R.F Cables

UR67 or RG213

Whatever the type number, both of these cables are equivalent. This is really the minimum quality cable that should be used for 23 cm. The only exception to this is for very short runs within equipment, or between say a transmitter and an amplifier, where the flexibility and convenience of a smaller 5.5mm diameter cable such as UR43 may be useful.

An alternative such as 0.141" diameter semi-rigid cable could be used, although this and the necessary special connectors are more expensive. Returning to UR67, this is 10.3mm diamter cabl that is quire flexible, and is thus suitable for making turning loops around rotators. The cable has a plastic oversheath, beneath which is a thick layer of braiding. A thick ploythene dieelectric reveals a substantial inner conductor made up of 7 stiff strands of wire. Many different manufactureers produce cable to this specification. It is a very popular cable in the Amateur Radio faternity, and is widely used on the 2 m and 70 cm bands.

However, at 23 cm it produces a loss of 7.3 dB per 25 metre length. This is rather high, and in view of the better performance alternatives now available for very little extra cost, we would not recommend its use. Being 10.3 mm in diameter, standard N plugs were made to fit it. It is also possible to find BNC plugs to fit it directly, although these are still rather expensive.

H100

This cable is produced by the dutch manufacturer Popes, and is available from the well known Amateur Radio cable supplier W.H.Westlake. It is slightly smaller diameter than UR67, 9.7mm. This is one of its major failings, since standard N connectors are not a very good fit, and special connectors to suit it do not seem to be generally available. Beneath its plastic oversheath is a very light braid covering a layer of copper foil. Beneath this is a semi-airspaced dielectric covering a solid centre conductor. The overall construction is significantly less flexible than UR67, and the copper foil screening is liable to fracture if flexed excessively. Hence it is definitely not recommended for turning loops around rotators. The good news is that the loss is much less than UR67, at about 4.2 dB per 25 m and it costs about 20p per metre more. However, in view of the difficulty of fitting connectors to it, and the availability of an alternative, it is once again not particularly recommended.

WESTFLEX 103

This cable is a special one again available from W.H.Westlake. As its name implies, it has a diameter of 10.3mm, thus fitting standard N connectors with the exception that the inner conductor is slightly larger than UR67. This can be overcome by filing it down a little, or by using the special connectors which are now available from Westlakes (price about £5.00 each ). Westflex 103 is also quite flexible. The loss characteristics are very similar to H100. It is thus a combination of the better qualities of UR67 and H100, and the cost is about the same as H100. Hence it is the first cable which i would recommend for 23 cm use.

ANDREWS HELIAX

Andrews Heliax is manufactured by the American Company Andrews, who produce a wide range of RF equipment for professional use. Being a professional product, the new cost is probably beyond that which most amateurs can afford. However, it is the practice of many professional radio equipment installers to replace lengths of cable on a strict time basis, regardless of wether it is faulty or not. These secondhand lengths of cable often appear on the market at rallies for a fraction of the new cost, and are a good buy. However, do not buy any such lengths if they exhibit dents in the sheath, serious mechanical damage or puncturing, or any sign of internal dampness. Now lets consider the cable itself. Generally, Heliax cables are constructed from a gorrugated solid copper sheath with a plastic outer covering. The dielectric is composed of a rigid white foam, and this covers a solid inner conductor. It is avilable in a variety of sizes, the most common of which are LDF-250 (3/8" nominal, 11 mm diameter) and LDF-450 (1/2" nominal, 16 mm diameter). Special Andrews connectors are needed for all types, and be warned, they are not cheap ! However, these are often available "surplus" at rallies for much less than the new cost. This cable is not very flexible, a fact recognised by Andrews who also produce flexible Heliax cables if this property is needed. However, i have never seen these flexible Heliax cables available at rallies. The RF performance is excellent, LDF2-50 producing a loss of 3.3 dB per 25 m, LDF4-50 2.2 dB per 25 m. These cables are thus highly recommended for fixed runs, provided you can obtain some at a reasonable cost. Brand new, the cost may be somewhat prohibitive for most Amateur budgets.

JAPANESE FB SERIES CABLES

These cables with their distinctive white oversheath are imported from Japan by the Portsmouth based firm of Nevada. The construction comprises the aforementioned white plastic oversheath, beneath which is a thick layer of braiding. This covers a foil screen and a rigid white foam dielectric. The inner conductor is a solid core. The cable is available in 3 sizes ; 5D-FB is 8.1 mm in diameter, 8D-FB is 11.1 mm in diameter and 10D-FB is 13 mm in diameter. It is just possible to use standard N connectors with 8D, but the other sizes require special connectors which are about twice the cost of standard types. 8D produces a loss of 4.2 dB per 25 m, whilst the best type 10D is 3.4 dB per 25 m. Hence 8D has similar loss characteristics to H100, but far superior construction. It is just about flexible enough to be used in a turning loop around a rotator. It costs about 50% more than H100 or Westflex 103. 10D offers very similar performance to LDF2-50 Heliax, at about twice the cost of H100. Even though the essential special N connectors for it cost about twice as much as standard types, it is a high performance cable that is affordable on an Amateur budget. The largest size 10D is best suited to fixed runs, since it is starting to become a little inflexible. In conclusion , these Japanses cables are highly recommended.