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40438Re: [softrock40] Re: Si570 desoldering tips

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  • Mr Doug -
    Feb 3, 2010
      It might be a good idea to never connect theses boards to a high current supply and if you do make sure you have a fuse in the circuit.  1/4 A fast blow or less for the RX boards.

      If you put enough current through the toroid antenna coil primary to burn it open I am sure you would either see smoke or smell something. Even though it is relatively small wire it still would require a good deal of current to burn it open. I doubt a wall-wart would have enough current to do this. The antenna input is an isolated loop though and even if you had one side grounded the current applied would only go through that loop or to ground. 

      This is also a good reason to use back-to-back diodes across, and a lamp or fuse in series, with the antenna input.   

      From: Preston Douglas <pdouglas12@...>
      To: softrock40@yahoogroups.com
      Sent: Wed, February 3, 2010 6:23:08 PM
      Subject: Re: [softrock40] Re: Si570 desoldering tips


      Y'know, Barry, something you mentioned has been running around in my head (along with the squirrels!).  If the way you killed your 6.3 was by misconnecting the PA daughterboard so you shorted 12V to the amplifier board, you can't burn out chips that way.  They are isolated from the antenna inputs.  All you can do is burn out the secondary of the output transformer or the output inductor in the little RX filter.  I would check them and maybe rewind them.  Also check the traces on the little RX board for burn through.  Please do not ask me how I learned this.  Too embarrassing.  

      I agree that you should check the output of the LO.  There are two test points on your board where you can pick up the signal near the CMOS jumper.  You ought to be able to put a test wire on there and jumper it over to your antenna if you don't have a counter.  You should get all your signals as you change the switches.  

      Preston Douglas WJ2V

      -----Original Message-----
      From: g8voip <g8voi.reeves59@ tiscali.co. uk>
      To: softrock40@yahoogro ups.com
      Sent: Wed, Feb 3, 2010 5:58 pm
      Subject: [softrock40] Re: Si570 desoldering tips

      Hi Barry,

      An obvious question, but you are actually changing over and using the different RX filter and TX PA / filter modules when you are trying to receive on the higher frequency bands?

      To have good image rejection at the lower frequency suggests a problem with the phase splitter transformer on the RX filter module for the higher band.

      If you are listening for the LO on another receiver, remember the LO is running at 4 x the tuned frequency.

      To me it looks like you might have a combination of problems.

      You never did comment quite how you managed to destroy your v6.3 TX/RX in the first place. Knowing that might provide some clues to what has gone wrong, assuming that the board was completely working on all bands before the problem occurred.

      73, Bob G8VOI

      --- In softrock40@yahoogro ups.com, Barry Michels <bmichels@.. .> wrote:
      > g8voip wrote:
      > > Hi Barry,
      > >
      > > Looking at your Rocky screen grab, you have no image rejection at all. Although that would not explain your apparent tuning problem above 10MHz, there is something pretty fundamental wrong with your receiver or PC / soundcard set up / configuration.
      > >
      > > I think you need to go back to basics and determine what is actually still working on your PCB.
      > >
      > > A good place to start is to find out exactly what the Si570 LO is doing.
      > >
      > > Do you have a frequency counter available you could hook up on say U9 pin 3 (clock into the 74HC74. If you use Fred PE0FKO's 'CFGSR' program, you can use the 'Tune' tab and select 1MHz steps and easily tune from 1MHz up to 30MHz, and you should be able to measure the Si570 output which will be at 4x the 'VFO' frequency ( 4 - 120MHz). That will confirm whether or not your LO is functioning correctly.
      > >
      > > If that is ok, then you will need to go on to the divider stage and confirm the two outputs to the RX mixer are correct. Access to an oscilloscope would be useful to see what is happening.
      > >
      > > In effect, follow the original build / checkout procedure.
      > >
      > > 73, Bob G8VOI
      > >
      > >
      > When I get some more time, I will run thru the checkout procedures.
      > Below 10Mhz, I get very flat response (no hump in the middle, just a
      > thin spike) with great image rejection. The screenshots I posted only
      > look like that above 10Mhz (more like 10.2Mhz). Last time I checked, I
      > could hear the LO output on a nearby receiver even above 10Mhz. Will
      > try that again later.
      > The only oscilloscope I have access to is my 32Mhz digital scope that
      > isn't worth much other than working with digital signals. It's an old
      > PCS32 parallel port model from Velleman.
      > Thanks for the help!
      > Barry - KE4JUC

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