[minima] Re: My Minima is Alive and well

  • From: Mark G0MGX <mark.g0mgx@xxxxxxxxx>
  • To: minima@xxxxxxxxxxxxx
  • Date: Thu, 30 Jan 2014 18:04:08 +0000

It's the LO.
When the TX is tuned to 18MHz, the LO is at 38MHz. There is not enough attenuation in the 30MHz cut off LPF. 

M


On 30/01/2014 18:02, Mvs Sarma wrote:
while a trap helps for a while , perhaps we need to analyze the source of this frequency !
On Thu, Jan 30, 2014 at 11:26 PM, Mark G0MGX <mark.g0mgx@xxxxxxxxx <mailto:mark.g0mgx@xxxxxxxxx>> wrote: 

    .... which would... look something like the attached. Yellow is
    the current 30M LPF and purple is my new with one 38M trap.

    M



    On 30/01/2014 17:39, Mark G0MGX wrote:

    ....or.... could we keep two traps at 20MHz and move the third up
    to 38MHz? or even add a fourth trap for the LO at 38MHz?

    Mark
    G0MGX


    On 30/01/2014 17:21, Mark G0MGX wrote:

    I just remade my 15M LPF and have a much flatter response and
    sharper roll off; I will try something similar with the 30M and
    see what the result is. We can rely on the traps to remove the
    20MHz signal I would think.

    Mark

    On 30/01/2014 16:37, Ashhar Farhan wrote:

    Mark, the 18 mhz  is, as i suspected, a problem. one possible
    resolution is to increase the 1st lpf to corner around 20 mhz.
    then, we can use a 20 mhz lpf upto 18 mhz and the second lpf
    from 21 mhz onwards.
    however, this  problem is not very significant as the LPFs in
    the following stages may bury the 38 Mhz signal. There will,
    however, be a different nasty : the 38 mhz will intermodulate
    with the 18 mhz to create 20 mhz! you can see that blip in the
    18 mhz scan.
    - f


    On Thu, Jan 30, 2014 at 10:00 PM, Mark G0MGX
    <mark.g0mgx@xxxxxxxxx <mailto:mark.g0mgx@xxxxxxxxx>> wrote:

        Here's a rather nasty looking sweep of the 30M LPF with
        everything in the box - not the same as when it was on the
        bench!

        I have some work to do!

        Mark



        On 30/01/2014 16:28, John Greusel wrote:

        The Softrocks use a SI570 divided by 4 and you can easily
        sniff our the LO with a portable radio.



        ------------------------------------------------------------------------
        *From:* Mark G0MGX <mark.g0mgx@xxxxxxxxx>
        <mailto:mark.g0mgx@xxxxxxxxx>
        *To:* minima@xxxxxxxxxxxxx <mailto:minima@xxxxxxxxxxxxx>
        *Sent:* Thursday, January 30, 2014 10:17 AM
        *Subject:* [minima] Re: My Minima is Alive and well

        Here are some outputs as promised; it is definitely the
        30MHz LPF in circuit above 15MHz,  but I am surprised by
        the amplitude of the LO even when it is as high as 49MHz.

        I will check, check, check!

        Mark




        On 30/01/2014 16:05, Ashhar Farhan wrote:

        mark,
        note that the audio is 'hissier' than a usual
        transceiver, this is due to larger bandwidth. you could
        try a 0.1 across the two ends of the volume control to
        reduce the bandwidth.

        - farhan


        On Thu, Jan 30, 2014 at 5:44 PM, Mark G0MGX
        <mark.g0mgx@xxxxxxxxx <mailto:mark.g0mgx@xxxxxxxxx>> wrote:

            I'm very pleased with how it sounds; can't wait for
            the 1st QSO!

            I've just done some experiments this morning with a
            new design/replacement for the 15MHz LPF, which I
            can't get quite right as Farhan designed:

            http://g0mgx.blogspot.co.uk/2014/01/minima-remaking-15mhz-lpf.html

            I'll do the sweep requested later today as I move
            onto TX testing...

            Mark
            G0MGX


            On 30/01/2014 10:33, jerry@xxxxxxxxxxxxxxxx
            <mailto:jerry@xxxxxxxxxxxxxxxx> wrote:

                Good job Mark, the audio sounds great.I can't
                wait to finish mine. Jerry
                K5LRU


                -------- Original Message --------
                Subject: [minima] Re: My Minima is Alive and well
                From: "Steve VK2SJA" <vk2sja@xxxxxxxxxxx
                <mailto:vk2sja@xxxxxxxxxxx>>
                Date: Thu, January 30, 2014 4:13 am
                To: minima@xxxxxxxxxxxxx
                <mailto:minima@xxxxxxxxxxxxx>

                Way to go Mark!

                I knew you'd finish before I even turned on the
                iron!!

                Good audio on the video. Thanks for posting.

                73, Steve.



                    Morning Team

                    An update from me, RX demo video here:

                    
http://g0mgx.blogspot.co.uk/2014/01/my-minima-is-alive-and-well.html

                    the RX sounds great!

                    Mark
                    G0MGX





















--
Regards
Sarma

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