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Re: LF: Anyone good with Elsie?

To: [email protected]
Subject: Re: LF: Anyone good with Elsie?
From: DK7FC <[email protected]>
Date: Thu, 23 Aug 2018 22:34:01 +0200
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Am 23.08.2018 22:04, schrieb Chris Wilson:
Hi Chris,

I added a 470pF cheap disc ceramic across each
of  the 2000pF polystyrene caps, and indeed the filter moved lower, to
pretty  much the optimum spot (thank you Stefan). But I see a lot more
attenuation with these two caps added. I presume disc ceramics are not
ideal?
The Q of them should not be critical but things like temperature coefficients... I prefer to use styroflex caps for such RX filters but others can be fine too. Two caps? There should be 3 in that circuit. If you just tune two of the circuits to 137 kHz then the filter curve will be wider and have more attenuation. Actually there could be two resonance peaks close together, which you may not see due to the low Q. Just try to add a 3rd C. I would expect this improves things. It is good to play arround anyway, then you learn intuitively what causes what result.
    The  inductors  are  cheapo  pre  made  ones (look like 1/4 W
resistors), again off Ebay so probably far from optimal. I may need to
look  at  raising  the  Q of this thing! Are there high Q commercially
made  inductors in 680 and 2.2 uH or do I need to wind my own?
Wind your own! I built those: http://www.iup.uni-heidelberg.de/schaefer_vlf/LF/LF_RX_pot%20_cores.jpg
  How sub
optimal is using disc ceramics for parallelling the branded poly caps?
Quite, but still good for a first test.

73, Stefan

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