[hpsdr] PennyWhistle T1 construction and measurement

[Andrew Howell]

Graham,

Thanks, I did assemble it; almost done! I'm pretty sure its all ok. Just 
trying to learn as I go. I have a MFJ-269. I should have thought of 
trying that. Next time.

73 Andy - KF5JLJ


On 10/12/2014 1:48 PM, Graham wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
>
>
> Andy:
>
> Inductance of turns on a common core go as the number of turns 
> squared, not proportional to the number of turns.
>
> So I would expect the inductance of the secondary end to end to be 
> about 4 times the inductance of one side.
>
> That particular transformer falls apart, performance wise, below 1.8 
> MHz, so measuring at 10 kHz is not meaningful.
>
> The impedances quoted are for a loaded transformer, so if you have 
> some sort of antenna analyzer, like
> an MFJ-259, if you put a 50 Ohm load across the secondary, you should 
> see about 50 Ohms looking into the
> primary. But, only between about 1.8 MHz and 54 Mhz. Below those 
> frequencies, there is insufficient
> inductance for the transformer to work at or above 50 Ohms.  Above 
> those frequencies, parasitics dominate.
>
> If you think you have assembled the transformer correctly, I would go 
> ahead and continue assembling
> the kit.  If you have wound something incorrectly, the amplifier may 
> not work properly, but unlikely you
> will destroy something.
>
> Continue with the build, and troubleshoot afterwards if necessary.
>
> --- Graham / KE9H
>
> ==
>
> On Sun, Oct 12, 2014 at 1:03 PM, Andrew Howell <andy at gamubaru.com 
> <mailto:andy at gamubaru.com>> wrote:
>
>     ***** High Performance Software Defined Radio Discussion List *****
>
>     After sitting on my workbench for far too long, I finally decided
>     to assemble my PennyWhistle.
>
>     I have some very basic questions about T1 construction. I made the
>     bifilar secondary and connected it up as shown in the diagram in
>     the instructions.
>
>     The instructions say is should be 50 ohms impedance on the
>     primary, 50 ohms on across the secondary, and 25 ohms impedance on
>     between the secondary leads and the center-tap.
>
>     I have an LCR meter, but I don't think that is going to help me,
>     as it measures Z at a max of 10khz.
>
>     I do measure 12.9 uH on the primary, and 12.8 uH on the secondary.
>     The two sides of the secondary to center-tap are each 4.6 uH. 
>     Those two secondary to center-tap inductances seem low. I would
>     have expected 6.4uH, ie half the 12.8uH of the secondary.
>
>     So, are these the values I should expect? Why don't the secondary
>     to center-tap inductances add up to the inductance of the whole
>     secondary leads?
>
>     I expect I'm about to learn something :)
>
>     73, Andy - KF5JLJ
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