Date: Thu, 02 Apr 2009 09:49:13 +0200
To: rsgb_lf_group@blacksheep.org
From: Rik Strobbe <rik.strobbe@fys.kuleuven.be>
In-Reply-To: <FC0CD3E94EB84EB4BD3010311FB44018@gmc.net>
References: <FC0CD3E94EB84EB4BD3010311FB44018@gmc.net>
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Message-Id: <20090402074911.6B552F3866@smtps02.kuleuven.be>
Subject: Re: LF: Tune and match the ant for 50kHz...550kHz
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Hello Petr,

50-550kHz seems a "big shot".
If you want to tune (bring to resonance) the antenna using a 
variometer it would need a ratio of (550/50)^2 = 121.
The variometer I use on 500kHz has a range of 40-450uH, thus a ratio 
of 11. The variometer comes from an 500kHz marine transmitter and it 
would be rather complex to build a copy (mechanical).
Running low power you could use a parallel LC circuit. One end to the 
antenna and the other end to ground. The TX is connected to a tap at 
the coil, close to ground. You can tune the antenna to resonance by 
changing C (variable capacitor) and match to 50 Ohm by changing taps 
on the coil. I did that with success in the early days on 136kHz, but 
I could run only 30W power before the capacitor (plate distance 2mm) 
started arcing.
Now you will need a capacitor with a ratio of 121, but that is not so 
hard: most variable capacitors have a range of 20 or better and you 
can put some fixed capacitors in parallel (via switches).

73, Rik  ON7YD

At 09:26 2/04/2009, you wrote:
>Hi all,
>
>I want to make a small transmatch (RX, TX up to 10 Watts, or so) to 
>tune LW 41 m (or smaller T-ant) in the range 50 ... 550 kHz.
>I am not too good in theory... but I believe that the most efficient 
>system is the popular loading coil (home made variometer, and taps 
>to find 50 Ohms match).
>The simple variometer (cylindrical coil in another cylindrical coil) 
>is easy to make and works fine on 136kHz. However, it is possible to 
>change inductance in the range about 1:2 or 1:3 only, not much 
>better. Therefore the redudant inductance is too high to fetch the 
>ant to resonance on 550 kHz.
>Solution would be to make a more sophisticated variometer (best: 
>sphere in sphere) to reach the ratio 1:10 or so.
>Or, to use a different kind of network. Pi network, L network or T 
>network. BTW I would also prefer to use a rotary switch and solder 
>twenty condensers rather than to make twenty taps on a coil wound 
>with litz wire...
>
>How did you solve this yourself?
>
>Thanks, 73, Petr, OK1FIG
>
>
>


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Hello Petr,<br><br>
50-550kHz seems a &quot;big shot&quot;.<br>
If you want to tune (bring to resonance) the antenna using a variometer
it would need a ratio of (550/50)^2 = 121.<br>
The variometer I use on 500kHz has a range of 40-450uH, thus a ratio of
11. The variometer comes from an 500kHz marine transmitter and it would
be rather complex to build a copy (mechanical).<br>
Running low power you could use a parallel LC circuit. One end to the
antenna and the other end to ground. The TX is connected to a tap at the
coil, close to ground. You can tune the antenna to resonance by changing
C (variable capacitor) and match to 50 Ohm by changing taps on the coil.
I did that with success in the early days on 136kHz, but I could run only
30W power before the capacitor (plate distance 2mm) started arcing. <br>
Now you will need a capacitor with a ratio of 121, but that is not so
hard: most variable capacitors have a range of 20 or better and you can
put some fixed capacitors in parallel (via switches).<br><br>
73, Rik&nbsp; ON7YD<br><br>
At 09:26 2/04/2009, you wrote:<br>
<blockquote type=cite class=cite cite=""><font size=2>Hi all,<br>
</font>&nbsp;<br>
<font size=2>I want to make a small transmatch (RX, TX up to 10 Watts, or
so) to tune LW 41 m (or smaller T-ant) in the range 50 ... 550 kHz.<br>
I am not too good in theory... but I believe that the most efficient
system is the popular loading coil (home made variometer, and taps to
find 50 Ohms match).<br>
The simple variometer (cylindrical coil in another cylindrical coil) is
easy to make and works fine on 136kHz. However, it is possible to change
inductance in the range about 1:2 or 1:3 only, not much better. Therefore
the redudant inductance is too high to fetch the ant to resonance on 550
kHz.<br>
Solution would be to make a more sophisticated variometer (best: sphere
in sphere) to reach the ratio 1:10 or so.<br>
Or, to use a different kind of network. Pi network, L network or T
network. BTW I would also prefer to use a rotary switch and solder twenty
condensers rather than to make twenty taps on a coil wound with litz
wire...<br>
</font>&nbsp;<br>
<font size=2>How did you solve this yourself?<br>
</font>&nbsp;<br>
<font size=2>Thanks, 73, Petr, OK1FIG<br>
</font>&nbsp;<br>
&nbsp;<br>
&nbsp;</blockquote><BR>
<BR>
<FONT FACE=3D"Arial" SIZE=3D2>Disclaimer: <A HREF=  "http://www.kuleuven.be/cwis/email_disclaimer.htm">http://www.kuleuven.be/cwis/email_disclaimer.htm</A> for more information.</FONT>
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