Specifically for that reason, I try to steer clear of the classical
"T-Match".
Sure it is flexible and can match almost anything, but it is far too easy,
especially when in a hurry, to find a perfect match where 80% of the power
is eaten by the matchbox.
I wouldn't touch most MFJ and most Palstar tuners with a ten foot pole, just
for that reason.
However, as you pointed out, both use the "L-network" in the automatic
tuners.
For that reason I prefer the L-Filter, like Ten-Tec builds.
It may be a bit more difficult to "find" the correct match point, but once
it's found (per band), you record it and then it's a breeze.
Once again Ten-Tec is guilty of good engineering, but poor marketing.
People don't realize how good that tuner is!
"If" you want to go with a T-Filter, then choose one that is a "differential
T".
Then you don't have that problem, BUT, these, be it MFJ or Palstar, don't
have the broad matching range of the classical T-filters from the same
house, due to the physical limitations of the size of the differential
capacitor.
What did I do?
I have an MFJ Differential-T for general purpose, and if it doesn't match a
particular band, I switch to my Model 238 and match it. Viola!
Generally I use the MFJ Differential-T for stuff like 50 Ohm antennas which
"should be" 50 Ohms, but have high SWR on part of the band, like an 80m
dipole. The Differential-T is easy and fast to use and efficient for this.
For my Vertical Dipole where I can have some "funny" impedances, I got thru
my home-brew coaxial balun, straight to my 238.
73
Rick
-----Original Message-----
From: tentec-bounces@contesting.com [mailto:tentec-bounces@contesting.com]
On Behalf Of Dr. Gerald N. Johnson
Sent: Saturday, January 08, 2011 7:05 PM
To: tentec@contesting.com
Subject: Re: [TenTec] TT Eagle tuner spec: SWR v. impedance range?
Tuner loss is complicate by most tuners that have a myriad of tuning
positions with different tuned circuit loaded Qs and so circulating
current in the resonant circuit with different losses and bandwidth for
the same load. Some of the Tentec tuners that are L networks get away
from that, because there is only one set of L and C (presuming series L
and shunt C) that will tune any given load at any given frequency so the
tuned conditions are unique and the lowest loaded Q for the impedance
transformation ratio. If we still used an RF ammeter in the feed line
beyond the tuner and always tuned through the available tunings for
maximum RF current we would be minimizing the tuner losses.
Unfortunately some loads are so much bother to tune that we quit with
the first set that matches. I think most of the automatic tuners are
also L networks and so will come up with the single possible tuning
condition which is at the same time optimum. This is not true of T and
PI and other tuner circuits.
73, Jerry, K0CQ
On 1/8/2011 5:25 PM, Rick - NJ0IP / DJ0IP wrote:
> Another thing people should look at is "Tuner Loss", not just tuner
matching
> capability.
> There can be significant differences at certain extreme impedances.
>
> Unfortunately nobody publishes any specs on that.
> You have to measure it yourself, or wait for someone like ARRL to publish
> test results - which they have.
>
> In the last couple of years there have been two good tests by ARRL,
> comparing matchbox losses.
> Unfortunately each test only covers 5 or 6 matchboxes, and it seems like
I'm
> always interested in one that was not tested!
>
> And since this is a Ten-Tec reflector, I'd like to remind people that at
the
> extremes, the Ten-Tec Model 238B was more efficient than the other "noble"
> matchboxes it was compared to.
>
> 73
> Rick
>
> -----Original Message-----
> From: tentec-bounces@contesting.com [mailto:tentec-bounces@contesting.com]
> On Behalf Of Steve Hunt
> Sent: Saturday, January 08, 2011 5:05 PM
> To: Discussion of Ten-Tec Equipment
> Subject: Re: [TenTec] TT Eagle tuner spec: SWR v. impedance range?
>
> It's tough to find a way to express a tuner's capability in some
> succinct and meaningful way.
>
> This was my attempt:
> http://www.karinya.net/g3txq/temp/aat_chart.png
>
> Each "cell" represents a particular load impedance going from 3.125 Ohms
> to 3200 Ohms in binary steps, Resistive (X axis) and Reactive (Y axis)
>
> If the cell is green, the tuner was able to find a match, and the number
> in the cell shows the % power loss in the tuner. The darker the green,
> the better.
>
> If the cell is red it indicates that a power dissipation limit or a
> capacitor voltage limit was exceeded
>
> L+ indicates "no match - not enough inductance"
> C- indicates "no match - too much minimum capacitance"
> etc etc.
>
> One chart needed per band.
>
> The data was the output from the AAT programme on the Antenna Book CD.
>
> 73,
> Steve G3TXQ
>
>
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>
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>
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