[hpsdr] hardware question ( Mercury HPSDR)

[Scott Cowling]

Hi Gedas,

The ADC is an LTC2208CUP, 0-70C part.

Thermally it is probably better to glue the heatsink to the bottom of 
the PCB. Mechanically it is easier to glue it to the top of the IC on 
the front of the PCB. Either way will work well to reduce the 
temperature of the ADC.

The chip normally runs hot, but the surface of the chip will be over 
80C before the 125C junction temperature is exceeded. That is way 
hotter than you could even touch with your finger.

I have never heard of a hot ADC causing a blue screen on the PC. It 
generally just causes the noise floor to increase and a general 
degradation of receiver performance and appearance of spurs.  We saw 
this on one of the prototypes before we had adequate heat sinking in the PCB.

Did you bypass the F2 and F3 thermal fuses on the LPU, per LPU errata 
#2? That might cause your problem, since it removes the 5V power from 
the boards at a random time.

Here is the link to the LPU errata:
http://openhpsdr.org/support/LPU/LPU_Errata_V2_2.pdf

73 es GL,
Scotty WA2DFI


At 08:34 PM 7/11/2010 -0400, Gediminas Kasparaitis wrote:
>***** High Performance Software Defined Radio Discussion List *****
>
>Hello,
>
>I tested  my Mercury during IARU HF, put into log  135 QSO ( didn't 
>use any other receiver).
>
>The question is about LCT2208, is this 70C or wider range 85C chip ?
>
>Is here any recomended heatsink for this chip? And if it is where is 
>better to glue it,
>from the top ( on top of the chip)  or from the bottom of the board ?
>
>I could use extra fan too....
>
>I believe that was a cause of 3 laptop crashes ( blue screen with numbers),
>since to get laptop to work I had to unplug power connector from SDR.
>Chip was hot, I was unable to keep finger on it ( day was hot also).
>5V regulator is cold, but it seems in this my setup is not enough 
>air flow to cool
>LTC2208.
>
>
>After that it worked again  .....at the time of crash  I was using 
>CW skimmer and band
>was full of loud stations.
>
>I hope other should be familiar with similar situation, or my board is bit
>deffective ?
>
>But after that I used Mercury HPSDR with no problems for few hours.
>
>Nice thing, I like it:
>http://www.qsl.net/ly2bgp/index4.html
>
>73, Gedas, nx2px
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