Talk:Amateur television

message: * 33 cm band: "Signals transmitted on this band usually propagate only half the distance as on 70 cm for a given transmitter power and antenna gain."
* 23 cm band: "Signals transmitted on this band usually propagate only a third the distance as on 70 cm for a given transmitter power and antenna gain."
Sparkgap (talk) 20:47, 28 June 2011 (UTC)
replies: text: While the wording of these statements may not be the best, there is a truth behind them.  I'm not so doubtful a reliable citation couldn't be found, as I've seen similar statements in the past.  What is trying to be described is the effect of a frequency increase on Free-space loss or Path loss.  For a line-of-sight path, if all other factors are held equal (such as the antenna gains of the sender and receivers and the TX power, among other things), the path loss will increase with frequency, therefore the maximum distance a signal can be received will decrease when frequency is increased.  (Keep in mind a receiver has a minimum signal strength needed to demodulate a signal.)  What I do doubt in these statements is the nice, clean one-half and one-third reductions in distance.  I suspect these are very rounded numbers, made just to simplify the description of the effect.  A citation from a verifiable source is needed.  Sparkgap (talk) 20:47, 28 June 2011 (UTC)
replies: text: True, path loss due to atmospheric attenuation can be a factor at higher microwave frequencies, but at these frequencies it isn't usually more limiting than line-of-sight for communications links, except perhaps as you note at low power levels.  Suitably high-power transmitters are pretty common and commercially available, as are suitably sensitive receivers, so atmospheric attenuation shouldn't be a common limiting factor, except perhaps with homebrew or experimental equipment.  I will agree that the statements are too general, especially for a complex area of propagation theory. I'll see if I can dig up a few sources for atmospheric and other path losses to help clarify this. Pyrocatch (talk) 23:21, 28 June 2011 (UTC)

text: I also just reminded myself that this is in the context of ATV, where equipment isn't quite as commonly available at substantial power levels.  I'll try to keep that in mind, as it does make a pretty substantial difference when you're talking about a 6 MHz or so AM channel instead of a 200 KHz or so FM channel. Pyrocatch (talk) 23:28, 28 June 2011 (UTC)
replies: text: Yes, in the context of ATV, the signals are quite weak.  As I understand it, home-brew equipment is not uncommon for ATV, and transmitter power outputs in the range of 100 milliwatts to 5 watts appear to be the norm for most stations.  Also to save on expenses, it appears common to not use Vestigial sideband filters, if one can reasonably get away with it.  That effectively increases the ATV bandwidth from 6 MHz to about 9.5 MHz, further worsening the Signal-to-noise ratio. Sparkgap (talk) 01:32, 29 June 2011 (UTC)

text: After a little searching, I found that P. C. Electronics, an ATV equipment distributor, makes several similar statements throughout their website and publications.  For example on page 4 of their catalog they state, "... the 1200 MHz band goes 1/3 the distance of the 400 MHz band, and 2.4 GHz 1/6 given the same power and antenna gain..."  This is a rather simplistic view on propagation, but I can understand why they state it the way they do, in an advertisement. Sparkgap (talk) 01:32, 29 June 2011 (UTC)
replies: text: Chapter 20 of the 1991 ARRL Handbook says that path losses are higher at 24 cm compared to 70 cm, but that is partially compensated by being able to put more antenna elements on the same length of boom. --Wtshymanski (talk) 02:13, 29 June 2011 (UTC)

text: I've made an edit which hopefully straightens out the bits about propagation and includes a bit of extra information with links to articles and reference.  In a nutshell, I deleted the unsourced text I marked earlier, and added a paragraph in the (renamed) Transmission Characteristics section describing some factors which affect propagation. The source citeed is the 2005 edition of the ARRL Handbook.  How does this look? Pyrocatch (talk) 03:39, 29 June 2011 (UTC)
replies: text: Looks alright.  I could see a potential expansion of the section in the future. –Sparkgap (talk) 00:17, 11 July 2011 (UTC)
thread_title:  Dubious propagation statements? 

message: This is another area Radio Amateur of televion transmission. I added some slow scan images to this article by mistake. This particular article relates to high definition, high quality FAST Scan transmissions. I am adding this comment in case anyone else makes the same mistake as I did yesterday.Francis E Williams (talk) 11:24, 10 January 2011 (UTC)
thread_title:  Slow-scan television 

message: We could use a photo of an image transmitted by fast-scan ham TV, or photos of the equipment used (especially before it became an app on an iPhone). I found a "slow scan" image on Commons but that's not what this article is about. Leaving the photo tag on, since a coule of test patterns don't tell the reader much. --Wtshymanski (talk) 20:11, 9 February 2015 (UTC)
thread_title: Photo needed