We do not advertise operation of our system below MHz because of problems which occur in handheld scanners and other inexpensive general coverage receivers. The problem is that these radios typically do not have sufficient rejection of IF energy coming in their antennas.
The nature of SuperDF is such that there is a square wave at about 400 Hz present on the RF coax leading to the DF antenna. This square wave has significant harmonic energy at the IF frequencies of these radios. If the receiver does not reject these frequencies well, IF energy will reach the IF amplifiers and produce interference with a weak signal that is being hunted.
With a good receiver, the VHF SuperDF antennas will operate down to at least 30 MHz. (I have successfully operated our 1 GHz antenna at 30 MHz.) We have shown that the R7000 receiver works quite well. Its front end rejects IF frequencies much better than does the typical scanner. The primary noticeable effect is there is less DFing error signal for the unit to work with, because the antenna spacing is small compared to the wavelength, therefore the heading definition isn't as sharp as at VHF. Also one cannot DF signals that are 20 dB below the noise, as not as much error signal is present. It is still quite adequate to do most jobs.
George R. Andrews, President
George (Russ) Andrews, K6BMG BMG Engineering, Inc. 9935 Garibaldi Avenue Temple City, CA 91780 USA Phone: 1(626)285-6963 FAX: 1(626)285-1684 (dedicated line, automatic) Web: http://members.aol.com/bmgenginc (31 Jan 1996) Send E-mail to grandrews@aol.com. (A message window will open.)
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