On Jun 27, 11:07*am, m II wrote:
RHF wrote:
- c: Same antenna with a 9:1 ratio transformer

First most of the very broadband 9:1 Matching
Transformers that are shown for Shortwave Radio
Listening (SWL) are also designed to cover the
AM/MW/BCB down to 500 kHz and SW Bands
up to 30 MHz. *These usually recommend about
a 10-Turn Primary for the Feed-Line to the Radio
and about a 30-Turn Secondary for the Antenna
side.

Note - That you set a 5 MHz lower 'limit' so you
might want to cut the number of turns in half and
have a 5 -Turn Primary with a 15 Turn Secondary.

- Both the examples you give have a three
- to one ratio. If this is a nine to one example,
- I must be missing something in your explanation.
-
- Please enlighten me.
-
- mike

Mike [M II],

Basically the Ratio is the Square of the Turns
-ex- 1x1 = 1 & 3x3 = 9
-so- 10T & 30T = 100:900 ~ 1:9

Many/most Shortwave Listeners(SWL) Matching
Transformers use a Ratio of 9:1 for Random {Long
Wire} Antennas and for Dipole Antennas a Ratio
of 4:1
http://en.wikipedia.org/wiki/Balun

Please note that your standard TV Matching
Transformer is 300 Ohms to 75 Ohms ~ 4:1
-so- the 300 Ohms side is 4
* The Square Root of 4 is 2
* * the 300 Ohms side would have 2-Turns [2X]
-and- the 75 Ohms side is 1
* The Square Root of 1 is 1
* * the 75 Ohms side would have 1-Turns [1X]
-note- Usually for VHF&UHF TV Signals not
many Turns are required as for the lower HF
Radio Signals of 30 MHz and all the way down
to 500 kHz in the AM/MW BCB.

-fwiw- some SWL'ers will take the very small TV
Matching Transformer Ferrite Binocular Cores
{Two Holes} and rewind them with very thin Wire
to make them into SWL Matching Transformers.
http://www.surplussales.com/Inductor...FerMisc-5.html
Since these are Ferrite Binocular Cores {Two Holes}
they require half the turns as the common One Hole
http://www.surplussales.com/Inductor...FerToro-3.html
Round Donuts {Toroidal}.
http://en.wikipedia.org/wiki/Toroida...d_transformers

Some claim to get 5T & 15T on one of these
very small TV Matching Transformer Ferrite
Binocular Cores going through each of the
Two Holes. I however have only been able
to get 3~4 & 9~12 in these very small cores.
http://www.hard-core-dx.com/nordicdx...eed/feed1.html

Making your own Shortwave Listeners(SWL)
Matching Transformers :