40435Re: [softrock40] Re: Si570 desoldering tips
- Feb 3, 2010g8voip wrote:
> Hi Barry,When I get some more time, I will run thru the checkout procedures.
> 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
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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