That's why when I use TLW I initially specify large value capacitors so
I can see what's going on first. I do the same thing with the W9CF
online tuner app. I don't think there are many cases for an antenna
tuner where you'd want to specify a Q since generally speaking you
simply want it to be low ... you don't want to have to adjust the
setting as move around the band. Most of the time (not always), an
L-Network is going to give you the best efficiency, and the best
impersonation of an L-Network by a T-Network is when either the input
capacitance or the output capacitance is as high as you can make it.
Generally speaking, there are only three reasons to use a T-Network in
the first place:
1. L-Networks only match in one direction, and it makes a difference
whether the load is less than or greater than the source as far as which
side of the inductor (assuming a shunt inductor) the capacitor is on. A
T-network is capable of pretending it is an L-Network in either direction.
2. The L-Network capacitance and inductance values get almost
impossible to achieve for loads that are close to the source impedance.
Try some samples and you'll see what I mean. In those situations a
T-network essentially uses the extra capacitor to shift either the
source or the load impedance so that the L-Network portion can
accomplish a match. An older generally well regarded commercial tuner
billed itself as a more efficient L-Network tuner, but they included
provision for switching in a fixed capacitor (or two, if I remember
correctly) on the other side of the coil in order to match loads near
3. An L-network only has two degrees of freedom ... the coil and the
capacitor ... and both have to be continuously variable to achieve a
match. That means you have to use something like a rotary inductor,
which also requires a turns counter if you want to be able to quickly go
back to predetermined settings. Both are expensive. A T-Network allows
you to find a match for an inductance that is merely close to the
desired value ... i.e., a fixed coil with taps ... even if the resultant
efficiency might not be optimum.
On 12/1/2010 1:20 AM, Kevin Normoyle wrote:
> Steve G3TXQ said "If you want to get meaningful loss results with that
> simulator, be
> prepared to manually change the default Q value as you change bands and
> change inductance values."
> Yes, if you want to just see the result for a known combination. I ran into a
> surprise assuming I understood how some things out there create a "suggested"
> result, not even considering the constant vs varying component Q issue.
> I was comparing the suggested values produced by 3 T-Tuner simulations, and
> surprised to see the difference in results. Be interested in feedback about
> other people have used/done.
> 1) 4nec2 which allows you to specify min network Q (lower network Q = lower
> loss). Don't need filtering, so high Q result isn't useful.
> 2) ARRL Antenna Book TLW (n6bv 2004)
> 3) The very nice t_tuner.exe from G4FGQ (free) which allows you control L and
> ratios, and max C so you can get different results (varying L/C ratio and
> comparing different loss/volts/current results)
> 4) ARRL Antenna Book ATT. I just loaded this, and see it constrains things
> differently. Am playing with it running in DOSbox.
> t_tuner.exe and 4nec2 quickly let you see the effects of varying L and C for a
> given match.
> 4nec2 lets you specify a min network Q for the result.
> t_tuner allows you to control the L/C ratio with an artificial parameter "A"
> with small values given large C and lowest loss.
> (G4FGQ also has l_tuner.exe, (L network) but I focused on T)
> I got really confused looking at the TLW results. For my test case, they
> suggested a result, which was very bad for power loss?
> I played with both 4nec2 and t_tuner.exe, trying to get the same predicted
> result. I get them to create the one result TLW suggests, but it's clearly not
> optimum. It's a high Q result, when I want a low Q result. (low loss) (I'm
> using TLW high-pass Tee Network Tuner selection).
> At first I thought "This seems like a bug in TLW". I found the problem below,
> which I am calling a program design flaw..i.e. you have to have some knowledge
> to realize why it's a bad result. It's easy to believe there is only one
> possible result, and not tune things to get something good.
> t_tuner is best for getting different results and comparing.
> Even if I constrain t_tuner to use C of<350pf, a nice low Q result is
> The TLW suggested poor result, seems to have a Q of about 60 (reported when
> values used in the other programs)
> The TLW result is a correct match. (verified elsewhere)
> The suggested result in TLW doesn't seem to vary, if the unloaded component Q
> Those unloaded Qs just affect the final loss calculations.
> Here's the problem:
> TLW allows you to vary results by controlling one of the C's (Tee Network
> Capacitor). You have to "know" that it needs to be increased to get a good
> result in my test case (and may need to be small to get a good result for a
> different test case..or intermediate).
> If you keep that small, in my case, you get a bad result. (this goes to the
> question of the goodness/badness of different L/C match combinations)
> It would be nice if they all reported final network Q like 4nec2, but seeing
> power loss is related, so okay I guess.
> So what TLW is really doing is giving you a good result for what you
> but doesn't give you enough info to realize you need to tweak the input you
> it, to see different possible results.
> It is much nicer to specify a min-max range for C, or L, and maybe a final
> network Q, or have it find the lowest loss result.
> I haven't find a program that gives a single suggested optimal result using
> known Q of the unloaded components? Even 4nec2 seems to not use component Q's
> when reporting a "min network q" of the result, although he modifies the info
> used later, with component Qs.
> Are there some other good ways other there of getting comparative calculated
> results that I'm missing?
> It seems like this could all be easily automated. Computers are fast enough
> so that all the constraints could be described, and walk over all
> and draw the very nice info "map" like G3TXQ posted. (that represents
> doable" with the particular set of constraints in a single real tuner).
> Like an excel spreadsheet would be nice.
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