending on the balance of the loop. You will not be able to control the balance very well because it will be effected by masses in and around the loop. Sigs coming in on skip are randomly polarized (they say) so it shouldn't make much difference. >Because of the low height, low angle skip signals will not be as strong as they would if the loop was much higher. >There will be a null straight up reaching away from the zenith for a ways, reducing high angle sky wave. Its position and depth will depend on loop balance.
My gut level feel is that it might be very good for medium angle sigs coming in on skip. It may be good for other angles simply due to the large size and the sensitivity created by this. If it can be tried without a lot of trouble I would definitely "give it a go".
And you thought your post was long! 73, Garry