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Showing posts from June, 2013

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 leng…

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 lower…

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, and thi…

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 …

Antenna Topics: A Field Day Vertical with elevated radial system. Post #201

With the ARRL Field Day coming on 22-23 June 2013, there are plenty of antenna ideas floating around cyberspace.  Part of the fun of Field Day is the erecting of familiar antennas such as dipoles, verticals, loops, and hexbeams.  Now and then, a three or four element beam is pressed into service thanks to a generous club member, some fiberglass and metal tower sections always seem to appear, or even a "cherry picker" truck loaned by a service-minded company such as a tree trimming business, the telephone company, or the local cable company makes an appearance.  A good antenna raising team can put a formidable tower and beam into the air in a matter of a few minutes.

But what happens when you operate a Field Day station as a single operator, single transmitter entry with no other team members to help you?  You are the antenna raiser, the cook, the tent builder, and the over taxed operator.  Don't dispair.  With a little planning, you can pre-assemble a simple antenna tha…

Antenna Topics: A modified inverted v antenna for Field Day. Post #200.

The ARRL's Field Day is coming Saturday and Sunday, 22-23 June 2013.  Thousands of amateur radio operators in the USA and Canada will be trying to establish contact with fellow amateurs around the world in one of the oldest emergency communications exercises in existence.

Although many amateur radio operators will be joining their clubs at public parks, schools, and public safety buildings for the exercise, many amateurs, including yours truly, will be operating from our homes and even our work sites.  For those of us running in the single operator, single station category, our Field Day group belongs to us only...we are responsible for everything in our portable or home stations.  That means all antenna, cooking, and sleeping responsibilities fall on us.  Although I enjoy working with my amateur radio club (The Big Island Amateur Radio Club), there are times when I can't  drive out to the Field Day site and must work alone.

With that in mind, it pays to "pre-arrange&quo…

Antenna Topics: A Field Day Delta loop. Post #199

Over the course of the next few weeks, I'll be describing some of the simple amateur radio antennas suitable for the ARRL 2013 Field Day Communications exercise.  These antennas will be transportable for remote operations, easy to build, easy to take down, and will offer good performance under "field" conditions.  Most of the materials for these antennas can be found in the nearest hardware or home building supply outlet.

When you are done using these antennas for field day, store them in your shack for future use.  If these antennas perform well for you, consider erecting them on your property for regular contacts with your ham friends.

In my last post, I described a sloping dipole fed by 450-ohm ladder line.  Along with its associated 4:1 balun and a hefty antenna transmatch ("tuner"), this antenna rendered service on 40, 20, 15, and 10 meters.  I still use my sloping dipole when I operate on the weekends at a public park or some deserted pasture above my h…

Antenna Topics: A Simple Field Day Antenna

The ARRL (American Radio Relay League) 2013 Field Day is set for Saturday and Sunday, 22 June through 23 June 2013.  This is one of the biggest emergency communications exercises in the country and it attracts thousands of amateur radio operators to field day sites throughout the United States and Canada.  Many DX stations around the world participate in this event, so, if it's DX you're looking for, Field Day may just be the place for you.

Because of work or family responsibilities, many amateur radio operators can't join their clubs at a Field Day site.  Instead, these amateur will operate from their homes, using a variety of emergency power configurations, ranging from generators to solar-charged batteries.  Amateur radio operators specializing in emergency communications will run stations from civil defense headquarters, police stations, and even public schools.

Field Day will give you a taste of an intense, but fun operating experience without the comforts of home.  …