Fast automatic antenna tuner with wide tuning range.
The MFJ-939 automatic antenna tuner is shipped with control cable suitable for various radios of a manufacturer, depending on model. This greatly simplifies the operation, because you need only to press the 'Tune' button on the radio. . The '939' is characterised by a very wide tuning range from 6 to 1600 Ω. This is much more than most internal tuners can offer. The large tuning range is provided by a large number of capacitors and inductivities, which results in a very precise tuning using 256 combinations of C and L each.
By using more than 2500 memories the tuner offers a very fast tuning, because once found combinations of L and C are stored for each frequency, instead of calculating the combination each time again. And the tuner offers various acoustic and optical protection signals and diagnostics, for example against hi SWR or power input. In case of too much power on the input the tuner sends 'QRT' in telegraphy, an LED signals the error as well. But also in case of not enough power (2 W is minimum) the tuner sends 'QRO' in morse...
Another nice feature is the sleep mode of the tuner. In case no tuning has to be done and during RX, the tuner goes to sleep mode and turns off the microprocessor. This has the benefit of reducing power consumption as well as avoiding noise on HF. Further the MFJ-939 is prepared for the future - in case of a system change you can simply use a different control cable and continue to use the same tuner. MFJ offers various cables for different radios.
The maximal transmit power is 200 W SSB or CW. The industrial grade switching relays are rated for 1000V/10A. The minimum transmit power for tuning is 2W. Included in shipment is a control cable which is suitable for various or most radios of the selected manufacturer. In some cases the control cable is also used for the power supply from the radio, in other cases an external power supply is required (13.8V, 750mA).
 Other transceivers can be used with other interface cables of type "MFJ-5114x". On some radios the tune mechanism is started from a push button on the tuner, not from the radio.