N1AHH

Most of us really don't understand radio. It is sort of like a car. We insert key and drive away. We have some idea about how a car works, but it is only a sort of generalized idea. Most folks understand radio even less, even though we use every day.

Sorry for not posting for awhile. We changed trucks, which is a major undertaking. Also some personal issues distracted me for a bit. We intend to leave Tampa for Ohio, then to Maine for the summer.

We will be staying in the backwoods of Maine about half an hour down a dirt road in the middle of nowhere (actually in the middle of township 16 which is the same thing). There is of course no power and no water (perhaps a spring which we might use). So the solar system will be put to use to power the satellite internet, radios and of course the water pump and lights.

Oh, the truck we have now is a 2003, Dodge Diesel, One ton (3500) 4x4. It has been quite a project getting it re-fitted for our style of travel. Still not done and we intend to leave here (Tampa Fl) next week. When things quiet down a bit I will post some pictures. Will things ever quiet down? Hurricane season is about to begin. Not sure if we will volunteer to run an ECRV (see ECRV postings to the left) or not. Guess it depends on how bad the situation gets.


All is well and I will try to post a bit now and then as we travel.

...ron...

So many toys, so little time.

I feel bad that I have not continued with the series about radio. Not too bad though because the reason is very interesting. At least to me.

I have been writing a program that controls a radio. The radio is a Kenwood D-700, and one of these radios is carried on the International Space Station. Actually it is two radios in one. This Dual Band radio is designed for a unique amateur service called Amateur Position Reporting System (APRS). It is a digital mode that is sort of like text messaging on steroids. But more about that later.

The program provides automatic communication with the space station. When the space station is not above my horizon, the radio changes frequency and links into an amateur terrestrial network, providing a form of radio e-mail. It has taken me quite a bit of work to write and de-bug the program, but now it is working well. Yesterday I added a component that watches my solar charging system and monitors the battery charge.

Soon I will begin placing notices on the Space Station system that will advise interested hams that they can come to this blog to discuss the program and its application. You are invited to ride along and see what (if anything) happens. If you have used the link about our present position on the left side of this blog, you have seen the APRS system at work.

The program works like this. I use a very nice satellite tracking program called SatScape which provides, among other things, a list of times that the Space Station will be within radio range of my location (remember line of sight?). My program reads this information and at the correct time, switches to the space stations frequency, changes its mode to APRS and waits to hear the Space stations Beacon. When the program hears the beacon, it sends my beacon. Actually the beacon is a complex, but quite short digital burst crammed with information. It contains, my call sign, my location (accurate to about 15 feet), and then, in my case, a status message, “In Service” and a short text message. Usually something about it being an automated station. The space station, repeats my beacon. Some station on the ground, that is connected to the Internet, will hear the repeated beacon and pass the data thru to the Internet It then shows up on the Internet as a position report, about 3 seconds after I send it.

Other stations send similar beacons, although the details of their contents vary. If I were moving, it would send my location, speed, direction, altitude and more. If I happened to have weather instruments connected, it would send a complete weather report. There a a lot of beacon variations.

After sending my beacon, it watches the calls of other users. If I want to send a message to another user, I load the other persons call and a short message into the programs memory. If the program sees the other persons call being repeated from the Space Station, it sends the message to the space station which repeats it, sending the message to the other station. The other station receives the message and replies with an acknowledgment, which is repeated by the space station and the program hears and stores the acknowledgment.

When the space station moves beyond the horizon, the program changes the radios frequency and mode so that it can become a personal mailbox on the amateur terrestrial digital e-mail network.

It also watches the camper battery levels and displays a graph of the charge/discharge rate. We use solar panels for our electricity much of the time, although at the moment we are plugged into regular power. However between the various radios, computers and satellite Internet system, we use a bit of electricity and I need to monitor it closely. As long at the Space station program is running 7/24, I decided to add a few more things that need a computer running 7/24 as well.

So that is what has been providing a bit of “bubble gum” for my brain during the last several weeks. At some point, I will get back to the radio series, but it looks like it will be on hold until I get the radio control program running the way I want it.

I will get back to the radio series.....eventually.....

About line of sight. (So, how far can we communicate?)

Gloria and I, carry small radios in the 1 to 5 watt range. The most common question is, How far apart can you be and still communicate? Well the simple answer is 2 miles. But there is a complex answer as well.

The Simple Answer Explained: From experience we have observed that using our radios with the antennas we use in the normal areas we travel, we can usually communicate about 2 miles. This means we are both outside, not behind buildings, not behind a mountain, not in heavy wet foliage, not in areas with high radio frequency noise levels and a host of other conditions. Less distance inside of a large Mall, more over water.

In the old days, maps of unknown areas usually had a notation “Beyond here thar be beasties”. So be warned, Beyond Here Thar be MATHEMATICS!

A more complicated answer: It depends on the conditions between us. Suppose you are standing on a seashore. There is a person right on the Horizon. Assuming you are 6' tall and the other person is right down on the water.. How far away is that? Well under normal circumstances it is about 3 miles. The common formula is

Horizon in miles = 1.23 x (square root (height in feet))

or 1.23 * (square root (6)

or 1.23 * 2.25

or 3.01 miles.

But If they are 6' tall (and standing in a boat perhaps), and all you need to see is their head, then you can add another 3 miles for a total of 6 miles of separation between the two of you. The curvature of the earth limits your vision to Line of Sight. However Radio has a bit of an ability to bend just a bit so it can see a slight bit beyond the visible horizon. The rule of thumb is that the radio horizon is about 1.4 times the visible horizon.

The number 1.23 represents a “fudge factor” that includes the conversion between the measured feet of the antenna and the measured miles of the distance to the horizon as well as the radius of the earth. Unfortunately, the earths radius is a pretty huge number whose actual value depends on where on the earth you are located. Also, most calculations assume the ground is absolutely level between the antennas. So the earths radius of 3964 miles which = 20,929,920 feet and the antenna height of 6 feet means that the earths radius makes up a much larger component of the formula than the antenna height. Therefore the formula will not provide very good real world results. Still it is useful to help in understanding line of sight.

But as I said before, The Radio Horizon is 1.4 x the visible horizon. So if we are talking about antennas, one at 25' the second at 36', then they can be 30 x 1.4 or 42 miles apart. Sounds good. All we need to do is get a bit of height and we can talk for 42 miles. Well, that is not quite the whole story.

Although the above is true, it assumes that everything is working at it's theoretical maximum. The best radios (very sensitive receivers), with the best antennas with the best signal path (no obstructions) etc. In practice, it is never that good. Well, How good is it?

To find out, I have run a number of tests. I won't get into the detail of the tests now as this post is getting long enough. But in general, I have a method of sending digital information between my truck and camper while I drive around. The system I created logs my position and the signal quality. The result is plotted on a topographical map. Sounds complicated, which it is, but it is mostly automatic now, so it is pretty easy to do. So I try different antennas at various heights, change the power levels and in general play with the system.

Using the above formulas. Camper Antenna Ht = 12', Truck antenna Ht, 5'. Doing the math (1.4*(1.23((Sqrt(12) *1.23(sqrt(*5))) = 9.8 miles.

What I find is that reliable communications using high power (50 watts) from my standard truck antenna to my camper is about 9 miles. Well, it seems to be similar to the theoretical answer.

So pushing the concept to extremes, Line of sight, when applied to radio means just that. If you can see it, ;you can communicate with it. It is common for Radio Amateurs (Hams), to communicate with the International Space Station using 5 watts and a hand held radio. The nominal height of the Space Station is 250 miles. I talked with the Space Station while I was in Maine and the Space Station was over Florida. I did not compute the :slant angle:, but it was quite a long distance. The point being that in the proper situation you can talk for a long distance with a hand held radio. But one needs to understand the relationship between height and range. Higher is better, but how much higher is how much better?

Lets say you want to put up an antenna in your backyard. How high should it be? I usually make a short mast with two 10' pieces of PVC Tubing. Total of course is 20 feet. Very easy to do. Is it worth my effort to make it 30 feet tall? The construction is much more difficult because the forces on the PCV pipe begin to exceed the pipes strength. So here is a table using the theoretical calculations.

Ht	Mi	Ht	Mi	Ht	Mi	Ht	Mi	Ht	Mi
		42	15.4	82	19.8	122	23.2	162	26.1
		44	15.6	84	20.0	124	23.4	164	26.3
6	8.4	46	15.9	86	20.2	126	23.5	166	26.4
8	9.1	48	16.1	88	20.4	128	23.7	168	26.5
10	9.7	50	16.4	90	20.6	130	23.9	170	26.7
12	10.2	52	16.6	92	20.7	132	24.0	172	26.8
14	10.7	54	16.9	94	20.9	134	24.2	174	26.9
16	11.1	56	17.1	96	21.1	136	24.3	176	27.1
18	11.5	58	17.3	98	21.3	138	24.4	178	27.2
20	11.9	60	17.6	100	21.4	140	24.6	180	27.3
22	12.3	62	17.8	102	21.6	142	24.7	182	27.4
24	12.7	64	18.0	104	21.8	144	24.9	184	27.6
26	13.0	66	18.2	106	21.9	146	25.0	186	27.7
28	13.3	68	18.4	108	22.1	148	25.2	188	27.8
30	13.6	70	18.6	110	22.3	150	25.3	190	28.0
32	14.0	72	18.8	112	22.4	152	25.4	192	28.1
34	14.3	74	19.0	114	22.6	154	25.6	194	28.2
36	14.6	76	19.2	116	22.8	156	25.7	196	28.3
38	14.8	78	19.4	118	22.9	158	25.9	198	28.4
40	15.1	80	19.6	120	23.1	160	26.0	200	28.6

Notice that at 10' the range is 9.7 miles. Doubling the height of the mast to 20 feet changes range to 12 miles. But adding the next 10 feet to 30 only changes the distance to 13.6 miles. 100 feet = 21 miles and 200 feet = 28 miles. That is why most of the radio towers you see are so tall.

So height does matter, but it takes quite a change of height to make much range difference.

OK, so you have enough height to talk as far as you want. Why would anyone want a 50 watt radio? Why not just ½ watt? And what is a watt anyway? .... well that is next.

So, now we know how to generate a continuous electromagnetic wave and that if we interrupt the wave we can send signals. But we want to be able to talk.




Another pretty bright guy discovered that if you put direct current through a bunch of very fine, compressed carbon granules and then yelled at the whole thing, you could make the direct current change its amplitude (or its “height”) in relation to the words you yelled. That is, with no noise there was no variation in the DC. When one yelled, the carbon compressed and caused a change in its electrical resistance so that the power in the DC current varied with the speech. Now we could talk. Simple huh? Well it many years to go from that simple experiment to speech over radio. But that was the beginning. Eventually someone discovered how to change the amplitude of the Continuous Wave Electromagnetic field according to the variations in resistance of that carbon thinggie.... which they called a carbon microphone.

Varying some characteristic of an electronic circuit is called modulation. Because we were now able to vary or modulate the amplitude of the electromagnet wave, it was called Amplitude Modulation or AM. So first CW, then AM.

Well by this time people were yacking all around the world. People had radios in cars, the cops (and crooks) had two way radios and a bunch of geeikie folks had formed a hobby called Amateur Radio. For some unknown reason they were called Hams. So all was well .......except.....

Lightning is amplitude modulated.

So right in the middle of the nice music, or the important message, the listener would hear a VERY LOUD NOISE. In fact, my hearing was pretty much destroyed by listening to AM radio during storms. I was an Air Traffic Controller. I talked aircraft down during storms using a very complex radar system and AM radio. Of course we did it mostly during electrical storms.

Then somebody had another idea. Suppose we keep the amplitude constant, and modulate the frequency. It worked. By shifting the frequency just a bit in relation to the electrical current generated by a microphone, it became possible to transmit speech by a method that did not hear the amplitude modulated thunder noise. It was of course called Frequency Modulation, or FM. So now we have CW, AM and FM. Pick a nice stormy night and listen to some AM radio, then switch to a FM station. Notice the difference? Very little noise is present in the FM station.

During World War 2, we tried to get every bit of range out of the radios. Somebody noticed that an AM radio signal was symmetrical. That is, the wave gained in amplitude to a maximum, then dropped to zero, then went negative to a minimum then back to zero. The positive half was exactly like the negative half, just in the opposite direction.

So, why send both the top and the bottom? If you just send the top part, you can create the identical but negative part in the receiver. Just send one “sideband”. It worked. So now all the energy needed to send both sidebands was concentrated is a single sideband with the missing sideband being generated at the receiver. It, of course, was called Single Side Band or SSB. One could send either the upper or lower side band. It has the advantage of being much more efficient than either AM or FM, actually more efficient than even CW. But it has all the noise disadvantages of AM. Mostly SSB is used for voice and data communications.

OK, so now we have CW, AM, FM and Upper and Lower SSB. And you understand them all. Good job.

So here they all are. There are other methods, but they are beyond the scope of this document.

So what does all this mean to us? Well, CB is AM so you get a lot of noise. Its frequency (26 MHz) is one that bends around the earth and under the right circumstances will go thousands of miles. So when the band is open, the electromagnetic wave is propagating for thousands of miles, you get to hear hundreds of signals (called skip) and much noise all at the same time.

Remember that MHz = Millions of hertz. So what'sa Hertz?

The hertz (symbol: Hz) is the unit of frequency. It is named in honor of the German physicist Heinrich Rudolf Herz, who made important scientific contributions to electromagnetism. In English, "hertz" is used in both singular and plural. (From Wikipedia, the free encyclopedia)

So, 150 MHz = 150,000,000 cycles (Hertz) per second

The approximate frequencies in common use for;

Public Service (Police, fire, Ambulanec etc.) = 150, 470, 800 MHz,

FRS (Family Radio Service) = 460 MHz

GMRS (General Mobile Radio Service0 = 460 MHz

VHF Amateur =146 MHz

UHF Amateur = 440 MHz

These frequencies are "high" enough so their range is limited to Line of Sight which makes them mostly immune to skip, and they are FM, so they are quiet.

So what is this Line of Sight thing? Thats next.