On Fri, 15 Dec 2000 17:19:49 -0500 "Tom Rauch" <w8ji@contesting.com>
writes:
>
>Hi Marv
>
>You should be able to find open frame relays larger than 10
>amperes that make the connection length about 2 inches total, and
>enclosed relays that are half that connection length.
I have P&B K10 series relays, which are essentially open frame units
with a plastic dust cover, that are about the smallest I've seen in a 10A
(277V) DPDT.
They are .8" wide, so 10 of them means 8" of interconnect in that
direction including shorting bars across one of the terminals and the
armature link to the adjoining relay. The contact leaf plus fixed
contact distance is 1.3", so 20 of those is 26". Add just a bit on each
end to reach the N connectors and that's how I got to 3 feet.
The "manufactured" relay approach is superior, in one aspect, to the
scheme I posted a couple days ago as there are only 20 contacts in the
signal path, rather than 40.
I originally considered making this device with coax transfer relays
but, aside from the cost, that would mean 40 contacts plus 40 coax
connectors. No matter how good the parts are, that just sounds kind of
lossy just writing it out!
>Even if you can't, the length isn't important if you make the
>impedance close to 50 ohms.
Best guesstimate, using a microstrip "Perrygraf" calculator to figure
the relay leaf impedance over ground, shows about 100 ohms. I really
can't get them much closer to ground, to lower the impedance, than that
as there are the fixed contacts and the armature assembly itself which
need a bit of clearance.
What effect do 10 short sections of 100 ohms interspersed with 50 ohm
line have on the operation of a 1/4 wave coaxial transformer???
73,
Marv WC6W
*
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