Last month we discussed the loss of the RF path to ground; the reason behind it and at least two methods to restore the RF path to ground. This month we will cover the cause and effect relationships between noise in the radio receiver and the ways to either eliminate or reduce them.

Relationship Between Noise and Grounding Systems -

     Actually, this relationship is not difficult to understand once we will have understood the basic theory.

     We have several sources of noise in the receiving end of radio stations.

      First and foremost is the noise the components in our radio equipment generate in their natural course of operation.  Generally speaking, most of these components generate more noise as we get higher and higher in operating frequency. Then there is a cut-off point in which the noise + signal to noise ratio is no longer acceptable; at that point it becomes necessary to replace the component(s) with a better “noise figure.”

     From the days of Marconi we have had this continuous problem of finding, developing or replacing our receiving systems with better components for lower noise. It is a continuing saga! I can remember the days of amateur radio communication receivers, operating from 160 to 10 meters, with a pattern of a component noise level increasing with the increase in frequency from 160 to 10 meters.  Cut-off point was between 20 and 15 meters.  As we would approach 15 meters the noise from the radio’s components would increase and sensitivity decrease until there was no comparison between the noise level and sensitivity between say, 80 meters and 10 meters.

     Today, with the advance microprocessor-based communication transceivers, it may not even be possible for most of us to even perceive a difference between the component noise level on 160 meters and 10 meters. It would take expensive electronic instruments to tell us the difference! Perhaps some people, with a particularly acute hearing capability, could
tell the difference, but certainly not the average person.

     Remember when TV satellite systems became available for the average American citizen?  Originally, the parabolic disks were sometimes more than 20 feet in diameter.  They would arrive on the site with a flat-bed, truck and trailer for the consumer at his home.

     Then, with the introduction of  “Low Noise Pre-Amplifiers”, the noise level of the individual components would be so low the TV signals would be much, much louder until it was no longer necessary to use such large diameter disks.  They began to get smaller ... and smaller ... until some of them are now less than a foot in diameter.

     Same thing is true in amateur radio.

     However, noise is much more complex than simply the noise generated from the electronic components in our rigs.  Noise comes from many other sources, from the microwave oven in the kitchen to the Cosmo, and it has become necessary for each of us to understand the subject well enough to reduce the noise for enjoyment and essential communications.

Other Sources of Noise -

     We will find all kinds of noises.  There is AC, DC, FM, PM, AM and Pulse with horizontal, vertical and even circular polarization. But most noise is DC, or direct current.  Very little noise is AC, or alternating current.  Some noise has a combination of AC and DC components, or a combination of many things.  Noise can have an amplitude variation, a phasing variation, a variation in frequency or a pulsating characteristic. All of these facts, plus others, determine the solution.

    If most of the noise coming into our radio receiver from the antenna and feedline is direct current, then it is obvious we would need a shunting device to block DC while allowing AC to travel back and forth between the antenna and radio receiver.

     Such devices exist.  We call them lightning arrestors, or type “DC-continuity to ground”, meaning they shunt or divert the DC component of noise into ground before they get to the radio receiver. We can mount this device on the bulkhead ground or, sometimes, elsewhere, such as the antenna or tower, depending on the physical circumstances.

     Such a device will eliminate perhaps as much as 90 percent of the atmospheric noise coming into the receiver in addition to the various noises from man-made sources, including much of the lightning discharge noises (not all of it).  There are always other components in the discharge of lightning which require different solutions.

     Certain vertical antennas, the DC-continuity to ground type, will do the same thing as these lightning arrestors.

     If the noise comes through the power line, a common occurrence, then we place a special kind of filter on the bulkhead ground to filter out the DC noise.  On one end of the filter is the AC-line from the receiver and, on the other end, an AC-line going into the outside AC-power line.

     If some of the noise going through the AC-power line has an AC com-ponent to it, then a high-voltage band-pass filter with the design to allow the 60 Hz AC high-voltage to pass through it while shunting to ground all of the AC low-voltage about 60 Hz. We can even make it shunt to ground anything not 115 volt AC 60 Hz, or anything else the radio receiver needs to operate correctly.