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BROADBAND
DISCONE ANTENNA
KIT
Ramsey Electronics Model No. DA25
Looking for a broadband antenna with a full 360 degree
coverage? Discover what communication professionals have
known for years using a “discone” antenna. Use this antenna to
bring a multitude of signals out of the noise making it ideal for
scanners and Ultra High through Microwave Frequency
receivers! Search the airwaves for signals with this unique kit!
• Omni directional performance, no need to point in any dir
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RAMSEY TRANSMITTER KITS • FM100B Professional FM Stereo Transmitter • FM25B Synthesized Stereo FM Transmitter • MR6 Model Rocket Tracking Transmitter • TV6 Television Transmitter RAMSEY RECEIVER KITS • FR1 FM Broadcast Receiver • AR1 Aircraft Band Receiver • SR1 Short wave Receiver • SC1 Short wave Converter RAMSEY HOBBY KITS • SG7 Personal Speed Radar • SS70A Speech Scrambler • BS1 “Bullshoot
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Ramsey Publication No. MDA25 Price $5.00 KIT ASSEMBLY AND INSTRUCTION MANUAL FOR BROADBAND DISCONE ANTENNA KIT DA25 TABLE OF CONTENTS Introduction .................................4 Discone Circuit description .........8 Parts list ......................................10 Assembly instructions .................11 Installation and Important notes ..16 Using your DA25 ........................17 Troubleshooting guide ................ 17 Warranty ..............................
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INTRODUCTION In today’s ever growing “wireless” society, it almost seems a bit ironic that antennas have become less and less the topic of interest in hobbyist circles. The recent advances in wireless technology have shrunk antennas to ever smaller an unobtrusive sizes. An example of this is the cable television industry. They have removed the larger “traditional” antenna arrays that were once commonplace for TV reception and replaced them with a single wire or two entering the household.
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before we snapped the rope, the sound waves would arrive much quicker than the “rope wave” would. In the case of radio waves, the rate at which the waves travel is much faster, reaching the speed of light (186,000 miles / second, or 8 about 3x10 meters / second) in a vacuum. Radio waves do travel slightly slower in air however. In a wire transmission line, they travel even slowly! Frequency and Wavelength Since all antennas collect electromagnetic waves, lets take a moment to think about
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What Are We Driving At? Time to pull some of that theory together and get some answers: Since: λ = v x T And T = 1 / f We can substitute and get: λ = v / f Since the velocity equals “c” we wind up with: λ = c / f The wavelength of the radio wave equals the speed of light divided by the frequency. Lets plug some numbers into our equation and work out a few wavelengths. We should notice some other properties of electromagnetic waves. 8 If f = 450 MHz
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one radio frequency (or RF) cycle. Since the charge traverses the wire twice, the length of wire needed to permit the charge to travel the total distance in one cycle is λ / 2, or one half the wavelength. Therefore, the shortest resonant wire length will be one half wavelength long. Let’s consider a “half wavelength” example to help it make sense. Picture a trough with barriers at each end. If a rubber ball is rolled along the trough from one end to the other it will hit the end and bounce
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What About Impedance Matching and VSWR ? Another consideration with electromagnetic wave antennas is the “match” presented to either the receiver or transmitter. In our discussion of wavelength and resonant frequencies it became apparent that the length of the antenna is critical to match that of the desired frequency. A small error in length can detune an antenna significantly and inhibit the antennas performance. For many communications systems, 50 or 75 Ohms are the desired “magical”
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Coaxial Cable Center Conductor Disk Coaxial Cable Shield Cone Mounting Pipe Coaxial Cable Ramsey offers two models of this particular antenna, one with no active components and the other with a low noise preamplifier to further boost the antenna gain. The DA25 kit which you are about to assemble is the non-preamplified version. The advantages to this particular model are its ease of use (no external power required) and the fact that it can just as easily be used as a transmit antenna
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PARTS SUPPLIED WITH YOUR DA25 KIT 1 3 Qt. funnel “cone” 1 7 inch pie-plate (CAUTION, EDGES MAY BE SHARP!) 3 #6 – 32 x 1/4” screws 3 #6 – 32 M-F stand-offs 3 #6 – 32 nuts 1 DCA2 circuit board 1 PVC coupling 1 3’ BNC cable RAMSEY "Learn-As-You-Build” KIT ASSEMBLY There are solder connections on the DA25 printed circuit board. Therefore, PLEASE take us seriously when we say that good soldering is essential to the proper operation of your discone a
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DA25 DISCONE ANTENNA KIT ASSEMBLY Although we know that you are anxious to complete the assembly of your an- tenna kit, it is necessary to assemble it in a specific order to insure the proper operation of the finished unit. Try to avoid the urge to jump ahead installing components. Since you may appreciate some warm-up soldering practice as well as a chance to put some landmarks on the PC board, we’ll first install some of the larger mounting components. This will also help us to get
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1. Carefully “tin” the center conductor of the cable by adding a small amount of solder to the twisted center conductor. Use care not to leave the soldering iron in contact with the wire for too long as it can melt the center insulation. Tinning allows us easier installation of the coaxial cable to the circuit board assembly and minimizes the chance of overheating the wire when this installation occurs. Have a look at the diagram to see what the complete “pre-assembled” cable should look
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Solder Here Bottom (Copper Plated) side Solder Here Coaxial Cable Now we are getting somewhere! All your careful preparation will pay dividends as we install the coax cable to the circuit board. We did this first as it can be quite difficult to perform this operation once the circuit board is installed on to the cone. 5. Using the 3 #6-32 screws provided, insert them through the circuit board as- sembly as shown. Fasten the screws into place using Bottom (Copper Plated)
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Solder Points 6. Install the circuit board assembly to the funnel cone as shown. Use care to center the circuit board before you solder the assembly completely. It may be easier if you “tack solder” the board into place before you run a ring of solder completely around the board. Careful now, the entire assembly will be quite hot while you are constructing this. You may want to use gloves to protect your fingers from being burned (Ouch!!). Solder all the connections using enough heat to f
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Solder Here 8. Solder the center conductor wire into place on the disk section of the an- tenna. Trim off any excess lead that is protruding from the disk. Have a look at the above diagram to help out if necessary. CONGRATULATIONS ! Your discone antenna is now complete! Have a final look over your work, paying particular attention to the solder connections. Remember that any problems you find now can save time and effort after the unit has been mounted. DA25 • 15
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Glue Here INSTALLATION OF THE ANTENNA MOUNT When you are satisfied that your solder connections are “just right”, we will install the PVC antenna mast coupler included with the kit. The mast mounting is a 1” PVC coupler. We recommend that you glue the coupling into place with some RTV or contact cement. Be sure to fit the coupler firmly into place after threading the cable assembly through it. If the glue sets up with the coupling in a little tilted, you will forever see a slightly “off
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USING YOUR DA25 DISCONE ANTENNA Now we are ready for the moment of truth, the running of your discone an- tenna. Were pretty sure by now you have a place selected to install it, you can use a couple of nylon wire ties and a bit of 1” PVC pipe to fasten it into place. A fairly good “poor mans” test is to search on your scanner or radio receiver for a weak station, one that is barely breaking the threshold of your receivers sensitivity. Note your signal strength indication of the station, and
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CONCLUSION We sincerely hope that you enjoy the use of this Ramsey product. As always, we have tried to compose our manual in the easiest, most user-friendly format that is possible. As our customers, we value your opinions, comments, and additions that you would like to see in future publications. Please submit comments or ideas to: Ramsey Electronics Inc. Attn. Hobby Kit Department 590 Fishers Station
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The Ramsey Kit Warranty Please read carefully BEFORE calling or writing in about your kit. Most problems can be solved without contacting the factory. Notice that this is not a "fine print" warranty. We want you to understand your rights and ours too! All Ramsey kits will work if assembled properly. The very fact that your kit includes this new manual is your assurance that a team of knowledgeable people have field-tested several "copies" of this kit straight from the Ramsey Inventory. If
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DA25 DISCONE ANTENNA KIT Quick Reference Page Guide Introduction ...................................... 4 Discone Circuit description ............... 8 Parts list ........................................... 10 Assembly instructions ...................... 11 Installation and Important notes ....... 16 Using your DA25 .............................. 17 Troubleshooting guide ...................... 17 Warranty .......................................... 19 REQUIRED TOOLS • Soldering Iro
