2nd harmonic filters

[LarryH]

This is a common question from techs on filters
- I can't find the right filter to perform 2nd harmonics testing on this spectrum analyzer.  Should I limit it?
Answer:  You don't HAVE to have the exact filter to perform the check.  As long as the filter frequency is between the test frequency and its 2nd harmonic, you can use it.  This test is an "equal to or better than" specification.  This means it is IMPOSSIBLE for a BAD unit to read GOOD - similar to risetime testing.  With this in mind, any filter can be used as long as the proper CW power is provided (-30 dbm to the 1st LO is typical).  I usually provide a little extra just to make sure there is no amplitude error.
If you are having a hard time finding any filters anywhere close to what is called for, go to Table 1 and look at the frequency range for the specs being tested.  From this table select a high and low frequency to test the same range.  If the K-proc calls for 80 MHz applied through a 100 MHz filter and measured at 160 MHz but table 1 says the same spec applies from 50 - 300 MHz, then test at 50 MHz through a 75 MHz filter and 200 MHz through a 250 MHz filter. 
Additionally, if you filters still won't get it to pass, you can stack DIFFERENT filters.  A 100 MHz and a 150 MHz filter would be fine to clean up an 80 MHz CW signal.

Hope this helps you RF freak, I mean Freq, technicians.