The expected effective range of ham radio is a subject that is constantly talked about but poorly understood among many preppers not specialized in radio communication skills.
For all but the shortest-ranged line-of-sight broadcasts there are many factors that will affect the range of your transmissions, and knowing what to expect within a given set of hardware, terrain and atmospheric considerations is essential for a realistic estimation of what your radio set can do.
There is no hard-and-fast rule that can determine the maximum effective transmission range of a given ham radio.
Most fixed ham radios under average conditions and assuming they have proper siting and hardware will have a range of anywhere from 10 to 30 miles. Less powerful sets or ones dealing with serious signal obstacles may have a range that is significantly shorter.
More powerful sets that can take advantage of ideal atmospheric conditions may have a range that is much longer.
Taking the time to understand the specific factors that affect radio range will help inform your choices about what set is right for you and what is required to get good results in your area. Those factors are signal type, signal wattage, obstacles and antenna specifics.
Another limitation to range that is universally applicable to all radios (and often overlooked by beginners) is the radio horizon.
Radio Horizon
Think of the radio horizon like the visual horizon. To help, imagine a perfectly smooth , flat and featureless earth that will allow you to see clear out to the actual horizon, not the horizon as determined by intervening terrain features.
Anything that lies beyond the horizon is actual below where you can see due to the curvature of the earth.
The radio horizon works similarly, but thanks to some effects from the atmosphere and radio waves ability to “bend” somewhat the radio horizon is a little bit farther than the visual horizon, but the effect is largely identical.
Consider that you can see farther, in effect extending the visual horizon, if you get higher off the ground.
You can see significantly farther in our magically flat and featureless place if you simply stand on a ladder, quite a ways farther if you were to stand on top of a two story building and a drastically farther if you were to stand on top of a ship’s mast.
Now take that analogy and apply it to your radio transmission and you’ll receive a similar benefit. All things equal, transmitting from a higher place (or just using a taller antenna) will extend your radio horizon regardless of other factors.
In our example environment, only receiving radios that lay within the “shadow” below the horizon would not be able to pick up the ever-expanding signal transmitted by your set; they would need a correspondingly tall antenna or elevated placement to get out of the radio shadow cast by the “downslope” beyond the radio horizon.
Signal Type
Different types of radios broadcast different types of signals. The fundamental differences in signal type will significantly alter how they travel and interact with various mediums.
Radio waves are broadly categorized as either low frequency or high-frequency, with more specialized types being on either end of the spectrum, either ultra-low frequency (ULF), very-low frequency (VLF), very-high frequency (VHF) and ultra-high frequency (UHF) respectively.
Generally speaking, the lower the frequency the greater the distance the radio wave can travel. But low frequency waves also have drawbacks in that they are more susceptible to certain negative atmospheric conditions.
But on the other hand, as you get into higher and higher frequencies they have a greater tendency to travel in only straight lines and will generally have poor performance at or be completely unable to go beyond the visual horizon.
Any radio waves that cannot travel beyond the horizon (remember, the Earth is round and the curvature of the earth beyond which we cannot see is the horizon) are limited to line-of-sight only applications without signal boosting and relaying.
On the other hand, VHF waves perform well when passing through obstacles with the exception of buildings and large, broad obstructions. In comparison UHF radio waves do poorly with obstacles with the exception of buildings.
In short, there’s always a trade-off with signal performance based on the signal wavelength. Understanding these differences and choosing a signal type based on your surrounding area and the terrain along the path where you are transmitting is essential for getting maximum range out of your radio.
Signal Wattage
The wattage, or power, of the radio signal is another important factor in determining its maximum range. In short, the stronger your radio signal, the more it can withstand loss when passing through or near obstacles.
The key to obtaining a powerful signal is your radio set output itself. Radio power is measured in watts, and larger fixed radios like those employed by commercial broadcast operations may have broadcast power in the tens of thousands of watts, or even hundreds of thousands of watts.
Small handheld radios by comparison may only rate a 1/2 or single watt, while more powerful versions may be measured in the tens of watts.
For portable systems another important factor in considering power output is the drain on batteries and other power supplies. More power means a faster drain, period. That is simply physics.
Before you go and invest in the most powerful radio set that money can buy, do keep in mind the power and thereby output of given types of radios is regulated by the FCC.
Furthermore power is only one part of the puzzle. An extremely powerful radio working with a shoddy antenna and tons of obstructions or interference will still have a very limited range.
That being said, if all other considerations are equal a more powerful radio will send its signal farther than one that is less powerful.
But you must keep in mind that distance takes its toll on all signals no matter how powerful they start out; for every doubling of distance traveled the power of the signal is reduced by a factor of four!
A weak radio signal is getting awfully ephemeral at the limits of its “theoretical” range. Add in obstructions and detrimental atmospherics and your range can drop precipitously, even with a powerful set.
Power alone is important, but not the end-all, be-all of radio range!
Antenna Considerations
A radio antenna is a major factor in determining its effective range. All things being equal, a taller antenna will considerably increase a radio’s range, and is often the easiest and most straightforward way to increase it.
If you do nothing else but swap out a short, dinky antenna for a taller one you will likely increase your set’s range significantly.
Mobile radio sets with long whip-style antennas mounted on the roof of the vehicle can have an average range of 10 or even 20 miles easily, with much of that performance garnered by the antenna itself.
Nautical radios mounted on boats often enjoy considerable range due to the lack of obstacles on the open ocean along with a tall antenna.
In short, the higher your antenna is the better your range. You can maximize the performance of a short antenna by gaining a height advantage yourself.
If everything else fails, climb on top of your car, the nearest hill or a tall building to gain a height advantage. In essence, you are making the antenna taller!
Antennas can also be had in isometric or directional varieties. Isometric antennas radiate the signal being transmitted in all directions equally.
Think of a sphere or a balloon that begins small at the source the moment you click transmit, but expands in all directions equally as the signal propagates, just like a balloon being inflated. That is how an isometric antenna works.
A directional antenna radiates and receives greater power in specific directions only, the net effect being increased performance when transmitting (meaning better range) and reduced signal interference from unwanted transmissions.
Due to the reciprocity effect, a directional antenna that transmits more effectively will also receive more effectively and equally on both counts.
Obstacle Considerations
Radio signals are blocked by solid objects, and depending on your signal type and strength will be blocked more or less easily. Radio transmissions in very hilly or mountainous areas depend on having antennas mounted above the tops of the hills to get any kind of performance at distance.
Similar setups are required in cities, which also present challenges for radio communication due to the preponderance of metal which is traditionally the one medium that is most detrimental to radio waves.
Some obstructions pose very little challenge to radio waves, in particular nonmetallic obstructions.
Most brick, rock and stone presents very little obstruction as do comparatively thin, light objects like wood, most other building materials like drywall, furniture and even the human body.
That being said, even these relatively minor obstructions will in great enough numbers or thickness, impede or even stop a radio signal from passing through them.
The more permeable obstructions your radio wave has to go through the worse the signal will be degraded. A great number of comparatively light obstacles will equal reduced range for your radio while.
Serious obstructions like buildings or large hills and mountains may limit you to line-of-sight communication only without use of signal-boosting or repeater stations.
Quick Tips for Increasing Your Range
When in doubt, get higher!
If you can get your antenna above intervening instructions, or just get it a little more height compared to shoulder level you will increase your range.
If you’re having trouble getting through when broadcasting or just having trouble receiving, don’t pull your hair out until you increase your altitude.
Even for fixed applications, mobile radios are probably best.
In comparable classes your average mobile radio can have anywhere from three to five times the range of a similar handheld radio.
Even if you aren’t taking your broadcasting on the road, a mobile radio probably has the chops to get you more range than a comparable fixed-site radio.
Install a better antenna.
A high-quality whip-style antenna is almost always a smart replacement for any radio set, fixed or mobile. Mobile, handheld radios in particular are notorious for coming with stubby, low-profile antennas.
This might make them easier to carry and handle but there are serious handicaps when it comes to broadcast performance. If the antenna can be switched out, it should be.
Check your power supplies and keep batteries fully charged.
More available power for your radio set means less power for the signal, and a weaker signal will not go as far.
Conclusion
Under ideal conditions, with a powerful enough set and care taken to minimize signal obstructions a ham radio can obtain anywhere from a 10 to 30 mile range on land, though this may be significantly increased, or decreased, depending on ambient conditions, obstructions and hardware limitations.
via Modern Survival Online https://ift.tt/2I7eHOd
No comments:
Post a Comment