To: <towertalk@contesting.com>
> Date: Tue, 17 Mar 1998 07:29:40 -0500 (EST)
> > Hi all,
> > I was wondering if is available a mod for the MN-2000 tuner, to add 160
> > meters on.
> > Thanks and 73's
> >
> > Luca IC8WIC
> Although some additional capacitance may allow some sort of match on 160,
> it often turns out to be a very lossy match. Low loss matching with
> network tuners (and link-coupled tuners as well) normally requires that
> the values of available capacitance and inductance be twice what one
> needs for 80 meters, while maintaining component Q throughout. While not
> impossible (for I would never sell amateur ingenuity short), this is
> exceptionally difficult to obtain.
Hi All,
The single largest problem with T network tuner power handling and
efficiency on 160 and 80 is most tuners have FAR too much Q. In
other words they lack enough capacitance to maintain a low Q on the
low bands. When the capacitance gets too low, Q gets too high.
In a common T network, increasing the capacitance will reduce Q and
improve efficiency and power handling, so padding the caps to extend
range to 160 can be a very good thing.
In a low pass Pi network adding parallel C will increase Q, but I'm
not sure there are any "real" low pass pi's in tuners. Every tuner
I've seen that was advertised and described as a "Pi" only looks
like a Pi in the schematic, while actually FUNCTIONING as an L
network (because it has some meaninglessly small capacitor that does
nothing added at one end so they can sell it as a "pi"--even though
it electrically isn't one).
What type of network does the MN2000 use (ie, T or L?), and what are
the component values and voltage ratings??
With that info it would be very easy to calculate the results of a
mod and the optimum impedance range the tuner operates into.
73, Tom W8JI
w8ji.tom@MCIONE.com
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