Convert RF signal to baseband signal
RF Blockset / Circuit Envelope / Systems
The IQ Demodulator
converts an RF signal
to baseband signal. I
stands for the inphase component
of the signal and Q
stands for the quadrature phase
component of the signal. You can use the IQ Demodulator to
design direct conversion receivers.
The IQ Demodulator block mask icons are dynamic and indicate the current state of the applied noise parameter. For more information, see IQ Demodulator Icons.
Source of conversion gain
— Source parameter of conversion gainAvailable power gain
(default)  Open circuit voltage gain
 Polynomial coefficients
Source parameter of conversion gain, specified as one of the following:
Available power gain
—
Relates the ratio of the power of a single sideband (SSB) of
the output I
branch to the input power.
If there is no gain mismatch, the gain at the
Q
branch matches the gain at the
I
branch.
Open circuit voltage gain
— Value of the open circuit voltage gain parameter as
the linear voltage gain term of the polynomial voltage
controlled voltagesource (VCVS).
Polynomial coefficients
— Implements a nonlinear voltage gain according to
the polynomial you specify.
Available power gain
— Ratio of power of SSB at output I
branch to input power0 dB
(default)  scalar in dB or a unitless ratioRatio of power of SSB at output I
branch to input
power, specified as a scalar in dB or a unitless ratio. For a unitless
ratio, select None
.
To enable this parameter, set Source of conversion
gain to Available power
gain
.
Open circuit voltage gain
— Open circuit voltage gain0 dB
(default)  scalar Open circuit voltage gain, specified as a scalar in dB.
To enable this parameter, set Source of conversion
gain to Open circuit voltage
gain
.
Polynomial coefficients
— Coefficients of polynomial specifying voltage gain[0 1]
(default)  vectorPolynomial coefficients, specified as a vector.
The order of the polynomial must be less than or equal to 9. The
coefficients must be ordered in ascending powers. If a vector has 10
coefficients,
[
,
the polynomial it represents is:a
_{0},a
_{1},a
_{2},
... a
_{9}]
V_{out} = a_{0} + a_{1}V_{in} + a_{2}V_{in}^{2} + ...
+ a_{9}V_{in}^{9}
a_{1}
represents the linear gain term, and higherorder terms are modeled
according to [2].
For example, the vector
[
specifies the relation V_{out} = a_{0} + a_{1}V_{1} + a_{2}V_{1}^{2} + a_{3}V_{1}^{3}. Trailing zeros are omitted. So
a
_{0},a
_{1},a
_{2},a
_{3}][
defines the same polynomial as
a
_{0},a
_{1},a
_{2}][
.a
_{0},a
_{1},a
_{2},
0]
By default, the value is [0,1]
, corresponding to
the linear relation V_{out} =
V_{in}.
To enable this parameter, set Source of conversion
gain to Polynomial
coefficients
.
Local oscillator frequency
— Local oscillator (LO) frequency0
Hz
(default)  scalar Local oscillator (LO) frequency, specified as a scalar in
Hz
, kHz
,
MHz
, or GHz
.
Input impedance (Ohm)
— Input impedance of IQ demodulator50
(default)  scalar Input impedance of IQ demodulator, specified as a scalar in Ohms.
Output impedance (Ohm)
— Output impedance of IQ demodulator50
(default)  scalar Output impedance of IQ demodulator, specified as a scalar in Ohms.
Add Image Reject filter
— Image reject (IR) filter parametersoff
(default)  on
Select to add the IR filter parameter tab. Clear to remove the tab.
Add Channel Select filters
— Channel select (CS) filter parametersoff
(default)  on
Select to add the CS filter parameter tab. Clear to remove the tab.
Ground and hide negative terminals
— Ground and hide circuit terminalson
(default)  off
Select to internally ground and hide the negative terminals. Clear to expose the negative terminals. When the terminals are exposed, you can connect them to other parts of your model.
Edit System
— Break IQ demodulator block links and replace internal variables by appropriate valuesUse this button to break IQ modulator links to the library. The internal variables are replaced by their values which are estimated using IQ modulator parameters. The IQ Modulator becomes a simple subsystem masked only to keep the icon.
Use Edit System to edit the internal variables without expanding the subsystem. Use Expand System to expand the subsystem in the Simulink™ canvas and to edit the subsystem.
I/Q gain mismatch
— Gain difference between I
and Q
branches0
dB
(default)  scalarGain difference between I
and Q
branches, specified as a scalar in dB. Gain mismatch is assumed to be
forwardgoing, that is, the mismatch does not affect leakage from LO to
RF.
If the gain mismatch is specified, the value $$\left(Available\text{\hspace{0.05em}}\text{\hspace{0.17em}}power\text{\hspace{0.17em}}gain+I/Q\text{\hspace{0.17em}}gain\text{\hspace{0.17em}}mismatch\right)$$ relates the ratio of power of the singlesideband
(SSB) at output the Q
branch to the input
power.
I/Q phase mismatch
— Phase difference between I
and Q
branches0
degrees
(default)  scalar in degrees or radiansPhase difference between I
and Q
branches, specified as a scalar in degrees or radians. The phase
mismatch affects the LO to input RF leakage.
LO to RF isolation
— Ratio of magnitude between LO voltage to leaked RF voltageinf dB
(default)  scalarRatio of magnitude between LO voltage to leaked RF voltage, specified
as a scalar in dB. Phase accumulation in the path from LO input to the
internal I
and Q
mixers (after
phase shift and phase mismatch) and then to the RF is assumed to be
zero.
Noise figure (dB)
— Signaltonoise ratio (SNR) between outputs and input 0
(default)  scalarSinglesideband noise figure of mixer, specified as a scalar.
To model noise in circuit envelope model with a Noise, Amplifier, or Mixer, IQ Demodulator block, you must select the Simulate noise check box in the Configuration block dialog box.
The following table summarizes the two competing definitions for specifying SSB noise, where the image frequency (IM) is defined as ω_{IM} = ω_{LO} + (ω_{LO} – ω_{RF}).
Noise Convention  Signal at RF Frequency  Signal at IM Frequency  IQ Demodulator Block Supports This Model? 

Singlesideband noise (SSB)  S + N, signal with noise  N, noise only  Yes 
IEEE definition of singlesideband noise (SSB_{IEEE})  S + N, signal with noise  No signal  No; you can create an equivalent model using an ideal filter created from an Sparameters block. 
Add phase noise
— Add phase noiseoff
(default)  on
Select this parameter to add phase noise to your IQ demodulator system.
Phase noise frequency offset (Hz)
— Phase noise frequency offset1
(default)  scalar  vector  matrixPhase noise frequency offset, specified as a scalar, vector, or matrix with each element unit in Hz.
If you specify a matrix, each column corresponds to a nonDC carrier frequency of the CW source. The frequency offset values bind the envelope bandwidth of the simulation. For more information, see Configuration.
To enable this parameter, select Add phase noise.
Phase noise level (dBc/Hz)
— Phase noise levelInf
(default)  scalar  vector  matrixPhase noise level, specified as a scalar, vector, or matrix with element unit in decibel per dBc/Hz.
If you specify a matrix, each column corresponds to a nonDC carrier frequency of the CW source. The frequency offset values bind the envelope bandwidth of the simulation. For more information, see Configuration.
To enable this parameter, select Add phase noise.
Automatically estimate impulse response duration
— Automatically estimate impulse response durationon
(default)  off
Select to automatically estimate impulse response for phase noise. Clear to specify the impulse response duration using Impulse response duration.
Impulse response duration
— Impulse response duration1e10
s
(default)  scalarImpulse response duration used to simulate phase noise, specified as a scalar in s, ms, us, or ns.
Note
The phase noise profile resolution in frequency is limited by the duration of the impulse response used to simulate it. Increase this duration to improve the accuracy of the phase noise profile. A warning message appears if the phase noise frequency offset resolution is too high for a given impulse response duration. This message also specifies the minimum duration suitable for the required resolution.
To set this parameter, clear Automatically estimate impulse response duration.
Selecting Polynomial coefficients
for
Source of conversion gain in the
Main tab removes the
Nonlinearity parameters.
Nonlinear polynomial type
— Polynomial nonlinearityEven and odd order
(default)  Odd order
Polynomial nonlinearity, specified as one of the following:
Even and odd order
: The IQ
Demodulator can produce secondorder and thirdorder
intermodulation frequencies, in addition to a linear term.
Odd order
: The IQ
Demodulator generates only "odd order"
intermodulation frequencies.
The linear gain determines the linear a_{1} term. The block calculates the remaining terms from the values specified in IP3, 1dB gain compression power, Output saturation power, and Gain compression at saturation. The number of constraints you specify determines the order of the model. The figure shows the graphical definition of the nonlinear IQ demodulator parameters.
Intercept points convention
— Intercept points conventionInput
(default)  Output
Intercept points convention, specified as
Input
(inputreferred) or
Output
(outputreferred). Use this
specification for the intercept points IP2,
IP3, the 1dB gain compression
power, and the Output saturation
power.
IP2
— Secondorder intercept pointinf
dBm
(default)  scalar Secondorder intercept point, specified as a scalar in dBm, W, mW, or
dBW. The default value
inf
dBm
corresponds to an unspecified point.
To enable this parameter, set Nonlinear polynomial
type to Even and odd
order
.
IP3
— Thirdorder intercept pointinf
dBm
(default)  scalar Thirdorder intercept point, specified as a scalar in dBm, W, mW, or
dBW. The default value
inf
dBm
corresponds to an unspecified point.
To enable this parameter, set Nonlinear polynomial
type to Even and odd
order
.
1dB gain compression power
— 1dB gain compression powerinf
dBm
(default)  scalar1dB gain compression power, specified as a scalar in dBm, W, mW, or dBW. The 1dB gain compression point must be less than the output saturation power.
To enable this parameter, set Odd order
in Nonlinear polynomial type tab.
Output saturation power
— Output saturation powerinf
dBm
(default)  scalarOutput saturation power, specified as a scalar. The block uses this value to calculate the voltage saturation point used in the nonlinear model. In this case, the first derivative of the polynomial is zero, and the second derivative is negative.
To enable this parameter, set Odd order
in Nonlinear polynomial type tab.
Gain compression at saturation
— Gain compression at saturationinf
dBm
(default)  scalarGain compression at saturation, specified as a scalar.
To enable this parameter, first select Odd
order
in Nonlinear polynomial
type tab. Then change the default value of
Output saturation power.
Select Add Image Reject filter in the Main tab to see the IR Filter parameters tab.
Design method
— Simulation typeIdeal
(default)  Butterworth
 Chebyshev
Simulation type. Simulates an ideal, Butterworth, or Chebyshev filter of the type specified in Filter type and the model specified in Implementation.
Filter type
— Filter typeLowpass
(default)  Highpass
 Bandpass
 Bandstop
Filter. Simulates a lowpass, highpass, bandpass, or bandstop filter type of the design specified in Design method
Implementation
— ImplementationLC Tee
 LC Pi
 Transfer function
 Constant per carrier
 Frequency Domain
Implementation, specified as one of the following:
LC Tee
: Model an analog filter with
an LC lumped Tee structure when the Design
method is Butterworth or Chebyshev.
LC Pi
: Model an analog filter with
an LC lumped Pi structure when the Design
method is Butterworth or Chebyshev.
Transfer Function
: Model an analog
filter using twoport Sparameters when the Design
method is Butterworth or Chebyshev.
Constant per carrier
: Model a
filter with either full transmission or full reflection set as
constant throughout the entire envelope band around each
carrier. The Design method is specified as
ideal.
Filter Domain
: Model a filter using
convolution with an impulse response. The Design
method is specified as ideal. The impulse
response is computed independently for each carrier frequency to
capture the ideal filtering response. When a transition between
full transmission and full reflection of the ideal filter occurs
within the envelope band around a carrier, the frequencydomain
implementation captures this transition correctly up to a
frequency resolution specified in Impulse response
duration.
Note
Due to causality, a delay of half the impulse response duration is included for both reflected and transmitted signals. This delay impairs the filter performance when the Source and Load resistances differ from the values specified in filter parameters.
By default, the Implementation is
Constant per carrier
for an ideal filter
and LC Tee
for Butterworth or
Chebyshev.
Passband edge frequency
— Passband edge frequency2 GHz
(default)  scalarPassband edge frequency, specified as a scalar in Hz, kHz, MHz, or GHz.
To enable this parameter, set Design method
to Ideal
and Filter
type to Lowpass
or
Highpass
.
Implement using filter order
— Implement using filter orderon
(default)  off
Select this parameter to implement the filter order manually.
To enable this parameter, set Design method
to Butterworth
or
Chebyshev
.
Filter order
— Filter order3
(default)  scalarFilter order, specified as a scalar. For a Filter
type of Lowpass
or
Highpass
, the filter order is the number
of lumped storage elements. For a Filter type of
Bandpass
of
Bandstop
, the number of lumped storage
elements is twice the filter order.
Note
For even order Chebyshev filters, the resistance ratio $$\frac{{R}_{\text{load}}}{{R}_{\text{source}}}>{R}_{\text{ratio}}$$ for Tee network implementation and $$\frac{{R}_{\text{load}}}{{R}_{\text{source}}}<\frac{1}{{R}_{\text{ratio}}}$$ for Pi network implementation.
$${R}_{\text{ratio}}\text{\hspace{0.17em}}=\text{\hspace{0.17em}}\frac{\sqrt{1+{\epsilon}^{2}}+\epsilon}{\sqrt{1+{\epsilon}^{2}}\epsilon}$$
where:
$$\epsilon \text{\hspace{0.17em}}=\text{\hspace{0.17em}}\sqrt{{10}^{(0.1{R}_{\text{p}})}1}$$
R_{p} is the passband ripple in dB.
To enable this parameter, select Implement using filter order.
Passband frequency
— Passband frequency for lowpass and highpass filtersPassband frequency for lowpass and highpass filters, specified as a
scalar in Hz, kHz, MHz, or GHz. The default value is 1
GHz
for Lowpass
filters and
2 GHz
for Highpass
filters.
To enable this parameter, set Design method
to Butterworth
or
Chebyshev
and Filter
type to Lowpass
or
Highpass
.
Passband frequencies
— Passband frequencies for bandpass filters[2 3] GHz
(default)  2tuple vectorPassband frequencies for bandpass filters, specified as a 2tuple vector in Hz, kHz, MHz, or GHz. This option is not available for bandstop filters.
To enable this parameter, set Design method
to Butterworth
or
Chebyshev
and Filter
type to Bandpass
.
Passband attenuation (dB)
— Passband attenuation10*log10(2)
(default)  scalarPassband attenuation, specified as a scalar in dB. For bandpass filters, this value is applied equally to both edges of the passband.
To enable this parameter, set Design method
to Butterworth
or
Chebyshev
.
Stopband frequencies
— Stopband frequencies for bandstop filters[2.1 2.9] GHz
(default)  2tuple vectorStopband frequencies for bandstop filters, specified as a 2tuple vector in Hz, kHz, MHz, or GHz. This option is not available for bandpass filters.
To enable this parameter, set Design method
to Butterworth
or
Chebyshev
and Filter
type to Bandstop
.
Stopband edge frequencies
— Stopband edge frequencies for ideal bandstop filters[2.1 2.9] GHz
(default)  2tuple vectorStopband edge frequencies for bandstop filters, specified as a 2tuple vector in Hz, kHz, MHz, or GHz. This option is not available for ideal bandpass filters.
To enable this parameter, set Design method
to Ideal
and Filter
type to Bandstop
.
Stopband attenuation (dB)
— Stopband attenuation40
(default)  scalarStopband attenuation, specified as a scalar in dB. For bandstop filters, this value is applied equally to both edges of the stopband.
To enable this parameter, set Design method
to Butterworth
or
Chebyshev
and Filter
type to Bandstop
.
Source impedance (Ohm)
— Input source resistance50
(default)  scalarInput source resistance, specified as a scalar in Ohms.
To enable this parameter, set Design method
to Butterworth
or
Chebyshev
.
Load impedance (Ohm)
— Output load resistance50
(default)  scalarOutput load resistance, specified as a scalar in Ohms.
To enable this parameter, set Design method
to Butterworth
or
Chebyshev
.
Automatically estimate impulse response duration
— Automatically estimate impulse response durationon
(default)  off
Select to automatically estimate impulse response for phase noise. Clear to manually specify the impulse response duration using Impulse response duration.
To enable this parameter, set Design method
to Ideal
and
Implementation to Frequency
domain
.
Impulse response duration
— Impulse response duration1e10
s
(default)  scalarImpulse response duration used to simulate phase noise, specified as a scalar in s, ms, us, or ns. You cannot specify impulse response if the amplifier is nonlinear.
Note
The phase noise profile resolution in frequency is limited by the duration of the impulse response used to simulate it. Increase this duration to improve the accuracy of the phase noise profile. A warning message appears if the phase noise frequency offset resolution is too high for a given impulse response duration. This message also specifies the minimum duration suitable for the required resolution
To enable this parameter, clear Automatically estimate impulse response duration.
Export
— Save filter design to a fileUse this button to save filter design to a file. Valid file types are
.mat
and .txt
.
To enable this parameter, set Design method
to Butterworth
or
Chebyshev
.
Select Add Channel Select filters in the Main tab to see the CS Filter parameters.
Design method
— Simulation typeIdeal
(default)  Butterworth
 Chebyshev
Simulation type. Simulates an ideal, Butterworth, or Chebyshev filter of the type specified in Filter type and the model specified in Implementation.
Filter type
— Filter typeLowpass
(default)  Highpass
 Bandpass
 Bandstop
Filter. Simulates a lowpass, highpass, bandpass, or bandstop filter type of the design specified in Design method.
Implementation
— ImplementationLC Tee
 LC Pi
 Transfer function
 Constant per carrier
 Frequency Domain
Implementation, specified as one of the following:
LC Tee
: Model an analog filter with
an LC lumped Tee structure when the Design
method is Butterworth or Chebyshev.
LC Pi
: Model an analog filter with
an LC lumped Pi structure when the Design
method is Butterworth or Chebyshev.
Transfer Function
: Model an analog
filter using twoport Sparameters when the Design
method is Butterworth or Chebyshev.
Constant per carrier
: Model a
filter with either full transmission or full reflection set as
constant throughout the entire envelope band around each
carrier. The Design method is specified as
ideal.
Filter Domain
: Model a filter using
convolution with an impulse response. The Design
method is specified as ideal. The impulse
response is computed independently for each carrier frequency to
capture the ideal filtering response. When a transition between
full transmission and full reflection of the ideal filter occurs
within the envelope band around a carrier, the frequencydomain
implementation captures this transition correctly up to a
frequency resolution specified in Impulse response
duration.
Note
Due to causality, a delay of half the impulse response duration is included for both reflected and transmitted signals. This delay impairs the filter performance when the Source and Load resistances differ from the values specified in filter parameters.
By default, the Implementation is
Constant per carrier
for an ideal filter
and LC Tee
for Butterworth or
Chebyshev.
Passband edge frequency
— Passband edge frequency2 GHz
(default)  scalarPassband edge frequency, specified as a scalar in Hz, kHz, MHz, or GHz.
To enable this parameter, set Design method
to Ideal
.
Implement using filter order
— Implement using filter orderon
(default)  off
Select this parameter to implement the filter order manually.
To enable this parameter, set Design method
to Butterworth
or
Chebyshev
.
Filter order
— Filter order3
(default)  scalarFilter order, specified as a scalar. This order is the number of
lumped storage elements in lowpass
or
highpass
. In bandpass
or
bandstop
, the number of lumped storage elements
are twice the value.
Note
For even order Chebyshev filters, the resistance ratio $$\frac{{R}_{\text{load}}}{{R}_{\text{source}}}>{R}_{\text{ratio}}$$ for Tee network implementation and $$\frac{{R}_{\text{load}}}{{R}_{\text{source}}}<\frac{1}{{R}_{\text{ratio}}}$$ for Pi network implementation.
$${R}_{\text{ratio}}\text{\hspace{0.17em}}=\text{\hspace{0.17em}}\frac{\sqrt{1+{\epsilon}^{2}}+\epsilon}{\sqrt{1+{\epsilon}^{2}}\epsilon}$$
where:
$$\epsilon \text{\hspace{0.17em}}=\text{\hspace{0.17em}}\sqrt{{10}^{(0.1{R}_{\text{p}})}1}$$
R_{p} is the passband ripple in dB.
To enable this parameter, select Implement using filter order.
Passband frequency
— Passband frequency for lowpass and highpass filtersPassband frequency for lowpass and highpass filters, specified as a
scalar in Hz, kHz, MHz, or GHz. By default, the passband frequency is
1 GHz
for Lowpass
filters and 2 GHz
for
Highpass
filters.
To enable this parameter, set Design method
to Butterworth
or
Chebyshev
and Filter
type to Lowpass
or
Highpass
.
Passband frequencies
— Passband frequencies for bandpass filters[2 3] GHz
(default)  2tuple vectorPassband frequencies for bandpass filters, specified as a 2tuple vector in Hz, kHz, MHz, or GHz. This option is not available for bandstop filters.
To enable this parameter, set Design method
to Butterworth
or
Chebyshev
and Filter
type to Bandpass
.
Passband attenuation (dB)
— Passband attenuation10*log10(2)
(default)  scalarPassband attenuation, specified as a scalar in dB. For bandpass filters, this value is applied equally to both edges of the passband.
To enable this parameter, set Design method
to Butterworth
or
Chebyshev
.
Stopband frequencies
— Stopband frequencies for bandstop filters[2.1 2.9] GHz
(default)  2tuple vectorStopband frequencies for bandstop filters, specified as a 2tuple vector in Hz, kHz, MHz, or GHz. This option is not available for bandpass filters.
To enable this parameter, set Design method
to Butterworth
or
Chebyshev
and Filter
type to Bandstop
.
Stopband edge frequencies
— Stopband edge frequencies for ideal bandstop filters[2.1 2.9] GHz
(default)  2tuple vectorStopband edge frequencies for bandstop filters, specified as a 2tuple vector in Hz, kHz, MHz, or GHz. This option is not available for ideal bandpass filters.
To enable this parameter, set Design method
to Ideal
and Filter
type to Bandstop
.
Stopband attenuation (dB)
— Stopband attenuation40
(default)  scalarStopband attenuation, specified as a scalar in dB. For bandstop filters, this value is applied equally to both edges of the stopband.
To enable this parameter, set Design method
to Butterworth
or
Chebyshev
and Filter
type to Bandstop
.
Source impedance (Ohm)
— Input source resistance50
(default)  scalarInput source resistance, specified as a scalar in Ohms.
To enable this parameter, set Design method
to Butterworth
or
Chebyshev
.
Load impedance (Ohm)
— Output load resistance50
(default)  scalarOutput load resistance, specified as a scalar in Ohms.
To enable this parameter, set Design method
to Butterworth
or
Chebyshev
.
Automatically estimate impulse response duration
— Automatically estimate impulse response durationon
(default)  off
Select to automatically estimate impulse response for phase noise. Clear to specify the impulse response duration using Impulse response duration.
set Design method to
Ideal
and
Implementation to Frequency
domain
.
Impulse response duration
— Impulse response duration1e10
s
(default)  scalarImpulse response duration used to simulate phase noise, specified as a scalar in seconds. You cannot specify impulse response if the amplifier is nonlinear.
Note
The phase noise profile resolution in frequency is limited by the duration of the impulse response used to simulate it. Increase this duration to improve the accuracy of the phase noise profile. A warning message appears if the phase noise frequency offset resolution is too high for a given impulse response duration. This message also specifies the minimum duration suitable for the required resolution
To enable this parameter, clear Automatically estimate impulse response duration.
Export
— Save filter design to a fileUse this button to save filter design to a file. Valid file types are
.mat
and .txt
.
To enable this parameter, set Design method
to Butterworth
or
Chebyshev
.
This table shows you how the icons on this block will vary based on how you set the Noise figure (dB) and Add LO phase noise parameters on the block.
Noise figure (dB)  Add LO phase noise: off  Add LO phase noise: on 

0 


10 


Behavior changed in R2021b
Starting in R2021b, the IQ Demodulator block icon has updated. The block icons are now dynamic and show the current state of the noise parameter.
When you open a model created before R2021b containing a IQ Demodualtor block, the software replaces the block icon with the R2021b version.
[1] Razavi, Behzad. RF Microelectronics. Upper Saddle River, NJ: Prentice Hall, 2011.
[2] Grob, Siegfried and Lindner, Jurgen, “Polynomial Model Derivation of Nonlinear Amplifiers”, Department of Information Technology, University of Ulm, Germany.
您点击的链接对应于以下 MATLAB 命令：
请在 MATLAB 命令行窗口中直接输入以执行命令。Web 浏览器不支持 MATLAB 命令。
Choose a web site to get translated content where available and see local events and offers. Based on your location, we recommend that you select: .
Select web siteYou can also select a web site from the following list:
Select the China site (in Chinese or English) for best site performance. Other MathWorks country sites are not optimized for visits from your location.