[TenTec] Filters and IMD

[W0YG, Charlie Summers]

W4ZV wrote:

>There's a funny story associated with this.  Shortly after I sent out the 
>18 original #352 kits in April 2004, one guy
sent his to Rob Sherwood for testing.  The results were TERRIBLE and I felt 
badly for having apparently caused 18 people a lot of grief for nothing.  I 
then sent Rob my filter (using SMD caps) and Barry N1EU sent his (using disc 
caps).  The reason I wanted both types of caps tested was to see if the type 
of capacitor could possibly be causing
the poor IMD results.  Rob's measured IMD results from both filters were 
consistent and excellent (WHEW!), so we concluded the first filter he tested 
had been improperly constructed and the type of capacitor used had no 
effect.

What Bill, W4ZV, reported above is not quite the way it went down and should 
be related.  The filter that is mentioned as being TERRIBLE above was the 
first INRAD 762 kit that Rob Sherwood tested.  When the close in DR came 
back as 79dB, we all just assumed this was it.  There was nothing wrong with 
the way the filter was constructed as it was built correctly.  Bill, W4ZV, 
was skeptical of the results so other filters were arranged to be sent to 
Rob.  After testing the new filters, Rob suspected a faulty crystal (after 
the fact) in the initial filter tested and mentioned that one of them 
exhibited microphonics which could degrade the operating characteristics. 
He did not suspect this until he tested the two other filters that W4ZV 
mentioned with marked improvement in the DR area.

I have built three or four of these filters for guys.  I had one randomly 
tested by Rob which reproduced the results he obtained from W4ZV's filter. 
I did not use surface mount technology on the one tested but instead used 
dipped mica caps.  I too saw no difference between SMT or dipped mica caps 
with the filters I built.

73,

Charlie, W0YG..>>