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RF relay ground connections

J

Joel Koltner

Jan 1, 1970
0
Has anyone here used the type of RF relay that's packaged like this one:
http://www.rfrelaystore.com/productdesc.php?pid=RDT-2P1D6 ? If you look at
the mounting drawing link on that page
(http://www.rfrelaystore.com/pdf/mounting/1500901.PDF), the idea is that your
hog out a pocket on your PCB for the relay to sit in and your microstrip
traces contact the relay terminals clearnly. However, shouldn't I be worried
that there isn't really a ground connector between the relay and the PCB's
ground plane that I can see? At 6GHz you're looking at wavelengths on the
order of an inch on a PCB, and the relay is a significant fraction of that so
it seems as though keeping proper ground references around would be necessary.
Perhaps the coupling between the bottom side of the relay and your ground
plane (a good-sized capacitor) is enough to make everything kopesetic?
Running a few numbers on the back of an envelope gives me somewhere in the
ballpark of upwards of 10pF (depends on where the ground plane actualyl is,
obviously) which is -j16 ohms at 1GHz -- not entirely ignoranble.

---Joel
 
J

John Larkin

Jan 1, 1970
0
Has anyone here used the type of RF relay that's packaged like this one:
http://www.rfrelaystore.com/productdesc.php?pid=RDT-2P1D6 ? If you look at
the mounting drawing link on that page
(http://www.rfrelaystore.com/pdf/mounting/1500901.PDF), the idea is that your
hog out a pocket on your PCB for the relay to sit in and your microstrip
traces contact the relay terminals clearnly. However, shouldn't I be worried
that there isn't really a ground connector between the relay and the PCB's
ground plane that I can see? At 6GHz you're looking at wavelengths on the
order of an inch on a PCB, and the relay is a significant fraction of that so
it seems as though keeping proper ground references around would be necessary.
Perhaps the coupling between the bottom side of the relay and your ground
plane (a good-sized capacitor) is enough to make everything kopesetic?
Running a few numbers on the back of an envelope gives me somewhere in the
ballpark of upwards of 10pF (depends on where the ground plane actualyl is,
obviously) which is -j16 ohms at 1GHz -- not entirely ignoranble.

---Joel

It looks like they want you to hog out a square-cornered pocket in the
pcb and then tap the board as well! I suppose you could sit it on a
ground plane, on the bottom of the pocket.

I have done plated countersinked holes on a pcb, but never tapped
holes!

John
 
M

Mark

Jan 1, 1970
0
Has anyone here used the type of RF relay that's packaged like this one:http://www.rfrelaystore.com/productdesc.php?pid=RDT-2P1D6?  If you look at
the mounting drawing link on that page
(http://www.rfrelaystore.com/pdf/mounting/1500901.PDF), the idea is that your
hog out a pocket on your PCB for the relay to sit in and your microstrip
traces contact the relay terminals clearnly.  However, shouldn't I be worried
that there isn't really a ground connector between the relay and the PCB's
ground plane that I can see?  At 6GHz you're looking at wavelengths on the
order of an inch on a PCB, and the relay is a significant fraction of thatso
it seems as though keeping proper ground references around would be necessary.
Perhaps the coupling between the bottom side of the relay and your ground
plane (a good-sized capacitor) is enough to make everything kopesetic?
Running a few numbers on the back of an envelope gives me somewhere in the
ballpark of upwards of 10pF (depends on where the ground plane actualyl is,
obviously) which is -j16 ohms at 1GHz -- not entirely ignoranble.

---Joel

the bottom surface in the drawing is the HOUSING not the PWB. The PWB
sits on top of the metal housing, the relay is screwd to the housing
and the PWB ground must also be well connected to the housing for this
to work

Mark
 
J

Joel Koltner

Jan 1, 1970
0
Hi Mark,

"the bottom surface in the drawing is the HOUSING not the PWB. The PWB
sits on top of the metal housing, the relay is screwd to the housing
and the PWB ground must also be well connected to the housing for this
to work"

Ah, gotcha. Thanks for the explanation...

Hmm... I wonder if it's easier (cheaper) to get your board house to build up a
..049" thick board than it is to hog out the housing to the appropriate
remianing depth?

---Joel
 
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