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Re: [softrock40] would like to recieve 138KHZ

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  • John RABSON
    ZL3DC, Please see attached* from M0BMU on the rsgb_lf_reflector (rsgb_lf_group@blacksheep.org). Note he used SoftRock Lite v6.2. For Lite II to work on 138
    Message 1 of 3 , Dec 17, 2009
    ZL3DC,

    Please see attached* from M0BMU on the rsgb_lf_reflector (rsgb_lf_group@...). Note he used SoftRock Lite v6.2. For Lite II to work on 138 you would need a 500kHz resonator as it does not have a divide by 8 setting.

    John Rabson
    F5VLF
    58800 Cervon
    France
    JN17vg

    *if attachments allowed - if not tell me and I will send it direct

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    On 09/07/2007 at 18:30 James Moritz <james.moritz@...> wrote:

    >Dear LF Group,
    >
    >I don't claim any great originality for this, but I have modified a couple
    >of the SoftRock Lite v6.2 kits by KB9YIG for use on 136k and 500k - the
    >details are attached.
    >
    >I changed the local oscillators to 4MHz for 500k and 1MHz for 136k, with
    >the
    >"x8" jumper set. This gives nominal LO frequencies of 500kHz and 125kHz
    >respectively, putting the output frequency within the range of a sound
    >card.
    >At 4MHz, the existing SoftRock LO circuit just about works, but it didn't
    >on
    >1MHz. I made some component value changes to the oscillator and buffer to
    >get a reasonable waveform on each band, which are detailed in the
    >attachment. 4MHz crystals are easy to get - I had several 1MHz xtals in my
    >junk box, but these seem to be harder to buy now than they once were. An
    >alternative for 136k would be to use a 1MHz DIL oscillator module, feeding
    >the flip-flop directly. Another possibility is a 500kHz ceramic resonator,
    >but the stability is not as good as a crystal.
    >
    >The original input filter could be re-designed for the LF/MF range, but the
    >components wouldn't fit on the tiny board, and the rejection of broadcast
    >band signals would not really be good enough. So I designed off-board input
    >filters with higher rejection of signals at harmonics of the LO frequency.
    >Like the original design, these require no adjustment and use fixed value
    >components - values are given in the attachment. I used 1/2-watt resistor
    >sixed axial-leaded chokes on 500kHz, which were fine. Similar components
    >had
    >insufficient Q at 136k, but the larger radial-leaded chokes wound on a
    >ferrite bobbin were adequate..The original tuned mixer input balun
    >transformer is replaced with an un-tuned ferrite-cored transformer.
    >
    >I have used the two SoftRocks with I2PHD's "Winrad" software, and DL4YHF's
    >SpecLab, both with excellent results. The Rocky software does not like the
    >PCs I have available. The sensitivity is not quite as good as my other
    >receivers, but since I normally use a preamp with various receiving loops,
    >this is not important. The sensitivity should be adequate when used with a
    >TX type antenna. It is important to set up the amplitude and phase balance
    >carefully, especially on 136kHz, where there is a lot of Loran noise in the
    >image sideband.
    >
    >Let me know if you have any problems viewing the attached schematic,
    >
    >Cheers, Jim Moritz
    >73 de M0BMU
    >
    >
    >
    >

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