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mixer downconversion - query - RF Cafe Forums
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| balajisu
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Post subject: mixer downconversion - query
Posted: Sun Oct 09, 2005 7:08 pm
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| Colonel |
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Joined: Wed Jul 06, 2005
5:54 pm
Posts: 28
Location: Germantown,MD
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Hi guys
I'm trying to downconvert the frequency
range : 800MHz to 840MHz to
100Hz to 40MHz with
LO being set at 799.9999MHz.
The mixer that
i'm using is ZEM-4300 minicircuits.
I swept
the RF signal and tried to study the IF signal.
The reading tells me that the IF ZERO has
shifted to 1.1KHz.
As i reduce RF from 840MHz
towards 800MHz with LO maintained constant , IF
frequency reduces respectively from 40MHz towards
100Hz.
With RF at 800.001MHz i expect to
see a 1KHz signal but i see a signal that is closer
to 60Hz(or DC). When i reduce RF beyond this the
IF starts to increase. i.e When RF = 800MHz i expect
to see a 100Hz signal but instead i see 1.1KHz signal.
The signals were observed using a Agilent Spectrum
Analyser and Dynamic Signal Analyser.
This
data tells me that the Zero of the IF spectrum has
shifted to 1/1.1KHz. Can anyone tell me what could
be the issue in this regard.
The power level
of the IF signal has been constant throughout the
spectrum.
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LRS |
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Post subject:
Posted: Mon Oct 10, 2005 9:17 am
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Do you have the RF and LO sources locked to the
same reference? If not, that alone cann create the
discrepency.
The 60 Hz you see has got to
be from a poor AC line ground or a strong AC field
in the vicinity of your DUT.
Hope that helps.
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balajisu |
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Post subject:
Posted: Mon Oct 10, 2005 12:35 pm
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| Colonel |
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Joined: Wed Jul 06, 2005
5:54 pm
Posts: 28
Location: Germantown,MD
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The RF source, LO source and the Spectrum Analyser
were locked to a common reference signal.
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LRS |
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Post subject:
Posted: Mon Oct 10, 2005 2:39 pm
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Have you tried making the measurement at a different
set of frequencies that don't use your currect frequency
settings? I'd try moving the LO to to a new frequency
that does not use any of your current numbers, then
make the measurement. That would tell you if the
signal generator is screwing up and outputting a
frequency other than that you tell it to. Have you
verified the LO and RF sig gens are actually putting
out the exact frequencies you are programming it
for? That 1 kHZ step sounds like a sig gen problem.
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balajisu |
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Post subject:
Posted: Mon Oct 10, 2005 2:57 pm
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| Colonel |
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Joined: Wed Jul 06, 2005
5:54 pm
Posts: 28
Location: Germantown,MD
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hey my initial settings were RF- 600-640MHz and
LO at 599.9999MHz. I have tried at various frequency
ranges too but seeing the same result.
Did
the check the signal generated from the two sources
they provide the right frequency content.
I thought the Spectrum Analyser might not be
too sensitive if we try to measure signals near
DC so went to OSCOPE measurements to see whether
i'm seeing the right frequency but the OSCOPE measurements
revealed the same.
I'm left clueless of
what is happening in this circuitry.
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Posted 11/12/2012
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