Thursday, July 19, 2012

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

KH6JRM's Amateur Radio Blog

Post #171


Thanks to some good weather today, I was able to get out of the house and work on my modest antenna farm in the backyard.  In my last post, I described a hastily built 20-meter delta loop fed by RG-6 coax.  The loop is working fine and I plan to keep it up for awhile.  Later, I will connect the loop to my station with 450-ohm ladder line, so I can use the antenna for 15 and 10 meters.

After that small antenna project, I was once again on the lookout for other simple antennas that even I could build.  It's true...I'm not the sharpest tool in the shed when it comes to building things, but I do better with each new project.  My fingers have solder burns to prove it!   Anyway, I wanted to improve my emergency indoor antenna without creating problems with RF emissions or TVI.  As I was searching antennas through the internet, I came across an article by Zachary Flemming entitled "How to make an indoor random antenna."  At the time of the article (06 January 2010), Flemming was a PhD candidate at the University of California, Santa Cruz and had apparently devised an antenna that gave him many contacts over the years from his small apartment.

Basically, Flemming ran 50-feet of Radio Shack wire around the ceilings of his apartment and fed the antenna into a RBA 1:1 balun attached to a LDG Z-100 automatic tuner.  He didn't say if a counterpoise was used.  Without a counterpoise, that antenna would "bite" a bit when you used a microphone.  Anyway, assuming he had a decent ground and a working counterpoise, the arrangement proved to be quiet effective in pulling in contacts. 

Here is his list of materials:

50 feet of wire, pushpins to hold up the wire along the ceiling, automatic antenna tuner (LDG Z-100 or equivalent), RBA 1:1 balun, short pieces of RG-8 or RG-58 to connect the transceiver to the antenna and tuner, and a low pass filter to reduce TVI.

Flemming advises those who wish to duplicate his success to run low power (below 100 watts), use digital modes (including cw), and reduce RF exposure and electronic interferrance (TVI) with low pass filters.

As an experiment, I made a similar antenna using 50-feet of wire with one end of some RG-6 coax connected to the wire and the other end of the coax connected to a counterpoise of 50-feet, which snaked along the floor panels and rugs in the qth.  I had an old 1:1 balun in the junk box which I interspaced between the coax and the Drake MN-4 tuner.  I had no RF feedback or "bite" when I used the microphone.  I also had my station ground connected to an 8-foot ground rod outside of the bedroom window.  The indoor antenna worked pretty well, as I received 569 to 579 reports on bands between 40 and 15 meters.  My trusty Yaesu FT-7 with its 10 watt output provide the RF source. 

Perhaps you can use Flemming's original idea for your apartment.  The antenna works given its limitations.  The important thing is getting on the air safely.

Until next time,

Aloha es 73 de KH6JRM--BK29jx15