[1000mp] ARRL REVIEW ROOFING FILTER

[Ian White, G3SEK]

Ron wrote:
>> IMD dynamic range 20 khz spacing before 88 db after 93
>> 2 khz spacing before 69 after 79

>Come on now  I have been there.   There  is no  way that anyone can 
>tell the difference between -69 and -79 .  The ear is just not that 
>good. Sorry.

Sorry, you are not interpreting those dynamic range figures correctly.
It is the 10dB difference in dynamic range that counts.

It means that two equal signals spaced 2kHz apart can be 10dB stronger 
before any IMD products appear. In practical terms on a crowded band, 
signals in general can be about 10dB stronger before any crud starts to 
appear; or for the same strong-signal levels, the IMD will be 10dB 
weaker. These are differences that anyone can notice, in terms of less 
CW clutter and clearer SSB.

>A lot of hype out there to sell radios and filters.   You spent the 
>money and wanted to hear and improvement so did.  The mind work wonders 
>to do what you want it to do.

The opposite problem being that we're all so hardened by hype and 
specmanship, we sometimes can't recognise the good things when they 
occasionally do come along.


-- 
73 from Ian G3SEK