QRP Forum : 1-3pm : Lone Star I


qrpMilt Cram, W8NUE: A New Approach to Understanding Loop Antennas

Most typical small Loop Antennas (1m dia) are designed for 20m to 10m and work poorly on the lower bands.....30m, 40m, and 80m. Many Loop Antenna articles don't explain the subtle details....or frankly, contain BS (K5BCQ editorial comment). Milt is here to clear air.
There is much miss-information about RF currents and where they flow, in Loop Antennas and when we say Low Resistance Joints, we mean LOW RESISTANCE. Milt has done considerable modeling in this area.
Milt has recently built up an efficient 45" diameter, 2 turn, 40m/80m Loop Antenna and he would like to share that information. He will describe the electrical behavior of a small transmitting loop antenna near the tuned frequency using an electrical circuit analogue.
  • Provide guidance in tuning the antenna for an impedance match to a coaxial transmission line.
  • Describe a measurement for determining the 'Q' of the antenna system.
  • Estimate the efficiency of the antenna (fraction of the applied power that is radiated to the far field) based on measured Q.
  • Compare model data with data obtained from measurements.

 Charley Hill, W5BAA: Since several people in the AQRP group have been looking into Loop Antennas and since their High Q requires constant (fast) retuning, Charley will demonstrate a stepper motor driven Loop Tuner, using one of Loftur Jonasson, TF3LJ, Automatic Loop Tuner designs which has a "Teensy 3.1" microcontroller.. Charley also has a nice loop antenna he built for the higher bands. 

Charley will also show and demonstrate the use of his recently designed Remote Wireless Watt Meter.  The advantages are obvious.

Steve Sparks, WK5S: Steve and several other members, like John Fisher, K5JHF, and Bill Sepulveda, K5LN, of the AQRP group have been working on a better way to learn CW. This is based on using WORDS for training as well as letters and numbers. A shortcoming of some of today's keyers is the inability to send at 30+WPM without small annoying delays. This has been resolved by using a different (faster) interrupt technique on the LPC812 microcontroller. Steve will explain it all to you, including why a sine wave is much more pleasant and relaxing to listen to for copy .....over a raspy "beeper".