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RE: Topband: Impedance Matching Transformers for Receiving Antennas

To: <topband@contesting.com>
Subject: RE: Topband: Impedance Matching Transformers for Receiving Antennas
From: "Chuck Hutton" <charlesh3@msn.com>
Date: Sun, 26 Dec 2004 20:09:44 -0800
List-post: <mailto:topband@contesting.com>
It is an excellent article. After reading it, you know exactly what the
writers did to test and make assumptions. Also, the testing was pretty
complete.

All I can add to the article is a bit of an explanation or guess about the
4:1 turns ratio. Here's a little chart I made:

Rg (generator impedance)        Xm / Rg ratio   Resulting Xm    Pout /
Pavail  dB Loss
                                
50      1       50      0.800   -0.97
50      2       100     0.941   -0.26
50      3       150     0.973   -0.12
50      4       200     0.985   -0.07
50      5       250     0.990   -0.04
50      6       300     0.993   -0.03
50      7       350     0.995   -0.02
50      8       400     0.996   -0.02
50      9       450     0.997   -0.01
50      10      500     0.998   -0.01


>From this, 4:1 is a good rule if you want to hold insertion loss below the
1 dB point.


I think 43 was the default choice some years ago as it covers all the bands
from 160 - 10 meters (and maybe 6 if you're not too picky). However, in the
range you mentioned, (.1 - 7) 75 & 73 are surely better choices based on the
permeability curves.


Chuck

-----Original Message-----
From: topband-bounces@contesting.com [mailto:topband-bounces@contesting.com]
On Behalf Of Tracey Gardner
Sent: Sunday, December 26, 2004 3:33 AM
To: topband@contesting.com
Subject: Topband: Impedance Matching Transformers for Receiving Antennas

<CLIP>
This surprises me as the findings of the article discount the use of Type 43
material in favour of Type 75 over the range of 0.1 - 7MHz.
<CLIP>


The article is "Impedance Matching Transformers for Receiving Antennas
at Medium and Lower Shortwave Frequencies" and was written in June
2003 by Bill Bowers, John Bryant and Nick Hall-Patch, VE7DXR. You can find
it at the following URL: http://radiodx.com/spdxr/media/imt_doc1.doc


Merry Xmas and a Happy New Year

Tracey G5VU



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