Re: Strange spurious in 8568B
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Hi,
I have one question to the OP, you say that the spur is there with different input frequencies. But have you always checked with the input frequency at the center frequency of the spectrum analyser?? If so, try to move the input signal a bit up and down, without changing any settings on the SA, and see if the spur follows the input signal, or is locked to -10.7MHz compared to CF of the SA.
If it follows the input signal, the spur must be related to the input signal and the first LO. As there is no sweeping in the IF section, I can't see how a spur only could show up i a single part of the sweeping performed in the input stage, if the spur was in the IF.? Maybe not entirely correct, the spur can come from many places, but it have to reach the first mixer, to show up like that in a sweep...? At least in my mind it has to be.
Br, Askild?
On Fri, Feb 22, 2019 at 5:59 AM Chuck Harris < cfharris@...> wrote: Not really, that pretty much tells you that the spur
doesn't actually come from the input signal.
-Chuck Harris
amirb wrote:
> I think the first test rules out any contribution from the harmonics of input RF signal
> It is still surprising that when the input changes from -10dBm to +10dBm the spur remains at -64dBm
>
> On Thu, Feb 21, 2019 at 06:03 AM, dk1vi wrote:
>
>>
>> I have been asked to make some additional tests and here are my results:
>> *? ? Input frequency 1500MHz -> spurious is here as well at -10.7MHz
>> ~-63dB
>> *? ? Sweep trigger set to LINE -> no change
>> *? ? Looking for line spurs -> not visible
>> *? ? Spurious is at -73dB with -20dBm input signal and ATTN=0
>> *? ? Performing sweeps at different center frequencies and span as
>> proposed by Ed B. does not reveal any anomalities
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