Talk:Ultra high frequency
|WikiProject Physics||(Rated Start-class, Low-importance)|
Many of the terms in the list of frequency allocations in the US need to be linked. What is an A&B Franchise, anyway? -- Beland 08:12, 27 Dec 2004 (UTC)
- 1 Is this a contradiction?
- 2 Lowered technical level
- 3 PLT and UHF?
- 4 High UHF channels
- 5 Is it used in Mobile phones video conferencing?
- 6 United States
- 7 France?
- 8 Disadvantages?
- 9 Global Positioning Systems
- 10 US Channel 34 radar use
- 11 US restriction on scanners with analog cell phone UHF reception
- 12 Clarins: spray to "protect skin from the harmful effects of electromagnetic waves"
- 13 UHF taboo
- 14 TV Guide article on UHF history
- 15 México
- 16 UHF (the frequency band) versus UHF (television)
- 17 maintenance tags
- 18 frequency allocation: high digital channels
- 19 UHF Islands
Is this a contradiction?
In this article we read: As well, the layer of the Earth's atmosphere called the ionosphere is filled with charged particles that can reflect radio waves. This can be helpful in transmitting a radio signal, since the wave bounces from the sky to the ground over and over, covering long distances. However, UHF benefits less from this effect than lower (VHF, etc.) frequencies. So, as I undestand it, UHF doesn't bounces alot. At least, it bounces less than VHF (as it benefits less etc.), so UHF transmisions is more likely to escape into space. But when I turn to the VHF article, I read: Unlike high frequencies (HF), the ionosphere does not usually reflect VHF radio and thus transmissions are restricted to the local area So, VHF transmissions are not bouncing at all. Is this a contradiction in these two articles, or the meaning is that both waves bounces very little? My question originate from the news that astronomers will look for tv transmissions in other planets. Do actually VHF and UHF waves can make it into space?
- The maximum usable frequency at which radio waves can be bounced back from the upper atmosphere is usually around 30MHz or lower, but varies widely depending on atmospheric conditions. Under very rare conditions, signals as high as 100MHz could briefly be being bounced thousands of miles; more often, however, these effects are observed on lower frequencies such as nighttime AM radio broadcast band or shortwave radio reception. See radio propagation. --22.214.171.124 (talk) 09:33, 12 January 2009 (UTC)
- We will have to agree to disagree on the above as it is my experience that vhf transmission will make it into space at about 10w qrp. I have no evidence of any transmissions below 900Mhz making it into space. I often work the ISS on 145.825Mhz simplex with no problems alost every hour of the day for about 10minutes of window from a co-linear at six feet from ground. G6XCJ/G0CJM —Preceding unsigned comment added by 126.96.36.199 (talk) 19:37, 4 August 2009 (UTC)
To work ISS, you wouldn't want the signal to be bounced back to the ground by a layer of the ionosphere - you would want it to go straight through and continue into space. To do this, you need to be above the maximum usable frequency for signals to bounce back down - so a VHF or UHF frequency would usually be suitable, while an HF frequency would be a poor choice. Basically, this is the opposite of the frequency choices made if you intended to CQ DX to a terrestrial station. --188.8.131.52 (talk) 15:38, 20 December 2009 (UTC)
Lowered technical level
Well, I think this page should now be largely understandable to someone without a background in broadcast engineering. Removed cleanup-technical tag. Still don't know what A&B franchise is though -- I'll have to come back to it with a full copy of the US frequency allocation table. Wordie 19:04, 21 Jan 2005 (UTC)
- The old analogue mobile phone service, as introduced in the 1980's, only allocated enough bandwidth to permit two 'phone companies to operate in any one geographic area. Typically these were the local Bell or other wireline provider (B) and one alternate provider (A), each of which were allocated half of the analogue cellular spectrum (in the 806-890MHz range formerly occupied by NTSC TV channels 70-83). --carlb 01:50, 17 March 2006 (UTC)
I changed AMPS to Cellular on the USA chart, since the analog AMPS format was discontinued by the major national carriers on 18 Feb 2008 (some smaller carriers may still use it in remote rural areas). I also cleaned up some other minor inaccuracies on the United States chart. —Preceding unsigned comment added by 184.108.40.206 (talk) 07:49, 16 June 2009 (UTC)
PLT and UHF?
As a licenced ham i have become aware of the complexities of operating uhf on low power (qrp) from a distance eg i am able on just five watts output to access a repeater on Olivers Mount from approx 15 miles distance just be placing my car within distance of a PL (power line). Taking into consideration the topography between Brompton and Scarborough and i have proved that its not possible to access this repeater away from a power line so its my intention to learn just how far PLT can assist us Hams to work qrp from considerable distances on uhf.G6XCJ.
- In response - I can certainly see where you're coming from - being limited to 10W myself (plus only 2W on VHF/UHF due to handie rig), any extra help when on such low power (without having to actually spend any money) is welcome news indeed. The amount of time I spend simply trying to make contacts on HF is criminal, roll on 2E0HSE. However, it's also definitely worth noting a few of the key problems wih PLT, such as potential interference with ham bands, and in cases such as mine where the rig is in close proximity to the TV, hi-fi, LP player, I have a small p2p wireless network, any interference is not good news. Imagine the potential problems for operators in urban environments - I dread to think. I'll contribute a few points about these problems soon, just to ensure a NPOV if anyone else decides to put on some of the various benefits of PLT.
M3HSE. Chris 1127 12:10, 2 January 2006 (UTC)
- Well, its getting better, the more time i investigate what i am now convinced is PLT. On just five watts and a handi with a magmount providing i am near (say 100yds) to PL i can still pickup and send to GB3NY with ease, this excercise has been carried out as far distant as 35/40miles from Scarborough and the reptr named, but i must point out that comms can only be near PL hence my feelings that the uhf tx/rx is very much part of PLT. G6XCJ
- My experiments on 433.000Mhz are closing now with GB3NY Having now reached Scarborough from as far away as Thirsk and Blue Bank at Whitby i have proved to my satisfaction that PLT is playing an active part in getting my 5w qrp signals into the repeater. 100yds is quite sufficient distance any further and it will not happen. Since the change that have been made to CTCSS et al i havee not had any chances to explore further on 70cms but i can see now why the military are anxious to take our qrg.
SPACE: It may be of interest that using only 10w on 145.825Mhz simplex i am able to frequently have comms with Sats travelling at 1570MPH including the space station itself from a co-linear mounted just 6ft from ground! No problems.
High UHF channels
Anybody care to comment on what happened to channels 70-83 in the US a few years back? I don't know enough of the background to change the article.
- They've been reallocated to analogue mobile cellphone use in the mid-1980's. This only provided enough band space for two mobile 'phone companies, a duopoly which was certainly no substitute for open competition, but additional bandwidth in the 1.9GHz range was opened with the introduction of the subsequent generation of digital mobile 'phones in the late 1990's. --carlb 01:46, 17 March 2006 (UTC)
Is it used in Mobile phones video conferencing?
I want to learn more about how video conferencing is carried out through mobiles.
- Some of this text needs to be reconciled with the DuMont_Television_Network and All Channels Act articles. "In the late 1940s/early 1950s, the four major TV networks (NBC, CBS, ABC and DuMont) transmitted their programs through VHF and the independent stations through UHF" doesn't quite correlate with the claim in the article on DuMont that the UHF spectrum was only opened to regular commercial broadcasts in 1952.
- Most of the TV's manufactured in the 1950's and early 1960's could not tune UHF, or could only do so by adding another tuner after the set had left the factory (a task for a TV repair technician, and most often even if space for the second tuner was provided the tuner was rather difficult to obtain as a replacement part unless the set was relatively new). The UHF converter (used to work around this problem) was an external box with a power switch and a UHF tuning knob; input was a UHF signal from the antenna, output was downshifted onto one of VHF channnel 2-6.
- The absence of any mention of educational TV operations such as PBS should be corrected - most of these (as well as TVOntario, TéléQuébec and the like in Canada) were built on UHF during the widespread expansion of the late 1960's and early 1970's and were one of the bright spots in this otherwise-dismal collection.
- The antennas designed for UHF were different in design from those intended for VHF only. Until factory-new TV sets included UHF tuners, there was relatively little incentive to insert extra UHF elements ahead of the existing VHF ones in antenna designs. The use of separate tuners for UHF and VHF in TV's also required that a signal splitter be used to separate the frequencies at the antenna terminals of the set.
- Another factor to keep in mind is the widespread use of varactor diodes and digital tuning in TV's, which didn't happen until the late 1980's. The old mechanical tuners used through much of the 1970's required that the viewer click sequentially through all the (up to seventy) channels to get from one UHF station to another - even though most of these frequencies were empty. Any VHF station could be tuned in at most six steps of the dial (as each band had a separate mechanical tuning dial). By the late 1980's, digitally-tuned TV's could be programmed to skip empty frequencies and on infrared-remote equipped sets would provide random access, allowing VHF and UHF to be tuned interchangeably. --carlb 02:10, 17 March 2006 (UTC)
- This section states that many smaller markets were not able to obtain any VHF licenses due to proximity to the fringe areas of larger markets’ VHF broadcasts, instead using exclusively UHF. The reason given for the use of UHF was “because the broadcast range of UHF is shorter, so fewer overlaps would occur between the mid-size market's UHF stations and the rather far-away big-city UHF stations.” I strongly disagree with this reasoning, however, because the broadcast range of major UHF channels often comes close to their VHF counterparts, due to the use of much greater power output. (5 megawatts, the maximum legal power, is often used for major UHF channels, whereas major VHF channels typically output several hundred kilowatts). Instead, the use of UHF for these smaller markets (who are in the fringe range of larger markets’ VHF) is due to the vastly greater number of available channels (56 total UHF channels vs. only 12 total VHF). I edited the article to replace the statement that cited a smaller broadcast range. Ds9kicks (talk) 12:39, 4 March 2008 (UTC)
- My current information is out of date, and low-power VHFs are sometimes added, but here's the picture up through about 1981. Los Angeles and New York have seven VHFs each (2, 4, 5, 7, 9, 11, 13). Chicago and San Francisco-Oakland have, I believe, six each. Smaller major cities like Detroit, Cleveland and Buffalo, even Rochester, have three VHFs each. (Detroit has four, if you count Windsor.) Smaller cities have two or fewer VHF channels, and due to urban congestion, comparably-sized cities may have none, while isolated small cities may still have three or four - Anchorage has four or five, Fairbanks and Juneau have three. All identified TV markets (over 200), however, have at least four channels, the remainder being UHF. If the FCC had chosen non-intermixture in 1952, very few cities would have had VHF, although you either limit a city to seven TV stations, or require LA and New York to change to all UHF! Perhaps today's digital technology would allow adjacent channels to be used, allowing all 12 VHF channels to be used in the same city. GBC (talk) 11:19, 6 December 2008 (UTC)
One shouldn't need "digital technology" to be able to tune adjacent channels. The inability to do so was largely due to poor (or low-quality) tuner design in many of the earliest TV's. Any TV which can be connected directly to cable television would need to be able to handle adjacent channels of equal strength (originally on VHF, although some cable block converters did move midband/superband channels onto UHF so that "cable 15" could land somewhere around UHF 50). Nonetheless, the spacing of channels (six degrees of separation) continued through the 1980's and beyond (Kingston, Ontario got 32 and 38 as its two local UHF channels in the mid-1980's). The absurdly-wide frequency spacings between UHF channels in local communities should have been scrapped years ago, as pushing stations way up the dial to maintain UHF taboo spacings was making other problems (such as propagation over terrestrial obstacles) much worse. Yet this is only being abandoned now as part of digital television transition, as new tuners will be needed for digital TV in any case and the double conversion receivers used for the original DTV test had no issues with adjacent-channel or image-frequency rejection.
25% efficiency in frequency re-use between cities (so one city only had 3 of the 12 possible VHF channels) is common, though, and to be expected in anything other than a single-frequency network. You mention Rochester (8, 10, 13)? If it can't overlap Syracuse (3, 5, 9) Kingston/Watertown (6, 7, 11) Peterborough (12) Toronto/Hamilton (5, 9, 11) or Buffalo (2, 4, 7) - all situated around Lake Ontario - then those three are all that's left. All too typical, much like colouring a political map without giving two adjacent regions the same colour requires a minimum of four colours, covering a region with TV requires four times as many possible channels as actual networks to be carried. Two adjacent cities can't use the same full-power channels without short-spacing problems (13 Albany to 13 Newark NJ is short-spaced, for instance). Ottawa (4, 9, 13) has used low-power stations (6, 11) which otherwise would be short-spaced to Montréal and Kingston (respectively) but the results leave much to be desired. An underpowered analogue station is very snowy very quickly. --220.127.116.11 (talk) 20:21, 28 December 2008 (UTC)
- Early cable television systems did not use adjacent channels. I would not be surprised if the fault lay equally in tuners and in transmitters, with tuners unable to completely eliminate strong signals on adjacent channels, and transmitters "spilling" over to adjacent channels in the neighbourhood of the transmitter. No doubt, improved technology eliminated the spill, while better tuners were faster to rotate out into the homes, since TV stations don't replace their transmitters as often. Perhaps it is this improved technology that enabled low-power VHF drop-ins in cities around the US. GBC (talk) 07:11, 1 February 2009 (UTC)
There is info in other articles, SECAM perhaps, regarding the switch from 828-line VHF to 625-line UHF images for TV in France. Should any of this be referenced, or at least linked, from this article? --carlb 02:31, 17 March 2006 (UTC)
There's a section entitled "advantages", should there be one entitled "disadvantages"? or would this merely repeat info such as the line-of-sight propagation pattern which is already described elsewhere here? --carlb 02:34, 17 March 2006 (UTC)
Global Positioning Systems
The GPS also works in the UHF range, specifically at 1575.42 MHz and 1227.6 MHz.
US Channel 34 radar use
At the moment, there is a notation that US TV Channel 34 is reserved for radar use, with a "citation needed" mark. I haven't found definite proof either way, but a quick [Google] shows at least two stations on or approved for channel 34, KNIC-CA and KMCC. The [spectrum chart] from the Department of Commerce does note the special use for channel 37, but has no special notation for channel 34. 18.104.22.168 10:46, 15 June 2007 (UTC)
- The list of channel 34 stations is a long one; it seems unlikely that there is any national reservation on this frequency either in the US or in Canada. --22.214.171.124 (talk) 09:59, 12 January 2009 (UTC)
US restriction on scanners with analog cell phone UHF reception
should it be mentioned how the us has made it illegal to sell scanners with tunable cell phone frequencies but that it is not illegal to own one or bring one in from another country? This is the only part of the electromagnetic spectrum that is restricted in this way. --Great Zarquon
- Importation is indeed illegal, but it's not at all difficult. Merely order from overseas and take your chances. Purchasing is also illegal. So, unless you can prove that your scanner was legally sold to you before the law went into effect, the gendarmes can assume that you either imported it or purchased it or that you know someone who did. Having said that, the law is obsolete and needs to be repealed; almost no one is using analogue transmissions on the 800 MHz segments and rumor has it the cell industry is going to lose those segments anyway. 126.96.36.199 Co149 (talk) 22:29, 24 February 2008 (UTC)
Clarins: spray to "protect skin from the harmful effects of electromagnetic waves"
Clarins are selling a new facial spray called Expertise 3P, which claims to protect the skin from the harmful effects of electromagnetic waves, specifically those "produced by different types of domestic communications equipment". They claim to have grown skin cells in the lab and exposed them to 900 MHz (signal strength not given) and seen changes in the skin cells. The ingredients in this spray are claimed to reduce the changes. Unfortunately this is not published yet but is it remotely plausible that our skin is being damaged daily by mobile phone and TV signals etc?! —The preceding unsigned comment was added by Purple (talk • contribs) 17:22, 20 February 2007 (UTC).
Drat; I was unclear about Image frequency rejection, so now someone who knows no radio theory has turned it upside down. Making it a link would help some, but that's a rather theory-heavy little article and I am unable to find an article that explains in simple terms what a double-conversion superheterodyne radio tuner does for UHF television. So, it looks like I'll have to write that explanation as a paragraph or two in one of the articles that have to do with Intermediate frequency and then link from this UHF article to that one. Or maybe write a brand new UHF Taboo article. Moan, groan, always there's more stuff to explain to a world that doesn't know television is radio. Jim.henderson 22:14, 26 June 2007 (UTC)
TV Guide article on UHF history
Back in the 1970s, TV Guide ran an article on how UHF came into the American broadcast system. The FCC put a freeze on new construction permits for TV stations in 1948, and began studying how to provide communities across the country with a choice of local television services. They were interested in seeing if so-called "upstairs broadcasting" could be part of the system. The freeze dragged on for four years.
During the freeze, some broadcasters, including Dr. Allen B. DuMont, pleaded for "non-intermixture" - some areas would be all VHF, others all UHF, in order to allow equal opportunity between stations in a single market. That, however, would have meant some pioneer VHF stations would have to change, and station owners opposed being forced to change after pioneering a medium that was belittled by their contemporaries in the 1940s.
When the FCC lifted the freeze in 1952, they ignored DuMont and others who made the same case, and issued a mix of channel allocations, though smaller cities tended to have more UHF channels than VHF. At the time, VHF-Lo stations were limited to 100 kW and VHF-Hi stations to 325 kW. The FCC allowed UHF stations a maximum of 1,000 kW, but nobody knew how to build a transmitter that powerful.
When the freeze was lifted, new applications poured in for TV stations, going after the VHFs where available, but quickly oversubscribed. Where VHFs were filled, the applicants went for UHF channels. Stations were built and went onto the air, but the UHFs generally got into trouble if they had to compete with VHF stations. One station only lasted three months before giving up, though one of the first, KPTV Portland, lasted 12 years before a merger moved the call sign to a VHF station.
The FCC tried some patchwork fixes. They boosted the maximum power to 5,000 kW, and changed corporate ownership rules: previously an entity could only own 5 TV stations (and 5 AMs and 5 FMs); the FCC raised it to 7 TV stations, as long as no more than 5 were VHF. NBC and CBS each bought two UHF affiliates, found them clobbered in the ratings (NBC bought WBUF Buffalo, running against WGR 2 and WKBW 7, for example) and shut them down.
FCC decided it had made a mistake and, in the words of the TV Guide article, decided to unscramble the egg by changing to de-intermixture. Several VHF stations would have to convert to UHF. The station owners put pressure on their congressmen, who put pressure on the FCC. Congress produced a compromise in 1962, the All Channel Law that came effective in 1964. All TV sets would now be required to have a built-in UHF tuner, although it ended up almost always being a radio-style tuner (inner knob coarse tuning, outer ring finer tuning) rather than clicking into individual channel positions as the VHF tuners (inner knob clicking to a channel, outer ring used for fine tuning). UHF stations started up in the mid to late 1960s tended to be more successful, though still relegated to the minor leagues and having to innovate by providing niche programming: sports, foreign language, business news, movies, etc.
By the early 1970s, manufacturers were required to provide click-type tuning for UHF, and this took different forms - miniature position click tuning, or a mechanical digital display (1-8 on the 10s disc, 0-9 on the 1s disc) where the knob turned numerous rotations as the tuner was worked from 14 to 83, but not directly between 83 and 14 (unlike 13 to 2 on the VHF dial). The final point of convenience for consumers, making the distinction invisible and making stations more-or-less equal (except in terms of signal reach and quality), started with Magnavox's "Random Access Tuning System", STAR, which allowed set users to simply push a two-digit sequence on their remote control, like dialing a two-digit phone number. This method of channel selection has become universal.
Some VCRs in the 1980s had push button channel positions (14 or 16, usually), and you would open a panel, select a band (VHF-Lo, VHF-Hi or UHF), then rotate a knob to move through the channels to find the one you wanted at a specific button, then change small plastic tabs to show the channel lit up in the tuner panel. This is probably the last vestige of distinction between television broadcast bands. GBC (talk) 08:54, 2 November 2008 (UTC)
Much as I strive for correctness in the use of diacritical marks, I don't think we can justify the use of the spelling "México" in an English text, as this is essentially not merely a variant spelling, but rather a different name for the country altogether, one that we don't use in English. The country's English name is "Mexico", without the accent, and pronounced IPA: [ˈmeksɪkɜʊ]. "México", on the other hand, is the country's Spanish name, pronounced IPA: [ˈmexiko]. I have therefore removed the two instances of the name "México" and replaced them with "Mexico". Kelisi (talk) 01:57, 16 February 2009 (UTC)
UHF (the frequency band) versus UHF (television)
I notice that this article is dominated by television's use of the UHF band. I propose that UHF television be broken off into a separate article, with this article going into some high-level overview of the technical merits, historical discovery, and overall use of the UHF band around the world. Dinjiin (talk) 00:08, 12 December 2009 (UTC)
- Suggest UHF television broadcasting as a possible article title?
Hmm, there's got to be a Wikitag for this.Tagged for split. There's enough content to be its own article and all the television history is unbalanced in this article. --Wtshymanski (talk) 13:48, 13 April 2012 (UTC)
- Support. I had a quick glance at VHF for comparrison: There is a rough equivalent, FM Radio (one of the major uses of the band) is a substantial article in itself with VHF Radio as a disambiguation page for a few other non public broadcasting radio uses. A UHF Television article would therefore make a degree of sense in this context, as well as divorcing the more scientific and technical aspects from broadcasting which I believe would be useful. -- Fursday 20:21, 13 April 2012 (UTC)
I notice that a user has covered this page in maintenance tags; when I attempted to address the issue on his talk page he reverted me. The tags raised questions about intermixture and about HDTV. My understanding is that:
- The concept of "intermixture" referred to the manner in which TV channel frequencies were assigned to various individual communities by regulators such as the US FCC. In a system based on intermixture, each city would have a small number of VHF channels and some UHF channels. This would leave the UHF stations most often at a severe competitive disadvantage. At various points, the FCC had considered assigning channels in such a way as to give the largest cities all-VHF channels at the expense of having other cities forced entirely onto UHF. This proposal met with stiff opposition, was never implemented, and the idea was largely abandoned after the All-Channel Receiver Act finally required that all 1964-model or newer TV's leave the factory with UHF tuners already installed.
- High-definition television did not necessarily mean digital television. It would be entirely possible to get higher definition just by adding more lines of detail, while leaving the rest of the television system largely unchanged. That would have been possible even with 1940/50's technology, but at a price... as analogue TV has no data compression, the amount of frequency bandwidth needed to transmit that more-detailed image would have been huge. CBS had proposed a system which would generate a colour image of good quality, but at the expense of the signal not being compatible with existing monochrome TV's already on the market. That proposal was rejected in favour of RCA's NTSC-M system in 1953 and remains only an obscure historical footnote. Analogue HDTV was demonstrated on a wide scale by Japan's NHK years later, but the amount of radio-frequency spectrum to carry one channel jumped to 20MHz from the 6MHz for a standard analogue programme. By the 1990's, the concept of an analogue HDTV system would be supplanted by the newly-emerging digital MPEG standards, so modern HDTV is DTV. --188.8.131.52 (talk) 15:31, 20 December 2009 (UTC)
frequency allocation: high digital channels
The article states that high channels were auctioned off. However, from a lay viewpoint, stations that used to be on, say, channel 60, now are on digital channel 60-1 without problem. The article should mention where on the spectrum high digital channels were reallocated to. This information is also missing from North American broadcast television frequencies, television channel frequencies, and frequency allocation. Were they required to use virtual channels? And, if so, where are they most commonly reallocated, or is it on a case-by-case basis? Calbaer (talk) 19:07, 25 March 2010 (UTC)
The article mentions "UHF islands" mid sized markets located close to major cities where most/all local stations were UHF. However given their inherently longer range wouldnt VHF signals from the cities have overspilled into these markets ? How much of a problem did this cause for the (often newly established) local UHF stations attempting to compete with the (often longer established) big city stations. Particularly those which were affiliated to networks and therefore carrying largely similar programming ? 184.108.40.206 (talk) 12:05, 8 August 2010 (UTC)