Welcome to the fifth exciting, thrill-packed issue of Condo Communicator, a newsletter devoted to those amateurs who, for various reasons, must configure their stations to operate from restrictive areas such as condos, apartments, townhouses, neighborhoods with outdoor antenna restrictions, ships/boats, mobile homes, or wherever they fry their burgers and call QTH.
Whilst struggling to get a little homebrewed transmitter to work, I gave some thought to the concept of matching. Just as it's important to match the impedance between different circuit components to maximize the transfer of power, it's important to have a good match between your ham radio activities and station requirements in order to maximize the pleasure you can derive from the hobby.
For example, if you enjoy providing telephone patches between overseas military personnel and their families stateside, you'll derive considerable pleasure from smoothing the radio links for troublefree communications. It certainly is no waste of money to purchase the best equipment available, including beam antennas, high and sturdy towers, and amplifiers to overcome any obstacles placed in your path by mother nature. In this case, there is a good match between the activity and the station, maximizing the pleasure derived.
But if you live in an apartment, you're going to face considerable frustration pursuing the same activity. Even with sensitive receiving apparatus and an amplifer, you'll not provide the same quality of communications as often as the fellow with the space for large antennas. The families you're trying to help will not be happy with the scratchy and fading signals. In addition, your neighbors will certainly not appreciate the RF overload into their televisions and other appliances, and they will quickly let you know of their displeasure. Given such a mismatch between the activity and the station, you'll not derive much pleasure.
On the other hand, if you enjoy just trying to get a signal out of a "covert" location, then living in that same apartment could provide a great deal of fun indeed. Imagine the jollies I got when receiving a QSL card from a station I worked in Finland on 20 meters with less than a watt into an attic wire loop. Or the fun of building a small transmitter and getting it on the air, with no RFI and good, solid contacts. (So what if I had to seek troubleshooting advice from all my friends and loads of folks on Internet and packet?) The point is, there's a good match between my activities and station capabilities given the set of environmental restrictions within which I choose to live.
If you find operating from restrictive space frustrating, you may want to try reconciling your operations with your circumstances. If you want to run overseas phone patches from your apartment, you can fight the unit's management to install a tower, fight your neighbors so you can run high power, make a scientific breakthrough in the science of wave propagation, move, abandon the hobby, or you can examine what you're doing to see if you can make any modifications to produce a better match with your station and operating restrictions.
Dave, W8NF of Denver, Colorado, offers some advice about radio frequency interference. I had mentioned RFI problems with an old DX- 20 transmitter. Connected to a dummy load, and sitting on top of the family TV, the DX-20 produces zero interference. But, just hook it up to the attic antenna and the TV picture gets wiped out, worst on channel 2 but bad enough on all the others.
I wonder what would be a good ferrite composition to use and if anything of the appropriate mix is sold that will just clamp over the AC cord. I've had no luck with the variety sold by Radio Shack. Anyway, for those of you having similar problems, give Dave's suggestions a try.
Some more technical advice from Dave regarding limited space antennas, who suggests using the G5RV design. As radiation from a wire antenna occurs at high current points, then it's important to get the middle of a center-fed antenna (the high-current point) as high as possible, and it's less important to get the ends as high. Neither is resonance as important as getting as much current as possible into the wire. If you're not overly concerned about directivity or radiation angle, and if you can match the thing, then you're getting current into it, and it'll emit a signal.
The G5RV antenna is essentially a configuration of wire that shows an SWR of less than 5:1 on all bands when no tuner is used. The G5RV is a center-fed, 102-foot wire. You feed it with ladder line that's about 30 feet long (or 1/2 a wavelength at 20 meters). Now you have an antenna that's 3/2 wavelength of 20 meters and resonant on that band. Then, to the ladder line, attach your coax, first making a coaxial balun composed of 5 to 6 turns at about 6 to 8 inches in diameter. This produces an impedance at the transmitter side of the coax that most tuners can match from 80 through 10 meters.
If, like me, you don't have enough room in your attic for 102 feet of wire, even snarled, then Dave suggests cutting everything by half for an antenna you can match from 40 meters through 10 (with a tuner). That means a 51-foot length of wire, center fed, with the open wire feeder cut for about 15 feet (a half wavelength on 10 meters).
While we're on the topic, Dave will be using the G5RV design at his new house where the attic is larger. Currently, Dave lives in a house with two attics. His station is:
1. Tiny attic: 6/10/15 meter dipole. Also works on 12 and 10
meters. No tuner. 10 watts. No RFI.
2. Larger attic: 40-meter dipole, with center point as high as
possible and the ends "bent, twisted and gnarled in
whatever shape needed to get the thing to fit."
Tuner used. Won't match on 80 or 20, but operates
on 40, somewhat on 15.
When Dave fires up the SB-220 amp, however, his garage door goes up and down!
As you know, I've asked folks who live in buildings higher than two stories to send in their station descriptions. While no one living in on the 20th floor of an apartment has sent in anything yet, Howard Miller, N9RUI of Skokie, IL, near Chicago, has sent in a description of his third-floor setup.Howard uses an inverted vertical. It's made of thin magnet wire and is 35 feet long. With a small stone weight on one end, it's lowered from the window and blends in nicely with the brickwork on the side of the building and can't be seen. Howard has taped two counterpoise wires in opposite directions to the inside wall near the floor of his apartment. With this setup and a one-watt HW-8 Heathkit rig, Howard has worked into Indiana on 40 meters.
Howard's inverted vertical works fine from his third-story perch. I wonder how height affects the signal pattern of a vertical. Is the low-angle radiation of a vertical enhanced by being elevated? Although the building would block a good part of the signal, would an inverted vertical hanging from the 40th floor of a high-rise radiate as well in the free-space direction as an inverted vertical nearer to the ground? And what does inverting the vertical do to the signal pattern? Some of you antenna wizards write in and let us know. You could be helping a high-rise ham.
The newsletter is pretty short this month. After all, it's only as long as you make it. So, if you'd like more station descriptions and less editorializing from me, then send your notes, ideas, station description, war stories, editorials, and so on to me at:
US Snail: Art Winterbauer
428 Francis Street
Longmont, CO 80501
Also, listen for snippets of this newsletter on Hap Holly's (KC9RP) Radio Amateur Information Network (RAIN), heard on various nets or by direct dialup (708-299-INFO, no charge except for long-distance costs).
73,72. Art. , WA5OES