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 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.


--
73 for now
Buck
N4PGW

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

"Oliver Gebele" wrote
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.)


======================================

Matching networks, with 2 C's and 1 Coil, can be either Pi networks or
T networks. The Pi network, with the coil in series, also behaves as
a low-pass filter and for this reason it is to be preferred. But the
T network has more convenient and therefore less expensive values of L
and C. So for economic reasons manufacturers sell more T than Pi
networks. Pi-networks have considerably larger coils and capacitors,
but in general they are equally efficient when working between the
same transmitter and antenna impedances.

As has already been pointed out, with a T network, 2 series C's and a
shunt coil, least loss nearly always occurs when the coil, in
conjunction with the C's has it's lowest inductance. But component
settings are quite uncritical.

Problems occur only when one or other or both of the capacitors are
very near to their minimum settings, ie., little more than stray
capacitance remains in cicuit. The capacitors may then arc over
(which is immediately apparent). Or the coil turns may become
overheated when attempting to run 1 Kwatt or more (which may take a
minute or so when operating CW or FM).

I mention overload circumstances only because the effects and worries
are too often exaggerated in these newsgroups. So don't lose any
sleep! Even if half the power is lost in your tuner your signal
strength falls by only 1/2 of an S-unit.

To become familiar with series T-Match Networks download program
T_TUNER from website below. Any impedance R+jX can be matched to any
other R+jX. But usually the Tx or generator impedance is a purely
resistve 50 ohms which simplifies understanding of what's going on.

Other practical programs, from the very few I've seen, only manage to
match two purely resistive impedances. Which with radio antennas
seldom exist.

Download program T_TUNER in a few seconds and run immediately. Go from
"Index" to "Download Progs from Here" page and run immediately.

There are several other programs of various sorts which include
operation and component values of T and L-match transmitting circuits.
If you are accustomed to calculating how many rolls of wallpaper are
needed to re-decorate your shack then you will feel at home.
----
.................................................. ..........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. ..........