Monday, May 07, 2007 at 13:37
Michael. David has partially answered your question re ferrite suppressors.
They can be made by using a soft iron toroidal core - as used in toroidal transformers or baluns.
Also common are the clamp on type that open up and the cable is placed in the middle of it.
I found the easiest and cheapest method to simply use some ferrite rod - as used in A.M radio antennas- and simply wrap the cable around the rod, using tape and cable ties to hold it in place. An example where this was required was with my IC706Mk2G (amateur radio) with the front panel remote mounted. The connection cable is 5 metres long which is 1/4 wave length on 20 metres (14mHz). Operating on 20 metres caused so much RF feed back that the radio would turn itself off.
Ferrites can be used to help stop radio interference where RF is generally being picked up form somewhere else than the antenna, example long speaker wires in your car or
home connected to an amplifier / TV / radio etc.
Ferrite material used to be available from Dick Smith. You could try Jaycar,TTS systems etc.
Earth Straps.
RF is just AC (alternating current). It is just that the frequency is higher than the AC power at a power point. Voltage and current are 90 degrees out of phase. As the frequency increases, RF current tends to flow more on the outside of a conductor than through the middle of it. This is Known as the "Skin Effect". Thus earthing conductors with a greater surface area will be more effective than large solid conductors.
Earth straps should be kept as short as possible or else they may radiate stray RF. Antennas such as the Codan 9350 use just such an earthing strap.
In UHF base situations, a type of coax known as heliax is used this is low loss and uses a hollow copper tube as an inner conductor.
I have found that simple -short- earth wires OK for earthing things such as the remote head in my Codan 8528. No high RF currents should be present here anyway.
I hope that this helps, Cheers Tony - VK3CAT, VKS737 V5715.
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