Hi Jason, I'm after weak signals on the vhf and uhf aircraft bands, so I need all the shielding and suppression I can get. I've never needed an extension usb cable, so I don't have anything to test with (other than the 10 foot cable I just bought). I do have a 6 foot cable on order, with double shield and a ferrite on the braid. But, if I have to spend more money, I'd rather have something that I know is right, which is why I hoped to build my own cable and be done with it. I know about the RTL-SDR's shortcomings and about the need for front end bandpass filters. There is no way it will function without them-so many users are oblivious to the ramification of out of band signals causing overload. And, many of those that do know about overload assume a digital signals can't be compromised by strong out of band signals. BTW, the RTL-SDR is in a constant state of overload, even without the AGC and the proper 50 db gain control setting. With only 40 db dynamic range, the RTL-SDR doesn't even need out of band signals to cause non linear mixer responses, and the degradation of the desired signals reception. Ultimately, I'd like to just put the thing outside, at the mast location, but I need to do some USB cable testing before going any further. A fiber optic link would be neat, although it's overkill for the 50 to 100 feet transmission distance I'd like to ultimately have::> Any idea where I can find specs for the proper usb (raw) cable? Regards, Art On 07/08/2018 03:40 PM, Jason White wrote: > Have you tried using a different USB cable? Conventional USB cables with > their single layer of shielding should be more than adequate for your > application. I suspect that manufacturing your own cable may not the > easiest, cheapest, or fastest way of getting things to work. > > I have a RTL-SDR type dongle and a 125MHz upconverter. In my experience i= t > is noisy and strong signals produce aliasing* every 2.4MHz (sampling > frequency), every ~27MHz (SDR crystal frequency) and every 125Mhz (from t= he > upconverter). The internal 30-40dB AGC typically will typically boost > signals past the point where aliasing occurs. As a result AGC needs to be > disabled and the the dongle's RF gain has to be manually set - typically > never exceeding 20dB. > > * aliasing -> ghost signals, lines and spikes in the SDR's decoded spect= rum > > -Jason White > > > On Sun, Jul 8, 2018 at 3:09 PM, Art wrote: > >> I recently bought an RTL-SDR >> (https://www.nooelec.com/store/nesdr-smart-sdr.html), a small radio >> receiver that is powered by the USB connector on the punchbox. It >> digitizes the received radio signal and sends the digital information to >> the punchbox for processing via USB. >> >> It turns out that the computer generates to much noise for the receiver >> to operate in close proximity to the punchbox. >> >> So, I have to move the receiver and/or the antenna further away from the >> computer. I choose to move the receiver as low loss coax for the uhf >> band is pricey. >> >> So, I bought a high end 10 foot USB 2.0 extension cable, with 2 layers >> of shielding, and emi suppressors (ferrite) on each end of the cable. >> The cable has 24 gauge power bus conductors, mote than adequate for >> powering my RTL-SDR receiver. The RTL-SDR receiver uses 370 ma, worst >> case, so the 24 gauge power conductors in the cable should be adequate. >> >> The RTL-SDR unit has an internal (smt type) emi absorber on the power >> input terminal. The computer is a very dirty place in terms of rf noise, >> and having rf noise on the USB lines is like rolling out the welcome >> wagon for rf interference to the RTL-SDR receiver. >> >> The new USB cable works fine for the smaller usb flash drives I have, >> but it causes the RTL-SDR device and my USB HDD unit to fail when >> connected through the new cable. Neither of the higher power devices are >> recognized. The RTL-SDR requires the full USB 2.0 throughput, without >> it, it can't send data fast enough to enable the software in the >> punchbox to function. Both the HDD and the RTL-SDR work fine when >> plugged (directly) into any of the ports on the computer (without the >> extension cable). >> >> I concluded that I need to roll my own cable. That way, I know the cable >> itself is proper. I can buy the usb ends for the extension cable and >> solder them to the cable. >> >> However, I can't find the technical specs for the cable, so I don't know >> which type of raw cable to buy....in order to insure my homebrew cable >> works at it's full capacity (which is 480 MB/sec). There are USB >> repeater cables that extend the max cable length out to 50 feet, but >> they're expensive, they draw a lot of power and they don't work at the >> full data rate for USB 2.0. And, none of the repeater cables have >> shielding at the housing for the driver electronics. >> >> I've thought about using an ethernet cable and putting usb connectors on >> the ethernet cable. But, ethernet uses balanced transmission line >> (twisted pair)...it might not work well for usb because USB doesn't use >> a balanced line-so there is little benefit to be had by moving to >> ethernet cable for usb data transmission. >> >> I sure wish the RTL-SDR had an ehernet cable connector instead of a USB >> connector! >> >> My problem is I cannot find the usb 2.0 specification that outlines the >> critical parameters for the cable itself. Any ideas? >> >> Sorry to be so long winded::> >> >> Art >> >> >> >> >> -- >> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist >> > > --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .