Antenna Experiments and Explanations (FCARC Meeting 11/17/2014)
The original PowerPoint AntennaTalk141116.ppt shown at the meeting
is a large file. It was written using OpenOffice, but it was saved as a
Microsoft PowerPoint. so it should be readable with either program.
If you don't want to download the large PowerPoint file this page contains
the references and some other information from the presentation.
Maximum Usable Frequency predictions:
Critical Frequency predictions:
RBN (Reverse Beacon Network)
WebSDR: list of all sites:
Al's favorite webSDR site (New Jersey):
(Note he uses a dynamic DNS service, if this doesn't work look for
the current address on the main WebSDR site.)
Additional notes on using RBN:
- You can select a station to look for as DX. I showed an example where
I looked for my own call to see where it was detected.
- You can select another station you would like to contact - the example I
used was W1AW/5, the current W1AW portable operation, in Mississippi this week.
Once you see what frequencies the station is on you can then look for a local
listening post - K1TTT, the superstation in Peru MA is a good choice - and see
how well it hears the station you want to contact (look in the SNR column). I
have found that if K1TTT hears a station with a signal to noise ratio of
30 dB or more I can probably work that station even though I am using only 5
watts and a modest antenna.
- You can also use a wildcard, for instance W1AW* to find all of the current
W1AW portable operations (in any week there are at least two, sometimes three).
Or you could, for instance, look for GJ* to find any station operating from
the English Channel Isle of Jersey.
Additional note about WebSDR:
These stations may be capable of accomodating only a limited number of users
at a time. If the one you wanted to look at can't handle you, scroll to the very
bottom of the main WebSDR site to see a map that locates all of the listed
stations and choose one that is near your first choice.
PART 2 - The Magic of 1/4 wavelength wires
I found the various pictures of J-Pole antennas by Googling "j-pole images".
Each image has a link to view the image full size and another link to the web
page where the image is located.
How Long is a ¼ wavelength?
Quarter wave (ft) = 234 / freq (MHz)
3.5 MHz 67'
7.0 MHz 33'
10 MHz 23'
14 MHz 16'
18 MHz 13'
21 MHz 11'
25 MHz 9'
28 MHz 8'
50 MHz ~5'
146 MHz ~19”
440 MHz ~6.4”
Butternut, the company that designed the HF6V vertical antenna, is now owned
by Bencher. They have lots of manuals and technical notes for Butternut
antennas, as well as some general information on vertical antennas on their
website at http://www.bencher.com/pdf_download.html.
The HF6V antenna is designed to operate on the 80, 40, 30, 20, 15, and 10 meter
bands. The multiband radials I showed a sketch of are intended to work on 40,
20, 15, and 10 meters. How is it resonant on 10 meters? I still haven't figured
that one out. You may have noticed in the pictures I showed of my antenna I have
a lot of radials. I use two of the mutiband ones, but I also have three cut as
quarter waves on 80 meters, and two additional radials for each of the 40,
20, 15, and 10 meter bands. So I have a total of 13 radials. But only those that
are 1/4 wavelength long are effective on a particular band. And, I realized in
preparing for this talk that I don't have any radials for the 30 meter band, so
I should add these.
The manual for the HF6V with the plans for the multiband radial is at