Ham Radio Technical Discussion Net: Great Discussion by VU3JUS on Rectangular Loop Antenna for 40m

 Ham Radio Technical Discussion Net on 7065 kHz, 1:45 am UTC (7.15 am IST). Today we had great discussion by VU3JUS on his recangular loop antenna for 40m. Here is the gist of the discussion. He might also post it soon on a blog. Till then, this post will archive the discussion for the sake of SWLs and newbie hams.

The rectangular loop antenna is mounted on his terrace, with 136.7 feet of 1 sq mm wire. The ends are fed to 75 Ohms coax of 10m length (quarter lambda at 40m) for impedance matching. 75 Ohms coax is fed to 15m of RG 213 cable and then to the radio. All junctions have SO239/PL259 connectors, though direct soldering at the antenna feedpoint might also work. Elevating the centre point of the wire might improve the transmission as well reduce the space needed for mounting. He gets an SWR of 1.5:1 from 7040 to 7175 kHz with his setup. SWR may vary depending on the individual mounting pattern at their location.

500 pF double gang capacitor used for valve radios introduces in series could make the antenna work for 80m as well, without any sparking between stator and rotor plates of the metal gang capacitor. Sparking might occur if introduced in parallel. 

If you are not able to accomodate 136m of wire on your terrace, using 2.5 micro henry chokes for electrically shortening the antenna may be tried as an option. But it will need experimenting.

VU2JUS gets S7 noise only with this antenna, while I have S9 and more noise at my location, even though VU2JUS is located in a busier city than me. I always hear him quite loud and clear on 40m daily.

You can listen to the net from anywhere in the world on http://vu3wew.ddns.net:8073/, the OpenWebRX by VU3WEW. Today morning VU3WEW and VU2OJ had joined the frequency before VU3JUS.

73 de Jon, VU2JO

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