Letter Reply : Prepper Communications Primer – Antenna Tuning by theSurvivalistBlog.net Contributor on February 23, 2014 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. Approve | Reply | Quick Edit | Edit | History | Spam | Trash 0 0 Did you like this? Share This : 39More 17 comments MM February 23, 2014 at 2:21 pm Thanks Salem, I have much homework to do. With OhioPrepper’s helpful advice from the last thread, and some discussion with my Elmer (are you in Lima, he thought you sounded like someone he might know), I decided to try a 1/4 wave tiger tail on my UV-5R to get better quieting into the 2m repeater. One QSO this morning, and the report was full quieting with the tip of the tiger tail aimed in the direction of the repeater. 80% quieting when dangling straight down. I’m just using 19.5″ of 16 gauge stranded wire for the tiger tail, but I need to find a better way to both wrap/secure it to the radio when it’s not in use, and add a small weight to the bottom so it straightens out the loops easier when it is. Matt, N9WNI, prepper. OhioPrepper February 23, 2014 at 7:26 pm MM, If you were asking me, Lima is about an hour northwest of me, and I do know a few folks in that area. You mentioned an Elmer, which for those who don’t know, is simply a mentor who has more knowledge than you do in amateur radio and can guide and counsel you. I’m glad to see that you have one, because along with a good club, they can be a great resource. HEY ITS DAVE February 23, 2014 at 4:14 pm Wow…two very good posts. But there sure were a lot of daunting and intimidating terms and concepts presented at once. Let me see if I can clear one basic up that may help understanding the other stuff. FREQUENCY AND WAVELENGTH Imagine dropping a small pebble into a quiet swimming pool (plink). As the waves travel outward you can measure their frequency by the number of wave peaks that pass a given point in a specified amount of time and you can measure the wavelength as the distance from the peak of one wave to the peak of the next (or the valleys, if you’re a glass half-empty type). Now throw your MIL into the pool (SPA-LOOSH). Disregarding the difference in wave height (strength); you’ll see that the distance between wave peaks has lengthened and there’ll be fewer peaks passing that earlier point in the same amount of time, indicating a longer wavelength and a lower frequency even though both sets of waves travel at the same speed. Antennas are a fascinating part of ham radio, but the theory and terminology can be overwhelming at first. Just know you can make an antenna smaller by cutting it in half, quarters or eighths and by adding a coil at the bottom to make the radio think it’s a full wavelength. I hope I havn’t stepped on any toes by adding this. My literary epiphanies are unpredictable and erupt like flatulence. I sit in the rocker, light my pipe and when something occurs, jump up and step over to the computer. It sure ticks off Winston, the cat, when his human keeps dumping him on the floor. Salem February 23, 2014 at 7:07 pm I usually explain frequency versus wavelengths using trains on a cross-country track. If all trains were to travel at exactly 60 MPH, and trains leave the departure station at intervals of once per hour, the trains will be 60 miles apart on the tracks. If they leave 4 times per hour, they will be 15 miles apart. If they leave 10 times per hour, then the trains will only be 6 miles apart. So if all electromagnetic waves travel through free space at the speed of light, a frequency that vibrates four times faster than another one will have a wavelength distance one quarter the length of the second. As waves do travel slightly slower in wires or through the atmosphere than they would in free space, the resulting wavelengths are a little bit less than the pure length, and we figure this information into antenna and cable calculations. JP in MT February 23, 2014 at 6:28 pm With my HAM radio and supplies I did pick up a small SWR meter. They aren’t very expensive, Amazon has a couple to choose from, and they will kept you from having “issies”. JP in MT February 23, 2014 at 6:29 pm How about “issues”. Chuck Findlay February 23, 2014 at 7:17 pm Antennas are the most important part of any radio system. I love playing with them. And they are inexpensive to build, but they take time. Ham radio is a fascinating hobby for the techno-geek that likes to experiment. As far as the GMRS radio range I still see it of limited value as most people will only get the blister-pack radios and not invest in the more expensive ones that are made for the business market. After all the business market GMRS radios are at least as expensive as new ham radios and why not go with ham radio and save money buying used 2 meter radios and have many times the frequencies to use? And any used radio that needs a computer to be programmed is a radio to be avoided because of the knowledge, computer programs, interfacing cables and the computer that will be needed to get it set up and or re-set up if it goes down. And we all have had computer problems,this is a fact of electronic life today. Simple & reliable is always better. OhioPrepper February 23, 2014 at 8:12 pm It seems that we’re focusing the discussion on free standing vertical antennas, and that is probably normal for VHF and UHF; however, there are a lot of other frequencies and antenna types available, especially with a General class amateur license. Using the ¼ wave formula of frequency in MHz divided by 234 feet, we can calculate the length of simple wires used for a horizontal dipole. Although I do have a vertical for the low 5 HF bands, I also have inexpensive wire dipoles for these bands. The longest one would be for the 160 meter band and building one for the center of the band at 1.800 MHz (refer to the band pdf chart I listed) would be 234/1.8 or 130 feet on a side. For this antenna you would require 260 feet of wire (generally at least 18 gauge), some non-conducting material for the center (nearly any piece of stiff plastic will work, and the cable and connectors from the antenna to your radio. This is about as inexpensive as you can get. Keep in mind also, that all of the other bands require even short pieces of wire to do the trick. The only other thing that is required is enough space, and something at each end to connect to, such as a building or tree. In a situation where you live in a development with an HOA (Ugh!) you can use small wire and run it along the ridge line of the house, hidden from view, but still operational. There are so many areas in amateur communications available that anyone can probably find some aspect that they enjoy. I have been licensed for more than 30 years, and I still sometimes run just to keep up with all of the advancements like digital modes and combination control and communications over the internet. And then of course there are radio’s like the Baofeng that make getting started in the hobby the least expensive that I’ve ever seen. All I can say is that if you have any interest, dig, and ask questions. HEY ITS DAVE February 23, 2014 at 9:18 pm My currrent antenna is an end fed longwire 400 feet long (120 meters) strung across a small canyon out back. With just five watts output I’ve worked from Australia in the west to the Canary Islands in the east and points in-between. OhioPrepper February 23, 2014 at 9:49 pm I assume you’re using a tuner and running on HF. Chuck Findlay February 24, 2014 at 7:19 pm OhioPrepper February 23, 2014 at 9:49 pm I assume you’re using a tuner and running on HF. No 400 ft is the right length for UHF 440 MHz Isn’t it??? OhioPrepper February 24, 2014 at 9:26 pm That might work ok, but only with a tuner, LOL. My comment was meant to be demonstrative to the non hams reading this. Chuck Findlay February 24, 2014 at 11:28 pm I’m surprised, it seems that there are more hams here then I would have thought. MM February 25, 2014 at 9:06 am Not so surprising, ham and preparedness are nearly synonymous. If I wanted a list of the people in my area most likely to be prepared to handle an emergency (had extra supplies, alternate power maybe, ability to request or provide aid over long distances, access to current news and information), I’d start with a ULS search on my zip code. Chuck Findlay February 25, 2014 at 1:08 am As far as the Baofeng, I have to wonder how good a radio you can buy for under $50.00 is going to hold up. My Icoms I’m not worried about. I have trouble trusting Yeasu after I saw one get dropped and it broke in 2. I did buy a Radio Shack 2 Mtr HT years ago and after 20-years it’s still going, who would have thought that. But mostly I try to stay with Icom and a few Kenwood radios. nick flandrey February 27, 2014 at 10:04 am RE: Baofang, they are not Motorola, but they don’t cost like it either. :-) They are not waterproof, or exceptionally sturdy, but mine holds up to daily use and I’ve even dropped it (gently, not to concrete.) I don’t abuse it, but I don’t coddle it either. And at the end of the day, if you are using it and break it, you are only out $35. And since you now know you will use it, it is easier to justify spending more on better gear if you need to replace it. For $35 to $50 (depending on the vendor and the day) you can get a chinese 2 band radio and get started. That is awesomely low cost of entry. For a few $$ more you can add a battery eliminator, earphone/headset, extended battery, and flexible whip. $75 total for a well made, capable radio with great battery life. This is comparable to the cost of good FRS/GRPS blister pack radios but WAY more capable. The best thing about the small cheap ham radios is that they will get you on the air, with a Technician class license, and you can start exploring the hobby, or keep them in your bag… I recommend getting on the air. It’s all part of practicing. There are a couple of daily morning ‘nets’ that are open to everyone and very friendly. A repeater local to you is probably already connected to the allstar or echolink node, especially if you are in Houston, Vegas, Michigan, parts of Florida, or Alaska. Check out the “Worldwide Friendship Net” and the “Alaska Morning Net.” Searching online will get you more info. To sum up, like most prepping stuff, I think it is better to get started, and upgrade as you go. So, if you don’t have any food stored, buy a case of Mountain House. Put together a basic bugout bag, with stuff you have lying around. THEN start upgrading. Same with radios. I have a couple dozen FRS radios. I bought a blister pack so I’d have SOME comms locally. Now I pick them up cheap at yardsales and auctions for $1 or $2, throw them in a box. I add chargers as I find them. So I’ve got 10 different brands, and some without chargers (no big deal, use AA batts) but I could equip a CERT team. I bought the Baofang, then accessories, then I found a mobile cheap at an estate sale. Most recently I bought a used base station for 60% of ebay pricing at a yard sale (have to get an antenna up for that one.) I’ve mentioned before that I buy CBs whenever I see them cheap, and they usually include mag mount antennas. ANYTHING is better than nothing! Get covered, then start upgrading and expanding! nick OhioPrepper February 27, 2014 at 11:31 am nick, +10 I have FRS & CB (mobiles & handhelds). HF transceivers and general coverage receivers and a scanner or two. Even if you don’t transmit, being able to listen on a multitude of services provides information about the SITREP around you, and that can be gold. COMMENTS ON THIS ENTRY ARE CLOSED. PREVIOUS POST: New advertiser Seed For Security NEXT POST: Monday Miscellany
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