In looking to build a tuner, I was looking at an L-network tuner, with
switched inductance. If I also add a switch to make it a
series-network (capacitance "before" or "after" inductance), what would
be the limitations of such a design? I.e. What types of antennas, or
under what conditions would it be inappropriate?

Thanks.

"marc" wrote in news:1169823069.024417.273600
@v45g2000cwv.googlegroups.com:

In looking to build a tuner, I was looking at an L-network tuner, with
switched inductance. If I also add a switch to make it a
series-network (capacitance "before" or "after" inductance), what would
be the limitations of such a design? I.e. What types of antennas, or
under what conditions would it be inappropriate?

Thanks.


Hi Marc:

TenTec has made tuners of that design for many years. I have one in my
shack and it works very well for me. The advantage of the L-network over
the more common T is in ease of tuning. The L-network has only one
correct tuning spot for each load. The T network can have several
"matching points" some of which can result in large internal losses
instead of an efficient match. The L network has slightly less loss when
matched than the common T network. The main con for the L network is the
requirement to switch the capacitor around to match loads that are
greater or smaller than the input load.
Other than the above both networks do the same thing and there is nothing
T network can do that the L network can’t and it needs one less capacitor
than a T network.
You can see I’m biased to the L, try one you will like it.

John Passaneau
W3JXP State College PA

marc wrote:
In looking to build a tuner, I was looking at an L-network tuner, with
switched inductance. If I also add a switch to make it a
series-network (capacitance "before" or "after" inductance), what would
be the limitations of such a design? I.e. What types of antennas, or
under what conditions would it be inappropriate?

Thanks.



marc,

I am building something very similar to tune up a portable vertical
for use on a steel-hull narrow boat, 10m through to 80m. In my case
a centre loaded 3.3 metre vertical.

You don't say what sort of aerial or what bands you are going to use
but the following should tune most wires and verticals:

Coil: 100 turns of 13 AWG (15 SWG) on 2 inch diameter tapped every
10 tuns. Use a 12 way switch and have one contact to short out the coil.

For the variable cap use a two gang 500pf+500pf with a switch to
switch in the second 500pf and another switch to bring in an extra
1000pf.

Finally another switch to switch the caps from TX/RX side to antenna
side.

Because I will be using a tapped centre loading coil the inductance
needed in my ATU is much less than the coil I suggest above. In my
ATU the cap will be on the RX/TX side of the coil for 80m,40m & 20m
with no coil required on 20. On 80 I also need the extra 1000pf.

By the way, the above is designed and I'm in the process of building
the antenna and ATU - we'll see what happens when I try it out!


Charlie.

--
www.wymsey.co.uk