Using the matchbox
 

Hi,

i am using a Collins-Filter with 2 variable
capacitors and a switched inductor (Pi).
Obviously there are infinitely many possibilities
to match an antenna.Are there any preferred
possibilities? And how would i adjust my box
to do this? (Maybe there are already links on
the internet that i did not find.)

TIA & 73, Oliver

On Thu, 23 Jun 2005 08:14:34 +0200, Oliver Gebele
wrote:

Hi,

i am using a Collins-Filter with 2 variable
capacitors and a switched inductor (Pi).
Obviously there are infinitely many possibilities
to match an antenna.Are there any preferred
possibilities? And how would i adjust my box
to do this? (Maybe there are already links on
the internet that i did not find.)

TIA & 73, Oliver

If you go to the mfj website http://www.mfjenterprises.com and look at
their antenna tuners, you can download the instruction manuals for
them. The general adjustment instructions for their 2/capacitor/1
inductor tuners will work fine for you -- try the manual for their
989c tuner.

bob
k5qwg

Oliver Gebele wrote:
Hi,

i am using a Collins-Filter with 2 variable
capacitors and a switched inductor (Pi).
Obviously there are infinitely many possibilities
to match an antenna.Are there any preferred
possibilities? And how would i adjust my box
to do this? (Maybe there are already links on
the internet that i did not find.)

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.

TIA & 73, Oliver

w3rv

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


Oliver Gebele wrote:
Hi,

i am using a Collins-Filter with 2 variable
capacitors and a switched inductor (Pi).
Obviously there are infinitely many possibilities
to match an antenna.Are there any preferred
possibilities? And how would i adjust my box
to do this? (Maybe there are already links on
the internet that i did not find.)

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.

Let's examine this statement.

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.







TIA & 73, Oliver

w3rv

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


Oliver Gebele wrote:
Hi,

i am using a Collins-Filter with 2 variable
capacitors and a switched inductor (Pi).
Obviously there are infinitely many possibilities
to match an antenna.Are there any preferred
possibilities? And how would i adjust my box
to do this? (Maybe there are already links on
the internet that i did not find.)

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.

Let's examine this statement.

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.


(1) Physics must have changed, I guess I missed the revisions.

(2) Doesn't matter because old wives tales trump physics every time.

(3) The bloomin' file won't run in my version of Excel. I missed those
revisions too.

sigh

w3rv

On 24 Jun 2005 06:00:55 -0700, "Brian Kelly" wrote in
reply to my comments:

[snip]

(1) Physics must have changed, I guess I missed the revisions.

I don't recall any changes. The pi (and tee and other) network(s),
having three reactances, allow(s) the operating Q to be set by the
choice of component values. Efficiency is a function of the ratio of
operating (loaded) Q and the unload Q of the components.

For a single reactor it is: eff = Qu / (Qu + Ql)

Clearly, for highest efficiency (lowest loss) you want high unloaded
Q(s) and a minimum loaded Q. By reducing the inductance below an
optimum value, the unloaded network Q was increased, resulting in
lower efficiency.


(2) Doesn't matter because old wives tales trump physics every time.

Not sure what this means.

(3) The bloomin' file won't run in my version of Excel. I missed those
revisions too.

I thought my software was behind the times.

Wes Stewart wrote:
"Brian Kelly" wrote:
(1) Physics must have changed, I guess I missed the revisions.

I don't recall any changes.

Planck's Constant rendered Maxwell's Equations
discontinuous. :-)
--
73, Cecil, http://www.qsl.net/w5dxp


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On Fri, 24 Jun 2005 09:46:39 -0500, Cecil Moore wrote:

Wes Stewart wrote:
"Brian Kelly" wrote:
(1) Physics must have changed, I guess I missed the revisions.

I don't recall any changes.

Planck's Constant rendered Maxwell's Equations
discontinuous. :-)

Heisenberg suspected so, but he was uncertain.

"Bob Nielsen" wrote in message
. net...
On Fri, 24 Jun 2005 09:46:39 -0500, Cecil Moore wrote:

Wes Stewart wrote:
"Brian Kelly" wrote:
(1) Physics must have changed, I guess I missed the revisions.

I don't recall any changes.

Planck's Constant rendered Maxwell's Equations
discontinuous. :-)

Heisenberg suspected so, but he was uncertain.

Schroder said he had to look to be sure.

Bob Nielsen wrote:

SNIPPED

Heisenberg suspected so, but he was uncertain.

Could Heisenberg be certain that Heisenberg was Heisenberg? Was he
certain that the Uncertainty Principle was in itself certain?

Damn, Physics and Philosophy getting all mixed up!

VSWR is real! Deal with it.

VSWR isn't a REAL problem! Deal with it!

VSWR is real and ENGINEERS and Ham Radio operators make transmission
lines and antennas work; while Physicists wonder if it's real or
uncertain. [My 80 meter antenna has a VSWR of 30:1. It works just fine!]