A WebSDR is a Software-Defined Radio receiver connected to the Internet, allowing up to 80 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 antennas are two Clifton Labs Active Antennas.
The 160M antenna is an Inverted L with the L at 30 meters high (no
preamp). One active antenna is on 80M, 40M, and 20M. The other active
antenna feeds the 75M and QSR1 receivers.
The QSR1 receiver provides 7 bands of CW callsign decoding simultaneously. Connect directly using telnet to w4ax.com port 23. It also feeds the Reverse Beacon Network.
The active antennas plug into two separate Clifton Labs DC Power Couplers to provide power to the antennas.
The Power Coupler connects to an RF Input Limiter to prevent destroying the pre-amps 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-amps. (note: there will be massive disruption of received signals when I transmit.)
The next stage are two separate Clifton Labs Norton Pre-amps which have a +11 dB gain from 100 KHz to 30 MHz.
These stages in the chain then feed 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. Recently I've added a fifth Tony Parks RX Ensemble receiver. Since it has an Si570 oscillator this receiver can be placed at any frequency between 160M and 10M via a software command. Users of the sytem cannot make this change but I will move it to different parts of the band from time to time. Perhaps a CRON job is in the future to move it to different frequencies based upon the time of day.
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
five ASUS Xonar D1
and the motherboard Creative Labs sound card all at 192 KHz sample
rate. To accommodate 80+ users an
Internet connection with 40 Mb of upload bandwidth is used. Each
user connection consumes about 200 kb of upload bandwidth. Total
upstream content is 1.5 TB monthly.
Information about W4AX is available at QRZ.com.