Take back 40 Meters from foreign broadcasters
Powerful foreign broadcast stations discourage much nighttime Ham activity on 40- meter phone. Although they are strongest late at night, they seriously interfere during the early evening hours when the short-skip distance is still suitable for stateside activity. This low-cost, easy-to-construct receiving antenna can change each interfering broadcast station into two almost private channels (USB & LSB), for those who care to experiment. Hams with conventional antennas will still avoid those frequencies.
This idea has been tried by many Hams in the past, but apparently no antenna has proved effective or reliable enough to gain wide acceptance. Note that deliberately transmitting on foreign broadcast frequencies is permitted because U.S. amateurs have primary rights on our 40-meter band.
Plotting this antenna on ELNEC or EZNEC reveals why it can work so effectively. Two vertical loops in the same plane, separated by 1/8 wavelength and fed with 135 degrees phase difference (over real ground), yield deep nulls in both vertical and horizontal polarization at low and medium elevation angles. The cardioid pattern maintains a narrow cone-shaped zone that nulls out incoming waves of changing polarization, and probably explains why this system is able to maintain its deep nulls for extended times.
Obtaining this improved performance requires rather precise control of phase and amplitude, along with good stability over times suitable for QSOs. All of these are accommodated using two High-Q loops of about 4-foot diameter, made from 1/2 inch diameter surplus aluminum cable-TV coax, where the inner conductor is used only to deliver DC control-voltage to the varicaps.
They are tuned with a varicap, which on this model, is the internal-diode of a 400-volt power MOSFET. It performs exactly as a varicap. Most other low-cost Power MOSFETs perform similarly.
The 135-degree phase separation is obtained by making one feed line longer than the other. But if the feed-tap on one loop is oriented in the opposite direction, one feed line now need only be (electrically) 45 degrees, or 1/8 wavelength longer. The longer one attaches to the loop nearest the direction of the null. Termination impedances affect the accuracy of these phase shifts so it is prudent to allow for some change. Polyethylene dielectric with a velocity factor of 0.66 would be about 11 feet longer at 7.2 MHz. Cellular polyethylene dielectric would be about 13 feet longer.
With the required phase shift provided by the feed lines, the two High-Q loops can now be resonated near the exact frequency of the foreign broadcast station, to maintain good sensitivity. But since great accuracy in phase and amplitude is required, remote tuning with potentiometers at the operator position provide the necessary tweaking of these resonant loops to trim for small phase and amplitude changes that occur when the resonant frequency is changed. Each loop is tuned by its individual potentiometer in conjunction with a differential potentiometer which is common to both. One must accept that reaction will be very sharp to get 40 to 50 dB deep nulls, and very careful tuning will be required. It almost requires an AM carrier such as foreign broadcast provides, and even then, rapid QSB can be tedious.
Deeper nulls can be obtained if an isolated 9-volt battery is used at the junction box near the operator position, with the box grounded only to the three coax shields (see figure). Using an AC power supply instead of a battery adds stray capacitance and may degrade the nulls.
These loops were strapped to ordinary concrete blocks with rubber truck-tarp straps, and could be easily moved around the yard. Having the loops in exactly the same plane (as in a pair of eyeglasses) is not critical, but the center-to-center spacing should be fairly accurate at 1/8 wavelength, which is about 17 feet at 7.2 MHz.
Performance was very good, consistently nulling 15 dB over S9 AM stations down to the noise-floor at S1 and remaining there for extended time periods. A test generator with an AM tone, with strength about S7 (not in the null area) was tuned exactly on frequency with a 40 dB over S9 foreign broadcast station (i.e. when only one loop was used conventionally). Of course it wiped out the test generator, but when the second loop was attached (having previously been tuned for null), the foreign broadcast was severely attenuated, and the S7 test generator now dominated. Audio cassette tape recordings were made to demonstrate this. A typical Ham station, not in the null zone, would be quite easy to copy.
An interesting, less important feature, is the ability to quickly utilize one of the loops conventionally for 160M or 80M (or both). Tuning the loop to 160M is done easily by attaching a shunt capacitance across the MOSFET with small alligator clips. A combination fixed/variable of about 1700 pf resonates it. The MOSFET still provides just enough remote tuning to cover the 160M band. Sensitivity is very adequate as indicated by a winter-time noise-floor of S2, and strong signals reading at least 20 dB over S9.
Since this article is about receiving loops only, it is left to the reader to arrange a receive/transmit configuration. Note that the 400-volt MOSFETs will probably tolerate strong fields from your transmitting antenna without damage. But in the presence of very strong fields at close range, it might be very effective to reverse the DC voltage polarity to the MOSFETs during transmit to cause the varicaps to conduct lightly and partially short out the High-Q loops.
Reprinted from WORLDRADIO
Amateur Radio in Cuba
John Sweeney, N6ANQ, Geri Sweeney, N4GHI
Amateur radio is alive and well in Cuba. Cuban amateurs are proud of their hobby and their accomplishments and report that Amateur Radio in Cuba is growing in quantity and quality.
The Cuban emphasis on education has resulted in a strong capability base; Cubans can do most things, and do them well. They build and fix things themselves. From the standpoint of Amateur Radio, our QCWA members would feel at home. The Cubans build and maintain most of their own equipment. Their ARES-type nets are of tactical and strategic importance to the whole of Cuba; a fact overwhelmingly demonstrated during Cuba’s last hurricane, when some 450 radio amateurs responded to the call of duty and provide the nation with vitally needed communications.
One of our geographically closest neighbors, Cuba remains an enigma: while Communism is in full retreat having proved itself intractable in almost every other country (excluding China), it continues to function in Cuba. Officially we shun Cuba, yet President Carter recently visited with a statesman’s welcome. Immediately prior, a large group of American businessmen, with a handful of Congressmen, visited to discuss post-normalization relations. While Mr. Castro’s Cuba has many problems, it boasts a ten-fold reduction in infant
mortality and a near 100 percent literacy rate. The literature on Cuba provides almost as many views as reviewers. I was intrigued by the apparent freedom of Cubans to communicate with the world via Amateur Radio. I had worked many Cuban Hams myself. Yet no Cuban station, to my knowledge, has been a part of the International Traffic and Assistant Net (The ARRL ARES-type net that provides coverage of the Americas). We have a Third Party Traffic Agreement with Cuba, but it is not used. We have no reciprocal licensing agreement. I wanted to learn more about a specific slice of Cuba — Amateur Radio. World Radio provided us a commission to author an article on Amateur Radio in Cuba. To gain first-hand knowledge, we visited Cuba via sailboat with Ham equipment aboard that would allow us to work all traditional HF and VHF bands.
Two Cuban amateurs, Arnie Coro, CO2KK and Oscar Morales Jr., CO2OJ, were of particular help in setting up our visit. Arnie is a broadcaster and professor at the University of Havana while Oscar works at the Cuban Customs Agency.
Our first letdown was to discover that we would not be able to get permission to operate in Cuba, so that rather than participating, we could only listen (until we were outside of Cuban waters, then we could talk to any Cuban amateur). We did visit with many Cuban amateurs, we visited their homes, we attended a club meeting and visited a club station. The Hams we met were very friendly and informative. Our discussions demonstrated an enormous amount of common interest and perspective. Cubans operate all modes from Moon bounce to rag chewing; from PACTOR III to CW. When Hurricane Michelle tore through Cuba in November of 2001 with winds of 140 mph, telephone communication across the central part of Cuba was virtually non-existent. A major portion of the emergency communication, and the post hurricane clean-up coordination was carried out through Amateur Radio utilizing both HF nets and mountaintop repeaters. Francisco "Panchito" Rodriguez Lorenzo, CO6RL, a blind amateur, is the coordinator of the National Traffic Nets HF net (on 7110 kHz, at local noon) that helps about every possible need, including locating hard-to-find medicines, learning about relatives in hospitals etc.
the old saw “Where you stand depends on where you sit”, we did have a few
perceptional differences. We championed use of the third party agreement
between the U.S. and Cuba as a communication channel between families split
between the U.S. and Cuba (forbidden by the Cuban government); they viewed the
restriction as necessary to limit propaganda dissemination. They complained of
U.S. inaction in stopping deliberate jamming of their ARES nets, a problem that
happens on a very frequent basis from stations located in South Florida. We
were surprised to find that one of the Cuban amateurs, interested in sailing,
would not be allowed to even sail just off-shore with us. Still, surrounded by
Cuban amateurs at the club meeting, we found the same full-spectrum,
uninhibited exchange of views that exemplifies almost every Ham group in which
Cuba has a population of about 11 million with nearly 4,000 Hams. The road to becoming a Ham in Cuba is tough (perhaps, again like the good old days in the U.S.). One is tested on the ability to send as well as to receive Morse code. The tests require answers; not multiple choice. For the 3rd Class license, after passing the code (5 wpm) and written test, the applicant must demonstrate that he can tune a radio. Only then does he receive a construction permit to build a radio. On completion and inspection of the radio, the applicant receives his 3rd class license; with a CL prefix. An amateur must operate under a 3rd class license for a year before she or he is eligible to upgrade. Upgrading requires another test and an increased level of CW (10 wpm) competence. The 2nd class operator receives a CM prefix. The highest-level license (1st Class) requires a 15 wpm code test and another written exam on rules and theory. The 1st Class license is identified with a CO prefix.
Beginners generally build one of two radios; the vacuum tube Islander or the solid state Jaguey. The Islander is a DSB/CW Cuban design using a very clever low parts count circuit and a direct conversion receiver. The Jaguey, named for the Jaguey Grande Radio Club in Matanzas province, is a generic design, with a DC receiver, DSB and CW, using solid-state components. Many of its ideas are from Wes Hayward's W7ZOI's Solid State Design for the Radio Amateur. The lack of mechanical filters or quartz crystals to homebrew SSB filters made Cuban designers CO5GV, CO2JA and CO2KK choose a DSB and CW rig. Fitted with good quality capacitors for the VFO, it works quite well from a 12-volt car battery in hurricane emergencies.
Due to the difficulty in obtaining parts, many amateurs operate at club stations. We visited the station of the Federacion de Radioaficiaonados de Cuba, the Cuban equivalent of our ARRL. It was well equipped with HF and VHF operating in CW, voice, and digital modes. Our host for this visit was Club President, Ing. Pedro Rodriguez Perez, CO2RP.
We were honored to visit the home of Arnie Coro, CO2KK, in the Nuevo Vedado district of Havana. Arnie, a broadcaster and professor at the University of Havana specializing in mass communications, has long played a key role in generating enthusiasm for Amateur Radio in Cuba and abroad with his Dxers Unlimited program, that is on the air twice weekly over Radio Havana Cuba. His description of the development and present state of the hobby and insights provided much of the base for this article.
We found our trip to Cuba to be particularly interesting. When one meets another face-to-face, it is next to impossible not to develop a rapport, and to appreciate that for all their differences, people worldwide are not only pretty much the same, but also quite nice.
Reprinted from WORLDRADIO
GRUMMAN AMATEUR RADIO CLUB
MINUTES OF GENERAL MEETING – 8/20/03
by Pete, N2PYV
The meeting was called to order by Gordon at 5:30 p.m. Pat was on vacation.
All present introduced themselves.
Finances continue to be in good shape.
REPEATER REPORT –
Gordon got a call from the Plant 14 Maintenance Dept. stating that the repeater antenna would have to be taken down immediately because a contractor was going to repair the roof. The repeater will be off the air for a few days until the roof work is completed. During the blackout both repeaters were operating.
NET REPORT –
There was not good response on the Thursday Two Meter Net, but this was during the blackout. The propagation on the Wednesday net was good.
VE REPORT –
There were four applicants and four VE’s present. Two new hams made Technician and one failed. One applicant advanced to Extra.
Bob also reported that W5YI has stopped publication of the W5YI Report and is going into semi-retirement.
WAG REPORT –
The meeting tonight was held in the Bethpage Public Library because Bill, N2SFT was on vacation and there was no one available to escort us into the UL building.
Gordon stated that N/G is planning to lease the second floor of Plant 35 back from Briarcliff College.
Gordon reported that the US Coast Guard Auxiliary got good grades in communications in a recent Search and Rescue Exercise. All of the participants were hams.
Howie, W2QUV, stated that the election for the Hudson Division of the ARRL was coming up soon. He urged all ARRL members to vote.
Marty, NN2C, provided a tape about the Dxpedition to Kingman Reef in 2000. It was very interesting.
Bob, W2ILP gave a talk about Broadband Over Power Lines (BPL) that is being considered by the FCC. This will apparently create a large amount of interference problems with ham operations if it is allowed to be implemented.