On 10 December 2014 at 13:09, Maria Blackmore <[email protected]> wrote: > > On 10 December 2014 at 02:51, Gord Slater <[email protected]> wrote: >> >> >> In addition, two or more radio transmitters, or a single transmitter feeding >> several antennae, either by the most direct route or by adding delays or >> extra distance in the transmission line or signal path between the >> transmitter and receiver also cause interference patterns. They are utilised >> where needed and we try to avoid them where they would be a problem. We can >> even dynamically generate and manipulate these patterns in the time domain >> to provide performance gains or specific effects. That is far from a new >> concept. Look at a PAVE PAWS radar site for an easily-verifiable 1980's >> example. > > > The several versions of the US "Space Fence" system also give an interesting > look at beam forming going back to the 60s. Look out for the S-band system > that they're going to be bringing online in the next few years.
Likewise the "Battle of the Beams" used a lot of different antennae and receiver-path phasing methods for early conscious virtual beamforming in WW2 as the research stepped up on both sides (rather than just general directivity for the general sake of performance, providing gain purely to reduce power considerations for example) Sadly it isn't very mainstream stuff other than with general descriptions - I've just had a quick google and Wikipedia only has 1 page on it with scant technical information on what was truly groundbreaking research in several related subdisciplines. Prototypes for what became the X-Gerat harness and radiators in particular went through endless iterations as they tried to achieve a suitably narrow beamwidth for the ranges required. I can recall some of the ham radio or shortwave magazine articles in the early 90s going into the systems in a little more detail as the Berlin Wall thawed the Cold War slightly. Much of this topic has practical implementation that dates back to the Y-stations in the early stages of WW1. Mechanical attempts at near-real-time processing (with land-line voice telephony as a backchannel to coordinate the multiple DF sites in real-time for fixing) were tried, in similar manner to artillery calculation aids, immediately after the phasing methods of additive interference and especially, subtractive interference (due to the deeper SNR nulls possible) became practical for 3-dimensional DF, thus bringing the time domain into things. Now the phasing and cocked-hat geometry is being done with general-purpose silicon instead of with slide-rules and voice coordination on a backchannel and a naval chart. Same game, just much faster, on transmit too, and much lower stakes for those who were involved. This is, quite literally, 100-year old practically-applied electromagnetics research 1914 and 1915 for the inception of the techniques, with Frankie Adcock improving on the then-dominant Bellini-Tosi phasing method of direction-finding beamforming a couple of years later. Elimination (or at least the reduction of) the descending sky wave component (again, by subtractive phasing, leveraging the interference patterns in orthogonal/quadrature separation and orientation) also improved accuracy around the clock as the systems became more advanced. Other methods of phase adjustment were attempted around the same time but the Adcock performed the best. These were all quite conscious attempts beamforming to provide optimal positional information to peak or null the target station using mathematical methods of phase adjustment, not just random observation of empirical cause and effect or spacing, feeding, proximity and reflections - empirical methods were also tried in parallel with various results) We do understand the physics much more now and have the benefit or some excellent calculation tools and display methods for design, but it's identical in concept from a technical point of view - the aim was still a 3-dimensional fix in as near-real-time as possible. In particular, Zernike polynomials opened up faster visualisation methods in the 50s that became very useful in radio and more general EM work and not just optics. Even disguising the base station appearance is far from new - in 1939 onwards it became quite important for some sites. Most of us nowadays will have seen a tree disguised as a cell-site or vice versa: https://www.google.co.uk/search?q=cell+site+tree or bases and antennae attached to or behind extant street furniture, for example. RF guys are forever trying to spot antennae and base systems that are "nice" in one form or another, either covert or overt. Many techniques rely on phasing to disguise the camouflaged shape of the unit yet provide the required coverage pattern, especially for downtilt of the beam toward the mobile targets and to promote spectrum re-use in adjacent areas. It's a geek's dream, "worse" than trainspotting and there are several websites dedicated solely to it. There are clear social parallels with Pylon Appreciation, another niche topic popular with some UK ISP staff ;) > A "hifi" is not using interference patterns. In fact, one of the reasons why > there's a "sweet spot" in listening to a system with only two speakers, is > because you're trying to sit in a position which is a node at as much of the > spectral range as possible. You end up with parts of the room where you have > good high range response, mediocre middle, and good bass response, or > frequently were everything sounds good apart from bass frequencies. Aye, not "using" them as such, but suffers from them as you describe in detail later. I tend not to use audio analogies for wave propagation but $generic_consumer_audio has the big advantage that most people use it and can relate to it better than the RF transceivers (intentional and unintentional - getting my usual EMC dig in haha) that their "familiar" wave interference pattern concept portable devices. Until recently it also had the advantage of having two easily understood radiator positions (ignoring multi-driver speakers for simplicity) and was similar enough in practice to help visualise the electromagnetic . You can also bend the truth a little and suggest the balance control is akin to adjusting the phase (and not, in fact, the relative ERP of each speaker) to illustrate some basic 2D steering concepts. 5.1 and bigger has made it all more blurry though, on reflection :) I'm very aware that though UKNOF/T is by no means non-technical, I needed an example a bit closer to most people to tame down my rants and concerns about practicalities and a real-world comparison that i know many UKNOFers are very familiar with. None of my criticism will be an issue in 5 years time when there's enough of $everything to make the system work well at a very large scale. At the moment, it's looking too much like a patentable concept with salemsanship, when in fact it should be all that *with* provable figures up front in a quick concise manner, that's all. I'd love this sort of stuff to work well. But dressing it up as the next big thing for the benefit of XYZ who can only handle executive summaries (sorry - can''t find the right words) actually makes it harder to believe, comprehend or trust at a practical level as a hands-on RF guy. I used cocked-hat RDF (almost exclusively with SDR in the last 2 decades and always with actively phased beamforming, *hands on* almost every day of my working life in one form another until the last few months. Reciprocity means it works on transmit too, though different signal paths are needed above say 10dBW in my usage for example. I still do use it occasionally, remotely (such is the power of the internet these days) so I'm afraid see no real innovation in their work. Maybe it's news to shareholders and investors and possibly users if they can understand it, but from our point of view on the tech side it's a passing phase that is rather annoying especially if it muddies the extent of the achievements (ok, no more of the puns). After watching the (almost) hour of video I had less clue than before I started - the essence of my gripe. With no tech FAQ or outline paper with measurements, their presentations appears to me as the usual tiresome waffle from marketers, which (I am keen to stress about my rant) demeans the actual work they've done and tech successes. In my mind even dismal failure is a valid result of research of this kind - I realise that not everyone would agree with that, especially (I'm guessing) their target audience. There are many advances in electromagnetic research yet to be made and we understand our inversal environments, consumer mobile datacomms is only one outlet for the product of research, "good" or "bad", positive or negative results are all worth it. If we only concentrate on commercial success or let marketing and commercial pressure control finance then the human race will lose out on so much useful data. Unfortunately, many people will read this and assume I'm talking about aliens or free energy or morgellons :) I'm not against SDR, centralisation of signal processing, or any of the other "innovative" tech they are flag-waving about to their audience, but having worked in the field (bad pun) myself for a long time I've seen similar generalised claims over and over again but *still* my 3G is almost unusable and my 2G voice drops as I move around my town-centre home. Most end users have already shrugged and given up - this should not have happened for anyone's sake. The extent of my disappointment is hard to communicate - when I can't be bothered to watch a video about phasing methods there's definitely something wrong. Yes, I rant, and to be fair my rant would have been better on the UKNOT informal off-topic list (I initially thought it was, in fact, sorry 'bout that!) I just want stuff to get better faster. I want the tech to speak volumes, not the presentation get in the way. Usual commercial pressure I suppose. It always is except in Original Research. If they had saved the fancy video clips for marketing and produced reasonably full tech research for peer-review (even via Youtube, which is better than nothing) I'd be selling it to people myself on it's own merits. I know it will work, the physics is well known and as I've alluded to, been used for a century in one form or another. I simply think it's time we'd moved on from software methods of re-inventing wheels and get on with inventing radical stuff, good or bad. The "concept sell" birds-eye approach is simply so dumbed down it looks like all the other snake oil and in my view has parallels with some over-unity videos on YT and similar. RF should not be a fringe specialism, with more research and respect than it's currently getting. It's taken for granted by users and it's particularly badly understood by the internetworking business community as a whole, with a few exceptions, even though it is widely relevant in that field in many unusual ways. It cannot be treated as a wired method of delivery and the confusing collisions of terminology are extremely unfortunate between the two disciplines. We will all probably be carrying around at least one device that uses interference cancelling technology on both transmission and reception of audio and that same device will probably contain up to 4 or 5 separate transceivers (or more likely one or more SDR ones instead) and possibly two more radio receivers, both of whom use the interference effect of phase cancellation and addition in mathematically similar (though practically diverse) ways (FM stereo and GPS. This stuff is everywhere. -- sent via Gmail web interface, so please excuse my gross neglect of Netiquette
