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Re: [IRCA] SDR-14 quirks
At 12:07 6/20/2009, you wrote:
>After using the RFSpace SDR-14 for quite a while, I've noticed some odd
>behavior. First is a minimal thing. The spike for an AM carrier seems to
>drop slightly when the unit is tuned to that frequency. Drops by a couple
>of db. When there are two adjacent stations at the same signal strength,
>the one it's tuned to is always slightly lower.
Not noted here at first glance, Craig.
>The second issue is one of noise. At least in this installation, it's a
>problem that blocks out weaker stations. When it's tuned above 490 KHz
>there is a wide noise level that covers hundreds of KHz.
>http://www.am-dx.com/Graphics/490.gif
>
>When I tune below 490 KHz it goes away. It does this consistently like an
>on-off switch.
>http://www.am-dx.com/Graphics/480.gif
>
>I thought there was a gain change, but that doesn't appear to be.
This isn't noted either. What are your gain settings (RF and IF)? I'm wondering if whatever you have on 540 is starting to overdrive some part of the receiver, probably the IF....try decreasing IF gain and see if it is still a problem. Your display is the receiver bandwidth, and a strong signal there can overdrive the receiver.
> I noticed
>a spur at 505 KHz that is at the same -90 level in both pictures. This is
>consistent across several antennas, including one outside on the tower.
>Anyone else notice this?
I've seen this, but not on the one that I have here; I thought I had a poorly filtered switching power supply somewhere in the circuitry accompanying the SDR14, but now I'd better look more carefully.
best wishes,
Nick
*****************************
Nick Hall-Patch
Victoria, BC
Canada
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