On pages 47-50 of the April 2004 QST is an article about a guy who operated
from the top of Mt. Kilimanjaro. On page 50 is a photo of his traveling
station -- a Yaesu FT-857 with a "homebrew symmetrical double-L matchbox
tuner" feeding 300-ohm TV lead-in wire to an antenna.

Where would I find details of such a tuner?

I have an old Johnson Matchbox and I suspect the homebrew tuner on page 50
is similar -- but -- I'm looking for something much smaller -- a true
balanced-line tuner so I don't have to rely on a toroidal balun to feed
balanced line.

Thanks.

--

-----
Joe S.

There's a couple of them to be found on this web page:

http://www.somis.org/

The tuner described seems to be electrically what MFJ is now selling as
their balanced tuner.

73 Mac N8TT

--
J. Mc Laughlin; Michigan U.S.A.
Home:
"RB" wrote in message
. ..
There's a couple of them to be found on this web page:

http://www.somis.org/

"J. Mc Laughlin" wrote in message
...
The tuner described seems to be electrically what MFJ is now selling as
their balanced tuner.

73 Mac N8TT

--
J. Mc Laughlin; Michigan U.S.A.
Home:
"RB" wrote in message
. ..
There's a couple of them to be found on this web page:

http://www.somis.org/





If I understand correctly, the MFJ tuners have double balanced T networks
and
not double balanced Ls. The double balanced L has a number of advantages
over
the double balanced T, especially if the capacitor can be moved from input
to output,
e.g., the new Palstar or the Bliss tuner. This provides a low pass effect as
well.
Since on the MFJ, the inductor is the shunting element, this is a high-pass
network and
helps to encourage harmonics.

Regards,
Ed, N5EI




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Edward A. Feustel wrote:
Since on the MFJ, the inductor is the shunting element, this is a high-pass
network and helps to encourage harmonics.

.... and has virtually no effect on common-mode RF.
--
73, Cecil http://www.qsl.net/w5dxp

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On Wed, 27 Apr 2005 09:57:24 -0400, "Edward A. Feustel"
wrote:

|
|"J. Mc Laughlin" wrote in message
...
| The tuner described seems to be electrically what MFJ is now selling as
| their balanced tuner.
|
| 73 Mac N8TT
|
| --
| J. Mc Laughlin; Michigan U.S.A.
| Home:
| "RB" wrote in message
| . ..
| There's a couple of them to be found on this web page:
|
| http://www.somis.org/
|
|
|
|
|
|If I understand correctly, the MFJ tuners have double balanced T networks
|and
|not double balanced Ls. The double balanced L has a number of advantages
|over
|the double balanced T, especially if the capacitor can be moved from input
|to output,
|e.g., the new Palstar or the Bliss tuner. This provides a low pass effect as
|well.

The L network can be either low or high pass. It also has the
disadvantage that the loaded Q is set by the transformation and is out
of the control of the designer/user. With a tee or other network with
greater than two reactances, the loaded Q can be set by the design and
can provide lower loss and less critical tuning under some conditions.

|Since on the MFJ, the inductor is the shunting element, this is a high-pass
|network and
|helps to encourage harmonics.

Well, maybe "doesn't suppress" harmonics is a better way to put it.

Edward A. Feustel wrote:
. . .
Since on the MFJ, the inductor is the shunting element, this is a high-pass
network and
helps to encourage harmonics.

What's the mechanism by which a high-pass network "encourages"
harmonics? Because a network with a flat frequency frequency response
has the same high frequency response as a high-pass network, it follows
that a network with a flat frequency response must "encourage" harmonics
also. Why?

Roy Lewallen, W7EL

Dear Ed (N5EI):
Thanks for the correction. The last time that I went to MFJ's WEB
site, I was no longer able to see the tuner's schematic. I should have
made a better record when I was able to see the schematic. One does not
think of that until the manufacturer removes what should be an important
part of their advertising. I had remembered the configuration as having
only three reactances with two of them being ganged (and a BBC (big bad
choke) at the input)
73 Mac N8TT

--
J. Mc Laughlin; Michigan U.S.A.
Home:
"Edward A. Feustel" wrote in message
...

"J. Mc Laughlin" wrote in message
...
The tuner described seems to be electrically what MFJ is now selling as
their balanced tuner.

73 Mac N8TT

--
J. Mc Laughlin; Michigan U.S.A.
Home:
"RB" wrote in message
. ..
There's a couple of them to be found on this web page:

http://www.somis.org/





If I understand correctly, the MFJ tuners have double balanced T networks
and
not double balanced Ls. The double balanced L has a number of advantages
over
the double balanced T, especially if the capacitor can be moved from input
to output,
e.g., the new Palstar or the Bliss tuner. This provides a low pass effect
as
well.
Since on the MFJ, the inductor is the shunting element, this is a
high-pass
network and
helps to encourage harmonics.

Regards,
Ed, N5EI

J. Mc Laughlin wrote:
The last time that I went to MFJ's WEB
site, I was no longer able to see the tuner's schematic.

The manual, including the schematic, is available as a
..pdf file from MFJ's web site.
--
73, Cecil http://www.qsl.net/w5dxp


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Thanks for the correction. The last time that I went to MFJ's
WEB
site, I was no longer able to see the tuner's schematic. I should
have made a better record when I was able to see the schematic. One
does not think of that until the manufacturer removes what should be
an important part of their advertising.

If you are referring to the MFJ 974H, I printed out a schematic for
that some months ago. Glad I did, now that it is no longer available on
their web site.

If you really want a copy, I could scan it and email the .jpg file to
you.



Ed K7AAT