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Date: Sun, 15 May 2011 13:45:26 +0100
From: "Rob, M0DTS" <rob@m0dts.co.uk>
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References: <80703.53770.qm@web28515.mail.ukl.yahoo.com> <EE1078C1AE1542A39B4A6054378AA79F@lindavideo> <4DCEDBB3.1020808@iup.uni-heidelberg.de> <D6B1B6FB2BE84EE5A37FB6B8A3522D5A@lindavideo> <4DCFA642.5070305@m0dts.co.uk> <E793616BE1674C35BA7FFFE7243A5F95@JimPC>
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Subject: Re: LF: Re: LF SWR Bridge
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Aha now I've got it..
Thanks for the tips and it was the winding phase i had incorrect..
obvious now ;-)
I will examine at the tuning aids documents too, they look very helpful.
Cheers
Rob
M0DTS
On 15/05/2011 12:42, James Moritz wrote:
> Dear Rob, LF Group,
>
> The inductance of the transformer is probably a bit on the low side
> (the reactance of the total 24turn winding should be much greater than
> the 68R load resistance), but should be enough to get at least
> reasonably close to balance - you should be able to see at least some
> reduction on the "reflect" side with 50R load connected. Check that
> the phasing of the secondary winding is correct - the centre tap
> should be the connection between the "start" of one winding and the
> "finish" of the other.
>
> What should happen is the RF voltage on one half of the current
> transformer secondary is equal in magnitude, but opposite in phase to
> the load voltage sensed by the capacitive voltage divider when the
> load is 50R. The component values shown look about right to do this.
> One way to check this would be to:
>
> -Disconnect the "hot" end of the capacitive potential divider from the
> TX input terminal. Note the meter readings with the TX running into
> 50R load.
> -Disable the current transformer by shorting the 24 turn secondary and
> re-connect the capacitors .Check the meter deflections with 50R load -
> it should be possible to get these the same as in the first test by
> adjusting the trimmer capacitor.
>
> You can find some other ideas about LF antenna tuning aids in the file
> LF_Tuning_aids.pdf at
> https://sites.google.com/site/uk500khz/members-files/files
>
> Cheers, Jim Moritz
> 73 de M0BMU
>
>
>