Antenna Tuners

UNDERSTANDING MATCHBOX POWER RATINGS

Understanding Matchbox Power Ratings is TRICKY, and the manufacturers don't help us much.

 

JUST BECAUSE GENERAL MOTORS STATES


THAT THE CHEVROLET CORVETTE'S TOP SPEED IS 150 MPH,


THAT DOES NOT MEAN THAT YOU CAN DRIVE IT

 

150 MPH DOWN EVERY ROAD!

 

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MATCHBOX POWER RATINGS ARE SIMILAR

 

TO A CAR'S TOP SPEED RATING:


 

JUST BECAUSE A MATCHBOX MANUFACTURER STATES


THAT ITS MATCHBOX IS RATED FOR 1500 WATTS

 

THAT DOES NOT MEAN THAT YOU CAN RUN IT


AT 1500 WATTS WITH EVERY LOAD!

  


  

 

HERE IS WHAT PALSTAR WRITES IN ITS MANUALS:

 

 

[EXAMPLE:  PALSTAR AT-2K]

 

Power Maximum:   

2000 W PEP SSB, 1500 W single tone continuous

 

Impedance Range: 

20 to 1500 Ω 160 m to 10 m (assuming resistive load) -

Reduce power for lower Z range.*

 

 

*OK, so what does that mean?

  • Lower Z Range?  How low?
  • Reduce Power?  How much?
  • How is the user to know?
  • What should the user do

Palstar makes the user aware that its products cannot always be run at maximum power, "no matter what".

Palstar makes no attemt to trick potential buyers by over-stating the power ratings of its matchboxes.

 

 

MFJ IS MORE CONFUSING :

[And until recently, has been a bit dishonest in stating power ratings of its matchboxes.]

 

THERE IS A LOT OF CONFUSION AROUND THE POWER RATINGS OF MFJ MATCHBOXES

  • Most people wrongly believe that a matchbox that is rated 1500 watts can handle 1500w of OUTPUT POWER - ALL THE TIME - - - VERY NAIVE!
    • How much power a matchbox can really handle will vary, depending on the frequency in use and the characteristics of the antenna it is attemptiong to load.
  • People who are familiar with MFJ products know their matchboxes cannot always handle anywhere near that amount of OUTPUT POWER that their marketing leads us to believe.
    • They have learned to divide MFJ power ratings by 2.
    • If you do that, then you will probably be happy with your matchbox.
  • Up until a few years ago, all MFJ matchboxes were rated with "INPUT POWER" - NOT output power.
    • A couple of their very new matchboxes are rated with "OUTPUT POWER".
    • Another is rated with "Full Legal Power" (no mention of input or output).
    • You have to be VERY CAREFUL when attempting to determine how much power an MFJ matchbox can safely handle.
  • READ THE PARAGRAPH (below) SHOWING WHAT MFJ WRITES ABOUT POWER IN MOST MFJ MATCHBOX MANUALS... It states clearly that you must divide Input Power by 3 to get Output Power.

 

IN MY OPINION, PART OF MFJ'S PROBLEM WITH THEIR POOR REPUTATION FOR ANTENNA MATCHBOXES IS, PEOPLE DO NOT UNDERSTAND HOW MUCH POWER EACH MATCHBOX CAN SAFELY HANDLE!

 

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TYPICAL MFJ MATCHBOX POWER RATINGS:

 

·       MFJ-945E  “Ham Radio’s Most Popular 300 Watt Tuner"

o   “After minimum SWR is achieved, transmitter power may be increased up to 300 Watts.”

o   No mention of whether Input Power or Output Power is meant for this matchbox.  ASK MFJ.

 

·       MFJ-962D  “Compact  Tuner for Linear Amplifiers”

o   “Handles 1500 Watts PEP SSB amplifier input power (800 Watts PEP SSB amplifier output power)”

o   Input/Output = 2

 

·       MFJ-986  “KW Differential-TTM Antenna Tuner”

o   “3 KW PEP SSB (1500  Watts PEP SSB output power)”

o   Input/Output = 2

 

·       MFJ-989  “1500 Watt legal limit Antenna Tuner”

o   “legal limit” must mean 1500w output power

o   No mention of Input Power for this tuner

 

·       MFJ-9882  “2500 Watts ContinuousCarrierTM Tuner”

o   “Handles 2500 Watts continuous carrier output”

o   No mention of Input Power for this tuner

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CAUTION:  ALWAYS LOOK FOR THAT ONE IMPORTANT WORD:

“OUTPUT”

If it doesn’t say “Output Power”,

and it doesn’t say “Legal Limit”,

then you must assume it is “Input Power”.

[divide by 2 for Output Power]

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HERE IS WHAT MFJ WRITES IN IT'S MANUALS:

 

Understanding Power Ratings

 

There are no standardized power rating systems for tuners.  The names used (i.e. 3 kW Tuner) carry over from the time when amplifiers were rated by peak power input, and not the true RF power output.  For example, the one thousand watt Johnson Matchbox was rated to handle a 1000 watt plate modulated AM transmitter (four kilowatts PEP transmitter input and 3000 watts PEP RF output). The Heathkit SB-220 was called a two kilowatt amplifier, and the rated CW output was approximately 600 watts. Matching tuners were called 2 kilowatt tuners, and these tuners safely handled 600 watts of CW power and 1200 watts PEP SSB.

 

The FCC has changed the power rating system of amplifiers, and tuners no longer follow amplifier power ratings. Most typical 1500 watt tuners remain able to safely handle 400-600 watts CW, and 600-900 watts PEP SSB.

 

Load conditions and control settings also greatly affect the power handling capability of the tuner.  T-networks typically handle more power on higher frequency bands into higher load impedances. The worst operating condition for T-network tuners are low impedance capacitive reactance loads. T-network tuners always handle the least power when operated on 160 meters into low impedance capacitive reactive loads.

 

Follow the guidelines in this manual to avoid exceeding the ratings of this tuner.

 

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Huh?  INPUT POWER?

 

NOBODY ON THE PLANET TALKS ABOUT INPUT POWER ANYMORE!  


If you understood that, then you understood more than me!

 

  • If I follow their thought stream correctly, that their 1500w (input power) tuner can run about 400 to 600w (call it 500w) . . .  
  • . . . then this means we must divide the MFJ INPUT POWER RATING by 3 TO GET THE OUTPUT POWER RATING


- MFJ Marketing (see above) indicates that:  Input Power / Output Power = 2.

 

- Several of their manuals indicate that:  Input Power / Output Power = 3.

 

Therefore, a 200w MFJ Tuner is good for about 70w on CW.

 

MATCHBOX POWER HANDLING REALITIES:

  • Power Ratings of a matchbox should always be considered to mean:

 "Maximum Power Ratings"

  • Do not think for a moment that you can run the matchbox at maximum power all the time, with any antenna, no matter what.
  • How much power you can safely run without causing damage to the matchbox will depend on two things:
    • Frequency being used
    • Antenna Impedance 
  • In general, a matchbox may be run at full power over a broad range of frequencies and a broad range of impedances.
  • This range is referred to as the "Sweet Spot".  For more information on this range, see:

 "The Perfect Matchbox".

  • You may have to reduce power significantly when:
    • Operating 10m
    • Operating 160m (sometimes 80m)
    • The antenna has a particularly high impedance (greater than 1000 Ohms)
    • The antenna has a particularly low impedance (less than 20 Ohms)
  • ALWAYS TUNE THE MATCHBOX AT VERY LOW POWER, 
    • THEN GRADUALLY INCREAS THE POWER
    • REDUCE POWER IMMEDIATELY if it begins to make funny noises (caused by sparcs)

 

GOOD NEWS:  It appears that MFJ has finally realized that "truth in marketing" is a good thing.  All of its most recent matchbox products now show "Output Power" or at least state "legal limit" which means 1500 watts PEP SSB Output Power.

 

DESPITE what I have written above, which sounds pretty bad, 3 of my 7 antenna matchboxes are MFJ products.  MFJ makes some good matchboxes, provided you understand how to use them.

 

IMO, MFJ's bad reputation in the antenna matchbox market is due to users not understanding them and burining them up, etc.  I view this as MFJ's Marketing fault, NOT  the user's fault.

 

POSITIVE:  All of the MFJ manuals list examples of antennas that can cause problems, thus requiring you to reduce power.  MFJ sugests antenna lengths and feedline lengths to be avoided.  READ THE MANUAL.  It is very helpful.