[minima] Re: Fwd: Finally getting around to building my Minima...

  • From: DD4WH <dd4wh.swl@xxxxxxxxx>
  • To: minima@xxxxxxxxxxxxx
  • Date: Sun, 2 Apr 2017 17:23:54 +0200

I also built the Minima some years ago in a receive-only version (with the KISS mixer) as my first serious homebrew project.

The Minima receiver was awesome with very nice sound! Sensitivity was a bit compromised, but that was in comparison with a commercial direct sampling SDR and only became apparent at my remote site where there is much less man-made-noise (at home the antenna noise was always much higher than the internal noise of the Minima).

I still use the discrete audio amp circuit of the original Minima in my homebrew SDRs, because the noise is so low.

Also, I believe that LO phase noise problems are overrated in homebrewing, as we can experience when we use the Si5351 which has higher phase noise that the Si570, but nonetheless gives very nice performance (however I use it in IQ-SDRs where the phase noise is divided by 4 by the QSD).

Have fun, 73 de Frank DD4WH


Am 02.04.2017 um 11:23 schrieb Ashhar Farhan:

As receivers go, the minima receiver with the kiss mixer is the best receiver i have ever. the audio is sparkling with so little gain in the rf path. it is only in the transmit side that we have these problems.

A VCO running at 10 MHz might drip about 600 Hz in a minute, for simplicity's sake. That is about 10 Hz per second. This is easily fixed by the slow (and simple) huff and puff. A VCO at 20 MHz might drift over 2 2 KHz per minute, that is more than 30 Hz per second. This too can be fixed if the HnP sampling rate is increased to 50 Hz. the lock points are spaced out over 50 Hz, it will still be stable enough for PSK31, though not for any of the JT modes.

- f

On Sun, Apr 2, 2017 at 12:34 PM, Will Kimber <zl1tao@xxxxxxx <mailto:zl1tao@xxxxxxx>> wrote:

    Ashhar or anybody else that has tried it,


    Is the KISS mixer in the minima suitable for receive only. I'm
    looking at G.C. Rx only?

    Would the KISS mixer be O.K for use with the uBitx, again G.C. Rx
    only?

    Cheers,

    Will


    On 03/31/2017 07:54 PM, Ashhar Farhan wrote:
    It is trivial to move the IF of the uBitx to 55 Mhz. Just a turn
    of two off and we will be in business.


    About the Minima, there are two ways to get rid of the local
    oscillator spur.
    1. replace the kiss mixer with the regular H mode mixer. It takes
    two transformers and an FST3253. The local oscillator will be low
    enough that it gets stripped out.
    2. The local oscillator goes from 22 Mhz to 34 MHz when minima
    tunes from 2 MHz to 14 MHz. Between 14 Mhz and 30 MHz, instead of
    the low pass filter, use a doubly tuned band-pass filter with 365
    pf gang.

    There is another better, but of course, more elaborate scheme
    that you can try it. It is as follows:
    1. Move the IF to 12 MHz. Use band pass filters above 7 MHz for
    every band. This will give you a contest grade rig. Add linrad in
    the backend.

    - f

    On Fri, Mar 31, 2017 at 9:39 AM, Robert Toegel
    <rjtoegel@xxxxxxxxx <mailto:rjtoegel@xxxxxxxxx>> wrote:

        That's where I was playing with putting a crystal across the
        output of the mixer to ground so the series resonance would
        "suck out" the local oscillator leakage.  I noticed this
        years ago when I put a crystal across the antenna input of a
        receiver just to see what would happen and a station at that
        frequency nearly disappeared.  Pardon the pun but I had mixed
        results so far.

        Bob WA2EGP

        On Thu, Mar 30, 2017 at 1:46 PM Jerry Gaffke
        <dmarc-noreply@xxxxxxxxxxxxx
        <mailto:dmarc-noreply@xxxxxxxxxxxxx>> wrote:

            If anybody's thinking about building the uBitx, check
            this thread: https://groups.io/g/BITX20/message/23261
            <https://groups.io/g/BITX20/message/23261>
            Not a big hit, and I'm not aware of any other issues
            being reported yet.

            I previously said this about the old minima:  "can have
            trouble with clean transmissions due to mixer products."
            As Farhan reports on
            http://www.phonestack.com/farhan/ubitx/ubitx.html
            <http://www.phonestack.com/farhan/ubitx/ubitx.html>
            the issue is actually one of leakage through the KISS
            mixer of the local oscillator.

            Jerry, KE7ER


            --------------------------------------------
            On Wed, 3/29/17, Jerry Gaffke <jgaffke@xxxxxxxxx
            <mailto:jgaffke@xxxxxxxxx>> wrote:

             Subject: Re: [minima] Fwd: Finally getting around to
            building my Minima...
             To: minima@xxxxxxxxxxxxx <mailto:minima@xxxxxxxxxxxxx>
             Date: Wednesday, March 29, 2017, 8:16 PM

             Most of the discussion is happening
             now at https://groups.io/g/BITX20
            <https://groups.io/g/BITX20>

             Minima can work, but has a few issues regarding how
             reproducible that front end filter is, also can have trouble
             with clean transmissions due to mixer products.
             Ashhar moved on to a double conversion scheme with the
             HF_1: //www.freelists.org/post/minima/Updated-HF1
            <//www.freelists.org/post/minima/Updated-HF1> in Feb
             of 2016.
             This summer he started shipping a stuffed board along the
             lines of the original Bitx design for $59: hfsigs.com
            <http://hfsigs.com>
             And now he has described the uBitx, which is an improved
             HF_1: http://www.phonestack.com/farhan/ubitx/ubitx.html
            <http://www.phonestack.com/farhan/ubitx/ubitx.html>

             If I were scratch building today, I'd look first at the
             uBitx
             The uBitx may (or may not) eventually come out as a built
             board from hfsigs.com <http://hfsigs.com>

             Jerry, KE7ER


             --------------------------------------------
             On Wed, 3/29/17, Mark Pilant <mark@xxxxxxxxx
            <mailto:mark@xxxxxxxxx>>
             wrote:

              Subject: [minima] Fwd: Finally getting around to building
             my Minima...
              To: "minima@xxxxxxxxxxxxx <mailto:minima@xxxxxxxxxxxxx>"
             <minima@xxxxxxxxxxxxx <mailto:minima@xxxxxxxxxxxxx>>
              Date: Wednesday, March 29, 2017, 5:42 PM

              Well, it seems to be quiet around
              here.. :-)






--
---------------
Frank - DD4WH
RX: Teensy Convolution SDR - Selbstbau
https://github.com/DD4WH/Teensy-ConvolutionSDR
ANT: AAA-1 Doppelloop-Antenne

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