Then lock the main tuning dial if possible.Ģ. Ignore the received pitch at this point, or better yet, turn the BFO off until the signal is tuned so as to center in the receiver passband. Tune the receiver to the frequency of the desired RATT signal by observing the receiver INPUT or CARRIER LEVEL meter. First set the receiver passband to a fairly narrow value, on the order of 1 kHz. Receivers used for reception of RFCS RATT signals vary in their details, but in general the receiver should be tuned in the following manner:ġ. Only these two frequencies need be received, and the receiver should be set to receive them in the center of its reception "window " or passband.
This means that the transmitter would develop a mark signal of 8694.425 kHz and a space frequency of 8693.575 kHz. The teletype mark signal would be transmitted 425 Hz above the center frequency of 8694, and the space signal would be transmitted 425 Hz below the center frequency. Two signals would be transmitted alternately, and neither of the signals would be 8694 kHz. If the assigned frequency were 8694 kHz, this would be the center frequency to be radiated from the transmitter. Single channel teletype transmissions in the MF and HF bands use a radio frequency carrier shift (RFCS) of 850 Hz, or +/- 425 Hz with respect to the assigned frequency. The intent of this article, therefore, is to provide some understanding of the required tuning procedures for proper reception of RATT signals. This is often the result of improper tuning of the receiver. Many good RATT signals are so degraded at the receiver that they become either unreadable or take too many hits to be of much use. TUNING IN A SINGLE CHANNEL RFCS RATT SIGNAL