RF interfearing with oscilloscope measurements

I am having some problems trying to make some measurements. I am trying to measure some signals but an RF source keeps coupling into my
oscilloscope lines. I even went so far as to put the device Im trying to measure and the oscilloscope in an RF shielded box. It has cut down the RF a bit, but the problem is I have to connect the unit under test to the circuit outside the box, which is generating the RF. So no matter what I do there will still be some exposure inside the box traveling down the lines. I would like to measure a signal on the board without that RF creeping into the measurements but also be able to measure that same frequency on the on the signal in the circuit, if it is there.
With out the probe connected I see a significant signal. I can also connect the probe directly to a battery and see a significant signal. So it must be pretty powerful. Even using a differential probe brings no result. I know its not coupling into the scope itself because it does not trigger if the probe is disconnected.
Does anyone have any ideas?
Josh
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On 11/17/06 2:31 PM, in article zLq7h.6720$ snipped-for-privacy@newssvr25.news.prodigy.net, "Joshua K. Drumeller"

That is why God invented screen rooms.
Depending upon your signal source, you might try converting it to a low impedance source such as by using an emitter follower. That way coupled rf might be shorted out. You can also try using differential input scopes and short out the rf. Try cutting the bandwidth of your scope.
Bill -- Fermez le Bush
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If possible use transformer isolation at the scope to eliminate the common mode RFI.
Joshua K. Drumeller wrote:

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Joe Leikhim K4SAT
"The RFI-EMI-GUY"
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"Joshua K. Drumeller" wrote:

Make sure you are using high quality probes. Also, keep the ground leads from the probe to the circuit under test as short as possible and clip it to a ground close to the test point. The path from the probe tip, through the circuit and along the probe ground wire back to the probe forms a loop that can couple magnetic fields into the scope input. This must be kept as small as possible.
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Paul Hovnanian mailto: snipped-for-privacy@Hovnanian.com
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