Posts

Antenna Topics: A Junk Box Vertical. Post #206

I've been a "radio junkie" since age 8 when my father and I built a crystal set in the garage.  I was amazed what a Quaker Oats cardboard cylinder, some enameled wire, a crude slider, a piece of pyrite, a "cat's whisker", and a pair of high impedance headphones could do.  With about a hundred feet (30.48 meters) of #14 AWG house wire and a good ground, I was able to capture many AM broadcast stations, many all at once.  The pyrite crystal wasn't too selective, but I did have fun. From there I graduated to better receivers and some homebuilt Heathkit audio equipment.  Although my father was a "stereophile" and appreciated good jazz and classical music, he never did become an amateur radio operator.  I kept putting off getting my amateur radio license until I left the Air Force and became part of a commercial broadcast station.  One of the engineers at KHLO-AM (Hilo, Hawaii) finally persuaded me to take the novice examination.  Once I got the

Antenna Topics: Antenna Trimming Shortcut. Post #205

Most of us who use the general formula for a half-wavelength flat top dipole (468/f (Mhz)=L (ft), rarely give much thought on how accurate the dipole length really is.  We cut the dipole to its calculated length, cut the wire in half, attach center connector and insulators, attach a length of 50 or 75 - ohm coaxial cable, suspend the wire between two tall supports, and prepare for a day of radio fun.  In most cases, your dipole will work well, although a little trimming or pruning may be necessary to bring the wire antenna into resonance. I'll admit to being lazy in this department.  As long as the SWR falls below 1.5 to 1, I don't bother trimming.  Even if the SWR hovers around 1.7 to 2.0 to 1, I always can use my trusty Drake MN-4 to bring the SWR below 1.5 to 1. Suppose you wanted to make your antenna (in this case for 40 meters), as resonant as possible and do without a tuner altogether?  Instead of cutting and trimming, wouldn't it be nice just to cut the dipole l

Antenna Topics: Using your mobile station as your base antenna. Post #204

An article by retired ARRLTechnical Editor Joel Hallas (W1ZR) in the July 2013 issue of "QST" offered me another idea of operating in "stealth mode."  Hallas outlines a simple way to use your mobile antenna as a base antenna in areas where restrictive CC&Rs and HOA's prevail.  With a few simple components, you can use your vehicle-mounted antenna as your main antenna when everything else fails. Thanks to the use of two Bias Ts (devices that allow dc to share a coaxial cable without interferring with the RF), " you can easily supply power from your home shack to the vehicle's antenna system."  Hallas continues by saying that "the bias T at the end of the coax removes the dc.  The dc can either be used to power an automatic antenna tuner, or provide power to run a motorized antenna."  Hallas says "the usual  'monoband' mobile whip, either those with lumped loading inductance or helically loaded types, can be used on lowe

Antenna Topics: A Simple Multiband Vertical Antenna. Post #203

While I was searching for some antenna projects on Thursday (20 June 2013), I came across an antenna book I bought 25 years ago to help a new amateur radio operator make his first HF antenna.  The "Novice Antenna Notebook"  by Doug DeMaw, W1FB (SK) contains a wealth of simple, effective antenna ideas suitable for any license class.  I was drawn to this book a quarter century ago because it explains complex antenna theory and design in a simple, easy to understand manner.  I've used several of DeMaw's designs for my portable and emergency antennas.  All have worked successfully. I decided to return to my own novice/technician days (1977-1978) and create one of the simple antennas that got my friend on the air. The simple multiband vertical antenna described by DeMaw is easily made, cheap, and performs very well. As DeMaw says, "you may want to keep things simple when you erect your first multiband vertical...simplicity denotes reduced cost for materials, an

Antenna Topics: A Field Day Dipole. Post #202

One of the simplest and most efficient Field Day antennas is the common half-wavelength flat top dipole or doublet stretched between two trees or portable masts and fed with 50-ohm coaxial cable (RG-58, RG-8, or RG-8X) for single band use or fed with 450--ohm ladder line, a 4:1 balun, and an antenna transmatch ("tuner") for multiband use.  I 've used this type of antenna in various configurations, included the inverted vee and the half-wavelength sloper.  For single band use, I've also employed 75-ohm RG-6 coaxial cable with "F" to "UHF" connectors.  Used with an antenna matchbox, the RG-6 serves as a suitable  feed line if 50-ohm cable is unavailable. Placed a height of 30 to 50 feet above ground (9.14 to 15.24 meters), the  doublet will give you plenty of local and DX contacts.  Just cut your 2 antenna elements to the lowest frequency of use, feed with ladder line  into an appropriate balun and antenna matchbox, and you have an antenna capable