[hpsdr] ADC overload problems.

[Greg - ZL3IX]

Hi Jeff,

One of the group suggested that you try using Kiss Console to look for 
large signals, which is a good idea.  Another way of doing this would be 
to connect your antenna directly to the input of an oscilloscope.  If 
there's enough signal to cause ADC overload, there will be enough to see 
on a scope trace, if you have the sensitivity set to 100 mV per div, or 
so.  If you see anything of that sort of amplitude, try and get an idea 
of the frequency, and then look again using PowerSDR.

73, Greg, ZL3IX


On 2012-10-15 08:27 a.m., Jeff Cook wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
> I raised this point a few weeks back and received various suggestions 
> on how to solve my problem; unfortunately I have got absolutely 
> nowhere.  Rather than go back over old ground, I'd like to approach 
> this from the receive point of view, perhaps if I can crack this then 
> the transmit problem may also be solved.
>
> I use an octagonal magnetic loop made from 28 mm copper pipe, tuned by 
> a 50 pF vacuum capacitor, it works surprisingly well on 20 through to 
> 10 m.  I also use a long wire (20 m in length) fed at its far end via 
> an automatic ATU, this for use on 160 through to 30 m. If I attempt to 
> use the long wire on any of the amateur bands at all with PowerSDR's 
> preamp on (or more accurately its attenuator switch in the off 
> position) then I get the flashing red/yellow ADC overload warning, and 
> I'm talking receive only here.  Given that ADC overload occurs only at 
> -12 dB's (preamp on), and at +8 dB's (preamp off), and given that I'm 
> nowhere near any high power transmitting equipment, I'm at a loss to 
> know why this should be happening.  Now I realise that this can be 
> misleading but looking at signals and noise levels as displayed in the 
> pan adapter, I have a typical noise level of around -100 dB's and 
> rarely do I see a signal topping -50 dB's.
>
> Given the ADC problems that I've got in receive it's little wonder 
> that in transmit I have to limit myself to little more than QRP levels.
>
> Is it plausible that I'm receiving a false ADC overload warning?
>
> Jeff Cook, G0AFQ.
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