Re: size not a major consideration in wireline phone sets [Telecom]

The original reason I got a cell phone was mostly for emergencies in case my car broke down. Back then they had low-use plans with a high per-minute but low monthly charge.

Years back I bought an emergency-use CB radio for the car. It was a kit designed for special use only while stopped, not while moving. It had a magnetic mount antenna and a hand-held transceiver. I think I tried once to listen to the CB channel that had shared road-status on it but heard nothing, otherwise I never used it. I recently tried it out and it barely worked, apparently the [wire to the] cigarette lighter plug frayed inside and needed to be jiggled to make contact. I thought a friend could use it with his kids and a walkie-talkies, but apparently the new walkie-talkies sold now don't use CB channels.

The one disadvtg of a cell phone is that you can't hear the traffic CB channel, which I presume truckers still use. But the CB set I had was for stationary use only so not a big help while driving.

***** Moderator's Note *****

I do love this job: every so often, I get to pontificate about an area of communicaitons where I have a lot of esoteric knowledge, and that's the stuff that my dreams are made of.

The Citizen's Band (technically, the Class D Citizen's Radio Service) was a great idea put into action at exactly the wrong time. In 1958, the FCC sought to provide a low-cost alternative to the existing Class A and Class B CB allocations, and the commissioners reallocated the 11 Meter Amateur band to two new classes of operation, namely Class C (radio remote control) and Class D (voice).

The idea was that the lower frequency range of 11 meters, which is around 27 megahertz, would allow for cheaper radios and thus provide inexpensive communications for users such as country doctors, farmers, and small businesses: the Class A and B allocations were at about 460 megahertz, and since transistorized designs weren't yet available commercially, the vacuum-tube radios which could operate at those Ultra-High Frequencies (UHF) cost too much for all but governmental users and major corporations. Ma Bell, Electrical Utilities, Gas Companies, etc., all had their own, dedicated frequency assignments anyway, so the Class A and B channels were going unused by all but a few well-healed licensees. Class D was the solution.

Unfortunately, it worked.

At first, it worked well. During the first cab ride I ever took, as a

14 year-old Novice Class Amateur operator in Derry, New Hampshire, the cab driver bragged that having his Johnson Courier CB set was "Just like being next to the phone". For him and thousands of other small businessmen, a CB set was an invaluable aid.

Then, it worked a little too well: the Carterphone decision, which was the opening salvo of the fight to break up AT&T, came about because a man named Carter built a microphone and speaker into a cradle that would hold a telephone handset, and hooked them up to a CB set so that telephone calls could go on over the air. It was, of course, awkward and labor intensive, but the Carterphone allowed farmers out on the back 40 to deal with the feed store manager as their wives keyed the CB set, without coming in from plowing.

Then, it worked beyond the wildest dreams of equipment manufacturers, radio salesmen, and egomaniacs of all stripes. The sunspot cycle, an

11 year variation of the sun's effect on the Earth's geomagnetic field, passed its nadir just as truckers started to adopt CB sets as their own party line. As the flux numbers rose, so did the number of "skip" contacts between CB sets, which, although limited to five watts of input power, were able to connect ham-operator wannabees across transcontinental distances just as gas prices soared, truckers went on strike, and unpopular speed limit laws went into effect. The truckers abandoned any attempt at operating within the FCC rules, and used CB Channel 19 to report on speed traps as well as gas prices ahead.

Hollywood took note, and sales took off: films like "Smokey and the Bandit" were rushed into theaters so quickly that the actors didn't even have time to learn how to push the "Push To Talk" switch on the CB microphone before speaking their lines - an error so glaring that tinseltown spin doctors had to arrange for the manufacture and distribution of the "Foot Switches" they explained had been in use all along.

And, last, it stopped working. The tragedy of the commons was repeated in the new medium, with electronic bullies, deficient personality types, and plain old jerks turning 27 MHz into a radio cesspool that was, and is now, usable only for extremely short-range communications. Those who actually need to depend on the band, such as independent cab drivers, were forced to modify their radios to use unlicensed channels outside the range of the neanderthals that took over the (eventually expanded from 23) official range of 40 channels.

As the Citizen's Band stands now, the radio spectrum between approximately 26.9 and 27.4 MHz is a mass of heterodynes, profanity, animal noises, "Roger" beeps, echo generators, and (very occasional) meaningful conversations of those seeking directions or traveling in a convoy. The space about channel 40 has been taken over by "Outbanders", hobbyists who act more like Amateur radio operators than the hams themselves, and the space below channel 1 is used by taxis, moving companies, etc. Only children bother to explore the space in between.

Bill Horne Temporary Moderator

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So that is what is under that cap on the back of the phone. The price for that adapter is fine, now if it would work with a standard external antenna, I can't see spending that kind of money, maybe if I was in the car a lot and did my work there.

WB6VHI

Use the shortest possible available coax between the adapter and the antenna. At those frequencies an large amount of the cell phone power goes into warming up the coax.

Tony

That's always the way for any RF line to a new antenna position, you have to calculate if the line losses are outweighed by the extra signal by the newer/better/higher antenna, otherwise there isn't much point.

It's almost waveguide rather than coax territory for these frequencies now?

In article ,

In a test-lab environment, something like that is trivial to do. :)

For an end-user, in the real world, it's somewhat more complicated. If you have some sort of signal-strength indicator on the phone -- i.e. a " how many bars" thing -- *AND* you can get far enough away from the 'nearest' tower so that it shows a 'less than max' strength on the built-in antenna, then you can switch to the external one, and, maybe, see a visible improvement. Or, go out in the boonies -- just to the point you get a 'no service' when using the external antenna -- and see how much closer you have to get to civilization before service re-establishes itself.

I know from personal experience with an old analog "bag phone" (a Motorola), mag-mount whip on the middle of the vehicle roof gave me a _lot_ more range than the rubber-duckie on the back of the brick. e.g. I had service out in the "middle of nowhere" in th Rockies, some 17+ miles off the nearest paved road, in BLM wastelands.

That same antenna significantly outperformed the rubber-duckie, used *inside* an AMTRAK "Superliner" train -- antenna stuck to the inside of the roof of the rail car.

Depends *greatly* on the path. Coax has significantly higher losses per linear foot. Waveguides have higher losses at turns/bends.

***** Moderator's Note *****

Um, OK, but I wasn't looking for something that involved: the question should be "Is there a kind of waveguide that I can put in my car to get better cell coverage than I can get with coax?".

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For what it's worth, [my] emegency CB kit said the mag mount antenna-- placed on the metal surface of the car--was designed to work with the metal, that is, it made the metal part of the antenna. You weren't supposed to just hand hold the antenna or put it on the ground. I don't know the physics, but presumably the metal surface acted as some sort of radio wave resonator for the signal. (Maybe the radio folks here could explain this more accurately).

My present digital cell phone handset has a pull out antenna a few inches long. I don't get to fringe areas, but I had hoped the antenna would save on battery consumption, [however] this handset only gives about 75 minutes of talk time since it was new. (Now it dies at 55 minutes, but after it shuts down I can turn it on the next day and get another 20 minutes out of it when it dies for good and I have to recharge it.) I don't use the phone that much, but if I do go away for the day, I do need more talk time between charges in a single day's usage.

Bill Horne asked:

This is a complex issue. Coaxial cable almost always has considerably higher attenuation per unit length than waveguide. But waveguide requires specialized bends since flexible waveguide has its limits on how much it can be bent and still work properly. But the biggest issue is size.

Standard rectangular waveguide for the S-band (2.60 to 3.95 GHz) is WR-284 in the EIA designation and also as RG48 or WG10. This is 1.34 x

2.84 inches on the inside of the waveguide and 1.5 x 3 inches on the outside. This is a little big to run in an automobile, and D-band (2.2-3.3 GHz) waveguide is bigger still with inside dimensions of 1.7 x 3.4 inches. This has a loss of about 0.0267 dB/meter at 2.45 GHz. Compare this to RG-58 coaxial cable with a loss of 0.822 dB/meter or to RG-213 coaxial cable at 0.411 dB/meter at the same frequency. If you used tiny RG-174 coaxial cable, the loss would be a whopping 2.46 dB/meter.

So waveguide would be an ideal transmission line at a tall cellular tower having far lower losses than coaxial cable. But it would not be practical to connect a hand-held cell phone to an auto's rooftop antenna.

Probably the largest waveguide I have ever read about was at the Arecibo Radio Telescope in Puerto Rico. Its lower cutoff frequency was below 400 MHz. Today, the receivers are mounted at the "feed horn" eliminating the need for such immense waveguide.

I once visited the laboratory originally used by Charles Townes at Duke University. They were doing research into millimeter wavelength frequencies at the time. Instead of using waveguides, they were using quasi-optical techniques to transfer the millimeter waves around the room. What I found especially interesting was the use of lenses machined from PTFE (Teflon) to focus the beams. While Townes is mainly known for his work in the maser and the laser, he is also considered the father of microwave spectroscopy.

73, Dr. Barry L. Ornitz WA4VZQ snipped-for-privacy@charter.net ***** Moderator's Note *****

I was thinking that it may be possible to include a waveguide as part of the car's body: your S band dimensions would work for some of the support pilars (and I reserve the rights if anyone does it), but the question is how precisely a waveguide must be machined.

I'm surprised at the difference in loss of waveguide vs. coax: all the cell sites I've ever seen appear to use coax, so either they're using the flexible type or the cellular engineers are employing the coax loss to contribute a large part of their loss budget for the antenna arrays being used.

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Waveguide is moderately forgiving as long as you do not push the frequency close to cutoff. [Waveguide functions similarly to a high-pass filter.] With some simple adjusting screws, mismatch could be tuned out. But at each end of the waveguide you would likely need coaxial to waveguide transitions. You would also need to electroplate the inside of the waveguide to increase its conductivity. However, I really like your idea. Thinking out of the box...

Around here in rural South Carolina, large coaxial cables are used too. I believe they are Andrews Heliax cables or their equivalent. Depending on the size of the cable, they may use closed-cell foam dielectrics or even a spiral of insulation between the center conductor and the outer conductor (air dielectrics). Air or nitrogen has much lower dielectric losses than does plastic insulation. These are designed to be moderately flexed during installation only as the conductors are usually corrugated pipe. These cables have considerably less loss than the small, flexible cables usually used with Ham and CB installations.

At one time circular waveguide was considered by the telephone system for replacing long lines. However keeping the polarization maintained was a problem, Then fiber came along and the waveguide idea was dropped. [Well not exactly, the fiber is an optical waveguide!]

And cost.... Waveguide was/is solid copper, and recently many siteowners have had it stolen.

The AT&T 2Ghz KS-5759 antennas used plastics as delay lines to focus the output.

Note the coax types he cited would NEVER be used for microwave; the larger Heliax [?sp] coax style line is often air-insulated, not foam, and has much less loss.

Waveguide is expensive to buy, and expensive to install, and needs dry air and ....

You sometimes see long runs of waveguide & then transitions to coax for the final connection. There is also flexible [and I use the term loosely; "not rigid" might be better....] waveguide.

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The metal roof was supposed to act as a ground plane. But it was an equal voltage plane near 0 volts. It acts as a mirror and gives the whip an apparent length twice it's actual length. For each frequency there is an ideal whip length. For FM it's ~30 inches. The new cars often cheat by wrapping the antenna spirally around the rod to make the whip shorter. Rabbit ears are an example of an antenna that doesn't need a ground plane. It's differential between the two ears.

Mark L. Smith

Waveguide today is generally aluminum with the flanges and mitre bends hot-dip brazed. It has lower loss than brass which is sometimes used, but slightly more loss than copper. Large Andrews Heliax cable has lots of copper too.

The sandwitching of plastic with thin sheet metal creates an artificial dielectric as noted in the article. In the shorter millimeter wave (terahertz) region, solid PTFE is practical. Because of the differences in wavelength, the PTFE does not have to be polished to a high degree like a lens for visible light.

When we think of lenses, we think of the refractive index of the material the lens is made from. But refractive index is the square root of the dielectric constant.

But these small cables are used with computer networking antennas. I chose those cables to demonstrate that the added range obtained by elevating an antenna is often lost due to the increased cable losses. Andrews Heliax transmission lines still have more loss than waveguides. The gas insulated lines with spiral insulation begin to have problems at higher frequencies with propagation modes other than TEM being possible. And these cables require pressurization systems in the same way that waveguide does.

Yes, flexible waveguide is very much akin to liquid tight flexible metal conduit - only stiffer. It is also much lossier than regular waveguide. Short sections of flexible waveguide are sometimes used at the ends of long runs of regular waveguide because the thermal coefficient of expansion of copper or aluminum is quite different than that of the steel used to make the towers that support the antennas.

I wish I could answer more of Bill Horne's questions about microwave links and licensing. Unfortunately my specialty was online chemical instrumentation. Hence my knowledge about microwave spectroscopy and dielectrics. I do hold a FCC General Radiotelephone license (grandfathered from 1st Class) with Ship Radar Endorsement* and the Amateur Extra Class ham license. but these are not applicable to Bill's questions.

(i.e.trans-continental) microwave routes used horn reflector antennas

by a 2.812 inch diameter circular waveguide This waveguide shape and size was chosen for its extremely low loss (0.38 dB/100 feet at 3.8 GHz). Being symmetrical axially, it could support two orthoganal polarizations.

One drawback of this waveguide was that it supported more than one mode: 2 or 3 modes in the 3.7 to 4.2 GHz band (depending on frequency), and 6 modes in the 5.925 to 6.425 GHz band. Any non-uniformity, and also the transitions from square guide (used by the frequency and polarization combining networks) at the base of the tower to the circular guide, and from the circular guide to the antenna, would convert some of the energy to and from the dominant mode to the higher-order modes. Each mode traveled at a different velocity, so when energy from a higher-order mode reconverted to dominant, an echo resulted. The towers ranged up to 250 feet high, and thus the echos had appreciable time delays.

One of the worst offenders was an 8-foot length of flexible circular waveguide which connected the top of the vertical waveguide run to the feedhorn of the antenna, to allow the antenna to be pointed in elevation. Eventually, we had to replace each pieces of flex guide with a piece of rigid guide especially bent to shape, on site, to fit between the antenna and the vertical waveguide run. First, the crew measured the relative positions of the two flanges. Then an 8-foot piece of rigid guide was packed with sand to keep it from buckling, and put onto a machine which put a gradual bend in the guide.

***** Moderator's Note *****

You bring back a memory: my father was a pluber, and he used to bend pipe that way when he had to have a non-standard angle. I used to hold the torch, and he'd heat a copper pipe to orange, then use a lalley column to form the bend: every so often, there'd be some moisture in the sand, which would flash-burn any human flesh within a foot of the ends.

BTW, please explain what "Mode" means in this context. TIA.

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