HFU HF Underground
Technical Topics => Equipment => Topic started by: Capt. Kidd on March 27, 2018, 2310 UTC
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Lately I’ve decided to try to rebuild my shortwave station and do to space restraints I’ve had to build a loop antenna, I’ve had the thing for a while now it’s 150 feet of number 16 wire on a 5 foot pvc frame hoisted 20 feet in the air. The balun I have is 9:1 and I used it because it’s what I had. I’ve been told to use everything from 1:1 to 12:1. And ideas?
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Gee, you are pretty ambitious for a Kidd. Um... I've always done well with 4:1 W2DU current baluns. When you do your windings, don't put them too close together, or else that antenna will just RX FREQ's 5MHz and below, and little above that. Use the FREQ's of WWV, CHU, and 6070kHz CFRX (Since it's on-air 24/7.), to test RX with. Try the 9:1 balun, then try again without it. Good luck and Happy DX'ing!!!!!
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Loop design? For example, 5' circumference circle? 5' sides on a square loop?
Are you transmitting? If so, you probably are going to need to rethink the small loop concept. The type of loop you should look into is a magnetic loop. The big issue there is the need for a high-voltage variable capacitor if moving around frequencies. Something like 30 to like 230pF variable capacitor rated at a few thousand volts with a ~1/10-wavelength (at lowest frequency) secondary loop and a primary feed loop at 1/5 the secondary loop size. Feed the primary with coax, and resonant the secondary with the capacitor. There are lots of design plans on the net for research.
Are you just receiving? You could use what you have, or just a copper pipe loop of a few feet in circumference for that matter, and forget the balun IMO. Instead use a small preamp at the loop feedpoint to deal with the impedance variances and wideband gain design concerns. Instead of a balun you might consider some ferrites or a toroid on the feedline if really desired, though a well-balanced loop usually tends to be rather resistant to feedline common mode anyway.