Understanding the RadioShack SWR & Power Meter

By PrepperDoc

Many new hams, CB operators, and even boaters with a marine radio get their first standing wave ratio (SWR) meter from a convenient RadioShack. An antenna with an SWR greater than 2:1 may be in need of work! If you use an antenna tuner to match a “long-wire” antenna, then this device is indispensable.

sw figure 2

 

Their catalog # 2100534 fills the bill, but unfortunately the panel layout & markings may easily lead to confusion. Exactly what does one do with the three switches and the knob? Friends whom I’ve tried to help were completely lost because the front panel intersperses switches for the two different capabilities of this meter.

Figure 1 shows improved panel artwork with thick borders that more clearly separate the functions and better explains the controls. Using a photocopier’s enlarge/shrink function, make the top border about 3-3/8″. Cut out the switch rectangles and knob circle. Then tape it over the commercial front panel…

sw figure 1

Now to explain the meter’s operation: The instrument has two completely separate functions: measuring output POWER and measuring Standing Wave Ratio (SWR). The middle switch chooses which function.

To read POWER, the user moves the middle switch to its highest position, then selects from three different power ranges with the left-most switch. Both “average” and “peak envelope power” (PEP) can be measured, depending on the setting of the right-most switch.

In voice single side band, the PEP can be quite a bit larger than the average, and thus this meter can help the user avoid turning the mic gain up so high that he splatters his signal, taking up much more bandwidth than proper. (If turning up the mike gain no longer increases the PEP output, for sure you are beyond the limit! Back off a bit!) The rotary knob isn’t used at all.

To read the SWR, the user first positions the middle switch into the “FORW CAL” (forward relative power) position, sends out a steady signal (careful not to do this longer than safe for your transmitter’s amplifier!) and quickly adjusts the rotary knob on the right until the needle is at “full scale”.

There are multiple ways to create the steady carrier needed to allow the adjustment, depending on your transmitter: there may be a “TUNE” position; or you may be able to hold your Morse Code key down, or with an AM CB rig, simply push the mike button. Then flick the middle switch into REV (“reverse relative power”) and read the SWR from the top scales marked SWR on the meter. Try to keep your SWR 2:1 or lower!

LEGENDS:
Figure 1: Artwork for new panel markings.
Figure 2 — New artwork on SWR / Power meter

Reliable Ham Radio Post-Disaster Security Communications

Today’s non-fiction writing contest entry  written by PrepperDoc

antennaMany preppers’ post-disaster communications plans are built upon low power (“QRP,”  typically 1-5 watts output power) ham radio equipment, able to easily obtain power from small battery or low-power solar sources.    They may believe that after a disaster, interference from higher-powered stations, noisy power lines, electric motors, and a host of computers will be squashed, and their 5-watt level signals will easily make all the necessary communications.  Depending on their communications requirements, they may be badly disappointed in the real event!

Survivors may have widely varying communications needs which might be broken down roughly into three categories:  1) ability to listen to (and possibly contribute to) news reports to/from undamaged states or nations;  2) ability to obtain same-city, intra-state and next-state-over reports of situation-on-the-ground (5-300 miles);  3) short-range communications within a neighborhood.   #1 is easily handled by low-power ham gear (or even shortwave radio receivers) because there may be multiple possible transmitting stations from which to choose; simply find one you can hear.   #3 can be handled by direct (simplex) communications using low-power walkie-talkie FRS/GMRS or ham transceivers.  (Store several in a Faraday cage!)   It is middle-distance #2 — reliable communication/information gathering from 5-300 miles — that is problematic.   You may find a network of several reliable early-warning sites in nearby cities and just across the state border, and have a need to maintain RELIABLE  (not hit-or-miss) communications with them daily for updates on security issues.   It is nice to know of oncoming trouble farther than “smoke-distance.”

VHF/UHF walkie-talkies simply can’t fill this need with their line-of-sight propagation.   And ground-wave (limited at any frequency above 3.5 MHz) transmissions will not cover the distance.   One report found 7MHz ground wave unreliable even at 15 km.   This 5-300 mile range is the realm where Near Vertical Incidence Skywave communications (NVIS), bouncing near-straight-up radio waves off the ionosphere miles above us (usually the F layer but sometimes the E layer) is the only suitable propagation system.  [1]

The properties of the F layer are important to your success.   First, it is at least 150 km above the earth, so your signal is going to travel 300 km just to get to the other side of your town.   Modeling your antenna as a point-source, your signal is going to be significantly dispersed and therefore much weaker after traversing that 300 km round-trip distance!

Secondly, the F layer has variable ionization (more during the day, and during maxima of the 11-year sunspot cycle) and is only able to reflect signals at any given moment up to a certain “cutoff frequency” that depends on the both the ionization and the angle of incidence.   Vertical signals (needed to get to the other side of your city) are the hardest to refract/reflect.   The maximum frequency that successfully reflects vertically is called the Critical Frequency.    Somewhat higher frequencies may refract at lesser angles — but constrained by geometry, they will come back down much farther away, leaving you with a “skip zone” of impossible communications.

And unfortunately, you probably can’t use the exact OPTIMAL frequency at any given circumstance. Your prospective counterparties are mostly other amateur radio operators.   Ham radio equipment typically is designed to work only in certain designated frequency bands — the 3.5-4  MHz (“80 meter”) and 7-7.3 MHz (“40 meter”) are usually the key ones for reliable NVIS communications.   During nighttime around sunspot minima, only the 3.5-4 MHz band may be functioning for NVIS.   During the day, both 80 and 40 meters may reflect in more years of the sunspot cycle — but now add in the problem that the lower level D layer, activated by sunlight-accompanying xrays,  will all but wipe out 80 meter communications.   The D layer’s power-absorption declines by the square of the frequency.  As a result, you prefer to use the very highest frequency that works, optimally just below the critical frequency.  During daytime, the critical frequency may be 7MHz or even much higher, but many ham transceivers off only 7MHz,  14MHz, 21MHz & 28MHz choices.   Thus you may have additional D-layer absorption due to sub-optimal communications frequency.  During the night, the sun’s xrays disappear, and the D layer dissipates, so 3.5-4 MHz signals, which are usually safely below the critical frequency even during sunspot minima, become much more useful & important. For reliable nighttime NVIS, you probably need 80 meter capability, which requires large antennas for good efficiency (or else higher power).  [2]

The ultimate goal is simply to provide a signal to the desired receiving station that significantly overpowers the NOISE that the recipient encounters.   Inexperienced operators may require signal-to-noise ratios of 10 dB or more for successful communications.

Even after an EMP-type disaster, there may be more radio noise than optimistic low-power proponents expected.  Why?  Because much of the radio noise in the high frequency bands is the result of tens of lightning strikes every second, all over globe, whose radio-signature is carried around the world by the ionosphere just like any other radio signal. [3]   Even after an EMP, this noise source will still exist.   Further, ham radio stations in undamaged nations will still be on the air — and likely far busier than ever before!  There will be plenty of strong signals with which to contend.   Finally, while power lines may be silent and most computers dark, a new source of man-made radio interference may burst forth–dozens to thousands of power inverters of all types providing power to persons all over your city.   Even the sine-wave inverters have powerful switching signals as part of their makeup, and I was surprised to find a very troublesome amount of interference coming from my very own backup power system,  wiping out weak-signal reception!   The addition of a heavy-duty filtering device in my inverter’s power lines to my home knocked this down considerably, but few survivors are going to have prepared this well, so houses all around you may be radiating radio hash.  (Consider a device similar to:   http://www.amazon.com/Power-Single-Phase-Filter-CW3-20A-S/dp/B00D0U83D8/ref=sr_1_8?ie=UTF8&qid=1428329468&sr=8-8&keywords=power+line+filter )

For NVIS communications, your antenna can also squelch your effort to overcome the noise at your intended recipient’s site:  vertical or whip antennas put relatively little power straight up, further damaging your low-powered transmitter’s chances.   A very comprehensive investigation in the Netherlands demonstrated that a horizontal resonant dipole at 0.15 – 0.2 wavelengths height was optimal [4]  (corroborating work done in the rainforests of Thailand).   For an 80-meter antenna, that means a height in the range of 40 feet; for 40 meters, 20 feet.   Survivors with antennas at first-story roof-level may face a significant power loss of as much as 90% of their effective signal (10 dB).   Likewise, too-high an antenna (from a skyscraper) may also lower vertically incident power.

You can reduce the effective noise (and thus improve your chances) by eschewing voice communications and moving to narrow-band techniques such as Morse code or digital communications — IF your receiver has the ability to filter more narrowly, your operator has the required experience, and in the case of digital, your conversion equipment survived the disaster.   In our group, we have some new operators who simply cannot use these more-powerful techniques, so we are limited to voice (single side band, about 2 kHz bandwidth).

Beginning to see why QRP low-power ham radio may not meet your security communication needs post-disaster?  Basically, there were very good reasons why the most popular ham radio gear of the 1960’s and 1970’s offered a full 100 watts of output!   Furthermore, what if there is a second EMP strike? Or third?   Will your transistorized low-power ham radio is connected to an antenna during one of those strikes because you depend on it for communications?   It may well be destroyed.    The most impervious gear to simulated EMP attack in testing was vacuum tube gear:  the type of transceivers that had the 100-watt output.

So what is documented about successful and reliable short-to-mid-range NVIS communications in the real world?   Working in the rainforests of Thailand, with relatively optimized antennas, 15-watt output transmitters were reliable for NVIS communications 80% of the time.   My own group found that with newbie operators and horizontal dipoles at various heights, cross-city (30 mile) communications were sometimes possible on voice, and even more likely on Morse code, but that experience made a very big difference.    A Netherlands group did extensive research at a near-optimum frequency of 5.39 MHz for their conditions, using a high-power 850-watt output transmitter and had excellent signal to noise ratios of 50 dB in NVIS communications.[4]   Their powerful transmitter even showed evidence of a readable signal that may have been carried the other way–traversing almost the entire globe to reach their recipient; but this signal was some 40 dB weaker.   Their advantages over many low-power stations were significant:   Their 850 watt station was 22 dB stronger than a 5-watt QRP station,  had an optimized antenna (possibly 10-20 dB better than a poorer antenna) and optimized frequency (excessive D-layer absorption due to lower frequency might have added another 10-20 dB of loss).   Hence their 50 dB signal to noise ratio could easily have been obliterated by a ham operating a 5-watt station (-22 dB), with a suboptimal antenna (-15 dB) and suboptimal frequency (-15 dB)  (total degradation:   52 dB) even before considering the difficulties of inexperienced operators.  An excellent advisory on NVIS emergency communicates notes success with 25 watt (output) signals. [5]

My conclusion is that your communications preparations should definitely include a simple wire dipole antenna at 30-40 feet, either resonant or long-wire horizontal dipoles (with antenna tuner) for both 80- and 40- meter ham radio bands, and possibly additional higher frequency bands for daytime use.    You should also develop a healthy dose of experience (Morse code ability and a narrow receiver filter would be great!).   But it is obviously easier to “turn down” the transmitter power on a 100-watt (or higher) tube type rugged EMP-resistant vacuum tube transmitter to save energy, than it is to try and make a low power 5-watt QRP transistorized transmitter communicate amidst stronger signals and broadband inverter-generated hash interference, while worrying that your equipment might at any time be destroyed by a follow-up EMP strike.    So it might be worth it to plan ahead to provide both ham radio equipment and electrical power for a higher power transmitter, even if you do succeed at times with a QRP transceiver.

 

REFERENCES

[1] NVIS Army FM 24-18.  Appendix M with Graphics.    http://kv5r.com/ham-radio/nvis-army-fm-24-18/   (An excellent tutorial.)

[2]   HF Near Vertical Incidence Skywave (NVIS) Frequency Band Selection.    Accessed at:   http://www.idahoares.info/tutorial_hf_nvis_band_selection.shtml

[3]   Bianchi C, Meloni A:  Terrestrial Natural and Man-Made Electromagnetic Noise.  Accessed at:    http://www.progettomem.it/doc/MEM_Noise.pdf

[4] Witvliet BA et al, Near Vertical Incidence Skywave Propagation:  Elevation Angles and Optimum Antenna Height for Horizontal Dipole Antennas.   Accessed at:   http://www.agentschaptelecom.nl/sites/default/files/2015_-_witvliet_-_nvis_elevation_angles_and_antenna_height_-_ieee_ant_prop_mag.pdf

[5] Idaho Amateur Radio Emergency Service, HF Near Vertical Incidence Skywave (NVIS) Frequency Band Selection.  Accessed at:   http://www.idahoares.info/tutorial_hf_nvis_band_selection.shtml

Prizes for this round (ends April 23 2015 ) in our non fiction writing contest include… Please send your articles now!

  1. First place winner will receive –  A  case of six (6) #10 cans of Freeze Dried Military Pork Chops a $300 value courtesy of MRE Depot, and a  WonderMix Bread Mixer courtesy of FoodPrepper.com a $300 value and five bottles of the new Berkey BioFilm Drops a $150 value courtesy of LPC Survival – total prize value of over $750.
  2. Second place winner will receive –  A gift a gift certificate for $150 off of  Federal Ammunition courtesy of LuckyGunner Ammo.
  3. Third Place winner will receive –  A copy of my book ”31 Days to Survival: A Complete Plan for Emergency Preparedness“ and “Dirt Cheap Survival Retreat” courtesy of  TheSurvivalistBlog.net and copy of “The Survival Medicine Handbook” courtesy of www.doomandbloom.net.

Two-WAY Radio Communications Basics for Preppers

Today’s non-fiction writing contest entry was written by Hunter Prepper

There are no hand held radios that will ever cover any kind of range (beyond LOS (Line of Sight)) without some kind of special circumstances or a repeater. The laws of physics, solid matter and the curvature of the Earth simply get in the way. So, here are your realistic options for achieving long (er) range.

Amateur Radio (Ham) can offer coverage from a few miles to thousands of miles, depending on the band and equipment used. Portable VHF/UHF (Very High Frequency/Ultra High Frequency) radios will have a range by themselves of a few miles, usually less than 10, but can increase that range dramatically through the use of a repeater. HF (High Frequency) radios with good antennas can offer ranges of hundreds or thousands of miles depending on the band, time of day and atmospheric conditions. Repeater sites can fail and atmospheric conditions can be severely disrupted by solar activity, so depending on this is still a gamble, but it is by far the best option for reliable communications range.

General Mobile Radio Service (GMRS) High-end GMRS radios operate similar to UHF Ham radio equipment. GMRS users can use up to 50 watts, high-gain antennas and they can even use and own repeater sites. This is not going to happen using the common bubble pack available as a 22 channel pair of radios. You need real radios, such as the Motorola or Vertex variety. Hand held radios are not going to get more than a few miles range without some unusual circumstances or a repeater.

All other radio services are simplex or point-to-point and don’t offer repeaters, therefore limiting the radios range to no further than the horizon. Radio waves do not follow the contour of the terrain, they operate in strait lines, and any object of sufficient size will block them. What this means is, that they will not go through mountains, nor will they go over the mountain and back down the other side. They will not penetrate buildings very well, travel through dense vegetation such as a forest very well or follow the curvature of the Earth. Radio waves of sufficient power and that are below a certain frequency can be reflected off the upper layers of the atmosphere, but this is dependent on things such as time of day and solar activity.

The only reliable way to get communications range more than a few miles is to install antennas on tall masts or towers (you can hang them in trees) and with sufficient power and provided the terrain isn’t too mountainous and in the way, then you can begin to get some reliable and consistent range out of your radio system, but expecting a hand held radio to offer coverage of more than a few miles is asking too much. Hand-held Ham, GMRS and MURS (Multi Use Radio Service) radios on VHF and UHF frequencies will offer a standalone range of a few miles over average terrain. The FRS (Family Radio Service) bubble pack radios, that you can buy at a Wal-Mart or Academy Sports for example, can only be expected to be reliable at distances measured in yards rather than miles.

Here a few major things that limits your ability to talk to your buddy. This may be oversimplified, but I hope it will help you start to understand the big picture.

Propagation: This is the pathway of the radio waves you send to your buddy. If they are in LOS (line of sight)–which means you could actually see him if you could see 30miles–then you simply need the right antenna and power level to talk to him.

Most of us don’t have line-of-sight to the people we want to talk to. Usually trees, buildings, mountains or other barriers block the signal. They turn the “36 mile” radios into the 1 mile radios you have! There are a few ways to combat these problems, and this brings us to the next point.

Antenna design: There are antennas out there designed to “focus” your transmitting or receiving into one direction. Kind of like a flashlight you can point in any direction you choose. They are called “directional” antennas and have design names like “yagi”, “quad” or “log periodic”. Old analog TV antennas are commonly a yagi or log periodic design–that’s why you rotate them to get the best signal.

Anyway, if you and your buddy point these directional antennas at each other you will stand a better chance of hearing each other. Because they are physically large they almost always used at fixed locations like a home.

Other antennas are designed to broadcast in all directions. They are called “omni-directional”. Much like a light bulb, they send their energy out in all directions. It’s the type of antenna used by police cars and walkie talkies. However they aren’t good for talking over long distance unless you feed them some serious power. But sometimes you can use a radio with a directional antenna pointing at someone with an omni… and still have a good result.

Antennas do best when they are used at the highest geographical point. It gets you closer to the LOS mentioned earlier; you can better your position by transmitting from the top of a hill, from the highest floor of a building, or from an antenna on top of roof, mast or tower.

One more note. Your antenna needs to be tuned to the frequency you are using. This makes your antenna as efficient as possible. This efficiency is a huge concern–and it brings us to the next topic. (Tuning your antenna is too much info to put into this article, do your research and learn)

Power: You have to use enough power to create a signal that reaches your buddy. The best antenna in the world won’t work if you don’t feed it enough juice. And the most juice in the world won’t make your antenna work of its not tuned.

The general rule of communication is to use only as much power as you need. This is courtesy to others who use the same or nearby frequencies. You don’t want to overpower them. Also, it helps save money on your electric bill!

Summary: To achieve constant and reliable 30 mile range, You need to use enough power WITH a tuned antenna AT the best height you can manage.

The inexpensive FRS or GMRS radios (like the Motorola Talkabout radios) won’t do it. They put out a maximum 0.5 watts of power (half a watt!) Their antennas are very inefficient. However, they would be good for communications on your property.

Other public radio frequencies such as MURS band have very limited power output–2 watts.

CB radio can legally put out 4 watts. There’s also a mode feature that allows 12 watts in “single sideband” mode. It’s also referred to as “SSB”. Your voices will sound funny due to the mode, but it is a much more efficient use of your radio’s power. CB antennas tend to be long or very big. It will take some experimenting to find the best antenna position to use. You will also need to “tune” the antenna for optimal performance.

The only way you’re going to legally talk to your buddy with a relatively compact antenna and good audio quality is to get into Amateur Radio. It will enable you to use higher power (some mobile radios can put out 75 watts), and there are many antenna options for home and mobile use. I know not everyone wants to register with the Government, but sometimes it has its advantages. Besides just because you have a license does not mean you have a radio, if you understand. There is also no law against buying the radio “just” to listen.

If you choose amateur radio, you will likely need a mobile car radio that puts out 50 watts or more into a tuned mobile antenna that is not too short. You can use the same radio in your house… with a better performing antenna on the roof, inside the attic, or on an antenna mast. By having a radio of this type you will be able to have a mobile station and a base station using one radio and two antennas.

There are many, many other more involved options and details such as grounding, repeaters, etc. It is hard to cover everything in a single post, it is best to get a good book; I started with “HAM radio for Dummies” and one from the ARRL (Amateur Radio Relay League). But hopefully this will help you ask more questions.

Abbreviations and Explanations: VHF – Very High Frequency; is the ITU-designated range of radio frequency electromagnetic waves from 30 MHz to 300 MHz. Frequencies immediately below VHF are denoted high frequency (HF), and the next higher frequencies are known as ultra high frequency (UHF).

VHF propagation characteristics are ideal for short-distance terrestrial communication, with a range generally somewhat farther than line-of-sight from the transmitter (see formula below). Unlike high frequencies (HF), the ionosphere does not usually reflect VHF waves (called skywave propagation) so transmissions are restricted to the local radio horizon less than 100 miles. VHF is also less affected by atmospheric noise and interference from electrical equipment than lower frequencies.

Whilst it is blocked by land features such as hills and mountains, it is less affected by buildings and other less substantial objects than UHF frequencies. UHF – Ultra High Frequency; designates the ITU radio frequency range of electromagnetic waves between 300 MHz and 3 GHz (3,000 MHz), also known as the decimeter band or decimeter wave as the wavelengths range from one to ten decimetres; that is 10 centimeters to 1 meter. Radio waves with frequencies above the UHF band fall into the SHF (super-high frequency) or microwave frequency range.

Lower frequency signals fall into the VHF (very high frequency) or lower bands. UHF radio waves propagate mainly by line of sight; they are blocked by hills and large buildings although the transmission through building walls is high enough for indoor reception. They are used for television broadcasting, cordless phones, walkie-talkies, satellite communication, and numerous other applications.

I hope this has helped you or at least guided you in making an informed decision on what to purchase and what you can expect for your purchase.

Prizes for this round (ends April 23 2015 ) in our non fiction writing contest include… Please send your articles now!

  1. First place winner will receive –  A  case of six (6) #10 cans of Freeze Dried Military Pork Chops a $300 value courtesy of MRE Depot, and a  WonderMix Bread Mixer courtesy of FoodPrepper.com a $300 value and five bottles of the new Berkey BioFilm Drops a $150 value courtesy of LPC Survival – total prize value of over $750.
  2. Second place winner will receive –  A gift a gift certificate for $150 off of  Federal Ammunition courtesy of LuckyGunner Ammo.
  3. Third Place winner will receive –  A copy of my book ”31 Days to Survival: A Complete Plan for Emergency Preparedness“ and “Dirt Cheap Survival Retreat” courtesy of  TheSurvivalistBlog.net and copy of “The Survival Medicine Handbook” courtesy of www.doomandbloom.net.

EMP Trash Can Faraday Cage Testing in Lab

Tests are conducted to measure how effective metal garbage cans are at blocking high-frequency energy, such as that released by an high-altitude nuclear electromagnetic pulse (EMP). Tips are provided on how to greatly improve the shielding effectiveness.

Question About Survival Radios for Monitoring and Two-Way Comunications

From Terry:

Hi , I’m looking for a good two-way radio to use as “walkie-talkie” but that can also be used to pick up esp, ham communications. I have lots of the two way radios that everyone has but am looking for something with a little more distance and other options . I have no ham license. Theses would be used for when the shit hits the fan…

Terry, the one that I use and recommend is the “Wouxun KG-UV6D Two Way Radio“, it’s programmable (there is a slight learning curve) for VHF: 136-174 MHz; UHF: 400-480 MHz; FM: 76-108 MHz, which covers everything you’ll need. For example, I can program my radios to Ham, Murs, Local Police, Fire and Rescue etc.   And while it might not be legal to talk on all of these with this radio it is legal to listen in most states… M.D. Creekmore

Questions & Answers With The Wolf Pack : Communications…

Question from Terry,

Hi , looking for a good two way radio to use as walkie talkie but that can also be used to pick up esp. ham com. but other communications also. I have lots of the two way radios that everyone has but am looking for something with a little more distance and other options . I have no ham license. Theses would be used for when the poop hits the fan.

You Know What I’m Saying – Message Ciphers

Image By: Ludovic Bertron

By Wind Talker

In a survival situation, secure communications between two friendly communities can be essential for both security and commerce.

It would be ideal if external messages could always be carried by the most dependable people within the group, but those people are usually tied up with security planning, training, assignment of watch personnel, etc.  Therefore, people tasked as ‘messengers’ are usually young and relatively inexperienced.  Their capture by an enemy and the resulting loss of the critical message entrusted to them could be significant.  So how do we minimize the risk of an enemy intercepting our messages?

For centuries, simple ciphers have been used to address this need for more secure communications.  As an example, would you gain much knowledge if you intercepted one of the following enemy messages?

  1. SNRSREOCNWEDEEVFREOX
  2.  AFDX DXAX FFFX FDGF AXDD GDAX GFVG VVVX VFAA AF

While simple ciphers can be useful against an adversary who is inexperienced in encryption, they provide almost no protection against a trained decryption analyst with automated tools.  In other words, while the National Security Agency (NSA) would probably laugh at their simplicity, an attacking force of roaming thieves would find it time consuming or even impossible to decipher.

If given a couple of hours, you could probable break the fist code without reading further.  The second would probably take months of dedicated effort for a non-expert to break.

We will review some of the strengths and weaknesses of ciphers, and then explain how ciphers were used to create the two examples given above.

Ciphers allow a message to be coded in manner that makes the text unintelligible or hidden to a non-authorized reader.  This frees us from having to entrust the knowledge contained within the message to the carrier.  For example, a ciphered message could be handed to a traveling tradesman with a request to deliver to a designated person at a certain town.  Neither the messenger or a thief could easily decipher the message  if opened.

Simple Ciphers are appropriate for:

  1. Short messages so that unauthorized people cannot detect a pattern.
  2. Information that is only useful to an enemy for a short period of time.  In order to be prepared for a worst case scenario, one should always assume that the enemy has available a person with the necessary decryption skills.  Therefore, given time and dedicated effort, almost all manual ciphers can be broken. Therefore an appropriate usage  of a manual cipher is where the information contained within the message is of no value by the time the cipher could possibly be broken.  An example of such a message is one that delays by two hours an offsite meeting scheduled for the next day.  By the time the cipher is broken, the meeting would be over with.  An inappropriate usage would be to communicate group strengths or weaknesses which could still be true after enough time for an enemy to break the code.

 

  1.  Rail Fence Cipher  (also called the Zigzag Cipher)At first, the procedure seems complicated, but after a little practice it becomes quite easy.Suppose you want to send the message, “Send reserve force now”.

    Count the number of letters (excluding spaces); in this case 19.  If the number is a multiple of 4 then fine.  If not, add dummy letters at the end until it is divisible by 4 … in our case there are 19 letters which is not a multiple of 4, so we need to add 1 dummy letter to the end of the text to make a new total of 20 letters which is a multiple of 4 (i.e. 5×4=20).

    Remove the spaces between the words, and place the dummy letter at the end.  The new text becomes “SENDRESERVEFORCENOWX”.

    Now split the text into two lines where every second letter is lowered to the second line.  Like this:
    SENDRESERVEFORCENOWX
    becomes

S N R S R E O C N W
E D E E V F R E O X

Now, copy the first row letters followed by the second row letters.
SNRSREOCNWEDEEVFREOX

Above is the finished ciphered text.  If one does not know the procedure used for encryption, this simple cipher will take time for a non-expert to break.
The receiving person can decode the message easily.  First, divide the encrypted line in half:

SNRSREOCNW  EDEEVFREOX

Now he can read the original message by reordering the letters:  Take the first letter from the left group, then first letter from the right group, second letter from the left group, second letter from the third group, third letter from the left group, and so on.

Decrypted message is:

SENDRESERVEFORCENOWX

And spaces and remove the filler letter at the end (in this case the X), and you have:

SEND RESSERVE FORCE NOW.

Strength:     One of the simplest ciphers to learn and use.

Weakness:  This is one of the more easily broken ciphers.  All of the original letters
remain, only their sequence has been changed.

The next example requires slightly more coordination between the sender and receiver, but provides additional security.

  1.  Substitution Cipher

Draw a 7×7 matrix.  As in the example below, label both the rows and columns with letters that appear to be random (for this example, ADFGVX).  This column / row labeling needs to be agreed upon in advance by the sender and receivers so that both can set up identical tables.  This labeling can be used multiple times.

A D F G V X
A
D
F
G
V
X

Security is based upon a ‘keyword’ which should ideally be more than five letters.  The sender selects a ‘keyword’ that does not have a single letter used more than once in the spelling.  For example, as the word ‘Washington’ uses the letter ‘n’ twice; it is not acceptable.  In our example, let’s use the keyword ‘Plymouth’ and the message “Meeting starts 1230 pm.”)

In the matrix created above, start filling the letters row by row by using the keyword we selected: ‘Plymouth’.  Then continue to fill with remaining letters of the alphabet in order, but skip the letters already used by the keyword.  Then fill out the last blocks with the digits 1 through 9.

A D F G V X
A P L M O U T
D H A B C D E
F F G I J K N
G Q R S V W X
V Y Z 0 1 2 3
X 4 5 6 7 8 9

Now take your text and substitute the column and row coordinates for each letter as follows:

 

TEXT m e e t i n g s t a r t s 1 2 3 0 p m
CYPHER AF DX DX AX FF FX FD GF AX DD GD AX GF VG VV VX VF AA AF

To make easier to read, ciphers are frequently written in four letter groups:

The resulting message reads:  AFDX DXAX FFFX FDGF AXDD GDAX GFVG VVVX VFAA AF

The same matrix box that is used to cipher the message is also used to decipher the message once received.  As the receiver would already be trained on how to setup the matrix box (including the row and column headings), he would only need the ‘keyword’ in order to decipher the message.  A listing of unique keywords are usually provided to authorized communicators on a monthly basis with a different keyword for each day.

It is important to remember that a person trained in decryption and having access to computerized tools can break these codes very quickly.  But, the ciphers would likely confuse the average person for an extended period of time.  Certainly they are better than sending messages in the ‘clear’.

These are only two of the many ciphers available on the internet.  Be imaginative and make some subtle changes to make a cipher uniquely your own.

Questions & Answers With The Wolf Pack : Question About Ham Radio?

I have enjoyed reading your blog and thank you for the information you have shared with our community. As much as I have learned while reading the posts of you and your contributors, one of the most important lessons has been that we should know our limitations and never expect to master each and every aspect of preparation.

So, having written that, I would like to respectfully ask a question about ham radio. Please remember that I am entirely ignorant of the ham community and that my question comes from this ignorance.

Please also know that I am asking this question because, while I find ham radio operation necessary, I do not want to clutter and fumble through the airwaves in an attempt to find the limited operation I am in search of. I would rather have the resources available to me in times of need, and focus on things I find more applicable to my current situation.

I recently purchased two BaoFeng UV-5Rs, which I understand are very popular in the community. Is there someone that could assist me with a shortcut list of instructions designed to find four things: a line of communication in a time of emergency, the AM/FM band, the weather band, and the emergency scanner band?

I am hoping to provide my aging parents with a ‘quick start’ index card and the unit so that we can communicate in an emergency situation. Something so clear and easy it can be followed by an elderly person who has limited technical capability (ie bullet pointed instruction). They are many states from me and I have experienced times in which they were uncommunicable due to weather and other outages and this would give me great peace of mind to know an option is available in an emergency. Clearly, this would never be used in a manner disallowed by the rules and regulations of the FCC.

Thanks again for being such a resource. I really appreciate it. James M

Build Your Own Faraday Cage. Here’s How.

by Arthur Bradley

Introduction to Faraday Cages

There is a great deal of confusion about Faraday cages. Not only about how to build them, but also what they actually protect against. In this article, Dr. Arthur Bradley, author of Disaster Preparedness for EMP Attacks and Solar Storms, answers a few basic questions and perhaps debunks a few myths.

What is a Faraday Cage?

A Faraday cage (a.k.a. Faraday shield) is a sealed enclosure that has an electrically conductive outer layer. It can be in the shape of a box, cylinder, sphere, or any other closed shape. The enclosure itself can be conductive, or it can be made of a non-conductive material (such as cardboard or wood) and then wrapped in a conductive material (such as aluminum foil).

Faraday Cage box

Faraday Cage Construction

What does it do?

A Faraday cage works by three mechanisms: (1) the conductive layer reflects incoming fields, (2) the conductor absorbs incoming energy, and (3) the cage acts to create opposing fields. All of these work to safeguard the contents from excessive field levels. A Faraday cage is particularly useful for protecting against an electromagnetic pulse that may be the result of a high-altitude nuclear detonation in the atmosphere (a.k.a. EMP attacks).

Despite rumors to the contrary, a Faraday cage is not necessary to protect against solar coronal mass ejections because the frequency content of such disturbances is at much lower frequencies—they don’t couple energy efficiently into small-scale electronics, except through conducted paths (e.g., wires coming into the system). A better precaution against solar events is to unplug electronics and use quality surge suppressors.

How does field cancelation work?

Field cancelation occurs when the free carriers in the conductive material rapidly realign to oppose the incident electric field. If the cage is made from something non-conductive, the free carriers are not mobile enough to realign and cancel the incident field.

How thick should the conducting layer be?

The conductive layer can be very thin because of something known as the skin effect. That term describes the tendency of current to flow primarily on the skin of a conductor. As long as the conducting layer is greater than the skin depth, it will provide excellent shielding because the absorption loss will be large. The skin depth is a function of the frequency of the wave and the conductor material. As an example, consider that for a frequency of 200 MHz, the skin depth of aluminum is only about 21 microns. EMP pulses can have frequency content that ranges up to 1,000 MHz. Therefore, wrapping a box in a couple of layers of heavy duty aluminum foil (typically about 24 microns thick) provides the necessary conductor thickness to protect against high-frequency radiated fields.

Does it matter what type of conductor is used?

Not much. The conductivity of nearly any metal is good enough to allow the carriers to easily realign to cancel external fields. For example, if silver (the best conductor) is used in place of aluminum, the skin depth at 200 MHz is reduced to about 4.5 microns. Of course, the high cost of silver would prevent using it for such a purpose.

Can a Faraday cage have holes?

Yes, as long as the holes are small with respect to the wavelength of the incident electromagnetic wave. For example, a 1 GHz wave has a wavelength of 0.3 meters in free space. As long as the holes are significantly smaller than that dimension (i.e., a few millimeters), they won’t let in much of the incident wave. This is why fine conductive mesh can be used when constructing a Faraday cage. In practice, the cage’s lid or door usually causes the most leakage. Taping the seam with conductive tape helps to reduce this leakage.

Can you use existing conductive enclosures?

Yes, there are many conductive enclosures that can be used, including ammo cans, metal garbage cans, anti-static bags, and even old microwave ovens. Each has its own level of effectiveness as covered in my book, Disaster Preparedness for EMP Attacks and Solar Storms. The key criterion is that the gaps and seams remain very small.

Must the cage be grounded?

There is a great deal of confusion regarding grounding of a Faraday cage. Grounding of the cage (i.e., connecting it to some Earth-referenced source of charge) has little effect on the field levels seen inside the box. Grounding primarily helps to keep the cage from becoming charged and perhaps re-radiating. The bottom line is that an ungrounded cage protects the contents from harmful electromagnetic fields as well as a grounded one.

Anti-static Bags

Anti-static bags are readily available to protect electronic components against electrostatic discharge. They can be purchased in many different sizes, including some large enough to hold radio equipment. While they do offer shielding from EMP, not all products are created equal. Testing confirmed that products certified to MIL-PRF-8170 and/or MIL-PRF-131 offer the greatest protection from an EMP. The results from testing three different types of bags are provided in Disaster Preparedness for EMP Attacks and Solar Storms. When selecting an ESD bag, consider not only the shielding effectiveness but also the physical ruggedness of the bag. A tear or large hole can compromise the bag by allowing EMP energy to enter.

Static Bags

Anti-static Bags

Larger Faraday Cages

Storing a larger set of electronics might require an entire room. Engineers who work in electromagnetics often use “shield rooms” to conduct experiments because they do an excellent job of filtering out interfering signals, providing in excess of 100 dB of shielding. A poor-man’s shield room can be made by lining a small closet with heavy-duty aluminum foil, covering all four walls, the floor, the ceiling, and the inside of the door.

Overlap and tape the seams using either conductive or regular cellophane tape. There can be no conductive penetrations into the room, or it will seriously degrade the shielding. Cover all electrical outlets, light switches, etc. with aluminum foil. Do not plug anything into the electrical outlets. Also, lay a piece of plywood or cardboard on the floor so that it can be walked on without damaging the aluminum foil. Rooms built in this way have been shown to offer more than 50 dB of shielding up to several hundred MHz.

Larger Faraday Cages

For More Information

To buy Dr. Bradley’s EMP book please go to Amazon.com. To sign up for his free Practical Prepper Newsletter, Email: newsletter@disasterpreparer.com .

Questions and Answers with The Wolf Pack : SW Radio Recommendations…

MD- Please list again the SW radio you recommend? I saw you post awhile back but forgot the name brand. Thanks Jeff B…

I have several shortwave radios but the one I like the most is the Grundig Globe Traveler G3 Portable AM/FM/Shortwave Radio. Please share your thoughts and recommendations in the comments below.

M.D. Creekmore

My power source in the event of power failure or a SHTF scenario

By Mastertrooper

power cartI decided I wanted a readily available power source in the event of power failure or a SHTF scenario.

My cart itself consists of 4 Goal Zero solar generators on top, and 3 Duracell 12V golf cart batteries linked in parallel on the bottom. The solar generators stay plugged into a circuit that comes on when I flip the light switch. They pretty much stay charged up as I’m in there daily. The 3 batteries stay connected to a battery minder which is powered up all the time. It maintains them on a float charge. All connectors, fuses, etc. are loaded on the cart. I have connectors (on the right leg) for a cigarette lighter type plug-in, and a 2 prong inline connector to provide 12 volt power. The cart itself is a 500 lb. capacity service cart I picked up at Northern Tools.

The cart works in conjuction with a power inverter; I have 400 watt, 800 watt, and 3,000 watt inverters. I keep them all in EMP protection. I designed it from research I’d done on the internet, including YouTube videos. The main purpose for it is to power a sump pump, freezer, refrigerator, dehumidifier, and other essentials in case of a power outage when I’ve run out of gas and propane for my 2 generators.

I have 4 Goal Zero 30 watt solar panels and have built a PVC rack I can lock them into which will rotate with the sun on a pedestal from an old floor fan. It will be placed on the porch and the base weighted down with sandbags. All 4 panels can be linked together and power sent to the solar generators with an extension cord. I can connect three of them together and send the power to a charge controller with a clamp output to charge the batteries. The charge controller is limited to 90 watts.

I took the cart for a test spin the other day. I rolled it out into the wash room where I had access to a water pipe ground and connected my 3,000 watt inverter to my three GC12 batteries. I ran a dehumidifier and water pump off it at the same time and it didn’t even strain it enough to turn the inverter’s cooling fans on. Batteries seemed to hold up well, clocking in at 12.9 volts at the end. I haven’t run the freezer with it yet but don’t anticipate a problem. It’s rated at 5 amps, so the start up draw shouldn’t be that great. I also have 4 portable lamps (heat lamp type clamp-on with shade) fitted with low draw 2.5 watt LED bulbs to take care of lighting.

Letter Reply : Prepper Communications Primer – Antenna Tuning

By Salem

AntennaAntenna efficiency is also a factor in figuring range. Chuck mentions in the article all CB antennas need to be tuned, and then in the comments expounds that ALL antennas need to be tuned.

Natural tuning on any band is two quarter wavelength “elements,” with one being positive and the other negative at various points in time. In a mobile, the vehicle is usually one half of the antenna. In handhelds, the second half is usually the frame of the radio. For base stations, it could be another quarter wave element to make up a dipole antenna, or it could be a “ground plane” of whips or buried wires working with a vertical element. A J-pole is taller, and has both halves of the antenna, as do some end-fed half-wave whip antennas for fiberglass cars and boats.

Each natural quarter wave element is roughly the operating frequency divided into 234 feet. A natural UHF element is about 6 inches tall. The length on MURS and VHF High Band is about a foot and a half. CB is about 9 feet. A popular ham band between 3.5 and 4.0 MHz requires a whip about 60 feet tall, and a dipole would be twice that length. An AM station at 1000 kHz needs a 234-foot whip and buried ground plane radials, preferably in a swamp. A six-foot diameter vehicle roof is a natural ground plane only above about 80 MHz.

It is possible to “fool” a transmitter into delivering power into an antenna that is the wrong length by having transformers, coils and/or capacitors that “match” the wrong length to the radio. A “rubber duck” for a MURS or FRS antenna is wound into a coil shape to make the stubby whip look 18 or 6 inches tall. And mobile ham radios for short wave have all kinds of tuning designs to make them look much taller than they really are. But much of the power is distributed into this “fooling” business and lost as heat, and the percentage of power going into the air (“radiation efficiency”) will be less.

A common CB mobile rooftop antenna design has a coil in the base that makes a 3-foot whip look 9 feet tall. But this makes tuning the whip length that is being multiplied 3 times more critical. And the bandwidth, or the amount of frequencies above and below the center tuning point where the antenna works best becomes 3 times narrower.

Another common CB antenna design is the “Firestick,” which has a wire wound around an insulator inside a plastic coating, much like the “rubber duck” handheld antennas.

We can get “gain” by making antennas certain multiples of natural quarter waves, so that the plus and minus pulses from parts of the elements leave and arrive at the antenna at the same time (in phase), and don’t cancel each other out (out of phase). While this does not actually put more power into the air, what this does is focus more energy toward the horizon where it is being measured, and less energy is sent up and off into space.

A common gain antenna for VHF High Band and UHF mobile communications is using a 5/8 wave element instead of a quarter wave one. This would be about 4 feet for high band, and 14 inches for UHF. That AM station I mentioned probably would prefer a 585-foot tall 5/8 wave “whip,” if the FAA allowed it in that area.

5/8 wave antennas require a coil to match them to the transmitter. They are good for direct mobile-to-mobile or fixed station range toward the horizon, and would be highly recommended in the plains. But the upward center of maximum signal from the shorter quarter wave vertical whip is usually better for reaching mountaintop repeaters when driving through deep valleys. And if that tall whip bends back in a vehicle at speed, the “horizon” it aims at is now off into space. Mobile VHF/UHF gain antennas must remain vertical to get the benefit of that focusing.

By the way, don’t be fooled by dishonest advertising I’ve seen saying a short CB whip is a 5/8 wave, just because it has more wire wound on a loading coil. A 5/8 wave for CB must be about 22 feet tall above the ground plane to get the benefit of the gain.

In UHF, it is possible to have natural antennas stacked above each other on the same mobile whip. That coil or squiggle in the middle of a UHF or cellular gain antenna is not to make it appear longer, it is a actually a time delay so the whip above and the whip below transmit together in phase.

Antennas on the higher frequencies are more efficient for mobile and hand-held operation, since the vehicle and radio frames are closer to a natural length than at lower frequencies. So are the “acceptable” whip lengths for each, as in many cases we have to trade off convenience for performance. I have never seen a vehicle in motion on land with a 60-foot whip! But the lower frequencies “bend” more readily, giving better over-the-horizon performance. With more communications experience, it is possible to select the best trade-offs for your communications goals.

By the way, remember that 60-foot whip for 3.5 to 4 MHz? Chuck mentioned mobile operation with hundreds of watts talking halfway around the planet on short wave. A column in the March 2014 issue of the ARRL magazine (page 53) does several design calculations on various mobile antenna configurations for that band using a loading coil 2 feet below the tip. A straight 8-foot whip with the elevated loading coil calculates to -16.5 dbi efficiency. In layman’s terms, that antenna radiates about 1/50 of the energy that a base station dipole would with the same power. A 100-watt mobile would put the same energy into the air as a 2-watt radio on a base station antenna. A 4-watt CB with a nine-foot whip radiates twice the mobile power on its higher frequency.

Various “capacity hat” designs are described in the column to improve the signal from that short wave whip, the best being about 4.5 db better than the straight whip above the coil. The best designs would radiate between 2.5 and 3.2 times more energy, or about 6 watts to the air from a 100-watt radio. Don’t write off the “QRP” (telegraph code for “reduce power”) folks who use 5 watts or less on purpose!

But what really got me to comment is writing off GMRS as useless. GMRS does require a station license and callsign, as OhioPrepper pointed out. But the 1.5 watt limit that Chuck mentions is the design limit of blister-pack handheld radios that are targeted toward pirate FRS operators. Yes, they do include a note that you need to get a station license; nudge, nudge, wink, wink.

Licensed GMRS radios can transmit with up to 50 watts on the 8 main channel pairs (47 CFR 95.135). GMRS licensees can install repeaters on GMRS, just like business, public safety, or ham. There are certain power limits for different types of stations, and other limits and restricted frequencies near the Canadian border.

FRS was created on the split GMRS channels between the main channels. These were always 5-watt “low power” channels. Seven of these channels are now FRS only, and the other seven still allow GMRS users with call signs to use a full 5 watts.

The downside to GMRS is for OPSEC. The rules only allow unencrypted FM voice. MURS allows digital signals, and has no such restriction. You could conceivably obtain encrypted radios for MURS, but they would be “spendy.”

If considering GMRS, now is a good time to get equipment. As of January 1, 2013, only narrowband equipment is allowed on UHF for business and public safety, but no such restriction was placed on GMRS. Perfectly good radios came out of service because they were older and were not tested by the FCC for narrowband operation compliance. Many of these will go to the landfill or the crusher. There might be some public safety auctions selling these radios by the pallet for pennies on the dollar. Some 2-way shops may still have some that they can’t re-sell to their regular customers that can be had for a song.

It requires software and adapter cables to re-program some of the 1990′s versions, and the availability of technical skills to set up repeaters or re-tune older models of radio, but the initial buy-in can be down into the Baofeng range. It pays to have friends here.

To sum up, licensed GMRS can be a viable tool in the communications toolbox. And the 6-inch natural antenna length means that a handheld radio whip and case send more of the measured power into the air than an MURS radio with a rubber duck. A 6-inch mobile whip is also more covert than a big CB or shortwave antenna.

Note: The UHF band used by hams and GMRS will be absorbed by foliage, and is not as good a choice as MURS for operation on foot in the woods. On the other hand, the UHF band will ricochet off of concrete buildings and find smaller openings with which to penetrate into buildings, so it will out-perform MURS in an urban environment.

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