Topband: Impedance Matching Transformers for Receiving Antennas

[Chuck Hutton]

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 at contesting.com [mailto:topband-bounces at contesting.com]
On Behalf Of Tracey Gardner
Sent: Sunday, December 26, 2004 3:33 AM
To: topband at 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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