A Gnat That Won’t Annoy You

gnatOn one of the QRP mailing lists, there was talk about how minimal you could make a QRP transceiver. Several ideas were tossed around, but then Chris Trask, N7ZWY, nailed it.

The Gnat 1 uses a single 2N2222. The parts list includes values for 80m, 40m, and 30m versions, and the documentation even includes a PCB layout. Kits may also be available soon.

A Couple of Good Reasons to Cultivate a Good Relationship With Local Police

A couple of news items have been brought to my attention that deal with the relationship between amateur radio and the police. Gets me to thinking about what, if anything, I could do to improve the relationship between the Ann Arbor ham community and our local police forces.

  • Police Detonate Ham Radio Equipment Mistaken for Bomb, – KPTM-TV, Omaha,NE,USA
    … a midtown neighborhood briefly Thursday morning for what was originally thought to be a bomb, but in the end, it turned out to be ham radio equipment…

    Maybe this should have been titled, “How to Make a Bang With Ham Radio”……..Dan

  • Indianapolis Police Busted for Bootlegging on 2m – TheIndyChannel.Com
    Not only were the police using the amateur radio transceivers illegally, the radios were installed by police technicians AND they were using profane language on the air. Amazing.

Random Antenna Arrays Boost Emergency Communications

From the 2/24/09 NIST Tech Beat:

First responders could boost their radio communications quickly at a disaster site by setting out just four extra transmitters in a random arrangement to significantly increase the signal power at the receiver, according to theoretical analyses, simulations and proof-of-concept experiments performed at the National Institute of Standards and Technology (NIST).

The NIST work, described in a forthcoming paper,* may provide a practical solution to a common problem in emergency communications. The vast amount of metal and steel-reinforced concrete in buildings and rubble often interferes with or blocks radio signals. This was one factor in the many emergency communications difficulties during the response to the attacks on the World Trade Center on Sept. 11, 2001.

Antenna arrays have been studied and used for years, but the latest NIST work provides several new twists. Unlike the typical case in which antenna arrays boost signals to or from a distant target, a first responder’s radio would be relatively close to the portable transmitters, ideally within the perimeter of the array. More importantly, since disaster sites rarely allow for niceties of design, NIST studied the benefits of a fast and imprecise technique—randomly placed antennas combined with coarse signal matching. The signals produced by the radio and portable transmitters need to operate at the same frequency and roughly in phase, such that the radio waves are fairly well synchronized and thus build on each other. Phase-matching was performed manually in the experiments but might eventually be possible remotely.

The NIST experiments covered a range of communications scenarios, using up to eight transmitters at different locations as well as objects such as concrete blocks that scatter radio waves. Across all experimental scenarios, researchers observed at least a 7 decibel median power gain—roughly a five-fold increase in the median received power—when splitting the power among four in-phase transmitting antennas, compared to using just a single transmitter. More important, researchers observed a 2.5 to 4-fold increase in the median signal at the radio receiver when using four in-phase transmitters instead of four randomly phased transmitters. More than four extra transmitters offered diminishing returns. (Unlike conventional repeaters, which re-send signals to maintain transmission strength across long-distance networks, the antennas in the NIST scenarios transmit the same signal at the same time to multiply its strength.)

Project leader Chris Holloway envisions portable transmitter devices shaped like hockey pucks, incorporating a small antenna and phase-shifting electronics, which could be thrown on the ground or stuck on a wall with the antenna always upright. “The idea is that someone, or even a robot, would have a bag of these things and would drop them off as they go through a building,” Holloway says. Other authors include a guest researcher from Sandia National Laboratories and a collaborator from the University of Colorado at Boulder. The work was funded in part by the Office of Community-oriented Policing Services of the U.S. Department of Justice.

* W.F. Young, E.F. Kuester and C.L. Holloway. Measurements of randomly placed wireless transmitters used as an array for receivers located within the array volume with application to emergency responders. IEEE Transactions on Antennas and Propagation, (forthcoming.)

If you don’t subscribe to IEEE Transactions on Antennas and Propagation—I know I don’t—you could probably get a copy directly from NIST.

MAKE: Links

I recently took out an old Make: magazine from the local library. It had a lot of cool links. Here are some:

  • USBCell. These rechargeable, AA batteries plug into a USB port. A two-pack costs £11. Their website says that AAA, C, D, and 9-V batteries are in the pipeline.
  • Octopart. Type in a part number, and let Octopart find it for you. They now have a “parts list” feature that lets you build a parts list online or import a list from a .csv or .txt file.
  • All Electronics. Surplus house. Sells everything from cable clamps to wall warts. Some good deals.
    Weird Stuff. Another surplus house. Sells a lot of old computer gear (think Sun) and industrial equipment (valves, pumps, blowers).
  • Hobby Engineering. Tagline: A supply store for people who want to build robots, electronic gadgets, kinetic art or anything else that moves, beeps or flashes. Carries a variety of educational kits as well as microcontroller parts and electronic components.
  • FlyABird. Totally unrelated to ham radio. Sells machines called ornithopters that fly by flapping their wings. Very amusing.

CW Bass Ackwards

At the museum today, we got into a discussion of the reason for including both the Upper CW (UCW) and Lower CW (LCW) on the Omni VII radio. The explanation wasn’t on the tip of my tongue, so I decided to research this a bit.

On Icom radios, they call the Upper CW mode “CW-Reverse,” or CW-R. Here’s the explanation of how it works from the IC-756PROIII manual:

CW reverse mode
cw-reverseCW-R (CW Reverse) mode receives CW signals with a reverse side CW carrier point like that of LSB and USB modes. Use when interfering signals are near a desired signal and you want to change the interference tone.

If you have properly zero beat the signal of a station with which you are in contact, then the other station’s signal will sound the same in either mode. An interfering signal will, however, sound much differently, and, as shown, may be out of the passband altogether.

If you don’t zero beat properly, though, being in different modes will affect the way that the other station hears you. Say, for example, that both you and the other station are in normal CW mode (LCW on the TenTec). The other station’s transmit frequency is set to 7030 kHz. Your sidetone frequency is set to 500 Hz (meaning that the BFO frequency is 500 Hz above the receive signal), but you set your transceiver to hear a 600 Hz tone. To hear that 600 Hz tone, you will have to set your transmit frequency to 7030.1 kHz.

If you’re in UCW mode, or CW-R mode as Icom calls it, then the BFO frequency will be 500 Hz below the received signal, and to hear a 600 Hz tone, you’ll have to set your transmit frequency to 7029.9 kHz. In the first case, the other station will hear a 500 Hz tone when receiving your signal. In the second case, he’ll hear a 700 Hz tone.

To minimize the frequency difference between the two stations, it’s a good idea to check the setting of your sidetone frequency and zero beat as closely as possible with the other station. I would also avoid shifting between CW modes while in contact with another station, or if you do change modes, don’t change your transmit frequency while in contact. Use the RIT control to change the frequency of the tone you hear.

More Regen Receivers

Science Fair RegenA thread on the radiokits mailing list recently discussed the Radio Shack Science Fair three-transistor shortwave radio kit. The manual for this kit–and many other P-Box kits–can be found at KA9VNW’s Sparktron website.

This is a cool radio, but another subscriber pointed to another that seems like it would be easier to build. Designed by Charles Kitchin, N1TEV, the schematic appeared in the August 18, 1994 edition of EDN magazine. The article is titled, “$10 receiver has microvolt sensitivity.”

This radio uses three 2N2222 transistors, while the P-Box radio uses one NPN transistor and two PNP transistors. The 2N2222s are much easier to come by, I suspect, and I already have a package of 100 in my shack.

Last Weekend on the Radio at KB6NU

Last weekend was a pretty busy one here at KB6NU.

I got started on Friday night, working several stations in the NH QSO Party. I only worked five stations, but it was fun. Then, for some reason, I decided to tune around in the phone band and came across WX4MM, working the YL-OM contest. I gave her a QSO, then went QRT for the evening.

On Saturday, I spent a couple of hours working WA2HOM. The big news from the museum is that we now have our “ON AIR” sign. Currently, you can just turn it on and off. I’d like to add some kind of RF sensor that would flash the sign on and off when we’re transmitting.

Saturday evening, I got back on the air again. K5D was piling them up from about 7023 kHz to 7035 kHz, so I tuned around down below 7020 kHz. (Am I glad I finally got my Extra? Definitely!) It was there that I found the Dutch PACC Contest. I worked three PAs, then found EI9JF calling CQ. We had a nice QSO, then I QSYed up to the phone band again.

There, I found WA2TDC working the NH QSO Party and worked him. Tuning around a little, I found KC5GLC. He was working the Ole Miss QSO Party. Working him made it four different contests that I participated in over the weekend. After that, I pulled the plug and the XYL and I went out for Valentine’s Day.

On Sunday, I fired up the rig about 1 pm and decided to see what was happening on 30m. Lo, and behold, I found K5D actually calling CQ. He must have just gotten on the air. It only took me four calls to work him. If you ask me, 30m is the best band to work the DXpeditions.

I made a few other QSOs on Sunday, but nothing extraordinary. All in all, a great weekend for operating.

Geronimo!

Two quick tips:

  1. Parachute cord. A couple of subscribers to the qrp-l.org mailing list suggested the use of surplus parachute cord to suspend wire antennas. Dale, WC7S, says, “they stretch and allow for icing and frosting.” You can get a 1000-ft. spool for $60.
  2. Cheap electrolytics. While working Harry, K4IBZ, I looked him up on QRZ.Com and read that he often operates a Johnson Adventurer. Having just acquired one—someone donated it to the Ham Radio at the Hands-On Museum Project—I struck up a conversation with him about the transmitter. He told me that he enjoys restoring vintage rigs, and encouraged me to rebuild this one. His coolest bit of advice is that he salvages the electrolytics out of old CRT computer monitors. Great advice!

Need a Copy of the 2004 ARRL Handbook CD-ROM?

I used to run an Internet bookstore and sold quality control books and ham radio books. I made a few bucks at it, but it wasn’t worth the amount of time I spent doing it, so I closed up shop about four years ago. (Ironically, one of the most profitable parts of this venture was selling the domain name – qtb.com).

Anyway, I still have some books left over from that business venture. I’ve sold some at hamfests, but books don’t seem to move very fast there. So, I’ll try getting rid of the rest of them here and on Amazon. Some of the titles I have include:

  • Morse Code: the Essential Language
  • The 2004 ARRL Handbook for Radio Communications, CD
  • ON4UN’s Low Band DXing
  • ARRL’s Yagi Antenna Classics
  • Digital Signal Processing Technology
  • Stealth Amateur Radio
  • The Artful Solderer
  • Lew McCoy on Antennas
  • AC6V’s DXing101x: HF + Six Meters DXing

For most of these titles, I only have one copy, so get ‘em while they’re hot. For a complete listing, download this Excel (.csv) file. It includes the number of copies that are available, the price for the book (generally about half the list price), and the shipping cost. E-mail me for more info.

ShackBox

ShackBox is an all-in-one CD for amateur radio operators. Shackbox claims to include programs that will allow you to:

  • control rigs and scanners,
  • design antennas,
  • design PCBs,
  • etc., etc. etc.

The feature that attracted my attention is that it will run on Macs. Unfortunately, it only runs on the newer Intel Macs, and I only have an old G4 in the shack.