[hpsdr] Munin C25-C27 / IMD3

[georg Prinz]

Hello,

I was curious about the different behaviour between mica capacitors and 
SMD ceramic capacitors C25 to C27. Therefore I replaced the mica through 
4x 220pf SMD.
The result was marginal. But, what is interesting for both versions, 
that the IMD3 differs strongly with the drive level. Actually, this is 
not surprising at all, but I didn`t expect it with that amount and
in some cases, IMD3 was better suppressed at higher output level:

MHz    P [W]    IMD3 [dB]

1.85    118.0         -40.1
               99.6         -25.5

3.7        99.9         -30.3

7.1        94.2         -21.2
               94.2        -21.1
               98.5        -16.4
              85.6         -26.6
              86.7         -34.8

14.2     90.1         -32.4
            100.0        -19.8
              92.2        -22.0

21.2    89.6         -22.1
             87.8         -17.0
             91.9         -20.2

28.6    81.2         -13.4

50.2    77.9         -24.1
             86.2         -20.7

Furthermore, I have the impression, that there is a difference if you 
change the driver level through the PA-settings in the set-up window or 
with the slider on the main window.
Any idea why?

As a conclusion of this test, I would say, that during normal operation, 
you never succeed in an optimal IMD3 suppression. On one band I even 
experienced, that the IMD5 was
obviously stronger than IMD3.

All measurements were taken with munin feeding a dummy load.

Does anybody made similar measurements or is this a behaviour of my 
munin set-up, only?

Maybe, Kjell could comment on it comparing it with his measurements?

73, Georg, dl2kp




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