RF cable connection to board
in [Design]
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From: John Larkin on 9 Jun 2010 12:03 On Wed, 9 Jun 2010 16:42:20 +0100, "Grumps" <grumps(a)nothere.com> wrote: >"Jeroen Belleman" <jeroen(a)nospam.please> wrote in message >news:huocd7$l5i$1(a)speranza.aioe.org... >> Grumps wrote: >>> Hi >>> >>> How do you calculate loss due to a soldered coax cable direct to the >>> board? >>> >>> I have an RG316 cable with SMA connector on one end. But I'm trying to >>> decide if it is best to terminate both ends with RF connectors and then >>> plug this assembly into the board, or just to solder the wire to the >>> board (seems to be common practise with wireless routers). >> >> Seems to me the relevant issues are cost and convenience. >> The difference in loss hardly matters and could well be of >> either sign. And RG316 is lossy stuff anyway. > >Thanks. It's much cheaper to solder directly than use another connector >pair. Labor costs are low where this is going to be produced. A lot depends on how you manage the transition. If you use two thru-holes, and solder the coax inner and outer to them, you'll get a capacitive discontinuity from the pads and then an inductive bump from the coax loop. Those will be moderate effects at 5 GHz. It's better to try to make something more like an edge-launch transition. Here's a crude version, using hardline: ftp://jjlarkin.lmi.net/BB_fast.JPG The teflon pushed out of the end of the coax a bit when I tinned the shield, and that made my air loops a little bigger. Just that much extra distance affects matching and is quite visible on 20 GHz TDR. I didn't bother to tweak this one, because this circuit works in the 100 ps/3 GHz sort of zone. A better transition would be a plated slot at the edge of the board, that the coax shield would fit/solder into, with the coax center conductor soldering directly into a microstrip line with no bends. >Can you suggest another (flexible) cable that is good at 5GHz, and a >compatible SMA? Semirigid is nice at 5 GHz. You can learn a lot, fast, with a TDR scope and an x-acto knife. John
From: BlindBaby on 9 Jun 2010 12:03
On Wed, 9 Jun 2010 16:37:06 +0100, "Grumps" <grumps(a)nothere.com> wrote: >"BlindBaby" <BlindMelonChitlin(a)wellnevergetthatonethealbumcover.org> wrote >in message news:da9v061fn54a7i95vem9lerdlhqjeegtgl(a)4ax.com... >> On Wed, 9 Jun 2010 15:22:21 +0100, "Grumps" <grumps(a)nothere.com> wrote: >> >>>Hi >>> >>>How do you calculate loss due to a soldered coax cable direct to the >>>board? >>> >>>I have an RG316 cable with SMA connector on one end. But I'm trying to >>>decide if it is best to terminate both ends with RF connectors and then >>>plug >>>this assembly into the board, or just to solder the wire to the board >>>(seems >>>to be common practise with wireless routers). >>> >>>Ta. >>> >> The cable interconnect is more expensive, but far more serviceable. >> >> I thought that typical loss figures came from their (each connector) >> data sheets. > >For the connectors they do. >I was wondering about losses where the cable is soldered directly to the >board. > You can probably model it and any or all parasitic effects it carries. I think we call it guesstimation. |