80m Loop Antenna

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80m Loop Antenna

Finally finished, after two full days of tuning. This is the K5RP loop as discussed in ARRL Antenna Compendium no. 2. What a mechanically awkard antenna. It is extremely narrowband, covering only 40kHz of the band between 2:1 swr points and ground interaction is wicked.  I could change the dip frequency by retensioning the wires. The 1:1 bandwidth is 10khz. This narrowness makes tuning more of a challenge because it has to be smack dab on the frequency of choice. The purpose of building this is to help in finishing up my 5 band dxcc award. I still need 8 countries on 80 and the simple verticals of the past have just not been enough from Colorado. This loop is supposed to provide 3db gain over a vertical. The goal is to be able to work cw, psk31, and jt65. That’s more than 40kHz so I compromised. After multiple trips up and down the step ladder, I was able to get a dip at 3.573 mHz, half way between psk and jt65. SWR is 1:1 and resistance is 50 ohms. Very nice. No matching network needed. For the cw portion down to 3.500 I can switch in a tuner. Antenna gain only works with this design at it’s resonant point. Have you played with these loops? I’d really like to hear your experiences.

Construction:

Wire is 14 guage stranded insulated antenna wire from DX Engineering – 560 feet.

Support posts are Army surplus camoflage netting fiber glass poles – 28 feet tall.

I used clothes line pulleys at the 8 corners.

The antenna is two full wave 80 meter loops connected as a two turn coil.

 

 

 

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