I recently acquired an MFJ Versa Tuner II model MFJ-949D as well as a Kenwood TS-430S radio. The instructions for the tuner state (in part):

For optimum operation of the MFJ-949D, the transmitter must be tuned to a 50 ohm output impedance at the frequency of operation. Set the ANTENNA SELECTOR switch to DUMMY LOAD for tuning up the transmitter.

Does this mean there is something to tune on the radio before using the tuner to tune the antenna? And if so, how is that done on the TS-430S?

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    $\begingroup$ The instructions most probably apply to vintage valve radios, where you had to actually tune the output impedance matching network. $\endgroup$
    – Juancho
    Jun 13 '17 at 19:04
  • $\begingroup$ That makes sense. I did suspect the instruction didn't apply to this radio but better safe than sorry. Thanks. $\endgroup$
    – Lance
    Jun 13 '17 at 20:03
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    $\begingroup$ The TS-430S has a solid state power amp so it does not have an amplifier tuning circuit. $\endgroup$ Jun 13 '17 at 20:08
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    $\begingroup$ @Juancho Please post that as an answer, not a comment! Comments are not for short answers, and posting an answer get you the proper credit. $\endgroup$
    – Kevin Reid AG6YO
    Jun 13 '17 at 21:32

Your TS430S has a solid state final and no internal antenna tuner. As such it is designed to work into a 50 ohm load at all times. This means you can disregard this note in your antenna tuner manual.

If the tuner was used with a radio with tube finals then you would need to heed this cautionary note. If the tuner is used with a radio that has a built in antenna tuner, the internal ATU should be placed in bypass mode.


Good answers so far (two of them) but there is one more important item that is not actually a direct answer to you specific question. However, I have run across a number of new ham operators over the decades that did not know this.

The antenna tuner must be the last item in your RF chain between radio (e.g. transceiver) and antenna system. Thus, after the antenna tuner is transmission line (baluns or loading coils too) and the antenna.

A typical station with transceiver, amplifier, SWR meters, antenna tuner should be in this order:

Transceiver <--> Amplifier <--> SWR Meter <--> Tuner <--> Antenna System

The impedance between the Antenna Tuner and the Antenna System itself is likely not to be 50 ohms; that is, the SWR is NOT 1:1. Usually most of the equipment in that station expects to see a 50-ohm matching impedance (exceptions for tube based TX or Amps). In particular, the SWR meter expects to see 50 ohms both on its input and output and without this 50 ohm match the SWR meter does not give accurate results.

  • $\begingroup$ Your statement "In particular, the SWR meter expects to see 50 ohms both on its input and output and without this 50 ohm match the SWR meter does not give accurate results." Is not correct. The SWR meter simply samples the complex voltage and current at the point of insertion and calculates, in analog or digital form, the SWR for a 50 ohm (Zo) transmission line. The complex voltage and current at the point of insertion determines the transformed impedance of the transmission line at that point according to the equation Z=E/I. $\endgroup$
    – Glenn W9IQ
    Jan 15 '18 at 22:06

First of all there is no such thing as an antenna "tuner". The closest to that is the guy who trims a driven element to the resonance. You can "couple", you can "match", but not tune unless you change the physical dimensions of the radiating element.

An antenna is part of a system made along with the feedlines, coax, traps, etc. These are what must be dealt with by your transmitter. The mislabeled tuner is a box on the desk that deals with the reflected RF by "matching" energy from the transmitter to the mismatched load feedline and antenna. A "coupler” does the same. None of these devices "tune" the antenna.

With that being said, you are the one supplying the RF that RF goes from your final output stage to the coupling device, and on to the feedline then the antenna. An auto-tuner does not tune the antenna either, it cuts back the output power to a level that the final stage can safely tolerate. If you bypass the internal tuner and use your manual tuner, don’t use both.

Worried about the SWR? 1.5:1 = 4 w. Reflected; 2.0:1 = 11w. Reflected even a 3:1 SWR only returns 25 out of 100 watts. That 25 is, just like the others, burned up in the mismatched portion of the system. To grasp it - think of the power used by a train going along a straight track now think of the train going to the same point but around a hill to get there. The power delivered between the engine and the tracks requires more going around the curved route but the distance between the two points remains the same. Was the power lost? No, it was the same from the engine but the curve took that amount of power from the engine for a longer time.

  • $\begingroup$ "AN AUTO-TUNER ... CUTS BACK THE OUTPUT POWER TO A LEVEL THAT THE FINAL STAGE CAN SAFELY TOLERATE. " Sorry, that's just not the case. It is a matching circuit that lets the amplifier 'see' its design impedance. $\endgroup$
    – Mike Waters
    Jan 10 '18 at 0:30
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    $\begingroup$ I edited this answer to make it more readable but it still contains a few significant technical errors. As @mikewaters correctly points out the function of an antenna tuner is to provide an impedance match between the transmitter (typically specified as 50 ohms) and the impedance of the feedline at the transmitter end - which has likely been transformed due to the mismatch at the antenna end. Secondly, in the example given, the 25 watts is not all "burned up". There is some loss due to the feedline loss, but the power will be largely reflected by the tuner back towards the antenna. $\endgroup$
    – Glenn W9IQ
    Jan 12 '18 at 14:52

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