[DSP-10] heat problem?

[Rajiv Dewan, N2RD]

I just finished assembling the DSP-10 unit.  It is in its box with the
DSP unit in its box lying beside the dsp-10 box.  I have finished the
serial and PLL tuning and that went fine.  I get a lock from 143 to
148.2 and I am happy with that.

As I listen with my unit, I note that when I start it from cold with a
50ohm resistor at anenna input, the noise floor is often better
than -144dbm.  This however, begins to deteriorate in short order, at
the rate of about a db a minute till the unit ends up at -133dbm with
lots of audible noise from the speaker.  This is when I feed the unit
with 13.8V.  Even with 11v input, the noise floor does begin to
deteriorate, albeit at a slower rate.  A fan helps but does not solve
the problem.  I felt around and the hottest components are those
around U8 and U9.  They are hot to touch but not uncomfortably so.  My
guess is that they are around 110 to 120F.

Looking at the waterfal display (with brightness 65 and contrast 15),
it starts out with just a few dots every 5kcs, and soon it forms a
series of lines every five kc's or so.  The lines get thicker as time
passes, and in about 4 to 6 minutes, the lines all merge into solid
color.  I am attaching a jpeg image of the waterfall display.
It might be stripped by the list.  If you send me an email, I will
mail you a copy.

As an aside, I noted that the unit is 8.8kcs too high.  I am using the
TAPR supplied Epson crystal, and I haven't padded it with 10pf
capacitors yet.  I want to deal with the noise floor issue first.

Any help appreciated.

- -
Rajiv Dewan, N2RD
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