Wednesday, May 11, 2016

Propagation and EMCOMM

An EM advanced studies training module - by D. W. Thorne, K6SOJ

A few years ago I was involved in a Search and Rescue operation in extremely rugged country in the far NW corner of California. The primary search area consisted of two very deep and steep canyons that are separated by a 2,000 ft. ridge. Before the search was over about a dozen SAR units from as far away as 300 miles were called in to assist. There was no cell phone coverage and only one Sheriff's Department repeater was accessible. The IC (who was from an adjacent county) said the local Sheriff wanted to keep their SO frequency clear of the SAR traffic and asked that it be used (by SAR) for emergency traffic only.Around 2200 local time, one other emcomm volunteer (a trainee) and myself arrived at the SAR CP/base camp positioned in a deep canyon and we were asked immediately to establish contact with the Sheriff's Office the IC's home county. My first thought was about setting up a NVIS* antenna, and establishing an HF link either on 40 or 75 meters with one of several HF stations that had been previously alerted and were monitoring some previously designated frequencies and that could relay traffic to and from the Sheriff's Dispatch Center via telephone.
I knew there was a VHF amateur repeater located on a mountain top about 20 miles to the another state! I thought, why not give it try? I switched to the repeater frequency, keyed the mic, heard the identifier, and then identified myself. Immediately, I heard a familiar voice was my wife! She was at our home station over 125 miles away, but by using out tower mounted 13 element Yagi she had solid contact with the repeater. Needless to say, the IC, who was watching, was very impressed!The search went on for about a week before finally being called off. The missing person (or his remains) were never found. Most of the searchers were non-hams, so all tactical communications were on VHF public service simplex frequencies (NASAR, CLEMARS, etc.). By stationing a radio relay team (the young trainee and myself) on the ridge that separated the two deep canyons, effective communications were maintained. Every message between the two canyons was through our relay.
A portable repeater may have worked, but there are very few (if any) used by public service agencies and there are very few "spare" public service "frequency pairs" available for portable/field operations. Plus mutual aid responders may not be able to program the radios to an "new" pair. Frequencies such as NASAR, CLEMARS, NALEMARS and other SOA (scene of action) simplex frequencies should be in all SAR transceivers.(NOTE: Typical amateur radio gear is not FCC "type accepted" transmitting on PS channels. Listen only. Hams who are active in SAR, fire, EMS, or other public service, should consider buying commercial radio gear that can be legally operated on both public safety and amateur services.)Most local amateur emcomm (and nearly all public service communications) are handled on VHF, UHF, or higher frequencies. Which are line-of-sight whether direct or via a repeater (if available).One of the great advantages that we as radio amateur have is that we have a wider range of frequencies and modes option that just about anyone! With all the new emcomm volunteers now entering the world of HF, it is advantageous to know some basic and practical aspects of HF radio propagation.40 and 80 meters are the "Workhorse Bands" for Regional Emcomm:
While most local or tactical emcomm can easily be handled on VHF or UHF frequencies, most regional traffic (50-300 or more miles) is handled on the 40 or 75-80 meter bands. (The 160 meter band and the 60 meter band should not be ruled out, but by and large the 40 and 80 meter bands are the workhorse bands most used for emcomm networks.

I am not a physicist are these comments an attempt to explain and define all the intricacies and nuances of HF radio signal propagation. There are many excellent books available that can adequately explain that area of science that is wrought with multiples and rarely understood variables. As one ham friend of mine says, "It's all Voodoo!"

The SEA and the SUNMost of us who have studied the basics of radio know that the earth is surrounded by layers of ionized particles. The ionosphere is in a constant state of flux. It is affected primarily by the sun, and it varies immensely with the time of day, the time of year, the solar cycle, geomagnetic storms, and other factors. The ocean tides on the earth are influenced by the gravitational pull of the sun and the moon and to a small degree, the other planets, and is compounded by the winds. The ionosphere (envision a canopy above the earth), is ever expanding, contracting, fluctuating in the amount of ionization level, and possibly other factors that scientists may not have even discovered.

The D layer (closest to the earth) is only a factor present during the daylight hours and is responsible for the absorbing most MW and HF radio signals. This is why MW BCB signals do not propagate (over any great distance) during daylight hours. Then there is "sporadic E", which some liken to clouds of ions which come and go with the seasons often only lasting a few minutes or hours. Radio hams who enjoy the six meter band (50-54 MHz) love it when the "E layer comes to life!" The most commonly relied upon layer for HF radio is the highest...the F layer. To further confuse the issue, the F layer divides into two levels during the daytime. F1 and F-2. One or the other will refract (bounce a signal back to earth) from a point of refraction depending upon: 1) the frequency; and 2) the angle at which a given signal hits that refraction point.Most of us knowledgeable hams who want to be able to maximize their ability to communicate by bouncing radio signals off the ionosphere, have learned by experience what works and what doesn't work. Often by much trial and error. (This is what is known as experience!) They have learned and also realize that what works today, may not work tomorrow, but it may work again the day-after-tomorrow. Even at the same time and on the same frequency! In fact...what works now, may not work five minutes from now!

Most of us have played pool or billiards. The object in those games is to bounce (or ricochet') a ball off of the opposite bumper. The more direct, or acute the angle that a ball hits the bumper, the closer it will return to it starting point. (E.g. - the side pocket near to you.) If you "glance the ball" off the bumper at an obtuse angle, it will "land" farther way from the starting point. (Hopefully, in the corner pocket.)

Radio signals behave in much the same way. Where they go, depends (in part) at what angle they are directed towards the ionosphere. NVIS (near vertical) go up, and down, land closer to the transmitting station, and may not interfere with distant stations. Low angle (aimed at the horizon) will land a long, long way away, but may not be heard by who you want to talk to.

Now, if the ionosphere was a straight edged surface like the bumper of a billiard table, it would be easier to calculate just where a signal might "bounce to" or land. (This is actually done using solid passive reflectors on mountains for micro wave communications.) But the ionosphere is curved and it consistently varies in thickness. Imagine that you are playing pool on a circular table! Imagine also the cushion is constantly changing in its softness. Now imagine that the table is constantly changing it's circumference. (Like the iris of the human eye or a camera.) That would make for a very challenging game of pool!

The ionosphere is constantly changing in all of these physical characteristics. Therefore, so does the refraction point (distance above the earth) vary for any given frequency. And...just as in billiards...the angle at which a signal "hits" that refraction point will determine how far it will "skip" or return to earth. To further complicate tings, the layer varies in thickness and intensity. If it didn't, the radio signals would be very specific as to where they land. When propagation is marginal, signal paths may actually be very selective. When band conditions are is optimal, signals on many frequencies may propagate well and be received over a wide footprint. This is often called signal scatter.

A few generalities to keep in mind:

1. 40 meters usually provides a better signal path during daylight hours for communications in the 100 to 800 mile range.2. 75-80 meters is usually better during daylight hours for communications in the 30-200 mile range.3. During daylight hours, when the MUF* is below 7 MHz, or when the 40 meter band "goes long", 75 meters may work.
4. 75-80 meters is usually better during nighttime hours. (40 meters tends to "go long" at night.)5. On 160, 80/75, and 40 meters, lower (30 ft. or less) horizontal antennas (NVIS**) are usually better for closer ranges.
6. Normally, the higher any antenna is (above ground) the lower the angle of radiation. (Good for DX...but not as good for NVIS.)
7. A vertical antenna has low angle of radiation, and probably will not get your signal "up and out" of a deep canyon or over another obstruction.

*MUF = Maximum Useable Frequency
** NVIS = Near Vertical Incident Signal

Power Supplies and Batteries for Hams

Why have Battery backup? How much Power Supply or Battery for the Station? What connectors?

One of the items found in most ham shacks is a battery or a DC power supply. The reason for this is simple enough: most of our equipment is meant to be used in a mobile environment and that means a DC. power supply in the 12.5 v to 13.5 v range. Even a lot of our base equipment has the provision to be run from a DC. Supply.
How big a power supply to get has been the subject of some heated discussions on the air, so how do you pick a supply for the home? Past experience is that we tend to outgrow an existing supply. If you stay in this hobby long you keep on adding equipment that runs off DC and soon you are popping fuses. Start by looking at the equipment in the shack and adding up the currents in amps. Lets say that the Radio, Linear Amp and TNC add up to about 7 amps. The general rule of thumb is to double that number, in this case 14 amps, and then look for a supply in that range. In this case a 15 amp supply should serve you well and leave you room to change equipment around at a later date. Don't buy the biggest supply you can afford. If you have too little load on a supply, they don't regulate well. Picking a supply for mid range seems to be the
best compromise. Supplies on the surplus market have their hazards. Computer Power Supplies often use switching type regulators. These can generate harmonic interference on your radio. Supplies meant for the audio industry can break regulation when they get in a RF Field.
Since a lot of us want Battery Backup we tend to sooner or later get a battery that will run the station. For those of us who work the "Thons" (Walkathon, Bikeathon, or Runathon) or other Public Service Events the ideas of a battery for these events become very attractive. Batteries tend to become a ten ton liability after a few of these events. We tend to buy something like a Boat or RV battery to run a handi-talkie for 4 to 5 hours. You are never stationed near the car and lugging this battery all over the place gets old after an event or two How do you pick a battery that is the best comprise between weight and length of service? Batteries are rated in "AMP HOURS" meaning that 25 Amp Hour Battery can deliver 25 amps to a load continuously for 1 hour. Most radios only draw maximum current when transmitting so the specifications on the radio are broken up into Transmit and Receive current draw. A mobile radio (for example: 35 W output) draws about 10 amps when transmitting and 0.7 amps when receiving.
A 25 Amp hour battery would last 2.5 hours continuous transmit (25/10=2.5) or 35.7 hours receive only (25/0.7=35.714285) for most of these events. Unless you are the Net Control Station (NCS), this battery is much too large. When trying to size a battery for these
events, figure on a 30% transmit and 70 % receive cycle. A small battery such as a 1.2 Amp hour will power a 5 Watt handi-talkie for about 4.7 hours in receive and 18 minutes in transmit (These numbers assume a transmit current of 1.3 amps and a receive current of .250 amps.): more than ample for a public service event. Connectors for power sources vary widely from automotive lighter plugs to Banana Plugs and Jones Connectors and everything in between. The ARRL Field Service recommends the 2 pin **Molex connector. Regardless of the Battery or Power Supply you choose please have in addition to your connector, an adapter with standard RACES Connectors on your DC source. This lesson was recently learned the hard way this spring during a midwest tornado. Operators who were not in Emergency Service Organization such as RACES or ARES brought their equipment in to help. Some of this equipment could not be used without extensive modifications and there just wasn't time to tinker with it at the time.

Batteries and power supplies have become as much a part of the shack as Radio and antennas. Having the ability to help in a pinch is a great asset. Even if it's not a major emergency, being able to bring up the net when the lights go out in your neighborhood is a great comfort to you and your family.

**NOTE: Since the writing of this article the norm now is to use the Anderson Powerpole connectors in wiring for EMCOMM situations. See the link on this Blog re. the Powerpoles.


"Make Good Operating Procedures A Habit"

     Let's face reality, folks. When push comes to shove, and when the chips are down, the majority of emergency communications will be voice (radiotelephone). At least in the United States. 100 years ago it was all in Morse. Spark gap was the mode-of-the-day...then later CW dominated. That was all there was. If you weren't a Morse didn't communicate. 60 years ago, a reasonable guess might be that the ratio was 50% Morse and 50% AM 'phone, plus perhaps a little SSB and FM.
It makes no difference if your favorite mode is CW or digital, or that voice is the least efficient mode. The reality is that most emcomm is done by voice...and will probably remain like that for a long time. CW, digital, and other modes are more effective in many ways and still have their place, and they can (and will) be used very effectively to supplement voice communications in certain situations and for specific functions. However, the reality it or not...voice is where we are at.
We all learned to talk before we entered kindergarten. By the time we left grammar school, most of us could read and write fairly well. By the end of high school, we all (should have, at least) mastered basic verbal and written language skills. While some of us had learned the Morse language by that time, most had not, and struggled to learn it later in life. Many hams learned just enough Morse to pass an exam...and unfortunately never or rarely use it. SSB and FM prevail.
In all public service, good communication skills are essential. But, unfortunately, what we hear on the usually NOT a good example of effective communication skills. As EMCOMM operators, we must NOT allow ourselves to become mediocre (or worse) voice communicators. Sadly, many operators emulate what they hear on the air. And what they hear, from both newcomers and old timers alike, is often improper, sloppy and/or inefficient.
So how does a skilled voice radio operator...operate?


1. ALWAYS makes sure that his/her transceiver is properly adjusted. Mic gain level, on the proper frequency, not using excessive power, etc.
2. ALWAYS speaks clearly and succinctly...and not too fast (or too slow).
3. Establishes two-way contact and obtains a signal report before starting a transmission. (If you want a radio check take your radio to a repair shop.)
4. Avoids talking directly into a microphone. But rather talks "across the mic".
5. Knows and uses ITU PHONETICS
6. Uses ROGER solely to indicate that a transmission has been received and is understood. (ROGER is the voice equivalent of R in Morse.)
7. Does not use ROGER for "yes", "affirmative", or "I agree with you" and does not say: "That's a big ROGER" or some other similar slang term.
8. Says AFFIRMATIVE for "yes" and does not use it in place of ROGER. (They are not the same.)
9. Says NEGATIVE for "no". "Nega-tory" (or other similar slang terms) is not in his or her vocabulary.
10. Uses SAY AGAIN when they need something repeated. "Repeat" or "please repeat" may be confused with "received."
11. Says the call sign of the station he/she is turning the contact over to, followed by their call sign, followed by OVER. (Same as K or KN in Morse.)
12. Allows a one-second pause before transmitting. (If you wait too long...someone may butt in and say something like: "it's been passed to you.")
13. Keeps their transmissions reasonably short.
14. Pays attention and practices "TLC"...("To Listen Carefully").
15. Knows where (s)he is located and knows how to effectively communicate that location to another station.
16. On 'phone says: "Say your location" or "What is your location?" Never: "What's your QTH?", "What's your 10-20", or (worse yet) "What's yer twenty?". (Note: Law enforcement uses the "10 code" and their own phonetics. Amateur, commercial, maritime, aeronautical and other operators use the ITU standard prowords.)
17. Stays in a net (and pays attention) unless checked in and checked out.
18. Does not ask another operator to "check me in" (to a net) unless he/she plans to remain in radio contact with the relaying station during a net period. Telephone, email, Internet and other landline circuit relays are not radio...and do not count. Nor does: "Check me in to the net tonight. I'm going bowling." This puts the other operator on the spot and is worthless.
19. NEVER whistles, says "hell - oh", or blows into a mic when transmitting. (Use a dummy load instead.)
20. NEVER keys down on a frequency that is in use to adjust an antenna matching unit, and NEVER fails to identify when tuning up or testing.
21. NEVER slurs his or her call sign when identifying in voice.
22. NEVER "quick keys." On 'phone, always allow a pause of 0.5 to 1.0 seconds before PTT in order to allow another station break in. Then allow another 0.5 to 1.0 seconds before speaking. (This prevents cutting off the first few letters or words of your transmission.)
23. NEVER transmits using excessive power.
24. ALWAYS identifies at the end of each communication, and at least every ten minutes during a communication. (Part 97.119)
25. ALWAYS remains courteous and respectful of others on the air. (Even if the other operator is "a world class lid".)
Here are some transmissions that have actually been heard...during public service nets:
(After "doubling" on a net control station.): "Net? Is there a net on? What time is it? What frequency am I on?"
"BREAK!" (NCS says): "Go ahead". The "breaker" then asks: "Is the club breakfast this Saturday or next?"
"Uhh, in...Juarez!"
"Uhh, in...José."


Reliance upon repeaters or repeater systems for emergency communications is not wise. It is not uncommon for a repeater to fail, or be knocked out by some external force (e.g.- lightning, high winds, etc.). Repeaters can also be very "political."

Since the beginning of radio, the focus by most amateurs has been to see how far they can reach out with their signals. While DXing is an enjoyable pastime, it is rarely needed for EMCOMM, DON'T RULE IT OUT COMPLETELY FOR PUBLIC SERVICE! The ability to effectively pass traffic over long distances is often important, even lifesaving!

HF signals propagate either by a) line-of-sight; b) ground-wave (follows the contours of the earth); or c) sky-wave. Line-of-sight is usually good for a few miles.
Ground-wave is usually good from about 20 to 50 miles. NVIS sky-wave takes over at about 50 miles, and depending upon the frequency selected is good out to 500 miles. Beyond that, we are in the general area of low-angle DX.

Very often, a 40 meter signal at mid-day, can be heard near and far, all three types of propagation at the same time! To explain propagation, whether low-angle DX or NVIS, or somewhere in-between, I often use this illustration: Just as a billiard ball can be bounced toward a particular pocket by controlling the angle that it hits the bumper of the pool table, so do radio signals "bounce" (actually refract is more descriptive) off the ionosphere. Now, envision the earth as a round pool table with the ionosphere as the circumference or boundary. This "bumper" is constantly expanding and/or contracting in concentric circles, and varies in density often depending upon the time of day, the season, recent solar activity and/or the sun-spot cycle. This phenomenon is a science unto itself and is not the subject here. Just know that for local and regional EMCOMM, NVIS HF (usually in the 40 and 75/80 meter bands) can provide reliable communications over mountain ranges and under the most extreme conditions. The big advantage is that we are not dependent upon some remote mechanical device.

I (and others) have experimented with simple (1/2 wave doublet, G5RV, etc.) wire HF NVIS antennas as low as actually lying on the ground to 3 feet above ground, and they work amazingly well! A lot depends upon ground (earth) conductivity and how far down below the surface the moisture content may be. However, I recommend that any antenna be at least 8 ft. above the ground to prevent someone from tripping over it.

Remember that the higher you elevate a flat (horizontal) antenna (e.g. a simple wire doublet or G5RV) above earth ground, the more the NVIS effect will be lessened. A little height will allow for better line-of-sight and ground-wave propagation. I find that 25-30 ft above the earth works fairly well both near and far. Also the higher you go, the more directional it will be. An Inverted V antenna, at any height, will be less directional, but the NVIS effect will be less than a "flat-top."


Also, to avoid reliance upon repeater(s), don't rule out VHF simplex. Don't believe the myth that VHF is strictly "line-of-sight!" I routinely communicate PTP (Point-To-Point) over 50 miles on 2 meter FM simplex using only a simple ground plane antenna 20 ft. up...and with a mountain range between my station and the other! And over 100 miles routinely using a 13 element Yagi. I also communicate 300 miles on 2 meter SSB and/or CW using a 13 element Yagi (horizontal polarized). A skilled relay operator in the right location doubles these ranges! Also, consider six meters simplex FM, SSB, CW for EMCOMM.


There are so many variables, regular participation in nets will provide you with the experience and knowledge of what works and what doesn't!

As far as of lack of interest in serious EMCOMM by hams is concerned...I wish I had the answer! All you can do is to try to explain that skilled and disciplined operators become that way and also maintain their skills by regularly participating in regularly-scheduled properly-run (non-repeater) public service nets. If there isn't one in your area...why not start one?

Drawn from:

Back In The Saddle

After a battle with blog hosting sites it looks like I am possibly allowed back into the good graces of! We will see where this leads. I will tray and transfer some info over from the old EMCOMM blog that I for some reason am not allowed site control over any more, AKA, I will cut and paste! For now, stand by and lets see what happens!! 73 de W1KRP