Many shortwave listeners make their own antenna, for instance a longwire or a dipole. From an electrical point of view any type of wire can be used. But from a mechanical point of view not every wire can be used. Often low cost insulated copper wire, as used in the mains wiring of houses is used. The problem with this wire is, that the single copper conductor becomes hard when it bends by movement in the wind. After a few month's it will break at the bending point. This is also valid for enamelled wire as used for transformers and so-called hard drawn beryllium copper wire. Every single copper wire must be mounted in such a way, that the movements of the antenna does not cause bending of the wire. Household installation wire and enamelled copper wire have also the disadvantage of stretching. After a few month's the antenna sags considerable. The stretched wire becomes also harder and eventually it will break.
Flexible wire, for instance splitted zip cord, is made of many thin, stranded wires and is less prone to hardening and breaking. It's however very important not to solder such a flexwire! At the solder point it becomes hard and it will break at the solderpoint if the wire moves in the wind. If you use flexible wire, the solder point may never come under mechanical tension. So, clamp or knot the wire around the egg-insulator in such a way, that movement of the wire does not reach the solder points. It is better to use a clamping connection than soldering. (example: wires in cars never break because they are clamped and not soldered). Most flexible wires have also the problem of stretching. Another problem with flexible wire, for instance splitted zipcord, is oxidising.
Water damp is soaked into the space between the stranded thin wires. Most flexible wires are not made of 100% pure copper. The result is that the wire will oxidise. A greenish- or dark brown layer around the wires is the indication that the wire is oxidised, and has lost its strength. After a while the wire will break or contacts become bad. Oxidising can give also intermodulation problems: a copperoxide-copper contact acts as a diode rectifier. In the early days of radio a copperoxide/copper (cuprox) diode was used in battery chargers. Oxidising is also a great problem of the low-cost copperclad iron wires, because acid rain, copper and iron are great enemies... Sometimes even iron washing line, covered with clear PVC, is offered as antenna wire. Unfortunately, PVC cannot withstand the ultraviolet part of the sunrays. It will become hard and after a while, water will penetrate trough the PVC insulation. The iron wire will rust and the antenna will break.
Hanging an antenna is often a lot of work. Using cheap- or solid installation wire is mostly pennywise and pound foolish. The use of high quality antenna wire under the golden rule of "no mechanical tension on connections" will result in many years of service without problems.
RF Systems offers two types of wire for home-build antennas.
* Antenna litze in 25, 42, 100 and 500 mtrs reels.
The RF Systems antenna litze is a special litze antenna wire, made for RF Systems to our own specifications. This wire is pre-stretched and made of oxigene-free, large crystal copper. This prevents oxidising and so intermodulation on uV levels. The wire is flexible and the 32 x 0.31 mm stranded conductors are covered with a clear, UV- and air-pollution resistant poly-urethane cover. The outer diameter is 3.2 mm, breaking force over 70 kg. This wire is used in all our wire antennas, except in some professional- and military versions.
* Stainless steel antenna wire.
All professional- and military antennas, for instance the MLBA MK 3 and MK 4, used at embassies and by the BBC monitoring service, are made of very flexible A 316 stainless steel wire. It's outer diameter is 3 mm and the wire has 133 stranded conductors. Thanks to this large number of conductors, the RF resistance of this stainless steel antenna wire is only a fraction higher compared to copper wire of the same diameter. Especially with longwires and T2FD antennas this fractional higher resistance is of no importance, because these types of antennas are high impedance antennas whereby the ohmic resistance of the antenna wire it selves plays no role. The greatest advantage of this stainless steel wire is that the A 316 material is not detoriated by air-pollution, UV light, sea-water, icing or any other environmental influence. Besides that, its breaking force is over 500 kg! The weight is only 3.5 kg per 100 mtrs... Combined with our PU egg-insulators (with a breaking force of 600 kg) an antenna made with this wire can withstand hurricanes, tropical sea-water environment, polar- and other harsh climates. Stainless steel cannot be soldered, all connections have to be clamped. Some of our MK 3 and MK4 antennas are already over 12 years in service without problems, they still look like new... This wire can also be used as guy wire for antenna masts, because it will not stretch. Available in 25 mtrs, 50 mtrs and 125 mtrs reels.
* Dracon rope
If you make a dipole or longwire antenna, the insulators (egg- or dog-bone type) have to be attached to anchor points, for instance a tree or chimney. For the stainless steel antenna wire we advise to use also stainless steel wire between the insulator and the anchor point, seen its strength. For antennas made of copper wire its better to use Dracon rope. The advantage is that this rope is a little bit elastic, thereby preventing that the copper wire breaks during movement of the antenna in the wind. Besides that, Dracon rope gives also extra insulation, important at high impedance points (longwires and the ends of dipoles) A word of warning: the white "nylon" rope sold in most do-it-your-selves stores is made of poly-propylene. It's strong, low in cost but it is NOT ultraviolet resistant! After a year or so in sunlight, it looses its strength and it will break! Some watersport stores sell also poly-ethylene rope. It feels a little bit greasy. This rope is also not UV resistant and it stretches very much, and is therefore not usable as guy rope. RF Systems uses for all its antennas Dracon guy rope, made of 16 strands braided polyester with a polyester core. This white rope is UV- and air pollution resistant, very flexible and just a little bit elastic (ca 0.2%). The outer diameter is 3 mm, with a breaking force of no less than 240 kg. It's own weight is just 0.6 kg per 100 mtrs. It's available in 100 mtrs and 500 mtrs reels.
Coaxial cable
There are several types of coaxial cable. As long as the antenna is not used for high power transmitting, there is no need for heavy cables. The most used cable has a diameter of 5 mm and is known under the type number RG 58. Many listeners think that the attenuation of a coaxial cable is the only parameter which is important, and that a thicker cable (for instance RG 213) with less attenuation is better. Unfortunately, this is only a part of the story.
RG 58 coax with a length of 100 feet (30 mtrs) gives theoretically an attenuation of 2.3 dB at 30 MHz. Let's assume that your cable is a little bit longer and the connectors give also some attenuation, resulting is a loss of 3 dB. This means in fact, that this quite long cable absorbs halve the available power. For transmitting this is a waste of costly transmitting power, but for receiving the 3 dB loss results in a S-meter reading which is only a 0.5 S-point lower than without cable. For these higher frequencies (20 - 30 MHz), this can make a difference during the reception of very weak stations. For lower frequencies the cable loss (1 dB at 7 MHz) is so low, that in most cases this is not noticeable. For cable lengths over 100 feet (30 mtrs), RG 213, Aircell or Aircom coaxial cable is recommended. This cable is much heavier and gives a loss of 1 dB per 100 feet at 30 MHz.
But as said before, attenuation is only a part of the story. Probably you have noticed, that there is an enormous price difference in RG 58 coaxial cable. You can buy RG58 coax for a few Eurocents per metre, but also for up to 1 Euro per metre. On both cables the RG 58 mark is printed, so why shouldn't you buy the cheapest cable? The difference of these cables is copper. Copper is expensive and some manufacturers use less copper for the shield. RG 58 coaxial cable conform the mil-spec standard have a tight braided shield, which gives 95% or more screening. Cheap coax have shields which a less tight braided, the "30 eurocents-per-metre" coax shield offers mostly not more than 60% screening. This gives two disadvantages. First of all, the attenuation of this less screened coax is higher than normal. Manufacturers know, that most amateurs doesn't have the equipment to measure coaxial cable attenuation accurately, so they specify the standard RG 58 attenuation values or they don't give attenuation values at all. We have measured several RG 58 coaxial cables with less tight shields. We found attenuation values up to 6 dB per 100 ft at 30 MHz. For transmitting this means 75% power loss....
For receiving this equals the loss of 1 S-point, but there is another problem. The coaxial cable runs from your antenna trough your house to the receiver. In- and around every house there is an interference field, generated by fluorescent lighting, TV set's, VCR's, computers and so on. Even if you don't use such apparatus while listening, your neighbours do, and their interference is re-radiated into your house via the electricity mains wiring. The coaxial cable runs trough this interference field and if you use a 60% screened coax, than 40% of the interference field strength is picked-up by the coax! This gives a much higher noise- and interference level compared to high quality coax and can make the difference between receiving a station or not...
So if you are going to buy coaxial cable, peel off a piece of the outer vinyl cover. If you can see the insulation around the central core trough the shield, than the cable is less than 95% screened. The shield of high quality coax is very tight and you cannot see the insulation around the central core.
There is another problem with cheap coaxial cable: the vinyl cover. The black cover is made of PVC. In order to reduce the price even further, some manufacturers use low cost PVC. You cannot see it from the outside, but this type of PVC is not resistant against the ultraviolet spectrum of the sunrays. After a year or so, it becomes hard. By movement in the wind, the cover crackles and water penetrates trough the cover. Than the shield oxidises with very high loss as result.
So if you can afford it, buy high quality coax from a well known make, it safes you from a lot of trouble. Unfortunately, not every shop allows you to examine the quality of the coax they sell. Therefore RF Systems sells its own high quality, very competitive priced RG 58 AL coaxial cable.
* RF Systems RG 58 AL coaxial cable
This cable is especially made for RF Systems to our own specifications. It full fills all military standards for RG 58 coaxial cable. The shield is very tight and gives 98% screening. The black vinyl cover is UV radiation, air-pollution and seawater resistant. The cable remains very flexible, even after years in sunlight. Attenuation is 2.32 dB per 100 feet at 30 MHz. You can recognise RF Systems coaxial cable at our RF Systems logo, which is printed in white on the black vinyl cover. It is available in 100 mtrs reels, but most dealers sell it also per metre.
Flexible wire, for instance splitted zip cord, is made of many thin, stranded wires and is less prone to hardening and breaking. It's however very important not to solder such a flexwire! At the solder point it becomes hard and it will break at the solderpoint if the wire moves in the wind. If you use flexible wire, the solder point may never come under mechanical tension. So, clamp or knot the wire around the egg-insulator in such a way, that movement of the wire does not reach the solder points. It is better to use a clamping connection than soldering. (example: wires in cars never break because they are clamped and not soldered). Most flexible wires have also the problem of stretching. Another problem with flexible wire, for instance splitted zipcord, is oxidising.
Water damp is soaked into the space between the stranded thin wires. Most flexible wires are not made of 100% pure copper. The result is that the wire will oxidise. A greenish- or dark brown layer around the wires is the indication that the wire is oxidised, and has lost its strength. After a while the wire will break or contacts become bad. Oxidising can give also intermodulation problems: a copperoxide-copper contact acts as a diode rectifier. In the early days of radio a copperoxide/copper (cuprox) diode was used in battery chargers. Oxidising is also a great problem of the low-cost copperclad iron wires, because acid rain, copper and iron are great enemies... Sometimes even iron washing line, covered with clear PVC, is offered as antenna wire. Unfortunately, PVC cannot withstand the ultraviolet part of the sunrays. It will become hard and after a while, water will penetrate trough the PVC insulation. The iron wire will rust and the antenna will break.
Hanging an antenna is often a lot of work. Using cheap- or solid installation wire is mostly pennywise and pound foolish. The use of high quality antenna wire under the golden rule of "no mechanical tension on connections" will result in many years of service without problems.
RF Systems offers two types of wire for home-build antennas.
* Antenna litze in 25, 42, 100 and 500 mtrs reels.
The RF Systems antenna litze is a special litze antenna wire, made for RF Systems to our own specifications. This wire is pre-stretched and made of oxigene-free, large crystal copper. This prevents oxidising and so intermodulation on uV levels. The wire is flexible and the 32 x 0.31 mm stranded conductors are covered with a clear, UV- and air-pollution resistant poly-urethane cover. The outer diameter is 3.2 mm, breaking force over 70 kg. This wire is used in all our wire antennas, except in some professional- and military versions.
* Stainless steel antenna wire.
All professional- and military antennas, for instance the MLBA MK 3 and MK 4, used at embassies and by the BBC monitoring service, are made of very flexible A 316 stainless steel wire. It's outer diameter is 3 mm and the wire has 133 stranded conductors. Thanks to this large number of conductors, the RF resistance of this stainless steel antenna wire is only a fraction higher compared to copper wire of the same diameter. Especially with longwires and T2FD antennas this fractional higher resistance is of no importance, because these types of antennas are high impedance antennas whereby the ohmic resistance of the antenna wire it selves plays no role. The greatest advantage of this stainless steel wire is that the A 316 material is not detoriated by air-pollution, UV light, sea-water, icing or any other environmental influence. Besides that, its breaking force is over 500 kg! The weight is only 3.5 kg per 100 mtrs... Combined with our PU egg-insulators (with a breaking force of 600 kg) an antenna made with this wire can withstand hurricanes, tropical sea-water environment, polar- and other harsh climates. Stainless steel cannot be soldered, all connections have to be clamped. Some of our MK 3 and MK4 antennas are already over 12 years in service without problems, they still look like new... This wire can also be used as guy wire for antenna masts, because it will not stretch. Available in 25 mtrs, 50 mtrs and 125 mtrs reels.
* Dracon rope
If you make a dipole or longwire antenna, the insulators (egg- or dog-bone type) have to be attached to anchor points, for instance a tree or chimney. For the stainless steel antenna wire we advise to use also stainless steel wire between the insulator and the anchor point, seen its strength. For antennas made of copper wire its better to use Dracon rope. The advantage is that this rope is a little bit elastic, thereby preventing that the copper wire breaks during movement of the antenna in the wind. Besides that, Dracon rope gives also extra insulation, important at high impedance points (longwires and the ends of dipoles) A word of warning: the white "nylon" rope sold in most do-it-your-selves stores is made of poly-propylene. It's strong, low in cost but it is NOT ultraviolet resistant! After a year or so in sunlight, it looses its strength and it will break! Some watersport stores sell also poly-ethylene rope. It feels a little bit greasy. This rope is also not UV resistant and it stretches very much, and is therefore not usable as guy rope. RF Systems uses for all its antennas Dracon guy rope, made of 16 strands braided polyester with a polyester core. This white rope is UV- and air pollution resistant, very flexible and just a little bit elastic (ca 0.2%). The outer diameter is 3 mm, with a breaking force of no less than 240 kg. It's own weight is just 0.6 kg per 100 mtrs. It's available in 100 mtrs and 500 mtrs reels.
Coaxial cable
There are several types of coaxial cable. As long as the antenna is not used for high power transmitting, there is no need for heavy cables. The most used cable has a diameter of 5 mm and is known under the type number RG 58. Many listeners think that the attenuation of a coaxial cable is the only parameter which is important, and that a thicker cable (for instance RG 213) with less attenuation is better. Unfortunately, this is only a part of the story.
RG 58 coax with a length of 100 feet (30 mtrs) gives theoretically an attenuation of 2.3 dB at 30 MHz. Let's assume that your cable is a little bit longer and the connectors give also some attenuation, resulting is a loss of 3 dB. This means in fact, that this quite long cable absorbs halve the available power. For transmitting this is a waste of costly transmitting power, but for receiving the 3 dB loss results in a S-meter reading which is only a 0.5 S-point lower than without cable. For these higher frequencies (20 - 30 MHz), this can make a difference during the reception of very weak stations. For lower frequencies the cable loss (1 dB at 7 MHz) is so low, that in most cases this is not noticeable. For cable lengths over 100 feet (30 mtrs), RG 213, Aircell or Aircom coaxial cable is recommended. This cable is much heavier and gives a loss of 1 dB per 100 feet at 30 MHz.
But as said before, attenuation is only a part of the story. Probably you have noticed, that there is an enormous price difference in RG 58 coaxial cable. You can buy RG58 coax for a few Eurocents per metre, but also for up to 1 Euro per metre. On both cables the RG 58 mark is printed, so why shouldn't you buy the cheapest cable? The difference of these cables is copper. Copper is expensive and some manufacturers use less copper for the shield. RG 58 coaxial cable conform the mil-spec standard have a tight braided shield, which gives 95% or more screening. Cheap coax have shields which a less tight braided, the "30 eurocents-per-metre" coax shield offers mostly not more than 60% screening. This gives two disadvantages. First of all, the attenuation of this less screened coax is higher than normal. Manufacturers know, that most amateurs doesn't have the equipment to measure coaxial cable attenuation accurately, so they specify the standard RG 58 attenuation values or they don't give attenuation values at all. We have measured several RG 58 coaxial cables with less tight shields. We found attenuation values up to 6 dB per 100 ft at 30 MHz. For transmitting this means 75% power loss....
For receiving this equals the loss of 1 S-point, but there is another problem. The coaxial cable runs from your antenna trough your house to the receiver. In- and around every house there is an interference field, generated by fluorescent lighting, TV set's, VCR's, computers and so on. Even if you don't use such apparatus while listening, your neighbours do, and their interference is re-radiated into your house via the electricity mains wiring. The coaxial cable runs trough this interference field and if you use a 60% screened coax, than 40% of the interference field strength is picked-up by the coax! This gives a much higher noise- and interference level compared to high quality coax and can make the difference between receiving a station or not...
So if you are going to buy coaxial cable, peel off a piece of the outer vinyl cover. If you can see the insulation around the central core trough the shield, than the cable is less than 95% screened. The shield of high quality coax is very tight and you cannot see the insulation around the central core.
There is another problem with cheap coaxial cable: the vinyl cover. The black cover is made of PVC. In order to reduce the price even further, some manufacturers use low cost PVC. You cannot see it from the outside, but this type of PVC is not resistant against the ultraviolet spectrum of the sunrays. After a year or so, it becomes hard. By movement in the wind, the cover crackles and water penetrates trough the cover. Than the shield oxidises with very high loss as result.
So if you can afford it, buy high quality coax from a well known make, it safes you from a lot of trouble. Unfortunately, not every shop allows you to examine the quality of the coax they sell. Therefore RF Systems sells its own high quality, very competitive priced RG 58 AL coaxial cable.
* RF Systems RG 58 AL coaxial cable
This cable is especially made for RF Systems to our own specifications. It full fills all military standards for RG 58 coaxial cable. The shield is very tight and gives 98% screening. The black vinyl cover is UV radiation, air-pollution and seawater resistant. The cable remains very flexible, even after years in sunlight. Attenuation is 2.32 dB per 100 feet at 30 MHz. You can recognise RF Systems coaxial cable at our RF Systems logo, which is printed in white on the black vinyl cover. It is available in 100 mtrs reels, but most dealers sell it also per metre.
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