Mag loop aerial for the Den

[Terry]

... Of course solid dielectric co-ax isn't suitable for higher frequencies due to dielectric losses ... Not suitable for VHF and appalling for UHF.

I know you've said this before, Jeffrey but, the next time you go down to the museum, have a look through my collection of odd coax cables (if Peter hasn't appropriated them all for flyleads!) and look for a sample of a very flexible cable marked 'RG59 HEC' (Head End Cable). If you inspect the end, you will see that it has a solid dielectric and I can assure you that it works very well at both VHF and UHF. I don't know if it is a special type of polyethylene, but it works! (Don't be fooled by its slight blue colour - this is the colour of the bonding agent between the aluminium shield and the dielectric!)

You may also find samples of a type with foam dielectric but it doesn't have the flexibility of the solid dielectric one.

Most of the stuff sold as satellite cable is electrically OK but the cheap varieties usually have an aluminium tape layer which will rot if any moisture gets in. Decent stuff like Webro WF100 has copper tape.

I would hope that no cable ever suffers moisture ingress! Whether the ali really does rot, I have no idea.

There is, however, another very good reason for avoiding this cable, usually sold as RG6.

The original CT100 and later WF/PF100 cable is manufactured to a strict specification, whereas RG6 is a cable type, NOT a specification!

Provided it follows the correct dimensions, it can have as much or as little braid coverage as you are prepared to pay for - provided you are buying it direct from the manufacturer. If buying retail, you won't have a clue - but it is unlikely to be a lot, hence the price differential between WF100 and RG6. Essentially, the RG6, alongside the cheap 'contract' aerials, is aimed at the cowboy fraternity. Avoid, avoid, avoid!

Not all RG6 is rubbish. Thousands of miles of it are used in this country for CATV drop cables but, it has lots of braid and - Jeffrey will like this - a flooding compound under the sheath - a kind of non-setting goo, which oozes to fill any splits in the sheath caused by cable damage to keep moisture out.

Beware if you come across any of this - a drum with a length of cable on it abandoned by a CATV installer because there isn't sufficient length for another installation, for example - it is not your lucky day! It is strictly for external use only as the tough PVC sheath produces poisonous cyanide gas in the event of a fire. In a CATV installation it is spliced onto an internal grade of cable at the entry point to the premises. It will be ideal for a run down the garden between the house and a shed but very little else!