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.
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
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
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
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
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
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
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
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.
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
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