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DB9 extension cable for 4444 ?

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DB9 extension cable for 4444 ?

Postby nurber » Thu Apr 05, 2018 8:24 pm

Hi Forum. I need 3m ( 10' ) DB9 extension cable to locate scope in a nice environment for some tests. I suppose any "straight through" DB9 extension cable will work for low voltage, low frequency stuff but perhaps there is something that uses Belden 9271 or is rated for higher voltage than typical UART stuff ?
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Re: DB9 extension cable for 4444 ?

Postby Gerry » Mon Apr 09, 2018 2:29 pm

Hi nurber

When you say higher voltage than typical UART stuff, exactly what voltage are you referring to?

If you're also considering using higher frequency signals, then, if the cabling capacitance increases noticeably, they will get attenuated to a some extent. In the PicoConnect 442 this will be very noticeable (as the probe is passively performing the 25:1 attenuation) and any AC signal would look noticeably smaller, potentially leading to safety issues.

Regards,

GErry
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Re: DB9 extension cable for 4444 ?

Postby nurber » Mon Apr 09, 2018 4:13 pm

Thanks for reply Gerry. "Higher than UART" only meant to convey that I don't think some of these inexpensive serial DB9 extension cables are a good choice. Attenuation will happen before the extension cable so let's say 50V as the scope is limited to that. We have the terminals to crimp our own D-sub terminals, but I'd rather pay to get a molded cable.
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Re: DB9 extension cable for 4444 ?

Postby Gerry » Tue Apr 10, 2018 10:17 am

Hi nurber,

Belden 9271 is a good choice of cable, as it enables the PicoScope 4444 to perform within the specifications that we state (bear in mind that RG-58/U which is typically used for Scope Probes actually has a higher capacitance per ft/m). Any cable will attenuate higher frequencies if you increase it's capacitance too much by extending it too far, or by using inappropriate cable.

But don't confuse the PicoConnect 442 with the 441. The 442 is deliberately being used to attenuate high voltage signals significantly (which is why we recommend that you don't tamper with it). So, if you're restricting the voltage to 50V, then you would be using the PicoConnect 441 which you should be able to extend by 3m without any signal degradation (if you don't use, as you say, "inexpensive cabling" that adds significant capacitance).

The only other possible issue to consider is that, even with good cabling, you could change the identification of the probe via 'Connect Detect' (which identifies to PicoScope 6 which of the Probe types is connected).

Regards,

Gerry
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