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FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator

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aimc:
This is all well known, but did you notice that (with proper termination of course) the generator's output declines from 10-60 MHz by about half (-6dBv)? I am talking about the FY6800 actually and want to use it as VCO expecting a flat response. I didn't go inside yet to measure directly at the DAC but I suspect there is something fishy going on at the amplifiers. Has this topic been discussed here or anywhere? Is there a "hack" available to fix this?

Thanks in advance
Lutz

CDaniel:
I can't talk about FY6800 but an FY6600 is flat from 0 to 60Mhz ... maybe you did a simple mistake in your setup , it wouldn't be the first time in this thread  :-+

rhb:

--- Quote from: aimc on September 28, 2019, 06:35:23 pm ---This is all well known, but did you notice that (with proper termination of course) the generator's output declines from 10-60 MHz by about half (-6dBv)? I am talking about the FY6800 actually and want to use it as VCO expecting a flat response. I didn't go inside yet to measure directly at the DAC but I suspect there is something fishy going on at the amplifiers. Has this topic been discussed here or anywhere? Is there a "hack" available to fix this?

Thanks in advance
Lutz

--- End quote ---

What was the output voltage?  Check it at 1 Vpp.

aimc:
Thank you for the reply. I did measure it again just now (see attachment) and yeah - well it has some ripple reaching around 2.5dBv (~0.75) at 60MHz (my former statement was a bit higher due to a mistake, sorry). Not sure if a 0.75 drop is acceptable for a function generator, but then again its a cheap product.

rhb:
I don't understand what you're showing.

Is the sweep synchronized with the scope trigger?

Also please take a look at the PCB.  Is there any flux residue visible?  Flux absorbs moisture out of the air.  This results in an environmentally dependent parasitic capacitance.  It would not take much capacitance to  cause the drop in output you're seeing.

If you see any flux, clean it off with isopropyl alcohol and an old toothbrush and retest.  I've done quite a few repairs, including an HP 34401A which had been repaired previously that consisted of nothing but cleaning flux residue off the board.  The 34401A was completely non-functional until I cleaned it.  But after cleaning meets the factory spec.  It's the more accurate of my two 34401As.  The other one was a closet queen and saw very little use.

Have Fun!
Reg

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