Wednesday, April 4, 2012

KH6JRM's Amateur Radio Blog-simple antennas continued

Now that some clear weather has returned to Hawaii Island, I've been able to fix most of my antennas that were damaged by high winds and the 25 inches of rain my qth received during a very wet March.  Most of the repairs went well.  The fiberglass poles were a little scratched by airborne debris and the wire elements were a bit twisted around the masts, but, in general the antennas came through the storms alright.  I was able to lower the masts most of the time before I left for school and that prevented more damage from the high winds.

I erected my two verticals in their original configurations--one a 40-meter inverted vee with the apex at 33 feet and the other a 20-meter vertical dipole stretched out on an old 33-foot MFJ fiberglass pole.  Both antennas were fed by 35-feet of 450-ohm balanced ladder line into a MFJ W9INN 4:1 balun.  A short run of RG-6 coax (15 feet) was connected to my trusty Drake MN-4 ATU.  That in turn was connected to the old Swan 100-MX at the operating desk.  Both antennas tuned up without problems.  I use the 20-meter vertical dipole on 20, 15, and 10 meters, while the 40-meter inverted vee can be used from 40 through 10 meters.  I still have the 40-meter loop under my house.  The loop is my backup antenna in case the other skyhooks meet with an accident.  The loop is also the antenna for my Hallicrafters SX-62A general coverage receiver.

Once I reassembled my "antenna farm", I removed the 135-foot wire that was pressed into emergency service during the bad weather.  Unfortunately, the wire was visible to passerbys and I didn't want too many comments made about it.  The verticals have been painted to blend in with the environment and are usually lowered during the day, unless I'm not working at school.  My neighbors are a pretty good bunch of people, but, with our area being in a weak reception zone for television and FM radio, I really don't want to create any interference with those who depend on over the air reception.  Although most of the neighborhood has cable or direct tv, there are a few who still depend on broadcast signals from the Island of Maui for their television shows.  I keep a pretty low profile and usually operate with power levels below 10 watts.  I have received no complaints about tvi or any other interferrence since I adopted the qrp and stealth antenna ethic.

Despite these limitations, I still get on the air and have a lot of fun, even at 10 watts or less.  Speaking of fun, how about the new 630-meter band approved by WARC-12?  I'm  sure we amateur radio operators can figure out a way to use this band despite the huge antenna requirements for this segment (472 to 479 Khz).  The dipole dimensions would be in the range of 909 feet or so, with vertical elements stretching to almost 455 feet.  The radial field would be quite large as well.  Having working on several MW AM radio stations, I can assure you that putting in an extensive radial field of 120 or so wires, each 1/4 wavelenth long, can be quite an undertaking.  From what I gather in the various antenna forums (i.e. those at eham.net), you could use a large coil with a 160-meter antenna to get on the air.  Assuming a one-percent efficiency rating, you could use a 500 watt amplifier to get the 1 to 5 watts erp required by the WARC-12 document.  Experimental work by amateur radio operators near 500 Khz and efforts by "lowfers" running stations in the 160 Khz to 190 Khz band under part 15 restrictions show promise.  There are also rumors that Elecraft K-3 transceivers will be able to generate power in the 630-meter band.  So, the new frequencies may prove very useful for those of us inclined to experiment in the lower portions of the electromagnetic spectrum.  The FCC is working on regulations for this band and should have some guidance by 2013.

That wraps it up for now.  I'm on call for substitute teaching duty at Laupahoehoe High and Elementary School until Good Friday.  So, it's off to bed for some much-needed "beauty" sleep.  At my advanced age, I need all the help I can get.

Have a good and safe weekend!

Aloha es 73 de KH6JRM--Laupahoehoe, Hawaii.  BK29jx15