[ARC5] Receiver input impedance.

[J. Forster]

The advantage is very different. The transformer converts the differential
mode output of the loop to the single ended receiver input with very high
CMRR (Common Mode Rejection Ratio).

This reduces the system noise level considerable.

-John

===============




> Looking at the circuit for the BC-946 (similar to R23 etc) I see the
> tank circuit is connected to the antenna (or the aerial if you live in
> Australia) by a trimmer cap.  According to the theory (and working in
> the ideal) the impedance of a parallel tank  circuit at resonance is
> very high (infinite, for the idealist) and so the advantage in matching
> an antenna to THIS load comes from stepping-up Z from 50 ohms to a
> higher Z.  However, if the loop is also tuned to resonance, it will have
> a similar high impedance (infinite for the idealist) and so there is no
> need for a matching device.
>
> This is why the signal "peaks" when the trimmer is adjusted.
>
> That's my "teary" of how "de aerial" woiks.
>
> So:   we have just seen "our" Sandy wreck havoc in New Jersey & co.
> I invite group members to take the same approach with posting ....
> To echo  the words of Paul Goebells,  "[Group] rise Up, and Let the
> Storm Break Loose"
>
> I wait, with anticipation, for the foist postings to appear  ...
>
> Go for it ...
>
> --
>   Leslie Smith
>   vk2bcu at operamail.com
>
>
> On Wed, Oct 31, 2012, at 13:39, Richard Knoppow wrote:
>>
>> ----- Original Message -----
>> From: "Kenneth G. Gordon" <kgordon2006 at frontier.com>
>> To: <Arc5 at mailman.qth.net>
>> Sent: Tuesday, October 30, 2012 12:30 PM
>> Subject: [ARC5] Receiver input impedance.
>>
>>
>> > Does anyone have accurate data on the BC-453B receivers'
>> > antenna input
>> > impedance?
>> >
>> > I need to build an UN-BAL to match my BC-453B to a 3 foot
>> > diameter
>> > Stoddart loop which is fed with twin-ax.
>> >
>> > I have the Stoddart data, but need the other data.
>> >
>> > My particular BC-453B does not have the loop connections.
>> >
>> > Can anyone help?
>> >
>> > Kenneth G. Gordon W7EKB
>>
>>
>>      If you know someone with an RF impedance bridge its
>> easy to measure the actual impedance at the antenna input.
>> Someone on this list may have the equipment and be within
>> reasonable distance. I suppose it could be calculated from
>> the values of the input tank but I can't tell you
>> specifically how.
>>
>>
>> --
>> Richard Knoppow
>> Los Angeles
>> WB6KBL
>> dickburk at ix.netcom.com
>>
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