[hpsdr] Fwd: Re: HPSDR Signal Overload ( In the digital processing???) (Update)

[ct1izu]

Phil and All

I can confirm that the NB does indeed cause the effect described. I had 
prevoisly turned off the blaker when close to a heavy hitter and
only dicovered the cure last weekend  when playing with the threshold in set 
up. Its good to see a proper explanation and some info on a correct set up.

Merc is a very robust front end even feed with big Rhombics Long wire 
Echelons. As I have commented before ADC overload only happens at Grey Line 
time
 and is simlply cured by a HP filter set.
Shel CT1IZU



----- Original Message ----- 
From: "Phil Harman" <phil at pharman.org>
To: "Mike F" <mikecf100 at gmail.com>
Cc: <hpsdr at lists.openhpsdr.org>
Sent: Thursday, April 07, 2011 6:08 AM
Subject: Re: [hpsdr] Fwd: Re: HPSDR Signal Overload ( In the digital 
processing???) (Update)


> ***** High Performance Software Defined Radio Discussion List *****
>
> Hi Mike,
>
> Ah Ha.... Having looked more closely at your second screen shot I'm sure I
> know what the problem is.
>
> If you look in the waterfall at the signal at 14.195MHz you see the noise
> floor increases when this signal is present - and its a big signal.
>
> You also have both noise blankers on.  The first noise blanker actually
> sets the I&Q signals to zero once the user set signal threshold has been
> passed. If the threshold is set too low this creates massive IMD and
> raises the noise floor.
>
> Try turning the noise blanker off and/or set the threshold higher on the
> Setup screen.  I normally set the first noise blanker high enough that IMD
> is not present and then adjust the second blanker to take out the balance
> of the noise.
>
> I trust that solves the mystery.
>
> 73 Phil...VK6APH
>
>
>
>
>
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