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Graham,<br>
<br>
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.<br>
<br>
73 Andy - KF5JLJ<br>
<br>
<br>
<div class="moz-cite-prefix">On 10/12/2014 1:48 PM, Graham wrote:<br>
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<pre wrap="">***** High Performance Software Defined Radio Discussion List *****
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<div>Andy:<br>
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Inductance of turns on a common core go as
the number of turns squared, not
proportional to the number of turns.<br>
<br>
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So I would expect the inductance of the
secondary end to end to be about 4 times the
inductance of one side.<br>
<br>
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That particular transformer falls apart,
performance wise, below 1.8 MHz, so measuring at
10 kHz is not meaningful.<br>
<br>
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The impedances quoted are for a loaded
transformer, so if you have some sort of antenna
analyzer, like<br>
an MFJ-259, if you put a 50 Ohm load across the
secondary, you should see about 50 Ohms looking
into the<br>
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primary. But, only between about 1.8 MHz and 54 Mhz.
Below those frequencies, there is insufficient <br>
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inductance for the transformer to work at or above 50
Ohms. Above those frequencies, parasitics dominate.<br>
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If you think you have assembled the transformer
correctly, I would go ahead and continue assembling<br>
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the kit. If you have wound something incorrectly, the
amplifier may not work properly, but unlikely you<br>
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will destroy something.<br>
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Continue with the build, and troubleshoot afterwards if
necessary.<br>
<br>
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--- Graham / KE9H<br>
<br>
==<br>
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<div class="gmail_extra"><br>
<div class="gmail_quote">On Sun, Oct 12, 2014 at 1:03 PM, Andrew
Howell <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:andy@gamubaru.com" target="_blank">andy@gamubaru.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">***** High
Performance Software Defined Radio Discussion List *****<br>
<br>
After sitting on my workbench for far too long, I finally
decided to assemble my PennyWhistle.<br>
<br>
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.<br>
<br>
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.<br>
<br>
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.<br>
<br>
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.<br>
<br>
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?<br>
<br>
I expect I'm about to learn something :)<br>
<br>
73, Andy - KF5JLJ<br>
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