Leitrim - Current HF Antennas
Leitrim saw the first of its rhombic antennas installed during WWII. By the late 1990's, they were showing their age. Many of the masts were starting to rot and it was going to be an expensive fix. A study was done to see if they could be replaced by a different antenna system. Then came the ice storm of 1998 which caused substantial damage to the rhombic arrays. One eyewitness reports "When I drove into work following the storm, I remember at least 4 of the masts (and possibly as many as 7) lying on the ground. Several of the "still-standing" masts were canted over at odd angles". That ice storm hastened the decision to replace the rhombics with Beverage rosette arrays.
A Beverage rosette antenna system at Leitrim is mentioned in a government document FEAI 13799 which initiated the environmental assessment of the site. That assessment commenced in June 1997.
The beverage rosette arrays are situated in the large fields north and south of Leitrim Rd. thus providing omni-directional coverage. (Image courtesy Microsoft Live Search Maps). This view clearly shows the semi-circular support masts in the centre of the array in the south field. (Image courtesy Microsoft Live Search Maps).
A Beverage antenna is a non-resonant broadband antenna which consists of a long wire stretched horizontally above the ground and is, in essence, a lossy transmission line with the ground acting as the conductor for the return current. Its characteristic impedance is approximately 400-600 ohms. The antenna is terminated in its characteristic impedance at one end, via a ground screen, and the received signal is taken from the other end through a transformer, one side of which is connected to ground via another ground screen. The transformer is used to match the 400-600 ohm impedance of the antenna to a standard 50-ohm coaxial cable. The direction of the beam, or maximum sensitivity of the antenna to radio signals, is toward the terminated end.
|This rosette array depicts the experimental system that was built at
Cambridge Bay. Later on, a similar but larger system was built at Leitrim.
The system enables accurate bearings of radio signals to be obtained rapidly. It employs a "rosette array" of directional Beverage antennas. The antennas are rapidly scanned to find which one is receiving the largest amplitude signal. This gives an approximate bearing. Next,the signal is then compared with the signals of two adjacent antennas in the array and the results of these comparisons provide a measure of the amount and direction that the true bearing differs from the approximate bearing. (Source: Page 70 of CRC Report. No 1282)
|A classic Beverage receiving antenna requires a lot of space. Usually it is one or more wavelengths long, mounted parallel to the ground at an approximate height of 6 feet and oriented in the direction of the desired reception. A nominal 9:1 balun is required at the juncture of the wire and 50 or 75 ohm coaxial feedline. The far end is terminated with a nominal 600 ohm resistance. The Beverage antenna is highly directional, responsive to low-angle signals, has little noise pick-up, and produces excellent signal to noise ratios. Properly designed Beverage receiving antennas are very effective across the entire HF frequency range. (Graphic courtesy W8WWV)|
Due to the possible future realignment of Leitrim Road, DND Operations CFS Leitrim will be relocating two Beverage rosette antennas. Both antennas, one located south of Leitrim road and one located north of Leitrim Road, will be moved to an area in northern part of the Leitrim site that has been designated for the antennas. The scope of the project will therefore include: - Site preparation, dismantling and decommissioning of Beverage rosette antennas in their current locations, relocation of the Beverage rosette antennas, construction of the Beverage rosette antennas in the new location and continued operation and maintenance of the antennas. The project will commence in the winter of 2010.
In March 2014, DND issued a Request for Quotation to overhaul antennas at various sites across Canada. Shown below are the antennas for Leitrim. The satellite dishes were not included in the original RFQ.
QTY MODEL No. of
MFG DESCRIPTION 1 ? 5 1 x 110 feet
4 x 30 feet
Aluminum ? Crossed Loop 1 PVS1120A 48 24 X 20 feet
24 x 39.5 feet
Aluminum Plessey Elevated feed monopoles, Omni
1 ? 24 7 feet Wooden Petrie Comm 24 element , steerable Beverage
CONTRIBUTORS AND REFERENCES:
1) Bill Robinson <newman-robinson(at)rogers.com>
2) FEAI 13799 was on www.ceaa.gc.ca/regisrty/english/ont/013799.html. (downloaded 30/04/1998)
3) Microsoft Live http://maps.live.com/#
4) Description of United States Patent 4062015
5) CRC Report. No 1282 - BEVERAGE ANTENNAS FOR HF COMMUNICATIONS DIRECTION FINDING AND OVER-THE-HORIZON RADARS by J. Litva and B.J. Rook (1976)
6) Beverage relocation http://www.acee-ceaa.gc.ca/052/details-eng.cfm?pid=51735
7) DND RFQ for antenna overhauls. https://buyandsell.gc.ca/cds/public/2017/03/14/87288759e7f2c9bd239926ff13d5a1fa/ABES.PROD.PW__HN.B460.E72685.EBSU000.PDF