New Shortened Vertical for 17-20-30-40 Meters
August 19, 2006
Last night I tested my latest antenna: a 4-band, 20' vertical half wave
that uses two loading coils with taps. The results appear promising. On
20 meters I worked a Texas station. I was running 5 watts SSB and
used 800 watts. He had a rough copy on me, but there was much fading at
10 p.m. Later, on 40 I had a couple of nice CW chats to California
and Louisiana from here in Colorado. The antenna was only 10 feet from
the house and surrounded by tall trees - plus we have mountains on
three sides not far away. Halfway through the evening it started to
rain. I was sitting outside on a fabric-covered porch swing set up in
the front yard and stayed (mostly) dry. I'd started at 10:00 in
the evening and finally packed up around midnight after my last
contact. It was getting chilly.
The antenna is only 30% of full size on 40 meters. It is a
compromise, but I designed it specifically for an upcoming vacation to
the mountain town of Crested Butte, Colorado at the end of this month. I will be staying in
a 19-room lodge on the third floor with a walk-out balcony, so I
wanted something very portable and hard to see. Everything is black:
the pole, the antenna wire and I'll even painted the PVC support black. A
20-foot fishing pole will hold the antenna, and a PVC base will support
it up against the hand railing. Because it is an electrical half
wave, it needs no counterpoise or radials, something that would be
difficult to set up on a tiny balcony.
Details follow each picture.
The antenna consists of three sections
of wire and two coils. The outer two wires are 4' 4-5/8" long, and the
inner wire is 10' 8-3/4". I used 22-ga. stranded
wire for both the antenna and the coil windings. I began making coils
out of stranded wire on the hunch that it would reduce some of
the coil losses due to skin effect. After several shortened
halfwaves and a logbook full of successful contacts, I discovered
something called proximity efect that negates any benefits to using
stranded wire in coils. Oh, well. I continued the tradition here
The coils are wound on 1-1/4" thin-wall
(schedule-20?) pipe and are about 3-3/8" long. After winding the wire,
I wrap everything in black electrical tape.
There are four taps on each coil. The lowest tap on the coil (from
right-to-left) is for 17 meters, followed closely by the 20 meter tap.
Finally, the 30 and 40 meter taps. The tap for 40 is actually one turn
short of the full coil. I had intended to use the full coil centered
around 7.040 MHz and use the tap for the novice CW portion of the band.
During testing I discovered that the tap was a better fit, and the
additional wrap tested out below 7.000 MHz.
Here are the windings for each band. The windings are based on a
#22 stranded, insulated wire with an O.D. of 0.064" and approx. 15
turns per inch.
Band / total turns
17 m = 7.5 turns
20 m = 13.5 turns
30 m = 25.5 turns
40 m = 46.5 turns
Full coil = 47.5 turns (resonant below band edge - skip this turn)
Here is the PVC base I built for the high-mountain vacation and the top
floor balcony. The back leg and support is in case the balcony has a
solid railing with nothing to lash onto and it needs to be
self-supporting. This photo was taken before I had painted it "midnight
black." The antenna will be held up by a 20-foot fishing pole from
Cabelas. The bottom of the pole will slide down on the PVC. Everything
breaks down to 45" or less - the length of the fishing pole fully
Here is the tuner I use for this and most of my half waves. It's on the bottom half of the page.
August 30, 2006 update: This weekend I made a few contacts on 40 from the top floor balcony of a mountain lodge.
Tonight I set the antenna up in my front yard here in Golden, Colorado.
It was 10:00 p.m. and I only had time for one contact, so I talked to
Ed, W7GVE in Arizona for almost 25 minutes. He was 589 and gave me a
569. Not bad for a seriously shortened antenna. Here are two shots
taken in the dark.
What you don't see here are two huge
trees on either side of the antenna. It's amazing any RF escapes from
this small yard. The flash on my Canon G-2 really lights up the
otherwise pitch-black night.
On the table you can see the FT-817, a
SLA battery, headphones, a Palm Paddle, LED lamp and a UTC travel alarm
clock. Above the table is the matching unit taped to the PVC support.
I've discovered a big advantage to CW. I can be outside late at night
and not wake up the neighbors sleeping with all their windows open as I
might using a microphone.