Message-ID: <1074543877.400c3d051a334@webmail2.kuleuven.be>
Date: Mon, 19 Jan 2004 21:24:37 +0100
From: "Rik Strobbe" <Rik.Strobbe@fys.kuleuven.ac.be>
To: rsgb_lf_group@blacksheep.org
References: <C75A388845B4B54B9CF5E2ADB589B0E3031AEFE6@btss.siemens-pse.sk>
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Subject: Re: LF: RE: Re: AC feeder...
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Rich,

As long as the chokes have a "resonable" value (let's say 100 uH or 
more) it should be possible to match the antenna for 136 kHz at the 
base.
But you will not only need to make the antenna resistive but probably 
also do some serious impedance matching. Some calculations can be 
done, but most of the tuning will likely be according to the "try and 
error" method using no-so-conventional matching circuits.

Maybe this helps :
In my early days on 136 kHz I did test a lot of antenna 
configurations. As it was not always convenient to have a TX running 
when trying to match a strange antenna I did the matching in "RX 
mode", as I didn't had an impedance bridge for 136 kHz I used 
following procedure :
1. Take a RX and tune it to the DCF on 138 kHz, it will produce a 
strong signal on almost any TX antenna.
2. connect a 20 dB attenuator (50 Ohm) to the TX input, this will 
assure that the impedance "seen by the antenna configuration" is close 
to 50 Ohm regardless of the real RX imput impedance.
3. connect the antenna - via the matching network you wish to test - 
to the attenuator input and "play" with the matching network until you 
get the strongest signal on the RX.

In most cases I got the antenna matched pretty good to 50 Ohm (at 138 
kHz) and fine tuning with the TX was done easily.
The advantages are :
- Don't worry about dammaging the TX due to bad SWR during the 
matching procedure.
- No need a large collection of high-voltage C's and high current 
coils. Once you get the antenna matched in RX mode you can get the 
required high power components.
- No risk of burning your fingers (or worse) during the matching
- No need to put the TX off (or the risk to forget it) when removing a 
coil or capacitor.
- No risks of fireworks when making a shortcircuit by accident.

73, Rik  ON7YD

> Yes, this is idea. But there are lights and they can't be switched
> off
> (there are not fuses, fuser are 500m away on the TX site...hi).
> 
> Rich