Monday, July 23, 2012

Ham Radios in Space

NASA's Space Amateur Radio Experiment is connecting students and ham radio operators on Earth with astronauts in Earth orbit.
U.S. Astronaut Owen K. Garriott - W5LFL

For most amateur radio operators, it is the thrill of a lifetime to receive a "CQ", or general call, from an astronaut in space. But for some, like former astronaut Dr. Owen K. Garriott, call sign W5LFL, the thrill comes from receiving a response from "hams" down on Earth.

Garriott, who has been an amateur radio operator for over 40 years, was the first astronaut to take a ham radio into space, pioneering the way for an increasingly well developed amateur radio space program.
"It was my good fortune to take the first amateur radio into space on STS-9 in November 1983," Garriott said. "In my spare time only, I managed to hold up an antenna to the window and to talk to amateurs on Earth."

This contact was the first communication between astronauts and people on the ground outside of "official" channels, which are usually reserved for presidents and heads of state.

Owen Garriott pioneered the use of ham radio from Earth orbit during his "spare time" on shuttle flight STS-9. Now, the Space Shuttle frequently carries amateur radio equipment into space where astronauts communicate with students on Earth below.
Hams, as amateur radio operators are often called, use radio transmitters and receivers to talk to other hams all over the globe, as well as to those in space. There are more than 1.5 million licensed hams worldwide, including more than 400,000 Americans.

Every radio amateur must be licensed by the Federal Communications Commission (FCC). In order to obtain a license, a ham must pass an examination, which includes questions about radio theory, rules and regulations. There are three grades of licenses, each at progressively higher levels of proficiency: Technician, General and Amateur Extra. Any licensed ham can chat with the Shuttle.

Once the examination is passed, the FCC issues the amateur operator's call letters. The first letter indicates nationality. In the United States, the first letters are A, K, N, or W.

Garriott had originally proposed the idea of taking a ham radio into space on his first space mission, Skylab 3, but was unable to due to timing and other complications. Ultimately, though, he persisted and was able to obtain permission to fly a small hand-held transmitter/receiver aboard the Space Shuttle Columbia
This is U.S. Astronaut Owen K. Garriott - W5LFL - aboard the U
.S. Space Shuttle Columbia STS-9. He is holding a Motorola two meter FM ham radio.

"When in orbit over land, I could make a CQ, which is a general call, and see who responded," Garriott said. "I used a well-designed, hand-held antenna, known as a 'cavity antenna', which could be velcroed to the window. It was about 24 inches in diameter and looked somewhat like a large aluminum cake pan. The transceiver then connected to the antenna."
In addition to the general calls, Garriott had made a few plans to send out a call to specific Earth-bound hams at prearranged times and dates."I had specified particular times and frequencies beforehand," Garriott said. "Among others, I was able to speak with the Amateur Radio Club in my hometown of Enid, Oklahoma, with my mom, with Senator Goldwater, and with King Hussein, who was an avid ham."
Since that first voyage into space, NASA has continued to see the usefulness of bringing ham radios into space, and astronauts have been able to speak to hams on earth on dozens of shuttle flights, as well as on the space station MIR. "There has been substantial amateur radio activity in space since I first brought one up," Garriott said. "There is now a program called SAREX that is allowing for more and more activity."
The Space Amateur Radio Experiment (SAREX) is a long-running program to use amateur radio equipment on board the Space Shuttle to involve students in exchanging questions and answers with astronauts in orbit. Students in hundreds of different classrooms across the country are able to ask the astronauts questions about space flight and the experiments being conducted on the mission. It also allows for communication with amateur radio operators on the ground.
SAREX is sponsored jointly by the American Radio Relay League (ARRL), the Radio Amateur Satellite Corporation (AMSAT) and NASA. Students and amateur radio operators can attempt to contact astronauts flying on a SAREX mission through voice, packet (computer) radio, or television, depending on what equipment is flying on the shuttle and on what equipment is available on the ground.

In addition, in 1997, NASA approved plans to include amateur radio equipment as part of the payload of the International Space Station (Amateur Radio on the International Space Station or ARISS). Since astronauts will have more time in space while on the ISS, more opportunities for ham radio contacts will exist. "Shannon Lucid used a ham radio while on MIR," said Garriott. "NASA saw how using an amateur radio would be a good thing for astronauts to do in their spare time on the space station."
Onboard the Space Shuttle Endeavour, astronaut Linda M. Godwin (right) talks to students (left) via the Shuttle Amateur Radio Experiment (SAREX). The payload commander, as well as several other STS-59 crew members spent some off-duty time using the amateur radio equipment to communicate with "hams" and students on Earth.

And certainly hams on the ground are eager for contact with the astronauts. Specially designed shuttle "QSL" cards, which are postcards used by hams to confirm two-way contact or reception of a signal, are among the most prized in a ham's collection -- even to a king.

"(King) Hussein regarded his 1983 contact with Owen Garriott, W5LFL, on board Space Shuttle Columbia, as a high point in his amateur radio career," reported ARRL Executive Vice President David Sumner in a special bulletin following the death of Jordan's King Hussein, JY1. ("JY1" was King Hussein's call sign.)

Saturday, July 21, 2012

The Monoband HF Dipole Antenna

If you're looking for an easy antenna for your favorite HF band, you can't go wrong with a half-wavelength dipole! All you need are three insulators (one is used as your center connector) and some wire. Strong, multistranded copper wire will withstand the elements best. The only trick to making a dipole is cutting it to the right length. A dipole antenna is made of two equal lengths of wire with the total length adding up to a half wavelength at the desired frequency.
Here are the required dipole lengths for each of the Novice/Technician HF sub bands:

80 meters: 126' 6"
40 meters: 65' 7" 15 meters: 22' 1"
10 meters: 16' 6"
For example, if you're making a dipole for the 10-meter band, you'll need two lengths of wire 8' 3" long (8' 3" x 2 16' 6") plus enough extra so the wire can be looped through the insulator and secured tightly. Attach the wires to the insulators and center connector as shown in Fig 1. Attach your coax feed line at the center connector.

Solder the shield braid of the coax to one side of your dipole. Solder the center conductor of the coax to the other side. Be careful not to melt the coax while you're soldering it to the antenna. You can also purchase center connectors that feature built-in SO-239 jacks.
With a matching PL-259 plug on your feed line, you can easily disconnect your feed line from your antenna whenever necessary for portable operation, for example. What-ever way you connect the coax to the antenna, be sure to waterproof the connection if it will be outdoors. If water gets inside the cable its loss will increase in a hurry!

So, what type of coaxial cable should you use? If the distance from your transceiver to your dipole is less than 50 feet or so, RG-58 is fine. For longer runs, I'd strongly recommend a low-loss cable such as RG-8, RG-213 or Belden 8214. If you own an antenna tuner, you can try feeding your dipole with 450-Q ladder line. This type of open-wire feed line exhibits very low loss at HF.
Choose your antenna supports: trees, flagpoles, chimneys or whatever stirs your imagination. You can even install your dipole in an attic. If you decide to mount it outdoors, invest in enough high-strength rope or cord to do the job. You want to be sure your antenna will survive storms, ice loading and so on. Mount your dipole as high off the ground as possible. How high is "high?" Conventional wisdom states that your dipole should be mounted at least a quarter wavelength above the earth at the frequency you choose to operate.
Getting an 80-meter dipole 60 feet off the ground could present a challenge! If you can't raise your dipole to this altitude, don't worry about it! Your performance may suffer a bit, but the antenna will work. Watch out for nearby gutters, pipes, aluminum siding, window screens and other large pieces of metal. They'll detune your dipole and increase the SWR if they're too close. And, of course, never place your antenna near power lines!

If you've cut your dipole to the proper length, your SWR should be reasonably low (less than 2:1). Don't worry if the SWR seems to rise as you move in frequency toward the band edges—this is normal.
Of course, the dipole you've just designed is good for only one band, right? Well.  not necessarily! If you own an antenna tuner, try using it to load your transmitter on other  bands.

The SWR will be very high, but your tuner may be able to adjust it down to a flat 1:1 match. This won't do a thing for the actual SWR on the feed line, but if you've invested in low-loss cable or ladder line, it doesn't matter! Are you surprised to hear this? Many hams, even veterans, are slaves to the idea that only a 1:1 feed line SWR is acceptable. If your feed line is very "lossy," this is true.
If you invest in low-loss feed line, however, only a small portion of your signal is actually lost due to high SWR. The rest of it is radiated by your antenna. So if you've designed your antenna for, say, the 40- meter band, try it on other bands as well. You may find that your monoband dipole is really a multiband antenna!

Tuesday, February 21, 2012

DX Fun Web Cluster

DX Fun Web Cluster is in essence a "chatroom" or node into which amateur radio DXers can post information about DX either worked or heard. Physically, it is a central computer that collects, stores and disseminates information that ham radio operators send to it. There are thousands of nodes around the world, connected together via the internet or radio. Connection to a cluster is by either telnet or packet radio. The networked nature of DX clusters is perhaps its most powerful feature as it gives amateurs almost instant access to information about rare and unusual DX conditions such as meteor scatter or VHF ducting.

Cluster users will use computer software (for example, many logging programs have this capability) that is capable of communicating with the cluster. On initial login, users will be asked to provide station information. This allows other ham radio operators to compare DX openings to their physical position. DX is one of the most fascinating aspects of the hobby.

Sunday, January 8, 2012

Hamradio Homebrew 2 Meter Square Dipole Plan

Here is a plan for homebrewing a 2 Meter Square Dipole plan. The advantage of this antenna is that it is unidirectional, and it takes less space than the regular 2 meter dipole. The calculation included on the diagram below is for building the antenna using copper tubing, you should use MMANA-GAL or other antenna simulation software to come up with new dimension for other materials (aluminium, wire, etc).
2 meter square dipole plan2 meter square dipole plan
Click on the diagram to enlarge it. Hopefully this will help you in brewing new antennas! Original plan taken from KOFF website

Antenna In Less Space – The Inverted Vee

Another space saving installation method is to mount the antenna in an inverted vee configuration. This type of installation has worked well for me over the years and I highly recommend it for those of which enjoy HF Radio and are in a limited space situation.

Unfortunately, there is no such thing as the perfect antenna. There are just too many variables for that to be possible. So the theoretically perfect antenna just doesn’t exist.  Ham Radio is all about trying out new things, and homemade antennas are no exception.

Experimenting with Ham Radio Antennas and using your creation to talk with other Amateurs all over the world is definitely one of the most accessible and enjoyable aspects of the Amateur Radio hobby.

Short Ham Antennas For HF

For many ham radio operators, it is not feasible to put up a a full length dipole on HF.
But, a linearly loaded dipole just might fit in your available space!
A linearly loaded dipole, as illustrated below...
  • ... is about 30-35% shorter than a "classic half-wave dipole" at the same frequency of resonance!
  • ... has a radiation resistance around 35 Ohms. (You will need an impedance matching tuner at the other end of the coax!)
  • ... just as effective as a "full length" half-wave dipole! :-)
Linear-loaded short ham antennas for HF.
Note that it "looks" like a folded dipole, but the top part is open! You should add a ceramic end-insulator in the opening, to add mechanical strength. (The insulator is omitted in the drawing to make the opening obvious;-).

Shorter Dimensions!

Here are "ballpark" dimensions for a linearly loaded dipole for each ham radio band. These dimensions are intentionally slightly long! You will have to obtain the final dimensions experimentally, on site, by "pruning" to resonance.
Forgot the technique to prune a dipole to resonance? Refresh your memory on the page about the ham radio dipole!
Linearly-Loaded Dipole
Approximate Dimensions
10 meters (28.5 MHz)
12 meters (24.9 MHz)
15 meters (21.1 MHz)
17 meters (18.1 MHz)
20 meters (14.1 MHz)
30 meters (10.1 MHz)
40 meters (7.1 MHz)
80 meters (3.6 MHz)
160 meters (1.85 MHz)
3.5 m. (11.5 ft.)
4.0 m. (13.2 ft.)
4.73 m. (15.5 ft.)
5.51 m. (18.1 ft.)
7.08 m. (23.2 ft.)
9.89 m. (32.44 ft.)
14.06 m. (46.14 ft.)
27.74 m. (91.0 ft.)
53.97 m. (177.08 ft.)

Construction Of Linear Loaded
Short Ham Antennas

I use commonly available 390 Ohm "ladder line" with #14 stranded, copper-clad conductors. It is sturdy and lasts for years.
For the central "attachment" I use two LadderLoc center insulators, head-to-head (available at Radio Works).
I recommend 3/16 in. Mil Spec Dacron® rope to tie the ends to tall supports such as trees.

Bonus Configurations!

Linear-loaded short ham antennas do not have to be limited to horizontal installations!
You can save even more space by installing them as "slopers", inverted "V"s and inverted "U"s.

Free Yagi Antenna Designs for Ham Radio

Some months ago, Bent OZ1CT asked me for a X-pol LFA (two LFA Yagis, one in the vertical plane, one in the horizontal plane on the same boom). Whenever I have received such requests I have been reluctant to work on them due to the many complexities involved in not just getting the model working but getting it working correctly and as model.
There are designs from many well-known designers and commercial entities around today but none that I have seen get it right in the electromagnetic design or mechanical construction and this in part is due to the lack of understanding of off-sets (elements) and the impact certain materials will have upon this antenna and without doubt, this is the main reason many hams are not 100% happy with their X-pol arrays.

I have spent much time modeling X-pol array in EXACTLY the arrangement they will be in once built, established the issues and made every effort to avoid and reduce any distortions. The details and result fo these findings will be published within the pages of DUBUS a little later this year but for now, take a look at one of the first ever X-pol LFA Yagis at OZ1CT.