[Elecraft] TX IMD

[Geoffrey Mackenzie-Kennedy]

Jan Erik Holm wrote on Monday, January 26, 2009 8:52 AM

As you say, it´s getting rare these days with radios in the
-30 to -40 dB bracket. And we are just going to be content
with it? No not IMO.

Jan,

I agree in the context of Amateur Service radios.

The time might come perhaps sooner than later when it does not matter 
whether or not we amateurs are content to put up with poor Tx IMD 
performance, somebody else might set the limits for us if we do not. 
Although the Amateur Service has been allowed for decades to police itself, 
there is growing pressure from some users who have been assigned allocations 
adjacent to our bands to clean up what could be called "outside band edge 
whiskers" created by amateurs, be they key clicks or IMD products or other 
types of garbage.

Forty years ago in Canada the Type Approval specs for low power HF 
transmitters for use in commercial services set the limit for Tx IMD at 30db 
below each tone in a two tone test at full rated PEP output. Input to mic 
connector, also to any other audio input interface. I must own up to being 
involved in writing those specs. However today such a limit does not reflect 
what is required by responsible spectrum management nor does it reflect what 
can be ahcieved in practice at reasonable cost. We need to look for much 
better performance than 30db below test tone.

FWIW

73,
Geoff
GM4ESD