Thanks to everyone who has responded. I think the conclusion is that at the
frequencies I'm interested in, and the available space inside the radio (a
little RS DX-394 table radio), it's impractical to absorb the 455 kHz
crosstalk energy from 2nd IF to frontend. Better to attempt to
compartmentalize the radio. That may prove to be impractical also as it
would appear very difficult to make small (removable) shields over the IF
section that would not have gaps. However, I'll examine the pcb layout more
closely to see if there are any viable paths for the sides of the shield
box.

73, Tom

"Tom Holden" wrote in message
...
Thanks to everyone who has responded. I think the conclusion is that at
the
frequencies I'm interested in, and the available space inside the radio (a
little RS DX-394 table radio), it's impractical to absorb the 455 kHz
crosstalk energy from 2nd IF to frontend. Better to attempt to
compartmentalize the radio. That may prove to be impractical also as it
would appear very difficult to make small (removable) shields over the IF
section that would not have gaps. However, I'll examine the pcb layout
more
closely to see if there are any viable paths for the sides of the shield
box.

Small gaps won't matter as long as they are shorted out at one or both ends.
A well-fitting cover would do that. You'll observe that commercial gear uses
very thin tinned steel? for shield boxes. The lid edges are bent into spring
fingers to hold them in place.

On Sun, 9 Nov 2003 16:00:21 -0500, "Tom Holden"
wrote:

Thanks to everyone who has responded. I think the conclusion is that at the
frequencies I'm interested in, and the available space inside the radio (a
little RS DX-394 table radio), it's impractical to absorb the 455 kHz
crosstalk energy from 2nd IF to frontend. Better to attempt to
compartmentalize the radio. That may prove to be impractical also as it
would appear very difficult to make small (removable) shields over the IF
section that would not have gaps. However, I'll examine the pcb layout more
closely to see if there are any viable paths for the sides of the shield
box.

73, Tom


You'll never know before you have tried, and remember that Racal
solved a similar problem with their famous RA-17 series receivers
using a hacksaw to make a little mark in the chassis to stop unwanted
radiation from one point to another. Believe I've seen the application
of those carbonized foam used in the lids of boxes which were
definitely not microwave equipment

Such things are impossible to predict

It is also some definite requirement for the thickness of the walls to
act as screen on certain frequencies, as an example could be mentioned
that pcb laminates are not thick enough for good screening on 80m in
an application with two oscillators which need good screening to avoid
coupling to be used for third order IP measurements

73
Jan-Martin, LA8AK
Amateur radio techniques http://home.online.no/~la8ak/c.htm
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J M Noeding wrote:

You'll never know before you have tried, and remember that Racal
solved a similar problem with their famous RA-17 series receivers
using a hacksaw to make a little mark in the chassis to stop unwanted
radiation from one point to another.

Did Racal make a complete cut through the chassis or just a deep
scratch? How long was it?


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Sounds like the ol' ground loop problem.

Bill, K5BY