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Thursday, 28 December 2017

FeelTech 6600 - Another one - Really?


** UPDATE ** Since creating this post I have done a separate blog entry documenting the issues I have found with the unit here.

Following my recent musings on the FeelTech 3200 eBay sourced Function Generator here, I bought myself a model 6600 from Amazon.

Now, this one has a more fancy screen and has a spec claiming a 60MHz output on the sine wave function. The manual for the instrument clearly states that the outputs are 50 ohm, so I have connected the device to my 'scope using a 50 ohm transmission line and terminated it at 50 ohms.

My first observation is that the "Amplitude" setting on the generator has little or no resemblance to the output voltage measured into 50 ohms by the 'scope. The second observation is that there is some weird DC offset in the signal.

Here is the first example, 10 MHz signal at an amplitude setting of 2.0V (the manual says this is "default" peak to peak - I have found no way to change this "default" setting). For all these tests I have only adjusted the digit to the right of the decimal place, as highlighted in the image below:

and here is the resultant waveform:

So you can see in the 'scope image above that the signal is offset -ve DC.

Test 2, same frequency but amplitude now 1.4Vpp:

The signal is now 100% -ve. Test 3, 1Vpp:

Now, all -ve and some! Test 4, 0.6Vpp:

And then finally, at 0.5Vpp Amplitude setting there is a relay "clunk" inside the box and the DC offset becomes as expected:

I've managed to confuse the unit a few times by adjusting the amplitude several decimal places to the right of the point and then sometimes the amplitude seems to get stuck and doesn't change until you get to the 0.5V clunk point. I've also got the unit so that Channel 2 will produce no output - under both of these scenarios a mains power off then on fixes the issue.

The spectrum output of this 10 MHz signal seems quite clean:

And yes, the same poor PSU is in this device as the 3200. In this 6600 I've replaced the 2 prong mains input connector with one of a standard 3 pin variety and connected the earth line to 0V.

So what's that DC offset all about?

** UPDATE ** Since creating this post I have done a separate blog entry documenting the issues I have found with the unit here.

Here's Miss Luna Cat assisting with Satellite Tracking:

Bonkers, egh?

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