SMALL ANTENNAS FOR PORTABLE/FIXED LOCATIONS
"QRP" operation often means operating in remote places where a decent full-
sized antenna is not possible. I personally live in an appartment where I
am unable to erect large antennas. For QRP operation a reasonable antenna
is a necessity on the HF bands. I have had a lot of success with vertical
dipoles on balconies and window ledges, and I have worked as far as Japan &
Tasmania with only 50 watts on 14 and 18 MHz. These HF bands can be worked
with an Aluminium tube "fishing-pole-style" poked out of the window, but if
you want to go below 14 MHz. then there is a problem with the length of the
pole exceeds the practical limit of about 5 meters.
The "fishing-pole" can be taken down to 10MHz, 7MHz & 3.5MHz by adding some
extra wire, as shown in the SHORTANT.GIF file. The lengths shown are all in
millimeters and the antenna shown will operate at 7MHz. VSWR is about 1.2:1
across the 7MHz band using a 5 meter handrail (and other metal contained in
the building) as a groundplane. When I lived in Eskilstuna I was fortunate
enough to live in an apartment where the outside walls of the building were
metal-clad. The VSWR went down almost to 1:1 on 14MHz. On 3.5MHz use double
the length of wire and form 4 turns instead of the two shown.
The insulators at A are cut from a nylon chopping-up board (stolen from the
kitchen) and the aluminium pole C is 16mm Dia aluminium tubing, 2 meters or
so long. In my experiments I found that the TOTAL length of wire + pole +
top-section should be about one meter LONGER than a calculated 1/4 wave but
the wire may be "pruned", & the lower "A" spacer moved up the pole a little
to compensate.
The nylon insulator D is a 16mm x 30mm lump cut from the same "chopping-up"
board as the A insulators. Drill a 4mm hole down the length of it to accept
the upper section. I just trapped the end of the wire loop in the 4mm hole
to make the connection to the upper section.
This type of antenna can be easily stowed on a car roof, or broken into two
or more sections and transported in the back of the car. Results on-the-air are
very impressive for such a short antenna.
Have fun, de HARRY, Upplands Vasby, Sweden
I am very grateful to Harold, SM0VPO for allowing me to add his files to my web site. He can be contacted by email: harold.lythall@era.ericsson.se
Frank, G3YCC