To: | [email protected] |
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Subject: | LF: Field Strength Meter - advice needed |
From: | Chris Osborn <[email protected]> |
Date: | Mon, 4 May 2009 20:23:28 +0000 (GMT) |
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Thanks again Dave and Alan, I've spent a few more hours on the F/S meter today and still have not found the problem. I can blow with a drinking straw on any component and there's very little output change yet with time there's a slow drift with temperature - the output goes up with increased temperature. I thought I'd found the problem as by squeezing the ferrite rod 's screening tube I could get a fair change in the output (about 10 %). The tube's metal is not aluminium but I guess an aluminium alloy. In any case I changed it for a proper aluminium tube - no difference ! From the shack's temperature of 23 degrees and taking the F/S meter outside to an ambient 13 degrees the meter's output changed from 0.48 volts to 0.35 volts !! I have run out of ideas now and am thinking maybe it's even the permeability of the die cast box that's changing or maybe the perspex end caps of the ferrite rod. . . . I'm getting desperate ! 73 Chris G3XIZ From: Dave Pick <[email protected]> To: [email protected] Sent: Monday, 4 May, 2009 16:10:26 Subject: Re: LF: Field Strength Meter - advice needed Chris Have you tried a can of "freezer" spray to identify where the problem lies? Is it the ferrite aerial or is it the FET amplifier? If you have enough gain then a little negative feedback on the FET stage may help, add some un-decoupled source resistor. Dave 'YXM 2009/5/3 Chris Osborn <[email protected]>
-- G3YXM IO92BK Birmingham UK |
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