Re: Waveguide (was "size a major consideration...") [Telecom]

Wave guide would be a lot more efficient but for the frequencies > used for cellular (850-900 Mhz), or even the PCS bands (~2000 MHz) > it would be impractical due to size. > "Heliax" (Andrews trade name) as used on cell towers is actually a > hard line coax, not wave guide. There is a w/g product thats very > hard to tell from the hardline from more than a few feet away but > the w/g generally has an oval cross section where the hardline is > round. The lowest frequency I've seen the w/g used for is 6 GHz.

I stand corrected. And I understand your po > I thought the big "lightning flash" was a generic warning logo for > any microwave transmitter? (having seen them on the Telco towers > here in Australia).

The red lightning flash is Andrew Corporation's corporate logo. Andrew is now a subsidiary of CommScope, but it still uses the same logo.

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Neal McLain

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Neal McLain
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I have seen 450MHz waveguide used for early satellite antenna systems. It wasn't big enough to walk inside, but you could climb through it.

--scott

Reply to
Scott Dorsey

I was sure Heliax implied coax, but I looked.... There are both coaxial and waveguide products in similar looking jackets. As the poster said; the key is the shape. Coax shall always be round. If it's not round, I'd say it's gotta be waveguide.

I was amazed to hear of the cable co. stringing miles of waveguide. At the cost, I'd assumed they used microwave links or coax.

Reply to
David Lesher

*Snip*

Understandable, "heliax" has attained about the same status as "asperin' or "kleenex". I had to stop & think for a moment on my original post to remember whether or not the "Heliax" trade name also applies to the w/g product. :/

H.

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

While "asperin" is safely in the public domain AFAIK, it seems that some other "generic" trademarks are coming back to life, like undead corpses in old movies: "Kerosene", which is "generic" in the United States, can't be used to refer to kerosene, because the word still enjoys trademark status in some countries. This caused a lot of confusion when the media started to cover conditions in African refugee camps: reporters would talk about a "Lack of cooking oil", but U.S. audiences were puzzled, because "cooking oil" means "vegetable oil" in the U.S., and most viewers thought the lack of vegetable oil wasn't anything that serious.

It took several years, but now reporters covering refugee camps have learned to refer to kerosene as "cooking fuel", so that it's more clear what is being discussed.

Bill "Your treasurehouse of trivia" Horne Temporary Moderator

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Reply to
Howard Eisenhauer

For a really big waveguide, consider a highway tunnel. AM radio, at frequencies around 1 MHz, cannot penetrate the tunnel. But FM radio, at about 100 MHz, can penetrate. A 100 MHz signal has a wavelength of

3 meters, which is 10 feet. The cut-off frequency of a waveguide is that at which the longest dimension of the opening is 1/2 wavelength. For a 100 MHz signal, 1/2 wavelength is 5 feet, and any highway vehicle tunnel is larger that that. I have even picked up FM radio in the parking garage under Boston Common in Boston, MA. ***** Moderator's Note *****

... which would mean waveguide for 450MHz would be about 13 inches wide, so that's not likely to be economical. The 23 cm band could be done with ~4.5 inches, but the price of copper is too high for that unless someone knows a way to do it with less expensive material.

Bill Horne Temporary Moderator

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Reply to
Richard

You could, but copper pipe is very expensive. It's cheaper to move the transceiver up closer to the antenna in most cases today.

I'm not sure where the price breakeven point between hardline and waveguide is. You look at all those 2GHz Bell microwave towers with the cornucopia antennae, and you see waveguides coming down from all of them. These days that would all be done very differently.

--scott

Reply to
Scott Dorsey

Those horns often carred six circuits: 4 Ghz horz polarization, 4 Ghz vertical, 6 Ghz h & v, 11 Ghz h & v. They delivered a jaw busting 48dB of gain at 11 Ghz, with a beam width of about 0.75 degrees. But then they had 36 ft^2 of throat, were 14 ft+ tall and weighed several thousand pounds... despite being aluminum...

-- A host is a host from coast to snipped-for-privacy@nrk.com & no one will talk to a host that's close........[v].(301) 56-LINUX Unless the host (that isn't close).........................pob 1433 is busy, hung or dead....................................20915-1433

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

What puzzles me is how microwave could be retired in favor of fiber, given the immense investment required to lay it: the cost of labor alone would dwarf all other considerations. How is fiber so much "better" than microwave?

Did we just run out of radio channels?

Bill Horne Temporary Moderator

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Reply to
David Lesher

Blame Candice Bergen. Her Sprint "pin drop" commercials sold the country on digital trunkage vs the hissss of analog muxed paths. She forced Ma to wake up & start catching up. Now, there's zero analog trunkage left.

Digitized trunkage takes far more BW than analog, as Al Varney used to point out here regularly. Fiber offers many orders of magnitude more. (Contrast OC-768 to the 19,200 VF (300-3000 hz) channels in the newest TD {4 Ghz} microwave.

And microwave is very maintenance intensive; needing regular expert tweeking, etc. Massive power bills to boot. Fiber is high capital cost but low O&M. Your big concern is backhoe fade. -- A host is a host from coast to snipped-for-privacy@nrk.com & no one will talk to a host that's close........[v].(301) 56-LINUX Unless the host (that isn't close).........................pob 1433 is busy, hung or dead....................................20915-1433

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

I'm reluctant to challenge someone in an area where my knowlege is dated, but please bear with me.

Noise - L carrier had to have a noise generator (yes, that's right) to _ADD_ noise to the calls, because subscribers were so used to the "long distance hiss" that they would hang up during lulls in a conversation, assuming that the call had been disconnected. I question the "pin drop" effect: if it _was_ a factor, it was a marketing one, because all Ma Bell had to do to compete was turn off the noise generators.

Maintenance - I'd like to see more info on this, especially considering that techs don't require licenses anymore.

Power - typical power levels for microwave are measured in milliwatts, so that's not a factor. Where you refering to the whole system?

Capital Cost - I'm sure fiber is expensive to lay, but I suspect the rights of way are the big expense, and Microwave doesn't have that problem.

Bill Horne Temporary Moderator

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Reply to
David Lesher

I'm no expert...

L Carrier coax was different, but I'm not aware of the noise generator. I'd guess its function was to cover crosstalk between channels during quiet periods of a conversation. I'll ask.

People cost money; skilled people cost more; skilled people 24x7..... You needed a station every 20-30 miles. It took 150 stations to cover the 4000 miles coast to coast. (The stations zig-zag across the country so station #4's output towards #5 does not also spill onto #6 on some days....)

Yep. A station such as Garden City VA had a BIG 3 phase feed, and standby Diesels to match -- 500 KW and up.

Ma was worried about running out of Long Lines throughput by ~1980. She added 6 Ghz microwave which tripled a station's capacity; that of course is a drop in the bucket by our standards. 11 Ghz was another add-on, but it was shorter range....

To do more; She'd have needed a duplicate backbone say 50 miles south (or north) of the existing... and all that would do was double it.

Engineering & Ops in the Bell System table 9-10: Capacity in 1980:

Analog Radio (TD,TH uwave) 623E6 circuit-miles 60% Coax (L carrier) 197E6 19.3%

BTW, about then, Ma went to LARGE expense to add on a Data Under Voice microwave scheme to offer coast-coast digital capacity.... It provided a whopping DS-1, yes... 1.544 MB/s of room...

Reply to
David Lesher

Fiber rights of way are fairly cheap and usually run parallel to existing infrastructure such as highways or rail lines.[1] In the overbuild years of the late 1990s, they got even cheaper, and demand is only now starting to reach capacity in some parts of the country. The usable bandwidth of a single single-mode fiber is in the hundreds of gigabits per second, the equivalent of several million traditional

56kbit/s voice circuits (or far more even than that when using a low-bandwidth vocoder). And a typical fiber path will have thousands of fibers (because it was cheaper to pull them 192 at a time).

At one time I knew how much a pair of fibers from Boston to New York cost to lease for 20 years. Perhaps someone who's more up on that side of the market can give us an idea what the current prices look like.

-GAWollman

[1] In Massachusetts, one of the biggest dark fiber corridors follows the Massachusetts Turnpike. It was built by the Turnpike Authority to replace its own microwave network, and then surplus capacity was leased to private users.
Reply to
Garrett Wollman

Bill,

Re fiber v. waveguide:

The optical frequencies carried in telecom fibers are typically in the range from 2 X 10^14 to 3 X 10^14 Hz

-- that's 200,000 GHz to 300,000 GHz -- and a single fiber can easily transmit that entire band.

But let's say we use only a 10% bandwidth about a center or "carrier" frequency of say 200,000 Ghz. That's a useful bandwidth of 20,000 Ghz -- and there are so-called "erbium doped fiber amplifiers" (EDFAs) that are simple, robust, very long-lived, and just plain practical, that really can amplify that *entire* bandwidth, with zilch cross-talk and more than flat enough gain.

So, you can (in principle, anyway) put up to 10,000 separate subchannels, each a Ghz wide, with a GHz wide unused guard band between them, down this fiber; amplify the whole group ever 10 km or 30 km or so; and really quite simple optical technology exists to generate, insert, add, drop, pick off, and detect any channel most any time you want it.

[This is just a hypothetical example, to make the point. Real systems may use different choices of channel widths and spacings, and most likely many fewer channels. But, "many fewer" than 10,000 channels can still be a lot of channels!]

The carrier frequency in each separate channel is in essence a very slightly different color of light, generated by a cheap diode laser. Each of these carriers is digitally modulated at (in our example) a 1 GB data rate. They don't interfere; they have very low loss; they have excellent signal-to-noise ratio; they don't crosstalk; they can all be reamplified in parallel in these EDFAs -- they're just insanely good!

Reply to
AES

Wow, they were huge. I remember watching them remove what I think were TD-2 horns from the Bell building here in Providence back in the late

80's. When they got down on the ground I couldn't believe how big they were.

But 48db of gain is impressive.

Reply to
T

Back a couple years ago I worked for the Sec. State's office. We had three locations in the city of Providence.

The Admin Director asked how we could cut costs on the VAN circuits we employed.

I mentioned that the clock tower at the facility we were in had line of sight to the State House and the State House had line of sight to our other location in downtown Providence. Proposed an 802.11 based system.

The State House was the sticky wicket. I explained we'd have to run fiber from the 2nd floor to the top of the dome along with power so that the transcievers could be near the dish, actually Yagi's would have worked too but a little harder to conceal.

Did out the costing and then submitted it. It never came to fruition.

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

That's surprising: these days, every government-owned structure that offers more than ten feet of HAAT (Height Above Average Terrain) is festooned with antennas from every cellular provider, every paging, and every trunked repeater service - sometimes even, believe it or not, antennas for government use!

Bill Horne Temporary Moderator

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Reply to
T

I asked a retired L carrier tech. No noise generator, but N carrier [short-range urban; over 2 pairs of cable, not coax] did have a noise generator, and covering crosstalk was the reason.

Reply to
David Lesher

Some good examples of the cornucopia horns with the attached waveguides:

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The pictures are from a Long Lines relay station just west of Warsaw, NY taken in April 2001. The site is owned by American Tower these days.

It was through this site that television network signals would have passed from Los Angeles to Rochester, NY which I would have watched as a child.

Reply to
Curtis R Anderson

Nice pictures. I've previously heard these referred to as "horn-reflector" or "sugarscoop" antennas.

They played a major role in the 1978 Nobel Prize in Physics.

Reply to
AES

No antennas on this building. I jokingly said we could hand a small dish off the Indpendent Man's spear.

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The Independent Man (Stands about 17' tall and is perched on top of the central dome of the State House.

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Reply to
T

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