Wednesday, May 16, 2012

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

What do you do if you can't erect an outside antenna?  You could just give up and let the CC&Rs,  HOAs, and space restrictions win.  But that's not what creative amateur radio operators do to stay on the air.  I ran across this problem a few days ago when one of my younger amateur radio friends said he couldn't put up an outside antenna because of the restrictions of his area.  He lives in a crowded subdivision with neighbors all around.  Besides the restrictions imposed by his CC&Rs, space around his home is very limited.  So, without getting into the sticky area of tenant leases, housing committees, and noisy neighbors, I offered to do what I could to get him back on the air.  Fortunately, my friend can operate mobile and portable from parks and other public areas.  At first I suggested that he continue that type of operation until I could find a few hints for indoor antennas.

While I'm not a strong advocate for indoor antennas, such antennas, if properly designed and assisted by a wide-range tuner and a suitable counterpoise, can perform reasonably well.   Like me, my friend lives in a wooden house with a galvanized roof.  I've fed my metal roof against ground with some good results.  Although this design works, results have been only fair.  Unlike my friend, I do have access to a good backyard, which can support an inverted vee or a vertical dipole.  While my results haven't been in the same league as a station with a 50-foot tower and a tribander, I do get plenty of contacts.  So, the task ahead of me was to find an indoor design that could work without too much rf exposure or disruption of household electronics.

During my search for stealth antennas, I came across an article by Scott, K2ZS, called "An indoor HF Stealth Antenna"--a skyhook that could help my friend operate at home.  Basically, Scott strung a 60-foot closed loop around his apartment and fed it with a SGC antenna tuner.  He also fed the antenna with an old MFJ Versa Tuner he had in his shack.  Although the antenna was a bit noisy, he was able to make DXCC and enjoy many contacts around the country.  Scott says the SGC tuner will allow him to work between 3.5 Mhz through 30 Mhz.  Scott also included some of the indoor antenna designs from the SGC manual.  He also tried a small 3 X 4 closed loop with approximately 70 to 90 feet of close-spaced wire wound around 4 pegs in a wall.  The SGC tuner handled the load well, but results were less than those gained from the larger closed loop.

Since I had an old SGC tuner in the storage room, I decided to give Scott's design a trial in my own house.  Earlier, I described the 40-meter loop under my house and said that my Drake MN-4 tuner fed into a 4:1 balun and 450-ohm twin lead handled the load very well.  My fulll-wave loop is basically a NVIS antenna designed to work local HF nets in Hawaii--a task it does well at power levels around 10 watts.  I strung about 70-feet of 22 gauge hookup wire around the living room as a closed loop and fed the antenna to my SGC tuner.  With 10 watts from the old Swan 100-MX, I was able to make a few DX contacts and quite a number of local qsos.  The antenna didn't produce a sufficient amount of rfi to jam up my PC or home brewed audio system.

With my "experiment" done, I visited my friend and helped him erect a 70-foot closed loop around his living room and bedroom.  I had a spare 4:1 balun, some 450-ohm twin lead, and an old MFJ-941E tuner that he could use.  I suggested running his ICOM-718 with low power to see if any rf would interfer with his household electronics.  So far, so good.  He is getting contacts and seems happy to return to the air. 

Many thanks to Scott, K2ZS, for the suggestion.  Maybe you can use this idea for your station.

Aloha es 73 de KH6JRM--BK29jx15