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