Live To Air – National NC-101X finally back together tonight newly installed coil rack, with the bronze bushings and fabricated band indicator. Slides like it’s on glass, super smooth and low effort.
Listening to the melodious tones of the old Gray Hair Net, using Amplitude Modulation, on 160 meters shortwave. Exact frequency is 1.945 MHz. Not bad for a 80 year old radio, I think the original owner W1KEK would be pleased to know that his treasured set, that he bought back in 1937, has returned to the air.
Very pleased with how this project turned out. The audio is very sweet, with some nice wide bandwidth for hifi AM audio. Just waiting for the electrolytic filter capacitors to finish the project.
This was written back in the last 1990s when I lived near Buffalo, NY, in a suburb that had zero lot lines, and little space for antennas. A vacant field in back of my home became the antenna field for my station.
– Bruce W1UJR
As some of you may know, I am an advocate for wire antennas, and have been experimenting with horizontal loop antennas for HF work. I am currently running a 160-meter full wave loop that is suspended about 30-40 feet off the ground. Although the feedline for my loop is currently coax, in future installations I am considering the use of balanced, or open wire feedline for reasons of low loss, which may be the topic of a future article.
One caveat that I should mention before I start. The majority of my operating, and hence my observations, is on the lower bands, typically 160 through 40 meters. At these frequencies, the use of a yagi antenna is often impractical due to size constraints. If you do operate on 20 meters and up, you may find a yagi a better choice than the loop for its gain and directivity. That being said, what holds true for a loop at 160 meters, also holds true at 10 meters, so even those who operate on the “high bands” should find something of interest here.
The loop antenna has a long and distinguished history, but is often overlooked in light of the current focus on dipoles. However, loops do have some rather significant advantages over a dipole. Since the design of a loop is typically a circle or square form, the need for a long straight run of wire used by a dipole is diminished. A loop is quite forgiving, and perfect symmetry is not essential. It is necessary only to hang it in the configuration providing the greatest enclosed area. As such a loop can be strung up in unusual places and still perform well. Treetop suspension is ideal, but you’ll be surprised how well it works just lying on the roof where nobody sees it. Unlike a dipole that must be center fed, the loop can be feed at any point, allowing a most flexible feedline arrangement.
A loop is an efficient broadband radiator, even when low to the ground. The majority of the amateur bands are harmonically related, typically the 1st harmonic. This is where the loop really shines, as a loop is easily tuned to resonance on all even harmonics of its fundamental frequency. A dipole by contrast is easily tuned to resonance only on its odd harmonics. A loop starts out with 1.2 dB of gain over a dipole on its fundamental frequency, and gains are even higher if the antenna is less than a quarter wave off the ground because that is where the dipole efficiency plummets. For example, in my location my loop is quite close to the ground, only about 30-40 feet up at the highest point. Nevertheless, the antenna both tunes, and transmits just fine.
A loop’s gain over a resonant dipole increases with the increasing frequency of operation, so when used on its harmonics, a loop’s signal advantage over a dipole likewise increases. For a horizontal loop, that’s not the end of the good news, because as frequency rises, radiation angle drops lower and lower, producing increasing DX results that can rival a complex multi-element beam mounted on a 100-ft tower.
The venerable loop is easy for your tuner to match, even when fed with coax. The feedpoint impedance of a loop never gets as high or low as with an antenna that has free ends. Even a 40-meter loop can offer full 80- 10-meter coverage. My 160-meter loop allows me to both receive and transmit from the 160-meter band to 10 meters. Signal reception is also quite good with a loop for a number of reasons. As it is a terminated antenna, it is much less susceptible to atmospheric and man-made noise. As the majority of man-made noise is vertically polarized, the horizontal polarized loop can reduce electrostatic noise as much as 26db when compared to dipoles or verticals, so it is great for noisy RF areas.
The theoretical feedpoint impedance for a full wave loop antenna is approximately 100 ohms, but this does change, and is dependent upon antenna height above ground, near-by structures, and ground conductivity. When used with a 2:1 balun this presents a good match to the typical 50-ohm coax. Due to the low height above ground of my loop, I used a 4:1 balun which seems to offer a wider tuning range (lower Q). With the use of a transmatch (antenna tuner) I am now able to use my loop from 160 to 10 meters.
Loops can be either a 1/2 or full wavelength long. The formula for a full wave loop antenna is as follows: Length (feet) = 1005/fMHz. For example, a loop for the frequency of 3.800 MHz would be calculated as follows: 1005/3.8 = 264 feet. You can now divide 264 by 4 to obtain the length of each of the four legs of the loop. 264/4 = 66 feet each leg.
So next time you need a new antenna installation, consider the time-honored loop. Simple and inexpensive to homebrew, you can put the money you saved toward something really important…like a trip to this years Dayton Hamvention!
The above work was published in the September 2002 edition of Electric Radio magazine.
This article was to about last May’s AM Special Event in Portland, Maine, but with my recent move to the state, coupled with my search for a new business the writing was pushed to the back shelf. So when I contacted Barry a few weeks ago I offered a new twist, rather than just tell you about all the fun we had with the station, I wanted to exhort you to set up your own AM Special Event station, and in the process share some of my trials and tribulations, on how to go about getting your station on the air.
The first question you might ask is “Why set up an AM Special Event Station in the first place?” Which, after working on several of these events, from the Dayton Hamvention to the Buffalo Hamfest, I often ask myself. Why lug a couple hundred pounds of quite valuable gear out of your basement, wrangle with the hamfest committee over operation and placement, round up your contingent of operators, and spend less time operating than setting up the station? Why indeed! The answer is rather simple, because it’s worth it. Sure we can operate from the comfort of our hamshacks at any time, but if you do that you are missing fully half of the fun of this hobby. You see, radio is about people, radio isn’t just about vacuum tubes, feedlines and SWR.
Radio is also about people, their lives, hobbies, and passions. And no mode portrays the richness of the human experience like AM. Alright, I’m biased. I like Amplitude Modulation, in fact like may be too light of a word for it, I am in awe of AM. I have found time and time again that there is no finer mode to bring in listeners like the rich, full sound of AM. I see it time and time again when we run one of these stations, a small crowd will gather around the speaker, listening to our operator hold forth with another station. I can divide this group into two distinct subgroups, those new to the hobby, and those who once ran AM but left the mode decades ago.
The first step to getting a special event station off the ground is get approval from the club hosting the hamfest. Assuming you want to run the station at a hamfest, for nothing prevents you from making your own event, setting your station up for a local Boy Scout troop, church group, or in the neighborhood shopping mall. In fact, as you would not be “preaching to the choir”, it could be argued that these places might be even more effective than a hamfest. But for sake of argument let’s assume you are now trying to justify your stations existence to a local hamfest committee.
The first objection to come up will almost invariably be the concern of RFI to the public address system. Safety, too much power consumption or not enough space are usually next on the list. You can easily handle these objections by having a prepared station layout; photos are idea for this, showing antenna position, power consumption, and RF output. I used to lug the T368 around to fests, but after suffering a hernia –really, I have found that DX-100 power, anything over 100 watts is more than enough to make excellent contacts if the bands are in good shape and the antenna efficient. Our station at Dayton in 2000 was only a DX-100 transmitter and NC-300 receiver, coupled to a dipole fed with balanced line. The entire station, along with AMI and Electric Radio information, fit on a 24” x 36” folding table and while transmitting used well under 20 amps of current. It’s hard to object to a station of that size using that moderate level of power. If you can, bring along a decent external speaker, nothing will draw in passersby like a large public address speaker, at a moderate audio level, reproducing the rich fullness of the AM signal. Time and time again onlookers have been amazed at how good the audio can sound when it is not exiting via the 3” speaker in their solid state rig.
Be sure to mention to your hamfest hosts the attention you station will bring to their event. Often the powers that be are not aware of the significant following enjoyed by AM, too often dismissing it as an antique mode. Prepare ahead of time a ready listing of methods that you will be promoting the station, and their hamfest at hand. Free publicity, with the attendant rise in admission receipts can work wonders for small fest. Be sure to follow up on this, postings on the AM Window and AM Fone websites, as well as mentions in the Special Event QST can make a real difference. Don’t hesitate to let your local new media know about your “vintage station”. A simple press release, faxed to newspapers, radio and TV can do wonders in a small town. (If you would like an example press release just email me.)
Once you have the official thumbs up it is now time to scout out venue well before the operating day. All hamfests are not created equal and it is important to inspect the site for any “skyhooks” to use for antenna supports, power lines to be avoided, and a spot out of the sun to place your station. The obvious safety concerns of feedline placement distance for power lines and such apply, just use common sense. Make a written list of extension cables, coax, antenna supports, and other gear. Such a list assures you a quick station set up on the hamfest morning with a manual of headaches.
Now the easy part. Recruit your help. The effort to set up and operate a successful Special Event station can simple with the right help. I have been fortunate to always find a good number of volunteers who cheerfully chip in to set up and operate the station. Assign two teams, one for setup and breakdown at the end of the event, and another team to operate during the hamfest. I find that I am often too tired to do much operating after night and early morning setup project. Most hamfests last 4-5 hours, so be sure to have at least 3-4 ops to keep the station on the air, allowing everyone to get his or her turn at the coffee, donuts and other hamfest goodies.
I won’t enter into the debate of the “channel” AM operation, but it is important to operate near one of the key AM “windows”. Allow yourself some space, say 10kc as not to interfere with adjacent QSOs. I have found, the hours of the typically hamfest, the 75 and 40 meter bands are ideal. 3.875 and 7.280MC are idea frequencies for your station. Close enough to the AM window to be found easily, but separated by enough space so as not to cause QRM.
Plan for QRM, like it or not, it does happen. Try to find someone with a high power station to act as the “Channel Master” or anchor station and keep the frequency open. It is a good plan to have your QRO station come on at least ½ hour before your station formally goes on the air.
On The Air
If you can, have some, coffee and donuts waiting for your crew when they arrive to set up the station. Be sure to allow plenty of time for antenna and power supply issues. Once you get on the air, or as we say here in Maine, on the “ayah”, log, log, log. Keep a written log of your contacts; make some notes on each QSO for later reference.
Think about your audience, and remember, many of your observers will just be familiar with the standard banter of 2 meter FM, or the quick signal exchanges of DXing, so try to get a fast paced roundtable going. Make notes of the other stations configuration, how long have they been licensed, antenna layout and such go a long way toward showcasing the relaxed mode of AM for those listening in.
Be sure to invite the now gathering crowd to actually operate the station. This tax your persuasive powers for often times your audience will be mic shy. If you find this the case, gently coax and offer them a few questions to ask the op on the other end. If you are lucky enough to have an YL observing, be sure to invite her to operate. Nothing creates a pileup quicker than a female voice. Explain to how to tune the transmitter, how to zero beat the receiver, which may be terms and concepts new to many of your observers.
I find it helpful to have handouts at the station. The AMI brochure (contact Dale KW1I for this) or WB3HUZ’s explanation of how to properly run AM on a solid state rig is very good, as are the URLs of various AM and vintage gear websites. You might want to contact Barry to obtain some issues of Electric Radio to sell, and don’t forget the ARRL. The League, which after all exists to promote radio, is an excellent source of many free pamphlets regarding the radio hobby.
Radio parts, old tubes, variable caps, inductors, old QSTs, which many of us have in abundance, are excellent props to have on hand. Show the crowd what a vacuum tube really looks like. If you can, bring in a homebrew transmitter or receiver to show the crowd. People are fascinated when they can see and understand how a radio really works. Today’s equipment, as compact and versatile as it may be, lacks the charisma and “soul” that a nice old tube set has. Open the top of the reviver and transmitter and let your observers see the inside of the radio, the glow of the vacuum tubes, and the purple glow of the 866s. I will wager you that the “ohh” and “ahh” factor will far exceed what you will receive from the stations solid state cousins. If you can, have a small notebook where your crew and spectators can sign in with their name, call and email address. Such a guestbook is very helpful for developing next year’s operation, and provides the hamfest hosts of the station traffic.
Keep in mind our three goals; the first is simply to have fun. Lets face it, as magnanimous as it is to want to introduce newcomers to the joys of vintage gear; you are never going to want to make the effort to set up the station again unless you and the other ops enjoy themselves. Our second goal, to borrow a phrase is to be an “AM Ambassador”. This is something that we hopefully practice anytime we are on the air, but at no time is it more important that when operating a high profile Special Event station. Be courteous to those calling in, try to have short chats rather than just callsign exchanges, ask about their station, years licensed and then be sure to thank them for checking in. If you are able to get a roundtable QSO going so much the better, such dialogue really showcases the best of AM operation. Our last goal, and perhaps most important, is to introduce newcomers to the hobby, and to remind those older ops of the pleasures of operating vintage gear.
There is nothing like having an old timer sit down and explain his amazement that AM is still around and relate his experiences homebrewing in the 30s and 40s. Or the new ham, armed only with an HT, which is magically drawn to radios that glow in the dark. Get ready for converts and to hear many memorable stories.
Tying the Ribbons on It
Once your operation is done, the equipment packed away, be sure to thank your hamfest hosts for the space. Chances are your hosts are going to be pleasantly surprised at the turnout and crowd your small station drew. But just in case, be ready to address any concerns that they might have while mentioning that you would like to meet soon to begin planning next year’s station.
Next take your crew of ops, and be sure to invite any new converts, out for lunch and some well deserved cold 807s. This is an excellent time to critique the operation, discuss next year’s station and initiate the newcomers in the world of glow in the dark radios.
Everyone loves to look at photos of the latest hamfest event, so be sure to bring along your camera. Digital cameras are excellent for the ease of putting these photos up on the web. Do your best to shoot a group photo in front of the station, and send off a copy to your crew, aside from reminding you how much fun you had, it will go a long way to rounding up help for next years event.
If you can, scan in your logbook and put it up on the web. Or if you manage to find some very patient and considerate soul, you could even design and mail out your own QSL cards for the event. I still have the very attractive Dayton QSL card that KW1I designed a few years back.
When all this is done, give yourself a good pat on the back. Setting up such a station is not an easy task, but take heart, it does get easier and more enjoyable each time. Know that while you are providing a fun morning diversion for you and your ham buddies, you are also doing a great service for the hobby. Your station can demonstrate the magic of radio to a prospective ham, enrich the radio experience for newcomers, provide an impetus to get back on the air for the inactive, trigger some fond memories in our older hams, and end up costing you no more than a few cold beers. I would say that is bargain indeed!
73 Bruce W1UJR
AM Is Hardly “Ancient Modulation”!
Although at times it is jokingly referred to as “Ancient Modulation” by its detractors, AM is “Angel Music” to those who enjoy this special mode of modulation. AM refers to the method of modulating the RF carrier, in this case, Amplitude Modulation. Amplitude Modulation (AM) was the first voice mode used in amateur radio, and is now very much alive at it enters the 7th decade of its life. AM is a well-regarded specialty within the radio hobby, and its operation offers a warm, rich audio quality that provides for more personal interaction. AM is rich with tradition, and the time honored tradition of elmering and homebrewing equipment are no exception. AMers often build and maintain their own antennas and transmitters. The simplicity of AM circuit design encourages hands-on restoration, modification and homebrew construction to an extent no longer found among contemporary radios.
You may find AM culture is a bit different than what you are used to. Often QSOs tend to center around technical discussion, especially relating to tube type gear. Antennas are also a popular topic, and different styles and methods of feedline construction are often debated. Transmissions tend to be more extended, and VOX is rarely used. In fact, the pace of AM QSOs is often quite leisurely. AM slang is very descriptive, do not be surprised to hear some rather interesting terms, from some quite interesting people!
Technical items are not the only issues discussed however, and established nets deal with topics ranging from UFOs to historical events. Two of the more interesting nets, in this authors opinion, are the “Future Net” found on 3.875MC Sundays at 4:00 PM and the “Gray Hair Net” on 1.945MC Tuesdays at 8:00PM. Not to be missed is the “AM Swap Net” on 3.885MC Thursday at 7:00PM, where equipment and parts are exchanged in a “tongue in cheek” fashion. Locally look for the “Sunday Morning Brunch” net on 3.815MC around 9:00AM, the “160m Early Morning Net” on 1.885 which starts around 6:00AM and the “2m AM Net” on 144.450MC Sunday evenings at 8:00PM.
AM activity can be found on a variety of other frequencies both day and night. For daytime operation check around 7.290, 14.286 and 29.10 MC. Evening and early mornings 1.885, 1.888, 1.945, and 3.885 are your best bets. Most AM operators will gladly welcome newcomers to the mode, give it a try!
That’s it; you’re ready to get on the air on AM. If you are running a solid state rig, you will want to reduce the RF output to about ¼ of the maximum valve. For most of today’s rigs this equates to 25 watts carrier. You might also want to reduce the mic gain somewhat from what you are running with SSB. These settings may not be exactly right but this should get you close. Once you get on the air, ask for an audio report to determine to determine if you need to do any tweaking. If you access to an oscilloscope, by all means, use it to adjust your mic gain. Using a scope, you can determine your percentage of modulation and if you are “flat-topping”. Flat topping refers to the distortion that occurs when a transmitter is driven past its max power output. Distortion, and splatter onto adjacent frequencies occur during flat topping, something that you want to avoid.
If you run your transceiver into an amplifier, follow the same steps with the linear in line. One important thing to remember is that your amp will be running at about 20 -25% efficiency, and what does not go up the antenna as RF is given off as heat. So, you may want to get your calculator out and determine how many watts you can run without exceeding the plate dissipation rating of your linear. Remember that AM is a 100% duty cycle mode, as opposed to 30-50% for SSB. So the tubes and the power supply in your amp will be working much harder. You may not want try to squeeze every last watt out of your rig. The difference in received signal strength is just not worth it. Err on the side of safety.
The AM mode can be a tremendous bit of fun. Although it is most often associated with older, tube gear, modern day transceivers can produce some very good sounding AM when properly adjusted. Whether you were an active AMer in the past, or new to the AM mode, by all means get on the air and give us a call. Welcome aboard!