In practical terms the current the dongles use is around 375 ms. USB2 current
allocations are coarse enough that the smallest allocation greater than 375 ma
is 500 ma. (This is also the largest normal allocation possible.) So you can
actually afford an efficient active extension as well as the dongle. The wires
are designed to provide rated voltages at the maximum rated current at the end
of a 5 meter extension. So you should be able to use one active extension plus
one passive extension both 5 meters long.
I experimented with this with a variety of DVB-T dongles. They all worked just
fine. Now I must decide whether I want a long coax (dongle inside with smaller
temperature variation and higher effective noise figure) or long USB cable
(dongle outside with WIDE temperature variation with lower effective noise
figure.) A third alternative exists, but is expensive. That violates the
spirit of the cheap dongles. {^_-} That option is an antenna preamp with
long coax. The cheap preamps roll off at about 900 MHz, making them deadly
for ADSB, of course. "How interested am I an ADSB?" I dunno. I played with
it a little and got bored soon enough seeing planes in a groove flying into
LAX and flying out of LAX over the mountains to my North East. (Remarkably
few flights seem to use ONT to my South.)
{^_^} Joanne/W6MKU
Post by Jay SalsburgI have a 3 meter extension on my SDR. Since the data rate for these dongles
are not pushing the limits of USB, it is possible to use those long extender
cables. I bought mine at Amazon.
-----Original Message-----
Sent: Thursday, May 29, 2014 6:06 PM
Subject: Close to antenna or close to PC?
Hi,
Someone suggest buy a 6 feet USB extension and plug USB just next to
antenna. Is there a performance comparison somewhere on the web? Is there
any trade off?
Thanks
Dan
Sent from my iPad
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