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HF-Radio Installation Aspects

On sailing yacht with installed HF-radio used for long-range communication, extreme care must be taken that other electrical equipment in the vicinity of the radio station will not produce HF-noise, which may completely block radio reception of distance stations.

Special attention should be paid to the following devices:

  • Battery chargers/inverters
  • Charge controllers of wind generators and solar panels
  • Active shore-supply isolators
  • Personal computers and their peripheral devices (USB cables!)
  • All kind of electrical motors (e.g. refrigerator compressor, water pumps, electrical winches, ...)
  • Fluorescent lamps
  • ...

All of these installations have to be carefully checked on their HF-noise level and noise sources have to be removed or effectively blocked from transmitting.

Radio Noise

In general, anything involving electric power or electronics is a potential radio noise source. Electrical motors with commutator brushes are especially bad about creating radio noise. Lately, a new source of RF noise has been showing up. In an effort to reduce overall electric power consumption, electronic equipment manufacturers are required to change the AC power supplies in their equipment to use switching technology. Switching power supplies are prolific radio noise generators unless excellent shielding and filtering is used. It is likely that those switching power supplies, especially in cheap consumer electronic equipment, will leak RF noise.

Personal computers and their accessories are notorious radio noise generators. They typically contain switching power supplies, high-speed digital switching circuitry, and unshielded electrical cables. The noise levels generated by this equipment varies from manufacturer to manufacturer and model to model. Some equipment is nearly noise free while others of the same kind can blanket the HF radio spectrum with strong hashy noise and birdies.

How to reduce RF noise

Noise is a fact of life when operating HF radio. The important thing is to recognize its nature and source and then take whatever action is necessary to minimize it or its impact.
Internal receiver noise can be overcome by putting up a better antenna so more signal is being supplied to the receiver. Externally generated noise can be reduced using directional antennas and/or moving them away from potential noise sources. Eliminating potential feedline problems should always be part of any noise elimination campaign. Loose coax shield connections will allow electrical noise to enter the cable and be heard on your receiver. Make sure all coax connectors are properly soldered and tightened.

There are also receiver operating techniques that can minimize the impact of noise. Internal receiver noise can sometimes be overcome to a degree by adding a pre-amplifier. However, with today's low-noise technology available at low cost, this step is very seldom needed. Use receiver bandwidth matching the bandwidth of the signal you are attempting to hear. Wider receive bandwidth will obviously allow more noise to pass through the receiver without increasing much of the desired signal power. Reducing receiver gain by turning down the receiver's RF gain control and/or turning on its attenuators will often help minimize the impact of strong external noise. After all, you won't be able to hear signals weaker than the noise. As long as you can still hear the noise in the background, you will hear any signals that rise above the noise level. An additional benefit of reducing receiver gain is that it places noise levels further down on the receiver's automatic gain control (AGC) curve. That reduces the tendency of the AGC to try to hold both the noise and a stronger desired signal at the same audio output level.

Of course, it would be best to reduce the noise before it reaches the receiver. Locally generated noise can be reduced or eliminated by identifying and eliminating its source. Relocating the receiver antenna can sometimes reduce noise from sources that cannot be silenced. Noise from distant sources can sometimes be reduced using a directional antenna.

Internal Receiver Noise

Identifying internal receiver noise in modern HF transceivers is fairly simple. It is the noise that can be heard when the antenna is disconnected. The receiver's S-Meter reading should drop to zero and if the receiver's RF gain is set to maximum and the AF gain adjusted a smooth hissing sound can be heard. That is the receiver's internal noise.
If an appropriate antenna is reconnected to the transceiver and there is not a significant increase of the audible noise on any of the bands below about 20 MHz, there may be a receiver- or an antenna problem. There however exist rare times when there is very low radio noise. Below 20 MHz, this may occur for example during a large solar flare. Above 20 MHz, night time ionospheric conditions during the years of minimum sunspot activity may be such that very little noise will be heard.

In general, all modern HF transceivers are sufficiently sensitive that antenna noise can be heard on any antenna that is also suitable for efficient transmission on the selected frequency.

External Radio Noise

Once you determine that the noise you are hearing is arriving via your antenna feedline, the next step is to determine the source is nearby or distant. Nearby noise sources can often be reduced. Distant sources can only be reduced by making your antenna system less sensitive in the direction from which the noise is arriving. This typically means using a directional antenna. Figuring out whether your noise source is nearby or not is usually not difficult. Check whether your S-meter drops below about S1 or S2 when the band you are listening on is supposed to be closed. That would mean daytime on 160 and 80 meters and night time on 20 meters and above. If the noise is still strong when a band is supposed to be quiet, your noise source is almost certainly close by. Noise from distant sources is common on all HF bands but is especially noticeable on 160 and 80 meters. Even in very quiet rural locations where daytime noise levels on these bands is very low with the S-meter needle laying near the bottom stop all day, night time levels will commonly in the S5 to S7 range even without lightning storms. Some times of the year when distant lightning storms are common, the S-meter needle may not drop below S9 unless some sort of directional antenna is used. Noise sources can also be recognized by their individual characteristics. Lightning storms can be recognized by the crashes from lightning strokes. Power line problems will often have a strong 120Hz buzz though many nearby noise sources will have that same characteristic.

Finding Nearby Noise Sources

For most HF antenna installations, the closest potential noise sources are those in the house. The simplest way to determine if the source of your noise problem is in your own home is to power your transceiver from a battery and open all the circuit breakers to your house. If the noise drops to a low level or goes away, turn breakers on one at a time until the noise returns. Find the device or appliance on that circuit and repair of replace it.
Of course, life would be easy if our noise problems always come down to locating a single faulty item and disconnecting it. What often happens with new HF station installations is that there are multiple household noise sources. These can be things such as fluorescent light fixtures, TV sets, and computer equipment. Finding and eliminating the strongest noise source will unmask the next loudest noise source, and so on. Once you have eliminated your own household noise sources, it is time to move outside. Examine the area around your antenna. Is there a nearby power line that may be radiating noise that it has conducted from some other location? Power lines are notorious radio noise radiators.
It is often difficult to determine whether noise coming from power lines is created by the power company equipment or being introduce by equipment at a nearby customer's property. A simple method for finding the general area where a noise source is located is to carry a portable receiver through the area to find the area with the loudest noise. If you determine that the probable noise source is at a nearby home or business, eliminating it may be difficult if you are not on friendly terms with the owner. While a home or business owner is legally responsible for eliminating radio noise that interferes with licensed radio services, knocking on a door and quoting federal law is probably not going to be well received. A better approach is to ask them if they have been experiencing radio or TV interference. They usually will be if the source is on their property. Tell them you have so decided see if you could find the source and that the noise was loudest at their location. Explain that you are not only concerned about the noise but that there may be an appliance or other piece of equipment likely to catch fire or shock someone.
Never perform any electrical operations such as opening and closing circuit breakers on other peoples home or equipment. Do not touch their electrical equipment. Most of all, do not attempt to repair anything. At most, you can offer informal advice. Touching any of their equipment could make you legally responsible for anything that goes wrong with that equipment.

Antenna Location

As mentioned above, overhead utility power lines radiate radio noise. This is an inescapable fact of life. That leads us to one important conclusion. Our antennas should be located as far away from them as practical. Utility power line noise radiation is somewhat different from ordinary single point radio sources. RF levels from a point source decrease with the square of the distance from it. That is to say doubling the distance will decrease the level by a factor of four. It doesn't necessarily work that way with power line noise.
At HF frequencies, power lines can work like line sources. That is, the noise radiates from along the length of the power line, not from just one point along the line. The square of the distance rule does not apply to line sources. RF levels drop of in proportion to the distance. Doubling the distance from the power line may reduce noise levels by only a factor of two, not four. Distance from utility power lines is obviously important. After utility power lines in importance comes homes and other structures containing electrical and electronic equipment. First, of course, is the problem that the electrical wiring in the house will, to a degree, radiate RF noise conducted in from the utility power distribution lines. Second, the electronic and electrical devices connected to the power lines can radiate RF noise directly or by conduction via their power cords to the AC wiring.
How far do you need to place your antenna from power lines and structures? That of course depends upon how noisy they are to start with. For typical situations where no exceptional noise sources are operating, 100 yards from overhead power lines and 100 feet from other structures is probably plenty. Greater distances will probably make no noticeable difference. Most of us get by just fine with much shorter distances. Antenna height can be another important factor. Higher antennas can be farther away from household wiring and electronics than lower antennas. Higher antennas will sometimes provide stronger signal levels on desired signals than lower antennas. Those of us who live in neighborhoods with underground utilities and newer homes usually experience relatively few noise problems. There are obviously no overhead power lines to radiate RF noise. Newer homes tend to have newer, quieter electrically, appliances and electronics. It is yet to be seen though what the impact of "wall-wart" switching power supplies will have though.

Antenna Type

What type of antenna you use can make a difference. Vertical antennas tend to be more sensitive to local man-made noise. Man-made noise, like other RF, will conduct along the surface of the ground via vertically polarized ground-wave propagation. Vertical antennas also tend to be omni-directional, able to receive noise from all directions. Horizontally polarized antennas tend to be quieter than vertical antennas as they are cross-polarized to vertically polarized ground-wave propagated radio noise. They are also typically mounted higher above the ground than HF vertical antennas thus potentially locating them further away from noise sources.
The issue of noise pickup on vertical versus horizontal antennas is not cut and dried. Vertical antennas typically have an overhead null in their radiation patterns. Lightning storm noise from storms within a few hundred miles arrives at high angles above the horizon. Lightning noise from nearby storms can sometimes be significantly lower on a vertical antenna. Also, horizontal antennas are not cross-polarized to noise radiated by nearby utility power lines.
Whether horizontally or vertically polarized, directional antennas can have an advantage over non-directional antennas. A directional antenna aimed in such a way as to favour a desired signal over a noise source can provide an improved signal-to-noise ratio. There are many types of directional antennas, of both vertical and horizontal polarization. Most HF directional and beam antennas have very wide forward gain beam widths. They usually have narrow and deep side or back nulls that may be aimed to reduce interfering noise level without badly reducing a desired signal level.

It's A Fact Of Life

As you may have realized as you read the above paragraphs, finding and eliminating radio noise sources can be difficult. There are no magic bullets for curing HF radio noise problems. For most of us, tracking down and silencing noise sources is an on-going effort.
Many of us are able to set up stations and operate from new locations with only minor noise problems. Even when we encounter a serious noise problem at a new location, a few days of investigation will usually turn up the source of the problem, allowing it to be eliminated. After the initial noise elimination effort, new noise sources may be noticed but are usually infrequent enough that our enjoyment of HF radio is not seriously impacted.
Those of us living in residential neighbourhoods will never experience a complete absence of locally generated RF noise. That has not prevented to successful HF radio operation except in a very few unique cases. Of course, there are those who are fortunate and live in rural locations with very little local man-made noise.
Even with no local man-made noise sources, radio noise is never completely eliminated. Distant man-made noise sources are still received. Think of it as the sound of millions of bar blenders mixing Margaritas plus millions of vacuum cleaners running, each radiating RF noise.

The combination of local and distant man-made radio noise and local and distant natural radio noise is what we fight when we are trying to communicate with each other on the HF bands. The trick is to eliminate as much of it as we can. The rest we simply must live with.

Cover  <<  Sail Away  <<  Marine Radio Communication  <<  . .>> Radio Principles last updated: 16-Feb-2012