[hpsdr] Alex update?

[John Ackermann N8UR]

Henry, for the most part the toroids had somewhat different inductance 
than specified but other than that performed OK.  So the main work has 
been changing the turns count to get the correct inductance, and in a 
couple of cases changing the associated capacitance to optimize the 
filter performance.

After adjusting for the changed changed inductance, the stopband loss, 
insertion loss, and power handling weren't much different between the 
spec'd and actual toroids.

(We did network analyzer measurements of each filter with both the 
spec'd Amidon toroids and the Chinese ones -- over 40 captured data sets 
in all -- as well as 100W saturation tests of the transmit filters to 
measure both heating and spurious generation.  These filters are *well* 
characterized!)

John
----

Henry Vredegoor wrote:
> ***** High Performance Software Defined Radio Discussion List *****
> 
> Hi Scotty, Graham, All,
> 
> I have a few technical questions about the changes for Alex; could you 
> please explain a little bit more?
> 
> - I understand that the currently used cores are manufactured in China, 
> a lower price beïng the main reason for doing so, but that they 
> initially did not meet the quality standards of TAPR; where/why more 
> exactly didn't they meet the spec?
> - The circuits of the filters had to be changed to accommodate the China 
> manufactured cores.
>   Are the quality or spec's  of the filters on the Alex boards 
> compromised by this change and if yes what are the resulting 
> differences/new specs/consquences?
> - Would it still be possible to use the original cores (for maybe better 
> quality or  tighter specs) ?
> 
> I hope I am not bugging you too much with my questions, I highly 
> appreciate the outstanding job you are doing for us all.
> But "Ham-Radio minds" want to know.......................    :-)
> 
> 73's,
> 
> Henry.

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