duplexer or diplexer? - Page 1
Forum section: electronics / general

author: GiskardReventlov
author_rank: Frequent Contributor
timestamp: January 24, 2014, 04:22:19 am
content: After watching the analog-tv station tour and wanting to see those combiners or diplexers or duplexers.....I recalled this gsm rf equipment that Harald says are cavity duplexers. The purpose decides what you call them??Images from here:http://laforge.gnumonks.org/weblog/gsm/index.html

author: KJDS
author_rank: Super Contributor
timestamp: January 24, 2014, 10:24:14 am
content: I spent eight years working in a filter design place. I spent more time using a milling machine to mod prototypes then I did a soldering iron. They are fun things to design. I think that's a Filtronics design due to the circular cavities which were machined with a form tool. The RX path is interesting, must be a pig to tune round the canonic section.

author: Co6aka
author_rank: Unknown
timestamp: January 24, 2014, 08:40:44 pm
content: Diplexer: Basically a low-pass filter and a high-pass filter that share a common connection; think "band-splitting filter." There are also triplexers (and so on) which are low-pass, band-pass, and high-pass filters with a common connection.Duplexer: Basically two relatively narrow band-pass filters, usually high-Q tuned circuits (typically "cavities" at RF) with a common connection. There are also window-duplexers (and triplexers, etc) that, at RF, are usually high-Q combline filters with a common connection.

author: Co6aka
author_rank: Unknown
timestamp: January 25, 2014, 02:11:04 am
content: Quote from: GiskardReventlov on January 24, 2014, 04:22:19 amBTW, that's a combline window duplexer. For GSM and similar, the two passbands ("windows") usually cover the entire TX and RX bands, or specific sub-bands thereof.In the first photo, at the top-center is the common ("antenna") connection, and at the lower right/left are the TX/RX or RX/TX connections. The cylinders are (likely) 1/4 wavelength grounded monopoles, which are shunt fed (the lower-right connection offers the clearest view of the shunt feed.)Also BTW, another use of a diplexer (triplexer, etc) is to connect a multi-band radio through one feedline to an array of mono-band antennas. Or, diplexers (and etc) can be used at both ends to connect mono-band radios through one feedline to mono-band antennas. I built two quad-plexers to do just that; 150, 450, 800, 900 (MHz) mono-band radios through one 7/8 LDF feedline up to four monoband yagis. (First I split 150/450/800+, then 800/900 -- 800/900 was the tricky part; getting enough isolation at the radio end.)

author: GiskardReventlov
author_rank: Frequent Contributor
timestamp: January 25, 2014, 04:22:14 am
content: Very interesting stuff. The analog tv station video was an eye opener. I really wished they had cracked open that combiner. Maybe they still can and will? Also I'd never heard or seen coaxial (correct term?) with air as the dielectric and hollow center conductors. It's very fascinating because it is a vivid reminder that when you scale things up and make them big different things start to matter that didn't matter at smaller scales. How do they keep that stuff so shiny? It must be coated.And this rf gear is really not intuitive at first sight so for mere mortals it's a mind bender. It's settling in now though. Splitting signals in mid air seems like a magic trick until the "light goes on".

author: KJDS
author_rank: Super Contributor
timestamp: January 25, 2014, 10:51:25 am
content: What's in a name? that which we call a rose. By any other name would smell as sweetI've known diplexer and duplexer used for the type of product initially pictured and I think that diplexer is the more common name used for it.

author: Co6aka
author_rank: Unknown
timestamp: January 25, 2014, 06:34:47 pm
content: Quote from: KJDS on January 25, 2014, 10:51:25 amAnyway...Air dielectric is used to reduce weight and to almost eliminate dielectric losses. Hollow center conductors also reduce weight, and because of the skin effect at higher frequencies most of the current is carried on the surface of the conductor, so "more surface area" is what you want. You'll see these at small scale too; for example, LDF4 has a copper-coated aluminum center conductor, and LDF5 and larger has a hollow copper "tube" center conductor. The larger diameter cables typically switch to a spiral dielectric, which of course is mostly air, and sometimes (after installation) they're pressure filled with dry nitrogen. Most of the popular "LMR" type coax has a copper-coated aluminum center conductor. (Stranded copper is substituted when flexibility is required.) You'll also find silver-plated conductors in small low-loss cables used at high frequencies (because of the skin effect; less I2R loss.)"RF-plumbing" has always been a fascination of mine, but I'm just a jack rather than a pro. Ya gotta be a RF engineer, a mechanical engineer, and a machinist all-in-one... There was guy in Canada ("DCI") we affectionately dubbed "The Saskatchewan Metalbender"Made great stuff.

author: BravoV
author_rank: Super Contributor
timestamp: January 25, 2014, 06:39:47 pm
content: Quote from: GiskardReventlov on January 24, 2014, 04:22:19 amPut a little rat in it and cover it with a clear glass, you can now call it a mouse maze.

author: GiskardReventlov
author_rank: Frequent Contributor
timestamp: January 28, 2014, 02:55:16 am
content: Quote from: Co6aka on January 25, 2014, 06:34:47 pmAre you saying they have to be modeled by hand first? Computers can't simulate the designs? That really is art then.

author: KJDS
author_rank: Super Contributor
timestamp: January 28, 2014, 07:28:59 am
content: The sort of diplexer shown in the OP is now usually into production on using the original prototype drawing of it. Even 15 years ago, without the aid of 3d EM solvers I would be within a quick tweak with a manual mill to get the body right.

author: GiskardReventlov
author_rank: Frequent Contributor
timestamp: January 28, 2014, 04:42:00 pm
content: Quote from: KJDS on January 28, 2014, 07:28:59 amYou're saying that it would be made via CNC but using the original design? And 15 yrs. ago it would have been milled manually but is the design an iterative process or is there software that can spit out the drawing? From what I've gleened here so far the designs are iterative or were iterative. I'd be surprised if that's still true.It got me thinking (again) about just how little is left that machines/computers cannot do.

author: KJDS
author_rank: Super Contributor
timestamp: January 28, 2014, 06:14:09 pm
content: Quote from: GiskardReventlov on January 28, 2014, 04:42:00 pmThey always have been and will be machined on a CNC mill. 15 years ago then there would be a few iterations with minor changes made using a manual mill. Being able to use one is a huge advantage to tweak the design quickly, rather than marking up a drawing and putting it into the machine shop queue. Where I worked the CNCs would be run on a shift basis but the manual mills were operated on a day shift. So i'd start work at lunchtime and do my iterations through the evening.It's now possible to spend a lot of time using 3d EM simulators to get the design right first time, but I suspect I could still do it as quick without the EM provided there was a manual mill available to use.

author: GiskardReventlov
author_rank: Frequent Contributor
timestamp: January 29, 2014, 03:09:03 am
content: Quote from: KJDS on January 28, 2014, 06:14:09 pmI understand what you're saying. I could see someone spending too much time tweaking the model for very little gain.

author: ConKbot
author_rank: Super Contributor
timestamp: February 01, 2014, 04:47:45 pm
content: Quote from: GiskardReventlov on January 29, 2014, 03:09:03 amAnd someone can fart around in software for hours trying to tweak it for very little gainEither way the operator has to know what they are doing.

author: GiskardReventlov
author_rank: Frequent Contributor
timestamp: February 03, 2014, 10:46:18 pm
content: Quote from: ConKbot on February 01, 2014, 04:47:45 pmYep, I was reiterating what KJDS said just differently and seems you agree. Word processing software probably takes the cake in this category of maximum time wasted for so little gain.