[TowerTalk] Re: L-Networks, Stacked Beams

[Michael Tope]

Jay and Ken, please see my comments below.

73 de Mike, W4EF...................

> K7GCO@aol.com wrote:
> >
> >  >    Jay: I described my "Universal L-Network Tuner" in a previous Post to
> >  > match just about anything and it would be a good construction article for
> > one
> >  > of the mags or some Mfg to make.   I have 4 L-Network combo's, Series L&C
> > and Shunt L&C "instantly selectable".  (No mfg has a tuner like this)

Ken, take a look at the Ten-Tec 4229/229 Tuner. This tuner uses a single air variable
and 12uH roller inductor to form an L-network. A ceramic switch is used to re-configure
the tuner into two configuration for matching Hi-Z (>50 ohms) and Low-Z (<50 Ohms).
For each configuration there are a number a settings which switch in varying amounts
of fixed capacitance to extend the frequency/matching range. My experience has been
that this tuner will match just about anything. The only weak point in the design is the
size of the ceramic switch. Ten-Tec probably should have used a bigger switch as the
one they choose arcs under some circumstances (I actually destroyed one of the
switches with an SB-220). Of course my unit is around 15 years old, so perhaps they
have made some improvements since then.

>
> Lets see if you can do the above excersize
>
>
> >
> >  This I know, a well designed T network will outperform an L network for
> >  bandwidth even with fixed Resistive loads.
> >  ********That I have not observed in comparisions.  You also have "3 KNOBS"
>
>
> Here again we are not talking the same thing. I am talking FIXED
> networks. Now do you agree? Let me rephrase my statement.
> A fixed network T can be designed to have a wider frequency range of
> function over a fixed L network.
>
>
> Its now becoming very obvious to me that you are talking about a GCO
> adjustable network.
>
>
> > (2 C's-1L) to adjust with a T which is a big pain, a big time waster and a
> > step in the WRONG  direction.  A pi and perhaps the T will attenuate
> > harmonics better due to the higher Q which generally means LESS BANDWIDTH.  I
> > have just "ONE KNOB TO TURN IN EITHER THE UNBLANCED OR BALANCED L NETWORK"
> > (with 2 variable L's&C's) I HAVE.  I call that the "Ultimate in Simplicity"
> > for Tuners.  I didn't say it was simplier than your no adjustment UN UN's as
> > you have no adjustements.  I have the least tuner adjustements and loss of
> > any tuner.  There is a reactance sensing circuit maintaining "1:1 SWR" I'm
> > going to use that makes adjustments--automatically.  How do you like them
> > design apples?
>
I have both T type (Dentron) and L type (Ten-Tec) tuners in my shack. In either
case, searching for match point is a pain in the butt, so I generally put a piece
of paper behind the knobs and mark each band I going to use with a preset.
Both the T type and L-type Tuners have eaxactly three knobs to mark and adjust.
The T type has two air variable caps and a ceramic switch to select the
appropriate tap on the air core inductor. The L-type has one air variable cap, a roller
inductor, and a ceramic switch to select the L configuration and the amount of fixed
padding capacitance. In either case, once the presets are marked, it takes a few
seconds to switch bands. In both cases losses seem to be minimal as I generally
observe little if any self heating of the network components when running 1 KW.
Based upon my limited anecdotal observations of the two tuners, my preference
is towards the L-network. It seems to have a wider matching range (there are some
loads I just can't seem to match on the high bands with the T network), but this
is easily explained by the fact that the L-network has the roller inductor whereas
the T uses a finite number of taps. The L-network seems to be a little better in
terms of bandwidth, but admittedly, I have never set them down side by side
and done a good scientific comparison test.

> >   >
> >   > Your doubts of practicality and time predictions of working out the
> > design or
> >  > whatever you were trying to say on what I have, are unjustified as you have
> >  > not seen what I have or how it works.
> >
> >  I have made lots of L and T networks. They work on one band and must be
> >  adjusted to work over an octave yet alone 4 octaves of frequency.
> >  ********You still haven't seen what I have.  I have said serval times I need
> > only ONE configuration for the application discussed here with a slight touch
> > up over the range but I can always obtain "absolute 1:1" at any
> > frequency--you can't.  The configuration is the same REGARDLESS OF FREQUENCY.
> >  Take a 25 ohm load and using the correct L-Network configuration and match
> > 25 ohms over 4 octaves.  The configurations stays the same, only the
> > reactance values of each component change.  Case closed.
> >  >

In a contest, if I had the choice between living with a VSWR slightly greater than 1:1
and having to touch up an knob every time I changed bands, I would go for the
former.


> >
> > Jay you have been sounding like W8JI who nit picks everyones sytems just to
> > intimidate them to get them to give him more information at their expense and
> > time because he can't understand what he's told and doesn't know how to
> > derive it himself.
>
> I am aware you have run off JI from this reflector.  But I am not trying
> to nit pick on you Ken, you started this by nit picking on me. I am
> still waiting for an apology or at least a comment on the accusation
> you made concerning my StackMatch product being compared to "an indian
> guide who stole somebody's money by taking them for a ride".  I asked
> for an explanation from you giving you the benefit of the doubt. But
> none came.
>
>
>   He bad mouth the Match Box and I defended it justifiably
> > as had didn't know what he was taking about.  Everytime I corrected him he
> > called it a "Persoanl Attack".
>
When I suggested a simple test that would settle this argument, you never
responded.




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