Bishop with Mobile Radio

Part II: Medium-Short distance communications

Medium Short Communications:

In the last article, we talked about local or short distance communications. We were concerned with being able to talk within walking distance from our camp, and had chosen some commonly available FRS radios. In using them, we found the 23 mile claim of FRS radios to be wildly unrealistic, but had found ways of extending the range by having an adult chaperone in-between where our “kids” were going to go walking and the main camp.

In this article, we will discuss medium short communications, like those typically found in a caravan driving together, although not necessarily always right together. For this article, we will look for a reliable distance of around 25 miles.

Building off of the last article’s scenario, we have returned home, having mixed feelings about the radios. Yes, the FRS radios did provide a link around the campsite, but they had failed to allow us to talk to our friends who were coming the second day until they were just minutes from the camp. Surely there must be something better available.

Last time, we found that typical line of site distance over flat ground is limited by the height of the antennas. While 2 FRS radios at eye level would provide around 6 miles of line of sight, we found that the real talking distance was far shorter. This is because FRS radios are limited to only ½ a watt of power. Even if they are high enough to have line of site, often they just don’t have enough power to have a readable signal at the end.

Bishop with FRS radio(Above is a computer generated simulation of the coverage of an FRS radio in Bishop, California)

In order to get the 6 miles, we are going to need substantially more power. In order to use radios with more power, we will need to get Amateur Radio Licenses’. These licenses are easy to get, and only require a couple of days of study to pass the test. I have paid as much as $15 for the test, and as little as $5. Most people just do practice tests over and over again until they feel comfortable with them. This article is more about showing you how having the license will help you once you have it, so we won’t spend any more time telling you how to get it.

A typical mobile VHF/UHF radio has about 50 watts of power, nearly 100x the amount of the FRS radios. These radios can typically make it to the radio’s horizon, and are generally limited by the height of the antennas. Radio waves have a tendency to follow gentle curves of the ground, making it possible to get signal, even when you can’t see the other radio. Because of this, it is a very real expectation that by putting the antenna on the roof of a car, you can extend the range by a couple of miles. Since radio waves follow the ground better the lower the frequency, dropping from UHF (like FRS radios at 470 MHz) to VHF (ham radio 146 MHz) allows for better coverage with the radios. The VHF frequency is still high enough that the antenna is easy to manage (between 19-62 inches long).

Bishop with Mobile Radio(Above is the same location, but using a 50 watt Mobile VHF radio with roof mounted antenna)

As a little aside, while it is helpful to think of the ground as flat, that is rarely the case. Instead, ground tends to have large valleys separated by ridges. Any position within the valley, either up the slopes or down at the bottom typically have line of site. Because of this, VHF communications at 50 watts of power will typically cover most valleys that would normally be encountered. This means that in the real world, the range of communications are more often defined not by distance, by ridges and obstacles to line of site.

Alright, you may be thinking at this point, sounds like amateur radio can provide some real distance gains over FRS, but is it REALLY worth all the effort to get a license and spend a few hundred on a radio and antenna to only get 6 miles of range? On the freeway, that is less than 6 minutes of talk time. Besides, this article is about 25 miles of range, not 6!

An alternative that may have crossed your mind is CB radio. CB radio, like FRS, does not require a license, but also has a higher legal output of 4 watts. Also, because CB radio is at a lower frequency of around 27 MHz it will have a tendency to follow curves of the earth even better than VHF. One property of radio is that when the frequency gets lower, the antenna size and required ground get inversely larger. At 470 Mhz, the required ground for the antenna is just about 6 inches. When we moved down to 146MHz, the ground extended to around 19 inches, which is still easily accomplished on the roof a vehicle. Unfortunately, by the time we get to 27 MHz, the required ground plain is 108” in radius. Since most vehicles don’t have the required ground plane area, the output efficiency of the radio suffers. It is quite typical for a vehicle mounted antenna on CB radios to have less than 1% of the power from the radio radiate into the air. At 4 watts from the radio, assuming a 1% efficiency, the radiated power is just about 1/20th of a watt, far less than even the FRS radios. For these reasons I steer people away from CB radios.

Remember how we extended the range of the FRS radios by putting a chaperone with a radio in between? What if we could do that automatically, without someone having to hear the message and relay it back to camp? It turns out that there IS a device like that, it is called a repeater. For years, amateur operators have been placing repeaters on mountaintops, almost anywhere they can physically get to and most of these are open for use!

It works like this, a repeater that is up high has much, MUCH more line of site than anyone on the ground. A repeater on a 5280 foot mountain can talk with stations just over 100 miles away. Since repeaters “repeat” what they hear, then anyone using the repeater within 100 miles can talk to anyone else using the repeater within 100 miles. This means that for your next trip, if you and your friend Jake both get licenses and radios you can talk many miles apart.

Typically, the way in which a caravan would work is that the radios are set to simplex, which simply means that you are not using a repeater. Let’s say that Jake and his family decide to stop for food and gas in a town, and you continue on, you will leave simplex range very soon. Before heading out, you agree that you will talk on the “Beauty Mountain” repeater, which you know from research has coverage in the area. So long as both you and Jake can reach the repeater, you will be in contact.

Hand held radios can be used on repeaters too, although they have significantly lower range. Amateur radio handhelds are typically around 5 watts and have much lower efficiency antennas. Still, they offer a huge improvement in range over FRS, often able to cover several miles.

You travel back to your favorite lake, being able to talk to Jake the whole time. But once you crest the last ridge and descend down to your favorite camping spot, you notice that you can no longer hear the repeater. Your magical link to the outside world is STILL severed, despite your expensive radio and antenna setup. What has happened?

VHF and UHF frequencies are still subject to line of site. The ridge that you have crested to go down to the lake is blocking the signal, and the drop is too sharp for the radio waves to follow. This works both ways, the radios have more than enough power to completely cover the entire lake area around the camp, but anything beyond the ridges is completely beyond range, even Jake’s truck.

Sabrina Lake with Mobile Radio(Coverage of Sabrina Lake using a mobile VHF radio)

Using this radio setup, there are a couple of solutions. It is possible that there is another repeater that does have coverage into your remote lake location and into the areas you would like to talk. Some repeaters are even linked, allowing you to communicate to people on separate repeaters. Sadly, in such a remote location, it is unlikely that there will be a repeater covering your exact valley.

Another option would be to set up your own portable repeater. Using a radio from the truck, and perhaps a taller antenna and mast, or even hiking the radio up a slope a ways with a battery, it is possible to re-establish connection.

Sabrina Lake Repeater(By moving the VHF radio up the mountain from Lake Sabrina, coverage in greatly increased.)

Both of these options would be preferred in a situation where extended setup times are permitted, but what if you don’t want or have time to setup such a repeater? In article 3, we will talk about leveraging HF radio to allow communications within 300 miles, even when line of site does not exist.