On Fri, 24 Jun 2005 23:40:45 -0400, Buck wrote:

On Thu, 23 Jun 2005 15:06:33 -0700, Wes Stewart
wrote:

On 23 Jun 2005 12:29:51 -0700, "Brian Kelly" wrote:

Inductors are lossy. Capacitors are not. Use the tuner settings which
provide a 2:1 VSWR match or better with the least possible amount of
inductance. In other words use the least amount of inductance you can
get away with.


First all should note that this is a pi-network. Suggestions to use
an MFJ (tee-network) tuning procedure are wrong.

Here is a random example made up on the spur of the moment.

Assume the load is 20 +j50 @ 14 MHz. SWR = 5.2

Also assume that the tuning capacitor(s) Q = 500 and the inductor Q =
200, both typical values.

A nearly optimum solution, from a match and loss standpoint is:

Cin = 140.3 pF, L = .958 uH, Cout = 333.6 pF.

The input z = 49.69 +j0.03 or SWR = 1.006 , Loss = 0.09 dB.

Now, let's force the inductance to a lower value.

Cin = 422 pF, L = 0.67 uH, Cout = 471.3 pF.

The input Z = 49.6 -j0.04 or SWR = 1.008 but the loss = 0.18 dB.

The loss doubled when the inductance was lowered.

All of this is easily calculated using a free tool: XLZIZL.xls.


Does anyone know what kind of network is in the TenTec 247?

I have one and noticed it will tune most bands with three different
inductance settings.

There might be some info at the vintage ten-tec site,
http://www.qsl.net/tentec/

bob
k5qwg