[amsat-bb] funcube dongle

Pavel Milanes Costa co7wt at frcuba.co.cu
Thu Feb 12 04:50:26 UTC 2015

On the subject of using ethernet UTP CAT 5/6 cable for making USB 

I have a kind if experience on that, you can reach about 15-20m runs 
easily without losing connection to the usb dongle (even wifi dongles)

If you want to go for sure, don't use more than 12m... from there on is 
a challenge, I use on daily basis a run of 14m switching from RTL-SDR 
and a WIFI dongle, as always your mileage may vary.

The better way to cable the extender with UTP CAT 5/6 is this (my 

The UTP5/6 has 4 pairs of cable:

- Use one pair (two wires) for the GND
- Use one pair (two wires) for the +5V
- Use one pair for the data transfer, one wire for D+ and the other for D-

If your dongle get disconnected or errant behavior use the free pair to 
add one more wire to each GND and +5 volts lines. (more wires in 
parallel = less resistance = less voltage drop)

Put a little ferrite core (1 cm OD, 3mm H) at each end of the cable 
(just a pass trough) plus a 10nF and 10uF at the far end from the 
computer between the GND and +5V (10uF is electrolytic, watch out the 

The ferrite will protect you a little from a nearby TX station (full 

With this setup I can run a wifi dongle at runs from 12, and some times 
I put the RTL-SDR there too...

Don't be tempted to put more uF on the far end 10uF is good, you can 
kill your USB port by putting something in the order of 3300 uF or more 
(Been there, done that, got my USB port killed)

Don't use this extension cable on accessory USB ports, use only the rear 
ports of your motherboard.

You will lose some bandwidth, My RTL dongle runs easily 2.8 Mhz on the 
PC and on the far end of the extension it only reach about 2.2 Mhz

Things to note:
- UTP cat 6 is better
- Shielded UTP is even better, the shield must be connected only on the 
PC side and not to the USB GND line, but to the PC chassis.
- if not shielded cable, you may get a USB reset if you TX on HF with 
high power, but 2m 50W don't seem to harm on my case (if you forgot the 
ferrites you will be killed by 2m TX too)

I hope this can help, 73 from CO7WT.

El 11/02/15 a las 21:41, Stephan Greene escribió:
> This approach would work well, I think for portable ops, too. Maybe without
> extenders, just a long USB cable.  I think USB 2.0 is rated to 10-15 ft
> without boosting the signal.

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