[1000mp] MP vs MkV vs K2

[Tom Rauch]

> Thanks for the reply.  So when these tests are run (5 or 20 spacing),
> do they then have (for example) one of them tuned into the center of
> the IF passband, and the other one 5 or 20 KHz. away (outside the IF
> filter, but inside the roofing filter)? 

GOOD or proper tests would normally be made with both signals INSIDE 
the roofing filter. The ARRL has to be careful to do this, or there 
is little reason to do the test.

Say the IF roofing filter is 70.000 to 70.010 kHz and the local 
oscillator is at 78.005 kHz with an 8 MHz second IF.

If we tested with 5kHz spacing and a signal centered in the 8MHz IF, 
even with a 10kHz roofing filter, the results would be flawed. The 
problem is the test signals would be well down on the slope of the 
roofing filter when the testing operator tuned in the IM product 
(which would be 5kHz above or below the desired signal), and this 
would inflate the results.

5kHz is almost certainly too wide for many receivers, and still would 
inflate the results.

What we really want to do is test as close to the real-world problem 
as we can, and always do a test that keeps BOTH signals well inside 
the roofing filter. That would mean we would have to test at a much 
closer spacing than the roofing filter bandwidth.

The ideal test spacing in a multi-conversion receiver with a roofing 
filter system (like most modern transceivers) would be just outside 
the limits of the narrow filters, perhaps at 1-2 kHz using a narrow 
CW filter.      

 If you are right, then the
> offending element is pre-IF, such as the first mixer (70M), or some RF
> amplifier before the IF filters.  I guess it's possible.

It is not only possible, it is that way virtually 100% of the time.

73, Tom W8JI
W8JI@contesting.com