A new front end (that part of the VLF receiver between the antenna and demodulator) designed to copy both USAF and USN transmissions could address some of these problems, but this feature would add new problems of additional signals from transmitters occupying dense space in frequency. Relying on Navy VLF Transmitters dispersed around the world could pick up the slack, but current USAF VLF receivers cannot tune to them. Furthermore, the threat to Nuclear Command Control and Communication (NC3) has arguably become more adaptable and global, demanding that USAF EAM reception become more adaptable and global in response. Since that time, USAF VLF transmitters have significantly decreased, providing a much weaker signal for VLF receivers to copy. Receivers were designed in the 1970s and 1980s to accomplish this task in certain environments, against certain threats. DESCRIPTION: Current airborne VLF receiver technology for Emergency Action Message (EAM) reception must meet stringent reception capabilities in harsh environments. The technology requires high sensitivity for distance reception of weak signals in the 14kHz to 60kHz range and high selectivity to discern a signal of interest from crowded VLF band. Home Contact info Matt Tucker Escondido CA.OBJECTIVE: Demonstrate new VLF receiver front end for NC3 airborne missions. Steve McGreevy A good explanation of a whistler Times a year, I haven't bothered to trace the oscillation down.Ī VLF listeners guide by "Mr. Since I still get plenty of volume and I don't use it more than a few
The only glitch with the unit is when the volume knob is turned up for almost full volume. I probably wouldn't have used the DC-DC converter because theyĪre expensive, but I received mine for free. Eventually I got a small DC-DC converter that takes 9V from a single battery and gives youĪn isolated 9V that can be used for the -9V. BT1īT2 on the schematic represent two 9V batteries that are set up to provide + and - 9V to power the The audio amplifier is the well known LM386 (also sold at Radio Shack). I got a great clearance deal on a radio shack speaker that wouldn't fit I used a Radio Shack box (not sure of the part#) that is a bit larger You can't miss my happy go lucky drilling that Switch, speaker on/off switch, and headphone jack. Looking at the picture to the right, you might be able to make out the red volume knob, LED (power on indicator), power on/off You are still going to here 300 HZ just fine. Since the filter has a fairly shallow roll off (slope) Plenty of pops and crackles, but keeps the 60HZ hum down. The filter created by the second op-ampĪnd surrounding components creates a 12dB/octave 600Hz high pass filter. Yard or parking lot for the reception to be acceptable. You still will have to be outside in the middle of Without getting too much hummm in your ear. It will let you listen at less than ideal locations Unfortunately, most of us don't live in a area where we can get miles away from the nearest power wire.įor that reason, the high pass filter was added. You will get beautiful reception that way. The receiver is meant to be used far from civilization. That means that you can't be anywhere near a wire carrying 120V 60HZ ( or like). Because this unit is a low frequency receiver, it is very good at picking Since TL082CP package has two op-amps inside, I used the second sectionĪs a high pass filter. That is why I chose to use a FET input op-amp (TL082CP). One of the most important features of Steve's design was a FET input for McGreevy's design (linked below) I was able to design my own I do not know my RF very well, but looking at Stephen P. That is the main circuitĪnd it is up to you to add a power LED, headphone jack, power switch, and other bells and whistles as To a volume control R3 and then to the well known LM386 audio amplifier IC. Of the low frequencies (trying to get rid of some unwanted 60HZ signal). The signal is then passed on to U1B to filter out some The links areĬ3 and C7 pass high frequencies to ground that were picked up by the antenna.Īnd get amplified slightly (gain=1+(2.2K/1K). The correction is : R6 should go to the other end of C5, where it connects to the + input of the TL082. Note that there is an error in the schematic.
You can view the schematic of my circuit in either the PDF format (preferred) or as a. Were received in remote locations after many hours of listening. "whistler" (a several second tone decreasing in frequency) right away. Don't be disappointed if you don't hear a Some of the links below have sound files of VLF "signals". This VLF (very low frequency) receiver is used to pick up natural occurring low frequency radio waves created by nature.