BBC DRM Digital Shortwave
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Digital Radio Mondiale (DRM) is a technology that allows high fidelity digital audio broadcasts to be made on regular analog radio frequencies. Mondiale is a French and Italian word meaning "worldwide." It requires a computer (or a computer chip inside the radio receiver) and a software program to decode the broadcast. In this case, I am using a computer with an external radio receiver on an outside antenna, a program to run the receiver, and a program to decode the DRM broadcast.
Using an SDRPlay RSPdx with SDRUno software and Dream DMR decoder I was able to receive a very fine DRM broadcast from the BBC on 3955 KHz. The antenna is a 204 foot Inverted L about 50 feet above ground level with a 9:1 UNUN at the base fed with coax. This DRM signal was received on 01-05-2024 at 06-57 UTC in Dennis MA US.
Listen to the recording using the player below.
You can hear how clear the signal sounds. It is FM radio quality without any static. The occassional drop-outs were bursts of atmospheric noise. This appears as noise on the raw DRM broadcast signal. Because the broadcast is being decoded from digital to analog, the noise disrupts the decoding so the noise appears as a drop-out (silence) in the decoded audio. The recording was made directly from the Dream audio feed to the computer.
Here is the QSL Card received from the BBC acknowledging the reception report.
Measure Height without Climbing
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In December 2023 I finally was able to raise the height and length of my End-Fed Longwire Antenna for 160 meters through 10 meter Ham Radio use. The main objective is to get the antenna as high as possible above the ground. Since it is dangerous for me to climb trees and it's expensive to hire professionals I decided to try an alternate method - the Tennis Ball Launcher.
I fill a tennis ball about half way with sand, attach it to a strong fishing line, and use an air cannon pressurized to 80 psi to fire the ball and string over the trees. Once the ball and line is found on the other side I attach a strong nylon marine rope to the fishing line and pull the rope across. After the rope is pulled to the other end I attach the wire to the rope and pull the wire.
Since tennis balls were involved, my dog Gracie seemed to think it was playtime. Of course, when she is with me, it's playtime all the time.
Now that I have my new wire antenna installed in the trees I wanted to determine exactly how high it is above the ground without having to climb to the top of a tree. I knew I could use trigonometry to solve this problem. If I could measure an angle from a viewing point to the top of the tree and then measure the distance from the viewing point to the tree I could calculate the height of the tree. Thank God I was paying attention in Algebra 2 and Science classes.
In order to measure the viewing angle I had to acquire or make a Clinometer. This was easily fabricated using a protractor and a weight.
I drilled a hole at the end of the moving straight part and attached a heavy weight. In this case it was a plumb bob. I hot-glued two tubular cylinders on the straightedge to look through when sighting the tree top. When I center the top of the tree while looking through the cylinders the weight will cause the straightedge to measure the viewing angle. The viewing angle Θ is 90° minus the angle shown on the protractor.
Here is a photo of the Unun I wound for the end-fed longwire antenna. Because the antenna is non-resonant, the Unun is a 9:1 device. I stacked three FT-240-31 Type 31 ferrite cores and passed nine turns of three conductor wire through the core.
The three coils are connected in series as shown in this diagram. Three ferrite cores were stacked to handle higher power. With only one core the energy will saturate the core and power will be lost in heat.