On Jan 29, 2005, at 5:49 PM, <
[hidden email]> wrote:
> Hi folks -
> Between the torroids and the relays on the right side of the RF board
> are unsed holes right at the edge of the relays - can anyone tell me
> what they are for?
> 73 Tim/NZ7C
>
Hi Tim,
The holes you mentioned are points at which the low-pass filter wiring
must transition from the top side of the board to the bottom or
vice-versa. To ensure low RF resistance and reliability, we use two
vias (feedthroughs), or a combination of a via and a component lead,
for signals that are in the main RF path that have to switch sides.
Another subtlety is that pins 4 and 5 of the relays have pins but are
not connected to anything internally; this allows us to use the pins as
robust top/bottom feedthroughs.
In many instances on all of our PC boards you'll find "helper" vias
used for reliability, to provide a convenient test point, or to ensure
that all traces terminating at a large part like a relay do so on the
side of the board opposite the part itself. (The latter technique
allows the board to continue to function even if you accidentally
remove one or more vias when replacing such a part.)
73,
Wayne
N6KR
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