A Comms Primer

Survival Communications Primer
By Vector_Joe
ModernSurvivalOnline.com

This  wiki or primer is a compilation of information gathered on various internet websites as
well as FCC and ARRL sources. Subjective opinions are included in this document. Inspirations
or ideas have also been taken from AR-Jedi, Scoutmaster, and GySgtD and others without
their permission (screen names from various forums are used to protect privacy). While a lot of
information here is ham related, almost all of it can be applied or applies to non-ham radio
systems.

One thing I have to mention here. We highly suggest a diversity in communications systems. I personally have computers, internet, landlines, cell phones, frs/gmrs radios as well as amateur radio equipment. The key is to
understand how each works and the limitations of the equipment.
 
Why do I need comms?

Well, unless you want to be a hermit during an emergency situation, you need at least
some sort of rudimentary communication system. At the very least some sort of receiver
system is necessary. Depending on the situation, you may need information on how to
take shelter (inclement weather), how to leave an area (terrorist, chemical spill, etc.) or
many other considerations.Your options are basically one way or two way comms. One way consists of am/fm radio, television, shortwave radio, internet websites and other radio services, etc. Two way
comms consists of am/fm/ssb/cw/digital radio on ham bands and other radio services, cell
phones, satellite phones, internet email and instant messaging, etc.

If you follow the rule of 3’s, then you should have at least 3 methods of distance
communications (not including yelling across the road or 2 cans on a string).

Do I need 2 way comms?
That is a bit subjective depending on your situation. However, it is highly recommended.
Needed for communication with friends and family in a disaster situation where you are
not together. Needed to call for help. Needed to ask for specific information from others
who may have information.

Considerations when using the transmit (tx) part of 2 way comms.
There are a couple of considerations one should consider when transmitting. In general,
all things being equal, more power equals more range. But there are many reasons why
one should limit the power of transmissions. The general rule is to use the MINIMUM
power required to communicate. For one, this reduces airwave pollution. If you are
talking on your radio, you don’t want some other radio operator talking over your
conversation booming out 1000’s of watts of power for no reason. Second, especially in
emergency situations, minimum power means longer battery life. Another consideration
is that when communicating, you may not want ‘everyone’ to hear what you are saying,
particularly in an emergency situation. By using the minimum power, you will limit the
number of ‘ears’ that can hear your comms.
A second consideration when transmitting is the reason and to whom you are
transmitting. This generally falls into 2 categories in emergency/survival situations.
1) Calling for help. In this situation, you need to transmit with enough power so that
‘aid’ can year your call but low enough that you can conserve your battery for extended
use. Perhaps you will need to guide any aid to your location, that would require using the
radio for enough time for help to arrive. In this situation, where lives are on the line,
using any method of wireless communication with any equipment is allowed.
2) Calling within your group. You may need to communicate with your group after some
sort of disaster or emergency situation where the communications are not dealing with life
and death. In this case, in general, you want to keep your power low. Also, as long as
there is some sort of governmental entity, you will probably want to stay within the legal
limits of your radio equipment. The FCC uses a system of ‘Type Acceptance’ where
specific equipment is authorized for use with specific bands of air spectrum. This basically
means that for most bands, you need a radio that is qualified for use on those
frequencies. In general, amateur radio equipment is not type accepted for any of the
services. You also, for example, would not be able to use a radio that is type accepted for
the AIR band on the Marine band frequencies (unless the radio happens to be type
accepted for both- I don’t know if they exist) NOTE: For use on amateur radio bands,
there is no type accepted equipment. You can build or modify any equipment and use it
on the ham bands as long as you follow the other ham regulations in terms of operation.
Background on wireless communications and the FCC (thanks Jim –ARJedi)

This part is excerpted from a thread by AR-Jedi.
Also, most of the text can be downloaded from http://cynthion.com/tacoma.txt
The usable-for-communications electromagnetic spectrum spans a frequency range
from about 100 KHz to 100GHz. (aside, only a portion of that is usable by inexpensive
equipment). In the USA, the federal communications commission (FCC) is responsible
for administering the spectrum for US users; however, the FCC works closely on this
with international bodies, for reasons which will soon become clear. The
"administering" that the FCC performs includes dictating what frequency bands are to
be used for what purposes, and also specifying operational requirements for those
bands (e.g. TX power output, ERP, modulation type, etc).
Since examples are worth thousands of words, I’ll provide a few. 1) The FCC has
decided that broadcast FM stations are to exist in the 88MHz to 108MHz range. There
are certainly power limits however I’ve no idea at hand what they are. 2) The FCC has
decided that CB exists at around 27MHz, and that the maximum TX power output is
4W. 3) The FCC has decided that FRS exists around 462/467MHz, with a maximum
ERP specified. And for the last example, 4) ham (amateur radio) has a number of
bands allocated, each with associated limitations on power/modulation etc. I could go
on and on with cell phones, marine radios, garage door openers, key fobs, microwave
towers, etc etc etc. basically, if the device is what is referred to by the FCC as an
"intentional radiator", they have an assigned slot (band) for it and constraints on it's
operation.

Why the constraints? Well, one reason is for your physiological protection. High RF
power can cause burns, blindness, and other problems. (The "invention" of the
microwave oven was an accident -- technicians working on early radar antennas were
developing burns when the units were powered). Another reason for the constraints is
public safety. The last thing a 747 pilot on emergency approach into Kennedy airport
needs is crosstalk with taxi dispatchers in NYC. Hence the wide berth the FCC gives
around police, fire, and EMS frequencies.

Now then, we see that the FCC regulates intentional radiator use by dividing the
frequency spectrum into bands, and then sets characteristics for each of those bands
that users must obey by.

A common question is, "is one frequency band 'better' than another"? The answer is
"sometimes". For certain applications (more on this in a moment), a given frequency
band may provide better range, fidelity, immunity to interference, and so forth. These
factors, and others, that make a frequency usable for a given application were taken
into consideration when the spectrum was allocated.

It is important to note here that transmitter power output is one of many, many
factors that influence the range at which you can communicate over a given
transmission path. While important, transmitter power output plays only one role in a
multi-faceted problem. Antenna gain, antenna polarization, modulation type, receiver
sensitivity, background noise level, path loss, and a dozen other issues factor into the
equation. Show me a well designed 2W transmitter and I will show you a way to
communicate ~6.5 billion miles. NASA does this every day with their Voyager 1 & 2
probes -- they are now twice as far away as Pluto.
.
Should I get my ham (amateur radio operator) license?
I think this is sort of a no brainer and there is a general consensus that everyone who is
serious about being prepared for emergencies should get their ham license. I can see
maybe 2 ‘legitimate’ reasons why not to get licensed, but I would discount them both.
One is that no one else you know is licensed. I discount this ‘reason’ because once you
get on the air you will meet many other people and many will have the same attitude
about being prepared as you and I. Also, once you get into communications, you *may*
be able to get other friends or family interested.

The other ‘reason’ that I can image that may hold some water is that you don’t want to
get on another government list. Well, you are probably on so many government lists, one
more isn’t going to make a difference. I think (IMO) that this is a bit on the too paranoid
side, but I don’t like to judge people.
Even if you decided that ham radio is not for you, I suggest you read over the next few
sections to get a better understanding of frequencies/bands/modes and equipment.

How do I get a license?
Go to http://www.ARRL.org to get much more general information about getting licensed
to operate as a ham. On that site is listed the local radio clubs in your area. It also lists
the times and locations for taking the FCC exams http://www.arrl.org/arrlvec/examsearch.phtml . The exams are given by other hams that have been certified to give the exams. There are four (4) testing elements.

Element 1 is a 5 word per minute Morse code exam. is no longer a requirement for any of the license classifications.

Element 2 is the technician level exam. It is 35 questions with some basic electronics
theory, radio safety and some FCC operator’s rules.

Element 3 is the general class exam. It is also 35 questions. The content is similar to the
technician exam except that it requires a bit more in depth knowledge. The question
pools are different.

Element 4 is the final exam and is used to get your extra class license. It is 50 questions
long with very in depth knowledge required about different operating modes, techniques,
theory, safety and rules.

To be licensed as an amateur radio operator, you must take and pass a minimum
of element 2.

When you go into a testing session, you can take as many of the four tests as you want
for the single session fee of $14.00. However, if you want to retake any tests that you
fail, you need to pay the $14.00 again.

As for studying, the technician license is fairly simple. This site has several free resources
to study elements 1, 2 and 3: http://www.frrl.org/education/ . Here is a link to the current element 2 test question pool: http://www.ncvec.org/downloads/2006tech.pdf.

As for the General and Extra exams, I personally suggest the ARRL ‘License Manuals’.
See here: http://www.arrl.org/catalog/lm/ . There are also Q&A books available,
however, they seem to be just covering the question pools (which are available for free on
the internet) rather than actually covering the complete theory behind the operating
modes and rules.

Also, go here http://www.qrz.com/p/testing.pl to take practice tests (elements 2, 3
and/or 4).

If you want to learn Morse code, and I suggest you do, you can download one of the many
freeware programs that generate random letters at specified speeds. They also generate
regular words and full conversations (QSOs). Here is the one I like:
http://www.g4fon.net/CW%20Trainer.htm

What is with the different license classes and bands?
For hams, there are basically 4 bands, HF (high frequency), VHF (very hf), UHF (ultra hf),
and microwave. At this point microwave is mainly for experimental communications, so
you will not see a lot of emergency communications on these frequencies.

What does 2M mean? Why is it seemingly used interchangeably with 146MHz?
Hams simultaneously use one of two terms to describe the band they are discussing:
frequency or wavelength. The two are related by a constant known as C, the speed of
light. It turns out that after you crunch the numbers, you can easily convert between
the two terms using the following rule of thumb...
300/freq in MHz = wavelength in meters
Or the same rule but turned around,
300/wavelength in meters = freq in MHz
Hence:
300/146MHz ~= 2 meters
And now you see why 146MHz and 2M are used interchangeably.

Similarly, some wavelength to frequency conversions for other popular HF and
VHF/UHF ham bands...
40M --> 300/40 ~= 7.5MHz
20M --> 300/20 ~= 15MHz
10M --> 300/10 ~= 30MHz
6M --> 300/6 ~= 50MHz
1.25M --> 300/1.25 ~= 220MHz
70cm --> 300/0.70 ~= 440MHz

HF is the region of the electromagnetic spectrum that goes from about 30MHz and lower
frequencies. VHF goes from 30 to 300 MHz and UHF goes from 300 MHz up to the bottom
of the microwave range.

VHF and UHF are basically line of sight methods of communications (not counting
sporadic-e, grey line, aurora, meteor scatter, eme and other less than common
propagation methods). So if your antenna can ‘see’ the antenna you want to talk to then
you should be good to go. UHF and VHF make extensive use of repeaters which are
radios which are usually connected to antennas in highly elevated positions. These
repeater radios receive on one frequency and transmit simultaneously on another
frequency. This allows a user to transmit and his antenna can see the repeater antenna
because of its elevated position. Also the retransmitted signal is sent from an elevated
position so that it has a much broader range. A repeaters range can be up in the 10’s of
miles (30, 40, 50 or more). Typical handheld transmitters (HT), which usually max at
about 5-6 watts of power, can maybe get 5 miles depending on the terrain without using
a repeater.

HF on the other hand is suited for medium to long range communications. HF frequencies
(depending on the season, time of day, and solar activity) will bounce off the upper
atmosphere. So a signal from your location may go up, bounce off the ionosphere and
come back down several hundred or thousand miles away. Communications between the
North America and Europe, Asia, Antarctica, pretty much anywhere, is possible and
happens all the time. You can set up your antenna system to send your main signal
toward the horizon to try and get the furthest contacts, or you can point your signal
mostly straight up (NVIS-Near Vertical Incident Skywave) and get the signal to bounce
back down relatively near your location to get communications within 40-600 miles.
During emergencies such as tornados, earthquakes, flooding,etc. 80-95% of emergency
communications will take place at the local level with VHF/UHF frequencies. There will
probably be less use by volume of HF because of the nature of the operations. This will
vary of course depending on the situation. In a more regional disaster such as a
hurricane or the SE Asian tsunami, the use of HF may be a greater percentage as
communication over greater distances and into and out of the affected area will be
needed.

To Be Continued