[hpsdr] Munin C25-C27 / IMD3

[Georg Prinz]

Hello Kjell,

thank you for your answer. I am fed up with all my power meters. I
bought a brand new PEP meter offered by a german OM, hoping that this
will be ok. But you never should trust anything, which you didn't check
by yourself, HI. I made a new test bed:

Penelope-munin-Alex-directional coupler-power meter-dummy load.

Measuring points: output munin : Oszi. Tek.2445
Directional coupler: Spectr. Anal. hp8566B

PEP=100 W at 50 Ohms results to 100V peak voltage. 

Now I am alble to check all my power meters. They are crap.

Munin is working ok and I has been chasing non existing errors.

Here the results:


1.8MHz	-35.4dB 
3.7MHz	-30.3dB
7.1MHz	-32.2dB
14.2MHz	-37.6dB
21.2MHz	-29.4dB
28.6MHz	-32.1dB
50.2MHz	-30.7dB

There is one thing left, for which I don't have an idea how to resolve.
Driving munin with single tone (tune signal) I get a very clean and
linear signal (pure sinus)at 28.6MHz and 50.2MHz. But on 7.1 and 21.2MHz
there are obvious distortions. Could this be a problem of my core
material for L4?

73, Gerog, dl2kp


Am Sonntag, den 26.01.2014, 09:39 +0100 schrieb Kjell Karlsen:
> Hi Georg.
> 
> You are not the only one seeing this.
> 
> The power you are referring to, is that what you read on the Power Meter  
> on PSDR? You will see that if the PA is in its very linear area, the  
> indicated power is the PEP, twice of what you measure on a Bird or other  
> normal Power Meters when running 2-tone test.
> 
> I have not seen any difference using the Drive level control or the GBB  
> settings.
> 
> Do you use Alex or any other LPFs? Have you seen any difference with or  
> without LPFs?
> 
> I have a new built Munin on my table so I´ll test through all the bands  
> and settings with it.
> 
> 73, Kjell
> 
> 
> 
> 
> På Fri, 24 Jan 2014 15:26:30 +0100, skrev georg Prinz <getpri at t-online.de>:
> 
> > ***** High Performance Software Defined Radio Discussion List *****
> >
> > 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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