Thursday, August 9, 2012

Simple Antennas for the Amateur Radio Operator--a continuing series

KH6JRM's Amateur Radio Blog

Post #182

Stealth and hidden antennas

One of my favorite interests within the Amateur Radio hobby is hidden, disguised, and "stealth" antennas.  I'm amazed at the creative ways amateur radio operators stay on the air despite severe space limitations, restrictive housing regulations, and proximity to power lines.  I'm one of the lucky ones--I do have a backyard.  It's small, but it does allow me to keep most of my HF and VHF antennas outside.  I'm always a little uneasy about using indoor antennas.  There are interference and rf exposure issues indoors which are sometime difficult to solve.

Whenever I feel the need to design a concealed antenna, I often refer to the work of Simone, IW5EDI, an Italian ham residing in the beautiful city of Florence.  Ham radio aside, Florence is a true wonder of the world.  I was in that city many years ago and was impressed with its cultural and historical background, parks, and natural surroundings.  Simone has writen a series of articles on stealth antennas that may give you some ideas on how to get on the air without annoying neighbors or homeowner associations (HOAs).

Simone lives in a third floor apartment which leaves him little room to erect a full-sized antenna for 40 meters.  However, by using an AEA magnetic loop antenna (MFJ sells a similar model) and a ham stick vertical with a tuned counterpoise, Simone is able to pursue his amateur radio interests without drawing attention to his station.  In a series of photographs, Simone shows how well the magnetic loop blends in with the furniture of his patio.  His 40-meter hamstick antenna is bundled with a bunch of fishing poles in the corner of his patio, with a counterpoise wire running through his apartment.  He tunes the ham stick with a wire tuner.  From the street below, one can't tell there are two HF antennas in his apartment.

Although my space problems are not as bad as Simone's, I've lived in places where the backyard is virtually non-existant and the neighbor's apartments are just a few feet away.  I'm blessed with good neighbors who don't seem to mind my homebrew vertical and delta loop in the backyard.  When I'm not operating, these antennas are nested to the ground, both for reducing the environmental footprint and for lessening the chance of a lightning strike.

Apparently, Simone has made antenna concealment an art.  He has submitted several articles to the "dxZone" website describing several vertical, loop, and dipole antennas he has designed and built.  In the use of stealth antennas, Simone says it's best to keep quiet about your antenna projects because "you can get blammed for every TVI, RFI, (and) interference incident in the neighborhood...'loose lips sink ships.'".

For more articles by IW5EDI, visit http://www.iw5edi.com.

That's all for now from this side of the Central Pacific.  Have an excellent day!

Aloha es 73 de KH6JRM--BK29jx15

Tuesday, August 7, 2012

Simple Antennas for Amateur Radio Operators--a continuing series

KH6JRM's Amateur Radio Blog

Post #181

A small loop antenna for limited space--the MFJ-1788 Super Hi-Q magnetic loop.

I'm a huge fan of loops.  They are quiet and can be hidden if creatively designed.  These antennas can be fed with either coaxial cable, ladder line, or ordinary 300-ohm television twin lead for a simple, effective antenna.  Loops do have their drawbacks.  A full-size 40-meter loop can be large--with a total length of approximately 141 feet.  In my situation, a large full-wave 40-meter loop fits under my house which is raised off the ground by pier and post construction.  A 20-meter full-wave loop is fastened under my garage roof.  Both of these antennas are invisible from the street or from nearby neighbors.  Since these loops are fairly low to the ground, they serve as NVIS (near vertical incident skywave) antennas, which give me strong signals out to 200 to 300 miles.  That range is perfect for afternoon nets and local emergency work.  The 40-meter loop is fed with 450-ohm ladder line and can work all bands from 40 to 10 meters.

But what can you do if a large loop isn't feasible for your situation or your backyard doesn't have sufficient space for a vertical with a suitable radial field?  MFJ Enterprises has manufactured a magnetic loop that can fit on a porch (lanai in Hawaii) or squeezed into a small spot in your backyard.  The MFJ-1788 Super Q magnetic loop antenna is rather expensive and a bit difficult to tune, but it may provide another way for you to get on the air.

In the 07 August 2012 issue of eham.net (http://www.eham.com), there is a review of the MFJ-1788, which can work from 40 to 10 meters.  A similar loop works 30 to 10 meters.  According to the amateurs who have used this loop, the antenna's performance is slightly less than an inverted vee or vertical.  Amateur radio operators reviewing the antenna fault MFJ for several quality control issues, which can be easily corrected with some basic tools.  The overall rating of the MFJ was 4.1 on a 5-point scale.  As N3OV states in the article, the MFJ-1788 is "expensive" ($429.95 USD) but  "not a bad package" for those who need an antenna with a small environmental footprint.  Although the MFJ-1788 is described by N3OV as "a bit of a chore to use" it does produce solid contacts.

Although I prefer homebrew wire antennas, I can see where this MFJ product could be useful in a limited space environment or for emergency use.  You may want to consider this product if your operating circumstances permit no other kind of HF antenna.  In the past, "QST" has published several articles on magnetic loop antennas.  A check in the magazine's on-line index should give you plenty of ideas should you choose to "roll your own."

Aloha es 73 de KH6JRM--BK29jx15

Monday, August 6, 2012

Mars and beyond--some random thoughts for Amateur Radio Operators

KH6JRM's Amateur Radio Blog

Post #180

Mars and beyond--some random thoughts about the Red Planet.

I was truly astounded as I watched the descent and successful landing of the "Curiosity" Mars Rover on Sunday evening, 1938 hrs local Hawaii Standard Time.  Of course, some of this was computer animation, but when those first grainy, black and white 64 X 64 pixel landing shots were received, all of the animation made sense.  The sophisticated cable release system did its job as the one-ton vehicle reached its intended landing zone.  Now, the testing and hard work begin.  As a sidenote, one of the 2004 rovers is still performing some of its mission, eventhough one of its wheels is stuck in sand.  It is continuing to send photographs of its surrounding environment despite the harsh martian conditions.  The American taxpayer has surely gotten a good return on those two earlier vehicles, as well as the intial data bank sent back by the two Viking landers in the 1970s. 

Speaking of survival in space, how about the Voyager 1 and Voyager 2 spacecraft?  Both of them are penetrating the perimeter of the heliosphere of our solar system and are ready to enter "deep space".  The RTGs aboard these craft are still working, albeit in a reduced fashion.  Pretty impressive work for a set of machines launched more than 38 years ago.  These craft are expected to send usable data from the edge of our universe for the next few years.

All of this takes me back to 1957, when as an impressionable 13-year old, I listened to the "beep, beep" of the first earth satellite--the soviet built "Sputnik".  I was visiting an amateur radio operator across the street one day after school when I heard him tune in the 20 mc (megacycles in those days) signal on his Collins receiver.  From that day forward, I was hooked on ham radio, shortwave listening, and all things electronic.  Although it took me many years to get my amateur radio license, that experience with "Sputnik" plus my work in the Air Force and engineering tasks  at several broadcast stations finally convinced me to take my code and theory test in 1976.  Back then, sending and receiving morse code were still requirements for amateur radio licenses.  Through the years, I've  held the entire range of amateur licenses--novice, technician, general, advanced, and finally amateur extra class. 

I suppose I wasn't the first kid to have been inspired by "Sputnik", "Vanguard", "Explorer I", and all the other early orbiters, but I felt the urge to learn more about the world of rf and the possibility of reaching new worlds.  While I lacked the imagination of the great science fiction writers such as Asimov, Clarke, and Bradbury, I could see life slowly imitating art as humanity pushed back the horizon of knowledge. 

And, now, here we are on the brink of new discoveries.  Many amateur radio operators have contributed to the fields of radio astronomy, deep space exploration, and communications.  I'm proud to be a part of this scientific community, although my contributions to the radio art are insignificant when they are compared the early pioneers of radio and the modern-day practitioners of the space sciences.  I wonder what Tesla, Marconi, or Popov would say if they witnessed what I saw on Sunday. 

So, as I design,build, and erect my homebrew antennas and squeeze the last electron from my aging equipment, I feel a distant kinship with the radio pioneers that went before me.  There's something "magical" and almost profound in sending out a signal and seeing what comes back.  Perhaps in the not too distant future, we earthlings will be able to bring up a repeater orbiting Mars and talk with the new "Martians" who have ventured far from home to seek the cosmos.  Ray Bradbury's "Martian Chronicles" may just happen...some of us may be around to hear that first qso.  That's when my mind drifts back to 1957 and hears the faint voice of man's first venture into space.  It's been a long journey from spark to space.  Who knows what will happen next?  This could be interesting.

Aloha es 73 de KH6JRM--BK29jx15

Friday, August 3, 2012

Simple Antennas for the Amateur Radio Operator--a continuing series

KH6JRM's Amateur Radio Blog

Post #179

Portable antennas for the unexpected

I've made it a habit over the past few years to keep an emergency "go" kit in my van in case I'm needed to provide communications backup for our local civil defense agency and the Hilo office of the American Red Cross.  Other than the 11 March 2011 tsunami (the one that damaged Japan and its Fukushima nuclear reactor), I haven't used my portable equipment that much, except for weekend operations in a local park or beach area.  When I worked at Pacific Radio Group, I kept an old Kenwood TS-520 and a Kenwood HT at the station for emergency backup to the Hawaii County Civil Defense office in Hilo.  But, since I retired, my forays into portable operation have been subject to personal whim or to opportunities I get handed to me.

Such is the case this weekend, where I revert to my 22nd year as the tower announcer for the Big Island Auto Club's monthly points meets.  I'm under contract to provide weekend drag race coverage for my former employer, as well as coverage during primary and general elections.  The work is part-time, which suits me fine.

Anyway, the track manager and I usually arrive at the track at around 0500 W to help the maintenance crew prepare the track for the races, which begin around 1100 W.  Since my work in the tower is fairly basic (turn on the generator, hook up the race computers, test the timing lights, and make sure track HTs are charged and working), I usually have a few hours of free time to explore amateur radio in a quiet zone just outside of Hilo town.  There are no power lines near the track, so all track power is produced locally by a state of the art diesal generator.  The track is very  quiet radio-wise until the race cars arrive--then you must put on ear protection to ward off the din of noise associated with drag racing.

As I've done in past races, I usually set up a mobile antenna on an adjoining chain link fence, run out several radials, and connect the arrangement to my trusty Drake MN-4 tuner with about 50-feet of 450-ohm ladder line.  Currently, I'm using a 54-inch Hustler mast with 40 and 20 meter loading coils.  The low-power Yaesu FT-7 provides the signal.  The early morning conditions shortly before sunrise are quite good on 40 meters.

When the track closes down after sunset, the clean up and lockdown of the track begins.  This task takes about two hours, depending on whether oil has spilled on the track or lights/sensors have to be repaired.  Tower clean up takes only about 30 minutes--mostly disconnecting computers and securing timing equipment in a secure area.  That gives me around 1.5 hours to have some fun on 40 and 20 meters shortly after sundown.  Once again, the same arrangement is used.  Results have been good on most race nights.  This schedule also gives me time to check out weak links in my own equipment and to improve the antennas.

Some of my fellow race fans have expressed interest in amateur radio after they see the system I bring with me on race days.  Perhaps, I'm having a good influence afterall.  I'm an old "gearhead" anyway, so any chance I get to combine radio and racing is an open invitation to explore new antennas and create a little "buzz" for amateur radio.

This will be a busy weekend, so it's off to the futon and a few hours of sleep before I drive through the pre-dawn mist to the Hilo Drag Strip.

Have a productive and safe weekend!

Aloha es 73 de KH6JRM--BK29jx15

Thursday, August 2, 2012

Simple Antennas for Amateur Radio Operators--a continuing series.

KH6JRM's Amateur Radio Blog

Post #178

Portable antennas

One of the things I like to do when the weather is nice (such as today) is to drive my van up an old sugar plantation road and set up a low-power emergency station at a clearing above Laupahoehoe town.  At an elevation of 1,200 feet on the east slope of Mauna Kea, I have a clear view of the Pacific Ocean off to the northeast and a fairly good shot at Japan over the summit of Hawaii Island's largest mountain.

Once I reach the clearing, I retrieve my homebrew 40-meter helix (see last post), 50-feet of 450-ohm ladder line, a 4:1 balun, the trusty Drake MN-4 tuner, about 10-feet of RG-6 coax, and the venerable Yaesu FT-7 qrp rig, which can be used for both cw and SSB contacts from 80 meters to 10 meters.  The vertical helix is comprised of two, 5-foot schedule 40 pvc pipes, which are joined by a pvc connector.  Sixty-six feet of #22 gauge hookup wire is wound in a spiral to the top of the vertical pole.  A 48-inch "stinger" from an old CB antenna is attached to the spiral to provide some top loading.  At the base of the vertical helix, I attach 8, 33-foot radials to the remaining part of the ladder line.  The radials fan out wherever the geography of the clearing allows.  For a power source I use a deep cycle marine battery and solar cells.  I can run the old Yaesu FT-7 for many hours with the solar array providing a continuous charge to the battery.  I've used automobile batteries in the past, but these batteries are not designed for extended periods of time.  They do work, but they have limitations. 

This arrangement works well and I've enjoyed many hours of low power operation (usually less than 10 watts).  This is the same emergency station I have installed at home.  The "go" kit is portable and can be set up quickly.

I've also used "Ham Stick" antennas with radials attached to achieve some success in stationary portable operations.  I've even resorted to using an old B & W apartment antenna on a picnic table to make enjoyable contacts (mostly cw).  MFJ's model 1622 is a good copy of the B & W design.

My portable station can be stored in the van and is available anytime I'm away from the qth.  Those of you who can't operate a station from your home because of HOAs, CC&Rs, and limited space may want to consider some form of mobile set up for your amateur radio station.  If you are clever, your vehicle might be part of an antenna system you can hook up to your home station.  Of course, this depends on just how nosey your neighbors are.  You can still have an enjoyable amateur radio experience if you let your imagination and creativity take hold of your antenna ideas.  Granted, a tall tower with a 4-element monobander beats anything I might dream up, but you can still run an amateur radio station if you let limitations become possibilities. There are several good books in the marketplace that address stealth and hidden antennas--many of these volumes are published by ARRL, CQ Communications, and the RSGB.  Sometimes, I just enter "stealth antennas" in the Google Search box and see what happens.  Occasionally, you can find some excellent information that can help you get on the air at a modest cost without creating what some neighbors call a "nuisance."

So, investigate the possibilities and take some time to design and build your "stealth" antenna.  You might be surprised at just how good your homebrew skyhook works.  I've built several antennas that have given me hours of enjoyment at almost no cost. 

Until next time,

Aloha es 73 de KH6JRM--BK29jx15