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USB cable extension tips, pics, and the dirty things your computer doesn't want you to hear

A project log for Enter the complex world of SDR

Tune the radio to your favorite FM station , and as the songs base starts to rev you up. The hacker within asks, "how does radio"?

Dr.Droopy NayheyDr.Droopy Nayhey 02/08/2015 at 21:132 Comments

So that computer of yours, I'm sad to inform you that your PC is a RF menace, and the DVB tuner must connect to it.

This isn't ideal for the SDR, it's like having a cell phone conversation while present at a Rock concert.

So our first step is to build a DIY USB extension for the device(Or buy one).


-you may be thinking

" psh, stupid Dr. Droopy I have tons of USB extension cables already".

My response


Your EXTENSION CABLE isn't good enough , or may EVEN worsen your SDR experience. The USB Cable itself must be shielded to the RF rock concert around you/it. This is achieved by ferrite beads.. well they're like clip things.

~In addition, the USB extension Cable itself may be confused and inappropriately used as an antenna by your Rtl-sdr. Remember this thing is cheap, and originally was not designed for this type of rf surfing. So we must correct for this stupid device and how it connects to it's Computer overlord


SO let's mash together a USB extension cable built with RF in mind.

A usb extension cable is pretty common, I bet you have one right now... Coiled around you leg

LOOK OUT!.........

Seriously though take a look around, if you don't have one BAM let's make you one.

Step One :

*Gather the beads, broken usb cables and the ol' soldering iron

Usb female:

Old computer bits scattered around? Grab that old Mobo and lets remove some Female Usb connectors

Every article i read on this was pretty much the same buy this buy that, and to this i say nah i can make it.

Let's assume i used heat shirk tubed each connection. Which i did for an already built one, I took the end and placed it through a plastic holder which i had from an old usb extension cable. I also stripped away the metal shroud, less metal= mo bettah

here is the end product

Are you a bad enough dude to trust your solder job?

No, you shouldn't assume it's all good.. Use a voltmeter to test continuity .

once it passes your voltmeter we're ready for a trial run!

use a USB device that means nothing to you. in my case an old flash drive.

Heck yes! The USB Extension cable works!

One bit i totally missed explaining was the ground wire.

In the above example, we simply removed the metal shielding from the female end of the USB cable. We do this because the cheap tuner can mistakenly use the ground connection as an antenna. Which is not at all a good thing. If we were to insert our sdr within a nice case we would use the ground connection to connect to the metal shroud within the case. We will cover that when we build a case together... as a family

now onto ferrite

I found that the ferrite beads are pretty conman, and I already had several USB cables which already utilized them, so I just needed to perform bit of a USB Splice operation . So i suggest looking around, trying different ferrite cores, or buy the ones the recommend. The once i salvaged seem to perform just as good as the ones i bought.

Actually I've done a lot of USB soldering in my day, and as we can see in my primary radio pic below I built a sort of USB break away system.

Reason i had to design a break away system; is due to the amount of cables I've tripped over + it's good for portability! (Broken at least 10 devices by being drunk and somehow getting them tied around my legs, which I break with the hulk like power )

So within that RF shielded case I have it wired to another externally attached (Glued) Usb connection. I'd open it up and show you the internal connection i made, but honestly i don't remember if i grounded through the top or bottom of the case, and I really don't want to re-do solder work. We will make an rf shielded case later in this project so don't-cha worry

The case errr..

~ This case

Rf drop amp, I work within the telecom field.. So i have access to discarded treasures. Such as this discarded rf drop amp.

I gutted the device and basically assumed if it works for that it will probably work for this. Since I enclosed the Rtl-Sdr in this drop-amp shell I have noticed nothing but improvements.

Before using this enclosure I did indeed try to design/use other cases, each with varying degrees of success. Sadly I didn't document my trial and error in this case...of different cases... Something I will do with my other DVB/rtl-sdr sticks, and with you the studio audience.

Back to the universal serial bus .

It's pretty simple to find pin-outs of a usb cable

Discussions

Dr.Droopy Nayhey wrote 02/21/2015 at 03:32 point

Word up! Though I have salvaged laptop pc's and I own custom built Pc's and I've tried both, i find as long as the distance between the radio and computer is decent and the chokes are in place the variance between the custom built and non-custom built is non existant 

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DainBramage wrote 02/16/2015 at 23:50 point

I use a good quality (Belden) USB cable with the shield disconnected at the SDR end for isolation. It also helps to have a computer built from quality components, which can really only be achieved if you build your own PCs. Anything store-bought is built down to a price, so you will be battling noisy power supplies, crap shielding, and poor quality cables, all of which add up to a nightmare for RF heads. 

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