8p6kx John Webster
around 11:15 am and my antenna was blown away, I then put my equipment into cases to try to protect it from the rain. Shortly after, I heard the top of my house breaking away and my cousin— who was on the top floor—was calling for help He was not hurt but afraid, and t told him to come clown below, which he did Things were flying all about outside by this time, and it was dangerous to be outside We put some boards and things on a bed so that in case of debris falling from the top of the house we might hopefully survive. After the roof ripped off, some of the floorboards which were covering the downstairs also ripped off, and water flooded inside the house. We then took refuge under the bedr where we remained lying in a pool ot v\ater two inches deep for three to four hours.
"As soon as the wind eased up a tittle later, I thought that the first thing to do was to get into the cellar of a neighboring wall house where we iould be safer, and maybe from there I could get my equipment back on the air, as it was still safe in the cases.
Carrying my equipment, I jumped through a window, along with my wife and cousin, and ran under that house, where I tried to set up the ng, However, when 1 looked outside for trees to which to tit- the antenna, 1 could not find any —all around was totally flat located whatever wire I could find and twisted the bits together to make an antenna 70-80 feet long, using sticks to support it about one foot above the ground This makeshift antenna allowed me to get on the air at about 5:00 pin Wednesday f managed to contact Allan 9Y4LG in Trinidad and spoke with him for about three minutes, just long enough to let them know that I still had my equipment but that as far as my eyes could see everything was flattened, and I would be back on later when the winds had fully subsided and I was able to make a better antenna
"It was around 7:00 pm when I completed a better antenna and got the center about 10feet high with a piece of stick off one of the broken-down houses. This antenna allowed me to communicate without as much danger to my rig as the first one A message was relayed to Radio Antilles by one ot the hams in Montserrat that contact had been made with me, and mv address was given so that I could be contacted This information was broadcast over Radio Antilles —which is very well received in Dominica and to which most Dominicans were usually tuned, unlike Radio Barbados which can hardly be heard-
"Around 10:30 pm, a reporter from Radio Antilles and some other guys came to me and said that they and the Prime Minister had heard the broadcast and lie had sent them to me to broadcast the following message: The Prime Minister has declared a state of emergency in Dominica.
genera/ state of disaster has been declared for the entire island. The Prime Minister ;s requesting all islands to suppl\ medical and any t\pe of assistance which they are able to provide to the island. It is feared that there are 60,000 people homeless. Two per-sons are so far known to have perished. Hospital has been partly demolished.
"After sending this message, I went off the air to conserve my battery power and spent the mght in the same cellar with 30-40 other people, two of whom were hurt, although not serious-
Next morning around 6:00 am (Thursday, August 50], some policemen came to move me to Police Headquarters in Roseau, so I sent my equipment with them while I went to try and lind some coaxial cable so thai I could put up a proper antenna. I arrived at Police Headquarters at 8:00 and managed to get my equipment operating trom about 12:00 noon. From this point on, I worked for 24-48 hours continuously passing information relating to requirements for aid, speeches by the Prime Minister and other ministers, and reports by newsmen in the island. The speeches and news reports were relayed to Radio Antilles via other hams, who then broadc ast them lor reception by Dominicans. Radio DBSr which normally operated out of Roseau, was very severely damaged and was not functional. 1 had to operate almost continuously until I got some help from outside. I think it was from 8P6GB from Barbados, late on Friday evening,"
Hurricane David battered Dominica for about five to six hours, with the eye passing over the southern part of the island during a twenty minute period be
Photo F Aerial photograph taken on Friday, August 31st, showing severely damaged warehouses on the outskirts of Roseau.
ginning Wednesday at about 12:30 pm After the passage of the eye, the winds, which have been reliably estimated in excess of 240 km hr, returned suddenly with renewed vengeance from the opposite* direction — from a westerly direction. This whipped up waves 9 to 15 meters high, and these waves pounded the west coast, causing extensive damage both to properties and to the roadway which runs at water s edge in most places.
Around 5:00 pm on Wednesday, most people began to emerge from the wreckage of their homes to be confronted with an utterly depressing scene, In five to six hours, the island had been completely devastated. It was estimated that out of a population of 85,000 souls, 60,000 were made homeless; miraculously, only 40 deaths were recorded
Damage to property was extremely severe, resembling photographs that I have seen of severely bombed-out areas in Vietnam. Large steel-framed buildings had been reduced to twisted heaps of junk (See Photos E and F ) The en-11re power distribution grid was destroyed, with hardly an electricity supply pole still standing, and the water supply had been disrupted, Roadways were impassable almost everywhere, being blocked either bv debris, fallen trees and poles, or swept away by the sea T he island, which largely is covered by dense tropical rain forest, appeared as though swept by fire. Almost the entire forest was completely stripped of foliage, leaving just broken and uprooted stumps of the trees (photos C through J),
I have always found it to be a beautiful green island, but on arrival there two days after David, I was overcome by a wave of great sorrow The forest was quite brown and denuded, and wherever you went the picture was the sametotal destruction of everything around —and you kept wondenng how this newly-independent nation could ever pick up the pieces and make a new start.
However, that was our reason for being inxolved — to help them begin to pick up the pieces and make that new start. Over the following days, Barbados, due to its geographical position, good airport and seaport, infrastructure, excellent communications links with the rest of the world, andH most
Photo G View overlooking the Kingshill area, in the vicinity oi ¡7DAY'S QJH There was nearly complete and total desfrucf/on oi the houses in this area and to the south oi Roseau.
Photo H. Ruins of the Roseau Anglican Church; miraculously, the stained-glass windows survived the wrath of David importantly, its well-organized and prepared Central Emergency Relief Organisation, became the center of all relief operations for Dominica.
The ARSB, because of the emergency situation, obtained permission at 7:45 pm on Wednesday, August 29th, to handle third-party traffic and phone patches relating to Dominica. This set the stage for several weeks of really serious relief work by the hams. That night, acting on the information relayed by J7DAY from the Prime Minister of Dominica, the hams in Barbados contacted the Barbados Govern ment and ail embassies stationed in Barbados I hese incfuded those for the USr Canada, the UK, and some European countries,
The British High Commission advised later that ntght that the Briiish FrigateHMS Fife, which was in the area and had a helicopter on board, had been instructed to change course for Dominica, where her men would render what assistance they could, The hams were advised that they should make radio contact with the Fife, calls were made throughout the night and next morning but she never came up on the ham bands—this remains a mys
Photo i Typical post-David view of fhe now denuded but once lush rain forest that once covered most of Dominica and flanked the roadway between the airport and Roseau. the capital.
Phofo K. The Cessna 182 preparing to take oft from the Massacre Bypass, The hams from Barbados used this method of transportation to gef mfo Roseau while the road across the island was Still blocked, ¡he opening of the cane field airstrip, located in the right background, trough r an end to this hazardous exercise. Fortunatelythe only damage resulting to aircraft using this roadway was a burst tire on the Cessna at touchdown, which grounded it for fwo days until spares arrived, and some w ing damage to another aircraft on takeoff. The latter was probably caused by a pole like the one seen overhanging the roadway in this photot but the pilot was able to make a successful landing in nearby Martinique even though the flaps on his right wing were torn away and flapping in the wind„
Photo /, Decaprtafed coconut trees at a coconut estate on the west coasf of Dominica. Official estimates indicate that 4,500 acre s oi coconuts were left in this condition by David and that it will take six to seven years to bring this crop back into production.
tery to the hams to this day.
The Fife arrived in Dominica by noon the following day — Thursday — but was unable to berth due to heavy seas. Men and equipment were ferried ashore by the helicopter, where they immediately assisted Dominicans with cleaning of the main streets in Roseau and in the repair of the hospital buildings and equipment, all of which had been badly damaged. Actually, the Fife provided through her distillation plants the only source of potable wafer available in Dominica for two or three days, until other methods of purification could be established. This was necessary since the normal water supply had been ciis rupted and the rivers—of which there are 365 in Dominica — had become polluted from the death of many animals, It took about a week before water was again flowing in pipes to the main housing areas, and much longer before it was in those to the rural areas throughout Thursday, all types of emergency and priority traffic flowed on 7.185 MH/ into and out of Dominica Most of this traffic was for Barbados or Montserrat Montserrat became very important to Dominicans, because on that island is located a commercial broadcasting station—Radio Antilles — which broadcasts on the AM band Radio Antilles became a vital link in making information available to the Dominican public. This was especially so since damage to Radio DBS kept it off the air. In addition to the emergency traffic, journalists in Dominica were allowed to pass their reports to the news services via ham radio
However, it was impossible at this stage for health and welfare traffic to be handled, and Fred I7DAY was working continuously, unassisted. There are not many hams in Dominica anil, unfortunately, ot the tew that exist onlv Fred (apparently) was able to carefully pat k away his equipment and make it and himself available to his country in this time of need Most of the other hams either had their equipment damaged, had no power, o; were so shocked at the disaster that they were unable to assist
It was at this stage, after midday on Thursday, that i decided to volunteer to go to Dominica Charlie Briggs 8P6CB did so also Our ot ter was acc epted by J7DAY that night, and we then had to find a way into Dominica Enquiries revealed that Barclays Bank, which maintains a twin-engined aircraft for use in the Caribbean area, had made a landing that morning al Melville Hall Airport This was the first aircraft to land in Dominica after the disaster, it took a rather heroic effort by the pilot, Mike Little page, as the winds were still very unpredictable, there
Photo L There was never any problem in finding wires tor antennas or running emergency power lines. One just walked into the street and cut ofi what was needed. Here the author can be seen obtaining wire from a fallen pole with which to erect his antennas.
Photo M. trection oi a 2-meter quarter-wave vertical with a chtcken-wire ground plane.
was no air traffic control, and there was little indication of what the landing strip was like. Nevertheless, Mike made a successful landing, and through his efforts the world was made aware that the airport was serviceable.
There was still, however, a serious problem in that the airport is in the north of the island and Roseau, the capital, is in the south, separated by a distance of some 36 miles. Most of the road is a rough, narrow road in dense tropical rain forest (see Photo I). This meant that most of the roadway was blocked by landslides and fallen trees, and supplies and personnel arriving at the airport could not be taken by ground transportation into the capital until the roads were cleared This clearing process took some five days, with crews working around the clock using bulldozers and chain saws from both the Roseau and airport ends,
Barclays Bank agreed to fly us into Dominica and on Friday, the 31st, at 1:45 pm, we departed from Grantley Aciams International Airport and headed for Dominica, along with an aging Heathkit S8-10Q transceiver.
On arrival at Melville Halt Airport three quarters of an hour later, we expected to be flown in to Roseau by the helicopter from HMS Fife This was not possible, however, as the helicopter was otherwise occupied shuttling injured persons and medical supplies to and from the airport.
Following some discussions with officials at the airport, we were introduced to an American missionary who had been living in Dominica prior to David, He had a small single-en-gined Cessna aircraft in which he had already made several flights that morning to the other side of the island, landing on a roadway known as the "Massacre Bypass/' some three miles from Roseau. On these flights, he had shuttled people back and forth — mainly journalists and their camera crews He offered to take two of us and our equipment across. However, as darkness was fast approaching and I was not very familiar with Dominica, it was de< ided that Charlie and another guy, a Dominican who had come down with us from Barbados, would be taken with the equipment In this way, Charlte should be able to find the Q i H from which we would operate, and I would return to Barbados that night to make another attempt for Roseau next morning
As we left Dominica for Barbados, we flew along (he west coast and were really shocked at the extent ot the damage. Our pilot made several approaches on the Massacre Bypass, and it was decided to bring in a Cessna 182 the following day in addition to the twin-engined aircraft I his small plane could be used to shuttle the wives and children of Barclays Bank staff from the Bypass to Melville Halt, from whence they would be flown to Barbados in the larger aircraft.
Later that night, after Charlie had made his way to one of the Barclays Bank manager's houses which had largely survived the onslaught of David, he passed the following information concerning the landing strip on the Bypass; "[it is] 350 paces long, 7 paces wide, with a slight left-hand bend on landing from the north— several potholes Bridge on the southern end; road severely eroded by the sea on northern end. telephone poles hanging over the toad slightly at southern end "
i was flown in to the
Bypass next afternoon on the second landing of the Cessna 182, after a very long delay at Melville Hall caused by severe conges tion I counted over twenty aircraft ranging from small Cessnas to large C-130 transports, all jammed together on the small park-
Photo N. John L. Webster 8P6KX/9Y4}W operating J73N (formerly SPbCfi \7\ He spent two weeks in Dominica from the I si to the 14th of September
Photo O Charlie Briggs 8P6CB/9Y4CEB, the third operator of 173N.
trig apron This naturally created a traffic jam, and the passengers on one com-men la J flight which landed during this time had to disembark tn the center of the runway
The landing on the Bypass was one of the most frightening moments of my lite, and I've never felt so relieved as when I was able to step out of that aircraft on to firm ground! (See
Photo P. Operating QTH oi SP6C8./7 f¡7IN). The CB half-wave ground-plane verticalI which was very successful used on 20 meters unaltered, and the 20-. 40-, and 80-meter d i poles may be seen.
Photo K J
Alter consultation with Fred, it was decided that we would handle health and welfare traffic mainly, on frequencies of 3.835 -MHz at night and 7 220 MHz during the day. Fred would continue to operate on the main emergency frequencies ofl805 MHz and 7 185 MHz We would shift to these frequencies if and when Fred required a break.
Internal communications between Fred and us were maintained via Cft equipment on channel 9 for the first tour or five days until we were able to obtain some VHF equipment. At this stage, we switched to 2m — 146.52 simplex — for internal communications.
Charlie and I arranged a program so that we could operate 24 hours a day in shifts. (See Photos L and M.) We operated as 8P6CB/I7, but this was changed after a week of operation to 17 as all emergencv stations assumed Dominican call-signs (See Photos O, and P.) Our 24-hour operation continued until early in the morning of Monday, September 2nd. when we suddenly realized that our receiver had lost all sensitivity and our transmitter also had developed some problems. Apparently, our aging SR-100 decided that 72 hours of continuous operation was the final straw and had packed up on us.
What does one do in such a situation to get spares? We were really at a loose end, but word was passed to the engineers on board the HMS Fife who were able to supply us with most oi the required components However, before we could install them, John Ackley KP2A offered us, and we accepted, the loam of a Kenwood TS-820S John, of the American Virgin Islands, is a pilot and owns a liyht aircraft; he arrived in Dominica about September 1st and brought with him a considerable amount of radio equipment. John actually ended up outfitting the three main amateur radio stationsFred, himself, and us. KP2A was set up in Red Cross HQ and handled mainly health and welfare and other Red Cross traffic, John was often on 20 meters working into the US, (See Photo Q )
Our health and welfare traffic was disseminated in the following manner HM5 Fife, by September 1st had started regular broadcasts to Dominica on the frequency normally used by Radio DBS —595 kHz-us*
Photo Q. lohn Ackley KP2A of the US Virgin Islands set up as I73A in Red Cross HQ.
ing the ship's transmitters, As these transmitters were not designed for continuous usage, the broadcasts w ere unconventionaI. Transmissions began every hour on the hour, and tor the first 10-20 minutes, health and welfare enquiries, including those we had received and passed to them by a runner and other messages, were broadcast, This was followed b\ music until twenty-five past the hour, at which time the same transmissions were made in patois — a corruption of the I rench language spoken in Dominica
After 50 minutes of transmission, the station would go off the air for ten minutes to allow the transmitters to cool and to make any necessary adjustments. Meanwhile, engineers of the Fife repaired the station at Radio DBS, permitting it to resume transmissions about one week after David. Even after Radio DBS resumed transmissions Irom their normal QTH, however, we continued to disseminate our health and welfare traffic in this manner
Charlie was relieved by mv XYL, Elsa (see Photo R), who is also a hamr licensed as 8P6MH, 9Y4LL, and ex-VP2DL. She took over for five days from September 3rd whiie he had a break in
Barbados. During this period, we had one of our finals fail (a 6146B), once again putting us off the air for some time However, Fred was able to return to the ruins of his home and locate a replacement amongst the rubble and get us back on the air
During the two weeks that we operated out of Dominica, power for our equipment was supplied for the first week by small portable, 300-Watt Honda gasoline generators —see Photo S. These proved adequate until we tried to provide lighting as well. At this point, we often used to FM somewhat on our transmissions as the light presented too great a load to the generators. During our second week we were provided with a 1.6-kVA diesel generator which, in addition to powering our equipment and lights, was also able to power a refrigerator which allowed us to have cold drinks —quite a luxury under the circumstances.
I should emphasize here that it was largely through the efforts of Barclays Bank that we were able to go into Dominica and render what assistance we coufd Barclays took us there and back on their own aircraft, provided us with the power generators, fuel, and food supplies, and even housed
Photo R t/sa Webster 8P6MH 9V4LL operating the station 8P6CB/J7. Lisa was the only female operator to come into Dominica during the early relief effort and she spent five days there.
Photo S. The author refueling a portable standby generator of the type used by the Baian tBarbadian) hams, in Dominica, to power their equipment These small 30(L\\att Honda generators a Ho wet/ continuous radio operation for about six hours on a half gallon of gas. They were used for about a week prior to Barclays Bank providing a 1.6-kVA diesel generator, shown in the background This larger generator ¿//owed the operation of a refrigerator and lights at nightr in addition to radio equipment.
us in Dominica,
As the relief effort progressed, other hams made their way to Domintca, each to make his own contribution I have already mentioned KP2A and his invaluable contribution to the relief effort-
Bob WpDX from the US was an early-comer who, I believe, walked a considerable distance from the airport to Roseau with his equipment. He operated out of Police HQ, near Fred,
Another outstanding contribution was made by Stanley VP2ARC from Antigua, Stanley maintained a radio link between Fred at Central Control in Roseau and the airport for some time prior to the passage ot hurricane Frederic.
Frederic was the hurricane which followed closely on David's heels which threatened Dominica for some time, causing vir-
Photo T. Emergency supplies irom the US being unloaded from a US Marine lolly Green Giant helicopter at \\ ind-sor Park, the main sports field in the capital. These helicopters ferried supplies from the airport to the capital even after the roadway was reopened, until an adequate stockpile was established> The boxes to the right of the photograph were a shipment of VHf equipment sent by the IARU to assist in internal communications, tual panic, until it veered northward, missing Dominica but bringing considerable flooding in the north of the island, especially at the airport. This flooding resulted in damage to relief supplies that had arrived at the airport and were being stored there Also, when the river adjacent to the airport overflowed its banks, one of the large US "lolly Green Giant" helicopters (like the one shown in Photo T) was swept into the sea and severely damaged.
After the passage of Frederic, Stanley was taken by helicopter to most of the outlying villages in the central and southern parts of the island. On each occasion he radioed back very detailed reports. He aiso was able to deal with health and welfare enquiries relating to these districts.
The International Ama-teuf Radio Union (IARU) sent a shipment of VHF gear for use in the relief effort (see Photo T) It included a VHF Engineering 2m repeater and about a dozen Genave GTX-2 2m transceivers, some with portable battery packs I hese were used to link all the local amateur radio stations, the hospital, and Radio DBS to Central Control at Police HQ Due to the verv rugged and difficult terrain m Dominica, 2 meters does not prove to be very effective over any great distances, but in the absence of telephones it serves a very useful purpose around the city and nearby villages, and will continue to do so for some time (photo U)
During the penod of relief that followed the devastation of Dominica by hurricane David, hams across the Caribbean area rallied together, passed thousands of messages, and made dozens of phone patches. Although a great many hams participated, I would like to single out a few who made outstanding contributions and greatly assisted with the smooth running of the relief effort At the top of the list are Ron 8P6BN (Photo V) and Richard 8P6FW (Photo W)( who worked around the clock from the beginning and were together responsible for most of the phone patches made. Arthur BPbAA as Emergency Coor-
Photo U. 17DAY and KP2A, both up in the tower, erect home-brew antennas for use with the VHF gear sent by the IARU. I hey are assisted by VP2ABC, to the right, from a safer location. The tower was located on top of the police HQ building. In the background may be seen the devastated botanical gardens and a damaged school.
dinator of the ARSB did much of the work behind the scenes, along with Toby 8P6AK who is president of the ARSB. Allan 8P6AH, although away from Barbados for about one week directly following Davids ravaging of Dominica, on his return was always around and handled some of the clearest patches we made, Also, Allan's witty character kept the spirits of al! high
Out of Antigua, we had Hya VP2AYL, who was the only YL operator, other than my XYL, participating in the emergency. Hya was noted for her relay of detailed weather forecasts for the Caribbean region from the Antigua Met Station, these weather forecasts were rebroadcast over Radio DBS
From Montserrat there were VP2MO and VP2MC, both of whom were important links in passing information to Radio Antilles.
However, in spite of all notable efforts by these and many other amateurs both in and outside the Caribbean region, it was most distressing at times to witness interference by unconcerned amateurs This interference generally took the form oi some sort of QRM on the emergency frequencies, but also included those amateurs who, even I hough advised that only
Photo V. Ron Armstrong 8P6BNr along with 8P6FW I Photo Photo U Richard Cale 8P6FW, together w ith 8P6BN, han-WI did yeoman service during the relief effort died most of the phone patches, emergency traffic was being handled, persisted in trying to get their heaith and welfare enquiries through The exercise has shown that many amateurs are not capable of passing and receiving messages
A true ham is illustrated in the words of Fred White J7DAV himself, who, when asked by a fellow ham about his personal situation replied, "The first thing I tried to save was the rig, because I knew if it got damaged, there would be no communication outside, "Actually, everything is lost on my side, and hopefully something can be done, sometime, but after t have taken all the emergency traffic here, then 111 start thinking of myself."
Fred's efforts have been acknowledged by the Government of Dominica, and at the island's first Independence Celebrations on November 1979, Fred was presented with his country's highest honor, the
I would like to express my gratitude to the Editor of the Bajan Magazine, Mr. Trevor Gale, for allowing me to use information presented in an earlier story by meP titled 'Unsung Heroes/' published in the November, 1979, issue of Bajan, ■
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A "Short-Yard" Antenna for 40/75
— fits where others won't
The problem of space in which to erect an antenna is, I suppose, as old as ham radio itself My first antenna consisted of four Wires strung between two sixty-foot telephone poles two hundred feet apart — but that was m 1920, and I just happened to live on a farm with plenty of space.
Few city lots today will accommodate a half-wave horizontal antenna for seventy-five meters, however; some even have trouble with forty meters.
Being in that category myself, I began looking around for some way to operate on seventy-five that didn't include running a wire over to mv neighbor's TV tower The first solution that comes to mind, of course, ts a ground-mounted vertical. That's fine and I enthusiastically recommend that method, but a base-insulated tower is not easy to manage and an aluminum tube sI.i< king up in the air sixty-odd feet ts not the easiest thing in the world to keep up there.
Having a forty-meter vertical already in operation, I came up with the following idea requiring onl\ about thirty feet of horizontal space. Fig 1 is self-explanatory, perhaps, but here is a simple verbal explanation,
I ran a copper wire up alongside the forty-meter aluminum tubing, insulated from the tubing at both ex tremities, and tied the bottom point to the inner conductor of the coax cable at the same place it is connected to the aluminum tubing. The coax braid is already strapped to the ground for the forty-meter vertical, of course. The horizontal part can be tied off, with an insulator at the end of the wire, to anything that is available—a house, shed, barn, or favorite tree Actually, it ire a 11 y does not have to be exactly horizontal. The outer end can be higher or lower than the end fastened to tlie forty-meter antenna. I tried several different angles, and, except for affecting the resonant length, it didn't seem to make any difference.
The length of the forty-meter tubing may have to be altered somewhat to bring it back into resonance where you want itr but I found very little difference after I put up the wire alongside. Of course, the horizontal portion will have to be trimmed to the por tion of the seventy-five-meter band where you wish to work, you'd want to do that anyway.
I found the performance of the forty-meter vertical unaffected and that of the seventy-five-meter wire as good as any half-wave hori zontal I've ever used.
This is an ideal "short-yard/' combination forty-
and seventy-five-meter antenna, but if you don't operate forty — or perhaps have a forty-meter beam — this same arrangement can still be used for seventy-five meters with slight modification. In that case, the horizontal wire is electrically fastened to the tubing at the top, eliminating the insulators and the wire running down to the bottom of the tubing îhe coax remains connected tn the same manner as with the two-antenna combination.
Another method might be to use youi beam tower to support the seventy-five-meter wire. In this case, the inner conductor of the coax would be connected to the wire only and not to the tower—the vertical portion oi the wire would have to be insulated from the tower as it was in the first instance. You would want to fasten the horizontal portion of the wire at about the th irty-foot level of the tower, give or take a few feet, remembering that the higher on the Lower you go, the shorter the horizontal portion will have to be (the idea being that from the coax connection to the far end of the wire, the electrical length should be a quarter wave of the operating frequency). Like most antennas, it should be trimmed to the frequency you mean to operate on.B
Fig, 1. A "short-yard" 75-meter antenna.
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Antenna Fans: Try the Skeleton Slot
— an improved driven element for VHF/UHF
One of the problems with simple yagi antennas is obtaining wide bandwidth while keeping the swr low over an entire band. Usually, one has to compromise and dimension the antenna for a particular portion of a band.
The main reason that the swr changes across a band is that the lengths and spac-ings of the elements used in the antenna do not change as the transmitted frequency is changed These physical arrangements, along with the wavelength change due to frequency alteration, cause changes in the mutual coupling to the driven element, and the feedpoint impedance of the driven element also is changing, and this contributes also to changes in the feedpoint impedance.
One classic approach to soiving this problem has been to make the driven element a folded dipole. The inherently wider bandwidth characteristic of the folded dipole element, as compared to a simple dipole, prevents the driven element impedance changing as much as the electrical length of that element changes. However, G2HCG has gone a step further and developed a driven element configuration which not only has broad bandwidth by itself, but when used in a yagi is far less affected by the influence of frequency-dependent electrical length changes of other elements in the yagi To top it off, the overall gain of the yagi may also be slightly increased by his form of driven element. Although his form of driven element is popular in G-Iand, it has not yet been used much here. Those amateurs who have simple, multi-element yagis and desire to increase the bandwidth characteristics will find this new form of driven element very applicable.
The skeleton slot-driven eiement, as it is called, derived from experiments concerning a true slot antenna A true slot antenna, as shown in Fig. 1, is not what most of us would visualize as being a 'Teal" antenna. It is, as the name indicates, a slot cut out of a sheet of metal. The slot thus formed radiates much like a conventional dipole. If one makes the slot wider, it is similar to making the length-to-diameter ratio of a conventional dipole smaller In other words, the dipole length remains the same, but the diameter of the elements increases This will increase the bandwidth. In the case of proper ly-dimensioned slot antennas, very large bandwidths can be achieved in the UHF range.
The skeleton slot resulted from experiments to determine how small the sheet of metal could be made and still retain the characteristics of a slot antenna. The final result was to demonstrate that a ' skeleton' made of tubing, and dimensioned as shown in Fig. 2 (a), acted much like a slot antenna. The antenna of Fig. 2 (a) can be visualized as shown in Fig. 2 [b), i e , as two Vi -A antennas spaced 5 8 A where the ends of each %-A section are bent.
The final practical form of the antenna is shown in Fig. 2 (c) along with practical dimensioning information for the VHF bands. If the antenna, used as a driven element in a yagi, is constructed of the tubing sizes normally found in VHF beams, the feedpoint impedance is approximately 300 Ohms. So, one can use twinlead as a feed-line for low-power installations or use a conventional 4:1 balun at the antenna for a 75-Ohm coaxial cable transmission line
Further practical experiments with the skeleton slot as a driven tig. The true slot antenna doesn t look like an antenna at all. It is a dimensioned slot cut in a large piece of sheet metal.
F I VHli
F I VHli
Fig. 2. (a) The original skeleton slot, (b) Showing how it might be visualized as stacked dipoles. (c) Showing practical dimensions, element showed that it worked best if bent slightly forward, as shown in Fig. 3 (a), at an angle of about 11 degrees from the vertical. Also, when using the skeleton slot as a driven element, the parasitic reflector elements in a yagi shouid be changed so there are two: each one at the approximate height of each horizontal member of the skeleton slot, as shown in Fig 3 (b). The reflector and director elements can retain their norma! dimensioning. There is
tmi some slight increase in forward gain using the skeleton slot as the driven element. This is probably due to the fact that the skeleton slot itself acts as two stacked dipole radiators, and also from the effect of the added reflector elements The gain increase can be about 2 dB.
It is difficult to say how much the bandwidth of a given VHF antenna will be increased by the use of the skeleton slot as the driven element. Increases in bandwidth of twice that using dipole elements are possible. Of course, this would be an increase in bandwidth in regard to keeping the swr low. It doesn't mean that the antenna would retain its forward gain characteristics over the entire band-
up to normal director director
Ftg. 3- la) I here is a small forward tilt to the skeleton slot. i b) J his is how the skeleton slot would be used in a vagi, with a modified reflector.
width Nonetheless, the ability to load into this antenna and get some gain at an increased bandwidth may well make the skeleton slot modification worthwhile.
Although the skeleton slot antenna has its main application at VHF frequencies, it also might have some applicability at HF frequencies as a wire antenna. The dimensions might suit some situation where only a small distance js available for the horizontal portion of the antenna on a given band, but height fs available. One idea that suggests itseif is to try the antenna on a tower using arms extending from the tower to form the horizontal portions of the antenna. Even on 7 MHz, only two approximately 13-foot-long arms would be required. Constructed of wire and used on the HF bands, the feedpoint impedance of the antenna might rise severalfold. This is because the dimensions of the antenna become so much larger than the diameter ot the wire that would be used to construct it Nonetheless, the idea is an interesting one, and such an antenna fed with a resonant transmission line might perform very well ■
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