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[time-freq] TADD-1 10 MHz filter

Don Graham degraham at people.net.au
Sat Mar 19 13:43:00 UTC 2011

I've recently built up the TADD-1 RF distribution amp kit, (but initially without the 10MHz filter 
option) and it looks like it will do the job nicely. Thanks to those involved in the design and 
kitting process! However as my Shera 10 MHz GPSDO source is a pseudo square wave I 
thought I would proceed to add the filter. And...you guessed it I've come across what appears 
to be an error in the Installation Advice which specifies two inductors for the filter, each 
wound on an Amidon toroid type  T50-2 with 27 turns to achieve the necessary 14.5uH. 

I now find from the archive that this has been pointed out before but I can't see what 
happened to sort it out.

It seems that the 14.5uh and all the other filter bits are absolutely correct (as per a filter 
design application) but two separate design formulae indicate that a T50-2 needs about 54 
turns not 27 to achieve that inductance. It could be a tight fit but when I get some toroids will 
have a try. Has anybody else sorted this out? Is there a hiccup in the toroid type? If there is a 
correction it would be a good move to update the Assembly Manual.

73...Don VK6HK

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