[Elecraft] K2: KSB2 T1/T2 Turns Ratio Question

[Wayne Burdick]

I started with textbook impedance ratios, then adjust the windings 1  
turn at a time to find the optimal combination of power transfer and  
passband flatness. This can vary with crystal characteristics, circuit  
strays, etc.

73,
Wayne
N6KR

On Apr 25, 2011, at 3:07 PM, John Magliacane wrote:

> Hi Folks.
>
> I've been perplexed for quite some time as to why RF transformers T1  
> and T2 that sit at opposite ends of the crystal ladder filter on the  
> KSB2 board have different turns ratios.
>
> T1's turns ratio is 22:7. while T2's is 22:4.
>
> The impedance of the crystal ladder network appears to be in the  
> neighborhood of 1200 - 1500 ohms.  Since the KSB2 sits inside an IF  
> having a 150 ohm impedance, T1's 22:7 turns ratio, which performs a  
> 9.87:1 impedance transformation, makes perfect sense.
>
> The Balanced Modulator feeds T2's primary with an impedance close to  
> 1200 ohms, which also makes perfect sense.
>
> However, T2's secondary, having only 4 turns, presents an output  
> impedance significantly lower than the 150 ohm IF system it is  
> feeding.
>
> What's the deal?   :-)
>
> And I ask this question as I troubleshoot a "narrower than expected"  
> crystal filter response.  I'm curious whether the T2 impedance  
> mismatch is intentional, or something else is going on that I'm not  
> aware of.
>
> Any relevant enlightenment on the subject would be appreciated.
>
> Thanks.
>
>
> 73, de John, KD2BD
> K2/100 #3563
>
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