Talk:Ultra high frequency
From Wikipedia, the free encyclopedia
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)
Contents |
[edit] 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?
[edit] 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)
[edit] 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
[edit] 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)
[edit] Is it used in Mobile phones video conferencing?
I want to learn more about how video conferencing is carried out through mobiles.
[edit] United States
- 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)
[edit] France?
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)
[edit] Disadvantages?
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)
[edit] Global Positioning Systems
The GPS also works in the UHF range, specifically at 1575.42 MHz and 1227.6 MHz.
[edit] 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).
