Uwe Hercksen wrote:> On Mon, 12 Feb 2007 22:30:39 +0100, john jardine > <john@jjdesigns.fsnet.co.uk> wrote: > >> Had trouble with crosstalk on a mass of video signals. Cured with a >> multilayer board where each signal was 'boxed in' by ground plane to the >> sides, above and below. Sort of square coax. > > > Hello, > > but how about a real closed square shield around the center conductor?To do that would need plated slots, and slots have the PCB fabs luke-warm at best : hard to do cleanly, they also weaken the PCB if long, and also have minimum router sizes, plus machine time...... A better direction would be thinner laminates, and using the space you would have lost to the slot anyway, as wider GND webs on the same plane, coupled with stitching vias (which can be smaller dia than slots) -jg
Building Coaxial transmission line on PCB?
Started by ●February 12, 2007
Reply by ●February 13, 20072007-02-13
Reply by ●February 13, 20072007-02-13
[...] "werty" <werty@swissinfo.org> wrote in message news:1171348634.104020.242500@l53g2000cwa.googlegroups.com...> > ---------------------------------------------------------- > > Boxed ! the wavelength is far greater than > your dimensions , thus higher modes can not > exist , thus you do NOT need sides . > When you reach 10 Ghz , then maybe > you need sides in ur boxed "coax" . > > But the big joke , is in the real world , > they use cheap PCB to xmit 2.5 Ghz . > No strip line , no microstrip , nada .. > It works well , so quit arguing reality . > > BTW , i saw some novice , trying to > use juice cans to launch WiFi . > He figured the more cans , the more > gain . He had 3 cans , T'd . > to divide the power . > Gain is not in cans , its in size of > the dish . > > Another book worm said all i needed > was $26 for 100 meters of blah blah > coax at 2.5 Ghz .. > > 10 times that price ! > and 1.8" dia hard line ! > > At these wavelengths , its lower loss > to send it TEM and thru the air , > not thru a coax . > > This is goin to FPGA ? Do those relics > still exist ?! Oh well , i supose ya gotta > try to "protect" your firmware by reinventing > the CPU ! >Que?. Don't listen to the worms. Video comes in forms other than digital. -- Posted via a free Usenet account from http://www.teranews.com
Reply by ●February 14, 20072007-02-14
On Tue, 13 Feb 2007 18:41:00 +0100, Geronimo Stempovski <geronimo.stempovski@arcor.de> wrote:> Now I'm looking for a diagram like frequency (some MHz to 10 GHz for > example) versus loss tangent and / or epsilon R for FR4. I only found a > poor > black-and-white copy from 1991 in a paper which I searched with Google. I > wouldn't have thought it to be so hard to find a graph... Does anybody > know > where I can find that?Hello, I am sorry to tell that, but for frequencies of 1 to 10 GHz, FR4 ist not the right material, there are other PCB materials which are better for high frequencies, take a look here http://www.andus.de/Leiterplatten/Impedanz/hfmat.htm They write there that FR4 may be used up to 4 GHz. Bye
Reply by ●February 14, 20072007-02-14
On Wed, 14 Feb 2007 15:36:15 +0100, "Uwe Hercksen" <hercksen@mew.uni-erlangen.de> wrote:>On Tue, 13 Feb 2007 18:41:00 +0100, Geronimo Stempovski ><geronimo.stempovski@arcor.de> wrote: > >> Now I'm looking for a diagram like frequency (some MHz to 10 GHz for >> example) versus loss tangent and / or epsilon R for FR4. I only found a >> poor >> black-and-white copy from 1991 in a paper which I searched with Google. I >> wouldn't have thought it to be so hard to find a graph... Does anybody >> know >> where I can find that? > >Hello, > >I am sorry to tell that, but for frequencies of 1 to 10 GHz, FR4 ist not >the right material, there are other PCB materials which are better for >high frequencies, take a look here >http://www.andus.de/Leiterplatten/Impedanz/hfmat.htm >They write there that FR4 may be used up to 4 GHz. > >ByeFR4 can be used at 20 GHz, depending on what you're trying to do. John
Reply by ●February 15, 20072007-02-15
Again, I'm looking for a diagram like frequency (some MHz to 10 GHz for example) versus loss tangent and / or epsilon R for FR4 or other usual PCB material. I only found a poor black-and-white copy from 1991 in a paper which I searched with Google. I wouldn't have thought it to be so hard to find a graph but as noone replied to my previous question so far it does seem to be hard! :-) Does anybody know where I can find that? Regards Gero
Reply by ●February 15, 20072007-02-15
On Thu, 15 Feb 2007 08:55:05 +0100, "Geronimo Stempovski" <geronimo.stempovski@arcor.de> wrote:>Again, I'm looking for a diagram like frequency (some MHz to 10 GHz for >example) versus loss tangent and / or epsilon R for FR4 or other usual PCB >material. I only found a poor black-and-white copy from 1991 in a paper >which I searched with Google. I wouldn't have thought it to be so hard to >find a graph but as noone replied to my previous question so far it does >seem to be hard! :-) > >Does anybody know where I can find that? > >Regards Gero >Google gives lots of hits on stuff like "loss tangent fr4 frequency" But FR-4 varies a lot, so there's no definitive data. What are you trying to do? John
Reply by ●February 15, 20072007-02-15
On Wed, 14 Feb 2007 17:10:34 +0100, John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:> > FR4 can be used at 20 GHz, depending on what you're trying to do.Hello, well, if the transmission line is very, very short..... bye
Reply by ●February 15, 20072007-02-15
On Thu, 15 Feb 2007 08:55:05 +0100, Geronimo Stempovski = <geronimo.stempovski@arcor.de> wrote:> Again, I'm looking for a diagram like frequency (some MHz to 10 GHz fo=r> example) versus loss tangent and / or epsilon R for FR4 or other usual==> PCB > material. I only found a poor black-and-white copy from 1991 in a pape=r> which I searched with Google. I wouldn't have thought it to be so hard=to> find a graph but as noone replied to my previous question so far it do=es> seem to be hard! :-)Hello, look here for FR408 http://www.isola.de/d/ecomaXL/index.php?site=3DISOLA_DE_product_addition= al_information&sid=3D235&p=3D10 bye
Reply by ●February 15, 20072007-02-15
On Thu, 15 Feb 2007 16:15:49 +0100, "Uwe Hercksen" <hercksen@mew.uni-erlangen.de> wrote:>On Wed, 14 Feb 2007 17:10:34 +0100, John Larkin ><jjlarkin@highNOTlandTHIStechnologyPART.com> wrote: > >> >> FR4 can be used at 20 GHz, depending on what you're trying to do. > >Hello, > >well, if the transmission line is very, very short..... > >Exactly. John
Reply by ●February 16, 20072007-02-16
> work. I can imagine that John J. may well also. When you're aiming > at 100+dB isolation among traces, you do have to be pretty careful, > even at "low" frequencies. > > Cheers, > Tom- Hide quoted text - > > - Show quoted text -______________________________________ Its all theory . If its open , the RF will leak out . Like the holes in a MicroWave dish ---------------- 10:1 SWR , open lines , and NO radiation . ------------------- Transmission lines repulse , but that does NOT mean magnetic fringing and sending mag flds everywhere . ---------------------- BTW Study CAT5e Ethernet cable . garbage ! USB cables are much faster . I think ppl limit themselves to whats avail in PCB , then complain when it dont work , but if they'd experiment , they'd find the problem is using thin PCB . Then they limit on putting down 100 transmission lines per mm . You cant learn , unless you experiment. you can't choke the dimensions and get good results , a transmission line needs exact dimensions , or you lose . In coax for 2.5 Ghz , for example , it WILL have a large diameter and the center will have an exact dia and ratio .. No substitutes . Sending signals that will be amplified use high Z ( ~65 ohms ) and sending power needs low Z . These rules can't be bent . Thats what you're doin , is bending rules ... .
