Re: [softrock40] would like to recieve 138KHZ
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.
*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
>"x8" jumper set. This gives nominal LO frequencies of 500kHz and 125kHz
>respectively, putting the output frequency within the range of a sound
>At 4MHz, the existing SoftRock LO circuit just about works, but it didn't
>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
>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
>Let me know if you have any problems viewing the attached schematic,
>Cheers, Jim Moritz
>73 de M0BMU
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