Minima build log #3 – Sorting the crystals

Read first! I am no longer building this transceiver. Please check other interesting projects from Farhan on the discussion group, like HF-1 Transceiver, the replacement of the Minima and some cool RF jigs, Specan and Sweeperino. Also, since I’ve lost from both server and my drive the Eagle files of the PCBs, they will be no more available. Minima has become discontinued, check the group for more details. I will still keep the pdf files here for download for anyone still interested in hacking the rig.

The Minima main board is starting to take good shape. These days I have soldered the crystals, test the BFO and added some other components to the PCB.

Minima HF Transceiver

Minima HF Transceiver – Progress so far

My 5$ – 100 pcs pack of crystals finally arrived from China, so I proceeded to sort 8 of them. For measuring I have used the BFO schematic from the Minima, built on the small test PCB, and an ordinary PIC frequency counter. Since the counter is not super calibrated I did some relative measurements, just to select eight pieces with the most appropriate values.

Minima HF Transceiver

Crystals sorted

Because of the laziness, I have only tested 50 pcs, but enough to choice the right ones. Very helpfully was using an Excel spreadsheet. I’ve marked the crystals with an unique number, and write down the frequency value associated with that number in Excel, and then auto-sorted. From all the list, the best 8 crystals interval was this one below, with 90 Hz difference between the 1st and 8th in order.

Minima HF Transceiver

Excel list with measured crystals

When adjusting the BFO, I have considered 19.995.500 as the center frequency of the crystal filter, so the two sides frequencies adjusted by the trim caps are 19.994 and 19.997.

Minima HF Transceiver

Minima 20MHz Crystal Filter

The Si570 finally arrived from SDR-Kits. Actually the second package. The first one was lost somewhere by the post service. They were very kind to send a replacement, just paying only the shipping fees. By this way, I would like to thank to them for this gesture.

Minima HF Transceiver

Si570 and Toroids

More or less, I have collected all the parts for the Minima. Hope to put it to work very soon. Still to wind the coils, program the Arduino and wiring between boards and switches-pots.

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15 Responses to Minima build log #3 – Sorting the crystals

  1. mvs sarma says:

    lovely way of marking the crystals once tested, Adrian. I had also bought KDS make, 20 numbers from local market. i was thinking of making a circuit, but why not use Minima board itself ? i need to check how lucky i would be !!
    all the best Adrian.

    • Adrian says:

      Yes, its a way this also. I wanted not to alter the board to much by soldering some sockets to quick plug and play the crystals, so I did a BFO separately and inserting the crystals into two of the 8-pin DIL ic socket.

  2. mvs sarma says:

    hi,MVS sarma here from India. i know it is meant for audio amplifier.
    can you see the way a circuit is worked in link below.
    the electroytic cap across the diodes is confusing me .
    please moad this way and try.

  3. mvs sarma says:

    especially see the computer audio amplifier

  4. Mike A says:

    Where did you source your toroids from? I need to get mine ordered.

  5. Hello Adrian,
    have been following your yotube videos and this one “Minima Test 2 Low audio – Changed 100R @Q16 with 22R” i did not hunderstand what conponent did you change because Q16 is a 2N3904

    • Adrian says:

      Hi Pedro, its about the 100R resistor at the emitter of Q16 that I changed with 22R. But no luck with this also.

      • I am trying to make a very small board to put in replace of the amp compnents whit the
        TDA2003 when i get it done ir tell you the results.


  6. Adrian says:

    Tnx Pedro. I assume you have the same low audio issue?

  7. Max Coltro says:

    Good morning Adrian,

    Have you more PCB available?
    cordially. Max. EA7FGJ.

  8. HP Joshi says:

    Please let us know the present status of your minima build

  9. Jan says:

    Hi !
    Were you successful with the project?
    The PCB’s are very nice, and inspires me, but the Link for the eagle files are corrupted.

    73 de JAn

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