[hpsdr] ADC Overload (again)

Phil Harman phil at pharman.org
Sun Aug 2 00:45:14 PDT 2009

Hi Richard,

No need to be concerned. The ADC Overload indicator just lets you know that 
you are most likely going to see spurious signals in the bandscope.  In fact 
the ADC appears to overload quite gracefully, you can run well into the 
overload region without too many adverse effects.

With a reasonable antenna you should not need the preamp on  below 17m - in 
fact with my HF beam I don't use a preamp until 15m.

I'm fortunate to have a prototype Alex board so can use that if I have 
problems with broadcast stations causing overload.  Mostly the natural 
selectivity of my antenna and ATU etc is sufficient to  eliminate out of 
band signals.

You may want to try  KK and look on the wideband bandscope to see what 
signal(s) is causing the overload.  If it's a local broadcast station then a 
simple HPF will most likely do the trick.

The front end of Mercury does have overload protection which we know does 
work - one of our users accidentally transmitted into the Mercury input 
connector and the protection network saved the day!

73's Phil...VK6APH

----- Original Message ----- 
From: "Richard Ames" <richard at ames.id.au>
To: "HPSDR list" <hpsdr at lists.openhpsdr.org>
Sent: Sunday, August 02, 2009 3:20 PM
Subject: [hpsdr] ADC Overload (again)

> ***** High Performance Software Defined Radio Discussion List *****
> Phil -
> In this message:
> http://lists.openhpsdr.org/htdig.cgi/hpsdr-openhpsdr.org/2009-January/007932.html
> You said "you may see smoke from the preamp" when the ADC Overload is
> flashing.  Here in Sydney I occasionally see it flashing when the
> attenuator is out of the circuit ('Preamp on'). I suspect this is due to
> generally high noise level + broadcast transmitters about 10kms away.
> This afternoon with 80m having S9 noise - it was on all the time.
> How concerned should I be???  I often need the 'preamp on' in the
> amateur bands.....
> Regards, Richard.
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