What is an Antenna Farm?
An Antenna Farm is a piece of (rural) land selected for use in shortwave radio listening (SWL) and/or amateur radio activities, especially for the purposes of listening to or communicating with distant (DX) stations.
Why is it Needed?
The answer to this is simple: Noise. Every household, car, business, factory produces a great deal of radio frequency interference (RFI), which affects all forms of radio communications; AM and FM radio, cellular, and TV. The extent to which it affects these communications is directly related to the strength of the desired signal as compared to the local noise.
In most common uses of radio, in the cities and towns, the amount of RFI (noise) is very large, but the desired signals are also very strong and very local so there are no problems in communicating.
In the SWL and Amateur Radio worlds, the desired signal is often very weak and distant (DX) and is easily obscured or impaired by noise and more local signals. Coincidentally, the most desireable signals are in the 0.5 to 5 Mhz range where RFI is most intense. The primary solution to this problem is to move the receiving antennas away from the sources of noise.
A secondary reason for antenna farming is to obtain the space to erect the large antennas required for optimal reception of weak DX signals. Some of the most desireable antennas for DXing (Beverage antenna) are literally thousands of feet long.
Siting of Antenna Farms
The quality of an antenna farm is related to a number of attributes:
- Distance from Noise Sources
- Power Lines, Street Lights, Television Sets
- Towns and Cities
- Industrial Areas
- Topology
- Negative Horizon A negative horizon means that the actual horizon is below where it would appear if the ground were perfectly flat for an infinite distance. If you imagine standing on the highest hill in an area and looking into the distance, you would see a negative horizon in all directions. Conversely, if you were in a valley in the mountains, you would see a positive horizon. Generally, if the land has a slope, it should slope down towards the direction of desired reception. If the site is on top of a hill, the land will slope down in all directions, hence improving reception in all directions.
- Shadowing of Nearby Transmitters
In mid-western North America, the most distant targets are in Africa, the Mid-East, and South-West Asia. This means that the ideal site is higher on the western and southern edges, sloping down to the eastern and northern edges.
Distant hills and ridges can be an advantage if they shield the site from the strong interfering signals of local transmitters. This needs to be tempered with the fact that they will also adversely affect desired signals coming from the same direction.
- Soil Qualities
- Conductivity
- Size
Power Lines, Street Lights, and TV sets are the major sources of RFI, so distance from them is crucial for a good antenna farm. RFI can be radiated for several miles from a faulty power line, so the fewer and more distant the local power lines, the better. The same comments apply to the "yard lights" often found on farms in rural areas. A survey of the RFI at the site, at different times of day and night, and ideally in different weather conditions, is mandatory to evaluate the quality of the site.
Some other particularly nasty RFI generators include electric fences and "bug zappers".
Towns and Cities and Industrial Areas are filled with Power Lines and Street Lights, so distance from them is also critical.
Depending upon the exact type of antennas in use and the type of reception desired, the electrical conductivity of the soil at the site would ideally be either very conductive or not at all. In most cases, the best compromise is soil that is somewhat more conductive than normal. The ideal situation is to be adjacent to salt water (i.e. on the coast of an ocean), but in the mid-west this is difficult to arrange. Good quality farmland typically has slightly better than average conductivity and hence is ideal for these purposes.
Typical Beverage antennas are on the order of 1000 feet long, and typically an array of these to cover the most interesting areas of the world consists of 6 to 10 antennas arranged in a "wagon wheel" shape. This means that ideally, the size of the site should be about 2000 by 2000 feet or greater. This translates to approximately 100 acres, but depending upon the shape of the property, even 80 acres is sufficient. Sites of 100 acres or larger are ideal, depending upon the shape of the property.
It is important to note that the Beverage antennas are similar in appearance to a barbed wire fence line (albeit taller) and so the land they are over can still be used for agriculture or other purposes as long as care is taken to keep livestock or machinery from interfering with them or vice-versa. This implies that land which can be leased out for agricultural or oil/gas purposes is especially desireable due to the additional income leasing would generate and the fact that the land would not become idle. It is even better if the site can remain classified as agricultural land due to the taxation advantages and protection from urbanization that this status often confers.
It is even theoretically possible to purchase a much smaller site, just the building site (perhaps 5 to 10 acres), from a farmer and then lease the antennae rights-of-way from the farmer. The amount of land that the antennae occupy is minimal (like a barbed wire fence) and the farmer does not lose any of the agricultural use of the land. There are some slight inconveniences in maneuvering farm machinery around the antennae, but other than that there are no negative impacts on the productivity of the land.
Practical Considerations
Unless an unmanned site is being planned, a number of practical considerations affect the selection of a site. We will not discuss unmanned sites here, due to the complications related to securing such sites from vandalism and theft.
Each site requires an area which is suitable for building structures on. A piece of swampland which is ideal in all other respects could be difficult to place buildings on, unless it has a high portion. High and dry land is obviously ideal in this respect.
The site must be reasonably accessible at all times of the year. In order to continue operating it must be possible to travel to the site and to haul supplies into it. This factor also affects many other practical considerations including the cost of building and servicing the site. It should be noted that vehicles are also notoriously noisy in terms of both sound and RFI, so siting beside a busy road is depreciated. If the access road is kept open in winter by plowing or other means, it is an additional advantage. The distance of the site from sources of supplies, food, gasoline, etc. is obviously also a factor to be considered. The closer these supplies are the better, providing that they are not so close that they cause RFI at the site.
It must be possible to obtain utility hookups at a reasonable cost. In spite of the evils of noise carried on power lines, power is required to operate the equipment. It must also be possible to drill a good well at a reasonable cost or to obtain a water supply by some other means.
With the continually expanding use of the Internet as an adjunct to amateur radio and SWLing, the availability of an Internet connection is also a factor to consider. This almost invariably would go hand-in-hand with the availability of telephone service. It is generally an advantage if the nearest telephone exchange is less than roughly 3 miles away because this allows for the use of technologies such as ISDN, Frame Relay or ADSL for Internet access.
The presence of trees on the site can provide several advantages. They can shade and shield the building site from weather and wind, and they can act as supports for wire antennas. In exceptional cases (Pacific Northwest) the trees are very tall and are unequaled as supports for antennas.
The local municipal government (town, county, M.D., etc.) should be tolerant of radio antennae and towers. Some counties, particularly those which are very near to large cities have covenants and regulations on these sorts of things which are often more restrictive than those in the large city. Obviously the taxation rates of the local government need to be taken into consideration too.