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Online SDR
What is Online SDR?
First, what is SDR or software defined radio? For many years superheterodyne circuit design was the standard way to build a radio receiver. This technology was patented in 1917 by Edwin Armstrong and has served as the most practical way to build a radio receiver for all forms of radio signals. While practical and reasonably inexpensive, the design was hardware centric and was often limited to designed frequencies with little flexibility.

As the PC became more powerful it became possible that most of a radio receiver could be handled in the digital domain using the CPU in the computer for signal processing, amplification, and demodulation. The result is less expensive hardware since often the hardware was only preamplification and converting the incoming RF stream into digital data.

In recent years low-cost wideband software defined receivers (SDR) have become available that coupled with various PC software packages provide decoding of both commercial as well as amateur communications. These low-cost solutions are an excellent way for new amateurs to tune into a wide variety of amateur bands and monitor the activity. Quite often the investment in hardware ranges from $40 to $400 with the needed software being free. The frequency range for these devices varies but units with coverage from 500KHz to 1.7GHz is common.

But you don't need to buy anything to take advantage of SDR. All you need is a PC with an internet browser. To learn more, check out these links.

Background on SDR
ARRL - If you are a member the ARRL has a number of articles on SDR technology. If you are not a member this is still worth taking a look as a number of articles are still available to non-members.

RTL-SDR.COM - This site is a news site that covers all aspects of SDR hardware and software. If you are interested in purchasing your own solution this is worth a look.

Wikipedia - A complete overview of the hardware and software including charts and diagrams.

Hardware SDR Solutions
RTL-SDR - is a very popular dongle solution that simply plugs into your USB port on your PC.

SDR Play - A very popular and well-known solution to many amateur operators. Offering more hardware features than the typical dongle solution and includes a number of software packages for frequency monitoring or spectrum analysis.

KiwiSDR - An HF focused SDR solution with a frequency range of 10 KHz to 30 MHz. Fully self-contained and does not require the PC for anything other than a web browser. This solution is used in a variety of online monitoring sites.

Online SDR Listening Sites
WebSDR - This is a Software-Defined Radio receiver connected to the internet, allowing many listeners to listen and tune it simultaneously. There are sites located around the world.

KiwiSDR - Similar to WebSDR in that sites are located around the world and are available for users to tune into the supported frequencies.

Northern Utah WebSDR - A very popular site with links to four online SDR receivers. Several of these sites have substantial antennas. Also see their "how to" videos on YouTube.

Specific Sites on the West Coast of California
KA9Q - This KiwiSDR is in San Diego and has a reasonably low noise level.  This station uses an inverted vee antenna.

KB6C - This KiwiSDR is in Ventura and hears the San Diego 75/60 meter nets pretty well.

UCSD - This KiwiSDR at UCSD is located in the La Jolla area of San Diego.  This station has a high noise level and a vertical antenna that is not optimum for NVIS.

KPH - The Point Reyes, CA KPH receiver site.

Thanks to Brian, N6CVO and Rob, K6RJF for inspiring this page.
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