On Thu, 9 Sep 2004 07:17:25 -0400, Dennis Berry wrote:
>I can understand your comment above, somewhat. If this is, for example,
>coax coming into the receiver. Are you saying the center lead routes around
>the board and is connected to ground through various components
No. You have several misunderstandings here.
1. The so-called pin 1 problem is a mis-wiring of a SHIELD connnection.
2. It is NOT associated with intentional antennas -- that is, the antennas we
think of as antennas. Rather, it is associated with other inputs and outputs to
a radio (or
piece of hi-fi gear, or a computer, or whatever) that can ACT as antennas even
we don't intend them to do so, and don't think of them as antennas.
3. It is not associated with the center conductor -- most designers recognize
that RF can
be there, and put a filter on that input.
>The outside shield is typically connected to the chassis as
>it comes in to the receiver, yes? So how does one keep the center
>conductor's associated currents from flowing 'inside the box'?
>And the pin 1 problem. Is the fix just to ground the pin 1 to chassis? Or
>does that play with the 'single point ground' that is so talked about?
The simple (and correct) fix is to connect ALL shields to the CHASSIS.
Let's be careful about terminology. Remember, this design error is known as
"the pin 1
problem" because it was first published by an ex-ham working in pro audio, and
shield contact for XL connectors used in audio is pin 1. But the mic
connectors used on
most ham gear have the mic "hot" lead connected to their pin 1, so connecting
it to the
chassis will short the audio from the mic to the chassis. Not a good idea. :)
In many of
these radios, pin 7 of that connector is used for the shield of the mic cable.
So in those
mics, pin 7 needs to go to the chassis, NOT to the circuit board. That is the
Oh -- by the way -- if this problem had first come to light in a Kenwood or
transceiver, we might call it "the pin 7 problem" and the audio guys would
we were talking about. :)
Now, you say, why not connect the shield straight to the shell of the
question. The problem is that in some radios, the shell isn't connected to the
How did all this become common practice? Several reasons. First, a lot of guys
RF background got involved in designing radios, and they didn't know about
much. :) Many were computer guys, thinking of nothing but ones and zeros.
audio guys, and thought that everything stopped at 20 kHz.
Second, and maybe most important, the ways of building radios (and other gear)
changed a lot to become more efficient. In the old days, mic connectors were
and screwed down to the chassis, so their shells were properly connected. RCA
connectors were also screwed to the chassis, so they were properly connected
But at some point, roughly 25-30 years ago, engineers learned that they could
save a lot
of manufacturing cost by mounting connectors directly to a circuit board and
the connections to the board when the board was soldered by a machine. Then the
board gets stuffed into the equipment and screwed down -- BUT the connector
contacts never get screwed down to the chassis. So the only way the shield gets
chassis is via the circuit board. This manufacturing process is at the heart of
the "pin 1
Hope this helps. Feel free to ask more questions.
Jim Brown K9YC
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