Happy New Year, folks
>From more than 100 answers I've got for my posting regarding
MFJ-989 antenna tuner, I'm feeling that is one more from a
professional one, I want to share with all of you.
73 de Morel, 4X1AD
>Subject: Re: MFJ-989 antenna tuner comments review
>
>I'm an independent RF designer. I started going through the MFJ
>tuners about a year or two ago. I feel insight into engineering facts
>is important. People should understand a few things about tuners
>in general, and the 989 in particular.
>
>I've yet to find any tuner (except the ATR-15 as advertised by
>Ameritron in the 80's, and the old EF Johnson KW Matchbox) that
>alway met power specifications as advertised. The ATR 15 was
>rated at the RF output power over a specific load impedance and
>frequency range, and the KW Johnson Matchbox was rated for a
>1 kW AM transmitter (about 750 watts continuous carrier and
>3 kW PEP modulation peaks, so it easily handles 1500 watts CW
>or PEP output).
>
>Power ratings are an offshoot of when PA's were measured by
>plate input power. For example, the SB-220 (I am a former RF
>consultant for Heath-Zenith) was advertised as a 2 kW PEP
>Input Power PA, but the SB-220 was really a ~1kW SSB PEP
>and 600 watt CW output PA.
>
>Matching tuners were called 2 kW tuners, because they went
>with 2 kW PEP INPUT POWER PA's (that really only put out
>600 watts or so CW, and 1 kW or so SSB peaks).
>
>Enter Dentron. They made PA's that were called 3 kW PA's, and
>only put out the same reliable power as the 220. Dentron called
>their matching 600 watt CW output tuners 3 kW tuners. The
>name 3 kW became "attached" to any tuner of the same basic
>quality components as Dentron's, and it seems to have stuck.
>
>A typical 3 kW tuner is actually a 600-700 watt CW (1200 watt
>PEP SSB) tuner by today's OUTPUT power standards.
>
>The MFJ 989 used a roller produced by Oren Elliot Products. It is
>an industry standard roller, and is similar or the same as rollers
>used in high dollar tuners. Unfortunately, the Oren Elliot roller has
>a delron form, it is the overall roller design that seriously lowers
>the power rating. Roller Q is absolutely NOT a problem of cabinet
>size or anything external to the roller, it is a problem of materials
>used in the roller and the basic roller design. Even the expensive
>ceramic form roller from Cardwell barely offers an improvement. It
>has almost the same loss, but the ceramic form does stand heat
>much better. The new design air coil roller used in the MFJ 989
>does help solve Q and heating problems, and the manual was
>also re-written to correct misinformation on how to adjust the
>tuner.
>
>As for power ratings, it is NOT correct to specify a power rating
>without specifying a load impedance and frequency. ANY
>manufacturer who says "this is a 3 KW tuner" without being band
>and load specific is just howling out a number that may not and
>probably will not mean anything to you. The only way to know for
>sure a certain tuner will work is to try it with your own antennas.
>
>T network tuners (like the 989, Xmatch, Vectronics, Tucker,
>Murch, etc) handle the least power on 160 and with capacitive
>reactance low resistance loads. T network tuners handle MORE
>power into higher resistance loads or loads with some amount
>of inductive reactance.
>
>L network tuners (like the Ten-Tec, Nye Viking, etc) handle more
>power into impedances near 50 ohms, but often do a poor job
>matching reactive or very low impedance loads on low frequencies. (Sometimes
>these tuners are called Pi-networks, even though
>they do not really function as a pi except perhaps on 15 or ten
>meters)
>
>In a T network tuner, maximum efficiency and power handling
>generally occurs when maximum and equal amounts of
>capacitance are used in the capacitors, and the least amount of
>inductance is used. This is true even though many other settings
>will produce a low SWR.
>
>I hope this dispells some of the hyperbole about tuners.
>
>73 Tom
W8JI
>
>.
>
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