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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