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| To: | <[email protected]> |
|---|---|
| Subject: | Re: LF: Re: Help needed, mechanical filters |
| From: | "James Moritz" <[email protected]> |
| Date: | Sat, 30 Jun 2012 14:34:42 +0100 |
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Dear Stefan, LF Group, So, is a microphone effect possible? I suppose it is possible, but I don't think there are many intense accoustic sources of 473kHz, and in any case the filter assembly would have to be designed to minimise unwanted acoustic coupling between input and output, so would probably also give good protection from external sources. The ferrite transformer core in your PA is perhaps the strongest source, but I guess you won't use the PA and filter at the same time ;-) Good idea about the matching! So it is about like the input filter of JA8SCD's LF converter: http://icas.to/idc-136-kit/idc-136-kit-manual-eng.pdf (page 6 of 6). That's one possibility - the "dual" of that circuit has a capacitor in series with the low-Z source and a shunt capacitor across the winding - see the handbooks. According to the data sheet, the insertion loss (Durchlassdämpfung) is < 2 dB. So if one uses a well matched 50 Ohm transmit antenna and a RX with 50 Ohm input, i think no additional gain is needed. If the receiver sensitivity is reasonably good (it might not be though...), you could probably allow 10 or 20dB attenuation. You could reduce the effect of impedance variations with an attenuator pad, etc. Cheers, Jim Moritz73 de M0BMU |
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