• 23cm Filter

    From G8MNY@21:5/101 to TECH on Sun Aug 11 08:40:12 2019
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    From g8mny%gb7cip.#32.gbr.euro@i0ojj.ampr.org Sun Aug 11 09:35:56 2019 Received: from i0ojj.ampr.org by i0ojj.ampr.org (JNOS2.0k.3b) with SMTP
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    From: G8MNY@GB7CIP.#32.GBR.EURO
    To : TECH@WW

    By G8MNY (Dec 03)
    (8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
    Here is a simple filter that will remove most unwanted signals often found as unwanted images in 23cms Rx. eg UHF TV signals x2. It will also give some static protection for preamps as the double tuned line is grounded, but the loss can be as high as 2dB depending on materials! Bandwidth is quite narrow & the filter will need tuning top to bottom of 23cm band. It is not suitable for Tx over 1-2W due to the trimmer losses.

    The I/P & O/P can be coax leads soldered straight to the box & line or BNC/F connectors etc.

    <-1.5cm-> <-1.5cm->
    Coax or BNC Coax or BNC
    ^ ======= ! ======================== ! ========
    1.5cm ││_________________________________________││
    v ││ [^] Brass strip ││\...End Wall
    ====================! !======================
    0.5-3pF \..Side Wall
    < - - - - - - - - 8cm - - - - - - - - - - - >


    It is made from double sided PCB 2cm tall all seam soldered up with the bottom & end pieces slightly larger to allow inside & outside soldering of the side walls. Leave the lid off until after the initial tune up.

    The brass strip is 4mm wide (can be thick copper wire) & is soldered to both end walls. The trimmer is a bolt in type, but soldered in ceramic ones from old mechanical TV tuners will do.

    Once it is tuning well, tack solder the lid on & retune, you should have slightly better Q, make sure the tuning is OK before properly soldering up the seam.


    Why Don't U send an interesting bul?

    73 De John, G8MNY @ GB7CIP


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