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Showing posts with the label antenna

Simple Ham Radio Antennas: The 10 meter 1/2 wavelength sloper. Post #262

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The sloping 1/2 wavelength dipole is one of my favorite antennas.  "Slopers" are good antennas for restricted space areas.  They are simple to build, inexpensive, and exhibit some directivity in the your chosen direction. According to VK6YSF, VE2DPE, and other amateur radio operators, a properly designed 1/2 wavelength sloper radiates energy at low angles relative to the horizon with vertical polarization.  Slopers don't require a ground radial system and can be fed with a good grade of 50 ohm coaxial cable.  A sloper antenna only requires one tall support (tree, mast, edge of a roof, etc.) and occupies less space that a 1/2 wavelength horizontal dipole. So, let's build one of these simple, effective antennas for the 10 meter band , centering on 28.4 MHz --right in the middle of the techncian class phone band. MATERIALS: One tall support.  In my case, I used a 33-ft/10.06 meter MFJ telescoping fiberglass mast.. One 5-ft/1.52 meter wooden stake to support

Simple Ham Radio Antennas: A Low HF Band Triangle. Post #259

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Over the past few years, I've built a variety of HF antennas for my amateur radio station.  All of my verticals, inverted vees, dipoles, and loops have been a learning experience, especially when I've been faced with limited resources and space.  Operating from an apartment or a home governed by CC&Rs and HOAs has been a challenge. Now that I'm slowly moving into a full acre of space in the rural Puna District of Hawaii Island, my space restrictions are gone and there are no committees to oversee my antenna activities.  I count this as a definite blessing.  For the first time in many years, I can build full sized dipoles, verticals with a decent ground system, and large full-wave loop antennas without interference.  Since my new property is surrounded by tall trees approaching 50 feet/15.24 meters, my antennas are well shielded from prying eyes.  When I operate out of my rental home in Laupahoehoe, I'm still hemmed in by utility poles and neighbors.  My antenna

Simple Ham Radio Antennas: Antennas without "tuners", part 3. Post #256

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In some of my previous posts, I've investigated, built, and used multiband dipole and inverted vees using a single 50 ohm coaxial feed line .  With a telescoping fiberglass mast (33-ft/10.06 meters extended), a simple halyard and pulley system, and separate antennas cut for each band of use (40, 20, 15, and 10 meters), I've been able to change bands fairly quickly by lowering the dipole/inverted vee elements, substituting those of another band, and raising the new antenna.  With each band element cut for the desired frequency, the efficiency is high with low swr for that band.  Since each antenna element is trimmed for the lowest swr at my mast location, an antenna transmatch isn't necessary.  Sometimes, as in the case with the 40 meter dipole/inverted vee, an antenna cut for the cw portion of the 7 MHz band will often work well on the phone portion of 15 meters (21 MHz band). The 15 meter band will operate on the third harmonic of the 40 meter band . In order to save

Simple Ham Radio Antennas: Antennas without "tuners", part 1. Post #254

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Antenna transmatches or "tuners" are wonderful devices that make amateur radio operations easier.  They can help minimize swr on antenna feed lines and extend the band coverage of your present antenna. However, there are times when such devices may not be needed, especially if you're designing an antenna for a single band or are contemplating an emergency or portable antenna for your "go" kit.  By carefully designing, cutting, and trimming your basic 1/2 wavelength dipole for the lowest swr, you can just connect a good quality 50 ohm coaxial cable feed line and run the band of your choice without much difficulty. In this post, I will describe a few simple coax-fed dipoles and inverted vees that will serve your favored amateur radio band without the need for an antenna transmatch .  Of course, you could always insert a transmatch into the system to squeeze out the maximum power at the lowest possible swr if you so desire.  These antennas work either way.  

Simple Ham Radio Antennas: When to use antenna tuners. Post #253.

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Nowadays, the antenna transmatch ("tuner") is an integral part of many amateur radio stations.  With this device, a ham can match the output of his/her transceiver with the often unknown impedance of the antenna itself.  With a suitable balun (balanced to unbalanced) transformer, it is possible to use one antenna to cover several HF bands, especially if you're facing space restrictions on a small lot or have  to operate in "stealth" mode because of HOAs and CC&Rs.  This situation applies mostly to the use of 300 ohm tv twin lead and 450 ohm ladder line, which require a balun (1:1 or 4:1) and antenna transmatch to operate as feed lines in a multiband, single antenna system. There are times when you may not have an antenna "tuner" at your disposal, especially if you're operating in portable or emergency situations.  In my case, I remove my Drake MN-4 and MFJ 941-E transmatches from the antenna system for routine maintenance several times a