Topband: W8ji ATR-10 design 160M?

[N4XM Paul D. Schrader]

See http://n4xm.myiglou.com--click on the blue ribbon for sure.

I am a licensed professional electrical engineer and have a US Patent for
my unique tuner.

I have been an active ham for decades.

Belive what and who you want, or seek the truth.

I don't debate on the internet.

73

Paul  N4XM


At 11:42 AM 10/16/2013 -0600, you wrote:
>As Tom notes, the widest possible matching range for a T-Network is with two
>adjustable capacitors (and, presumably, a variable inductor, typically a
>roller inductor). Constraining any one of these parameters reduces the
>available matching range. Further, Tom correctly observes that many hams
>damage their tuners by unwisely choosing a combination of C and L that
>dissipates much of their transmitted RF in the tuner itself.
>
>Several years ago, I wrote a three-part series of articles for QST about a
>high-power homebrew T-match autotuner. Part I of the series (QST, April
>2002, p.40) shows two graphs (Figures 2 and 3) that give the range of
>adjustment values for Cin, Cout, and L for a T-match network, using the 160m
>band as an illustration. The first graph (Fig.2) shows the values of Cin and
>Cout (for different values of L) required to match resistive loads from
>3-800 ohms. The second graph (Fig.3) is the more interesting one for this
>discussion, however, because it shows the percentage power loss in the
>T-network for different values of L. 
>
>Here is the key point: With a T-network, the lowest power dissipation occurs
>with the smallest value of L that will give a match. To illustrate the
>importance of this rule of thumb, suppose one is matching a 6.25 ohm
>feedline (8:1 VSWR) at 1.8 MHz. According to the graph, the largest
>practical nductance that can  match this load is about 25 uH, while the
>smallest practical inductance is about 2 uH. Although each inductance will
>give a satisfactory 1:1 match (assuming Cin and Cout are properly chosen),
>the 25 uH choice dissipates nearly 40% of the transmit power in the tuner,
>which is about 600W at the legal limit. Goodbye tuner!  On the other hand,
>the 2 uH choice dissipates only about 45W. (Note that these values are only
>for resistive loads, but they illustrate the general principle.)
>
>There is a tradeoff, unfortunately, in using the smallest possible value of
>inductance to match a given feedline, and that is that large values of Cin
>and Cout are required. For this example, using a  2 uH inductance requires
>Cin and Cout to be greater than 1000 pF. With a 25 uH inductance, Cin and
>Cout only need to be about 100 pF. The problem is that designers of
>commercial and homebrew T-network tuners sometimes skimp on the capacitance
>range available, instead opting for larger (and cheaper) inductors. Buyers
>are initially pleased at the low cost and wide matching range of their
>spiffy new tuner, only to discover later that the tuner destroys itself when
>they turn on their amplifier. And, as Tom notes, the problem is compounded
>if they tune their T-networks incorrectly by following the wrong rule of
>thumb!
>
>73,
>Jim W8ZR
>
>> -----Original Message-----
>
>> Subject: Re: Topband: W8ji ATR-10 design 160M?
>> 
>> Respectfully, the X match is nothing but a  common T-match with a fixed
>> capacitor in one leg. In a normal T-match, operating Q can be varied over
>a
>> wide range by adjusting L/C ratios.  By restricting range of one leg,
>> operating Q range is limited. So it actually **is** a T match, it just has
>> two adjustable branches instead of the more common three adjustable
>> branches, restricting the operating Q range and matching range.
>> 
>> The ATR10 is more like the common old Johnson matchbox, with the
>exceptions
>> instead of a link it has a tap and it is single ended. The tap sets the
>> operating Q, just as the link ratio sets the operating Q in a Matchbox.
>> This restricts the matching range and operating Q range.
>> 
>> Tuners that fix the operating Q at a certain value, or limit the operating
>Q
>> range, will always restrict matching range. The operating Q restriction
>> limits peak voltages or currents by preventing grossly improper
>adjustments,
>> but the very same thing that limits voltages or current by definition also
>> limits matching range.
>> 
>> An L network limits matching range the most of any network for a give
>range
>> of component values, but also limits operating Q the most. It has only one
>> operating Q available at any given impedance ratio. The Q varies with load
>> impedance. You cannot have too much Q, or it won't match.
>> 
>> This is, unfortunately, the way the world works. Everything is a tradeoff
>of
>> matching range, cost, complexity, and power rating. No single network,
>just
>> like no single balun, is all things to all cases.
>> 
>> The widest matching range for a given cost is a T network with two
>> adjustable capacitors and one shunt inductor. Unfortunately, people think
>> (and articles repeat) the silly idea that the proper way to tune is to
>start
>> with capacitors at half and tune for maximum receive.
>> 
>> Most of any improvement centers around preventing people from doing
>> something silly, by limiting what they can do. There isn't any magic
>> circuit.
>> 
>> Tom
>> 
>> ----- Original Message -----
>> From: "N4XM Paul D. Schrader" <n4xm at iglou.com>
>> To: "Jim GM" <jim.gmforum at gmail.com>
>> Cc: "topband" <topband at contesting.com>
>> Sent: Wednesday, October 16, 2013 11:01 AM
>> Subject: Re: Topband: W8ji ATR-10 design 160M?
>> 
>> 
>> > Jim,
>> >
>> > I did not make the comments you said I made below.  And the XMATCH
>Antenna
>> > Tuner is NOT a "T" match.
>> > It is a patented circuit.  This unique circuit is a United States
>Patent.
>> >
>> > And see http://n4xm.myiglou.com
>> >
>> > Paul  N4XM
>> 
>> _________________
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