Our WebSDR Installation
Some time ago folks were unhappy that many of the Green Valley stations were difficult to copy on the various 20 meter nets. Casey, KF7RCS, took the initiative to build a webSDR and install it at his residence. It indeed worked well, but it seemed likely it would work better if placed at our Elephant Head site. This is a rundown describing that installation.
The heart of the system is shown in the picture SDR. The small package labeled rtlSDR to USB Hub is one half of a state of the art receiver. The output is fed to the other half, an Arduino computer, where the SDR output is massaged into what the user wants to hear. The USB Hub shown connected to the rtlSDR unit is there only to provide power to the unit that the Arduino is not able to do. The remaining white box is a router in which Casey can make the output of the WebSDR available to users on the internet. Ignore the IP address shown on the Arduino, access is via http://44.62.11.162:8901
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Ultimately the equipment was located in a data cabinet that also houses the 145.29 analog and the 449.375 DMR repeaters. The picture CABINET shows Ron, AA7RP working on equipment. The photographer didn’t notice the wires in Ron’s face when the picture was taken, but that’s the way it really is in that box.
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Of course, it is a radio and radios require antennas. Location is one of the key ingredients and in the picture VIEW we can see how this site actually overlooks Elephant Head in the foreground and shows Green Valley and Sahuarita in the distance. Ed, N9MW, set about building a vertical antenna that could withstand the weather elements on the ridge. Dave, K2SS, contributed heavy duty aluminum for the vertical section. A vertical is appropriate as most local line-of-sight users are limited to “flagpole” type antennas. A dipole would be cross polarized to most local signals and would cost about 30db attenuation.
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Performance met and exceeded our expectations. Well, not really, we were all very confident this thing was going to play very well. But, it’s not perfect.
Picture SDR VERT SWR shows the theoretical SWR curve and in fact the antenna appears to be best about one megahertz higher. At this time there are two issues to resolve, is the measured performance really what it is at 75 ohms or are the calculations off because there is no such thing as “real ground” up there on that rock for the modeling program to utilize. We can adjust the radial length since it is a raised radial system but, tweaking the system will probably not improve performance very much as users report excellent reception to and from the system.
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