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| Subject: | LF: Re: Ferrite wideband antennas? |
| From: | pws <[email protected]> |
| Date: | Tue, 30 Aug 2011 17:17:03 +0200 |
| In-reply-to: | <[email protected]> |
| References: | <16BC8B3CA8672445BC2A29B4C14A26D4379ED2AAB4@exlnmb01.eur.nsroot.net> <[email protected]> <[email protected]> <9CD1E11E8BC9402CB4AECECAC4088443@JimPC> <[email protected]> <[email protected]> <[email protected]> <[email protected]> <[email protected]> <[email protected]> |
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Hi again Daniele, I forgot some words about shielding.Do not use solid sheet. I just built a small receiver for rtty at 147 kHz for weather report reception when sailing. Using a fine looking u-shaped copper shield the signal went down of some 10 dB even if spaced 4 cm apart from the rod. And it did not improve the SNR considerably. Using an envelope from old SCSI flatline soldered together only at one side the SNR went up of >10 dB inside the house. The effect is incredible. My guess is that Eddy currents are responsible for this. So if possible shield your ferrite antenna coil by a "feathered", comb-like structure with multiple conductors running in parallel around the rod. They may overlap some cm if isolated. And in contrast to solid shielding distance doesn't matter. Peter, df3lp |
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