Graham,
Please see below from M0BMU.
73
John F5VLF
*********** REPLY SEPARATOR ***********
On 19/11/2009 at 23:29 Graham wrote:
>All .
>
>Where can a Soft Rock rx for 500 Khz be purchased from ./
>
>Or do you need to modify a 455 Khz version for 500 ?
>If so .. where from a 455khz version ?
>
>Tnx-
>
>Graham ..
BEGINS
On 09/07/2007 at 18:30 James Moritz <[email protected]> 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
ENDS
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