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For lambda/4 microstrip couplers 25dB to 30dB directivity should be in reach with a little tuning.
Waveguide measurement couplers can have e.g. 50dB directivity. They need extensive tuning by hand.
Broadband couplers like in Vector-Network-Analyzers are good if they reach 15dB directivity.
Perhaps you can solder the VCO to small PCB pieces and then use a microwave test-fixture to connect to the transmission-lines of the PCBs.
e.g. Wiltron and Connexion Rosenberger are manufacturing universal test-fixtures. Although they are not cheap, they offer reproducable measurements...
Sounds like your transistor was damaged.
If FETs are used outside the specified values they sometimes don't stop working completely. They sometimes just alter their S-parameters.
I would encourage you to change the FET.
As kid-the-great said I also experienced problems in a circuit simulation of a hairpin-filter. The circuit-simulator did only cover the coupling of two coupled lines at a time. The coupling to the other coupled lines were the reason my simulation did not fit with the measured results.
I've also seen the described structure in a commercial broadband amp. I don't remember the exact location but I think it was near the output and there was just one of these obscure structures in the amp. The substrate or the structure weren't coated with anything. The whole backside of the...
serial port under different windows versions in labview isn't always easy.
Have you tried the discussionforum in the NI developer zone?
There are quite a few topics about serial communicaion problems.
what is pmpo and rms
up to now I saw these PMPO-stuff only on cheap computer speakers.
You know, these insane rated 200Watts PMPO devices fed by a power supply capable of delivering 10Watts :wink:
For a dynamic point of view the crest factor is used, at least at serious amplifier...
it depends on your circuit. If you could be more specific it would be easier to help you.
If the signals you are interested in are much higher than the 50Hz you could perhaps get easy rid of the hum with a simple passive 1st order highpass filter.