WebSDR de W4AX

A WebSDR is a Software-Defined Radio receiver connected to the Internet, allowing up to 40 users to listen and tune it simultaneously. SDR technology makes it possible that all listeners tune independently, and thus listen to different signals; this is in contrast to the many classical receivers that are already available via the internet.

The antenna is a Clifton Labs Active Antenna. The 160M antenna is an Inverted L with the L at 30 meters high.

The antenna plugs into a Clifton Labs DC Power Coupler to provide power to the antenna.

The Power Coupler connects to an RF Input Limiter to prevent destroying the pre-amp when using my legal limit amplifier. I can't get the WebSDR antenna out of the RF pattern of my ham radio stations antennas so it is important to protect the front end of the pre-amp. (note: there will be disruption of received signals when I transmit.)

The next stage is a Clifton Labs Norton Pre-amp which has a +11 dB gain from 100 KHz to 30 MHz.
This stage in the chain then feeds a 1 to 3 RF splitter. This device maintains a 50 ohm input impedance to each of the receivers and provides isolation between ports to minimize receiver local oscillator interference. The penalty is a 5 dB insertion loss. At this point in the chain there is an overall +6 dB gain on the signal going to the receivers.

Finally, the signal is received by four separate Tony Parks, KB9YIG SoftRock Lite II receivers on 160M, 80M, 40M and 20M. These receivers convert the RF to I & Q signals to be processed by the WebSDR software on the computer. Their performance is amazing considering they cost $20 USD each.
My WebSDR server consists of a PC running Ubuntu and the WebSDR server software. It is a quad core processor with 12 GB of RAM. Sound cards are three ASUS Xonar D1 and the motherboard Creative Labs sound card all at 192 KHz sample rate. To accommodate 40+ users an Internet connection with 40 Mb of upload bandwidth is used. Each user connection consumes about 200 kb of upload bandwidth.

Information about W4AX is available at QRZ.com.

http://www.w4ax.com/

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