Stevens Institute of Technology



1. Introduction

Wireless Testbeds provide the experimental facility to test the validity of algorithms and also to test any wireless setup. The Electrical and Computer engineering department at Stevens Institute of Technology currently has a high speed radio testbed which is capable of transmitting and receiving at 2.4 GHz. 2.4GHz ISM band is free to all, so many applications now are using this band. These applications include digital cordless phone, WLAN (802.11b), HomeRF, RFID, microwave oven and many other proprietary technologies. The large amount of units using the same band has raised the issues of possible interference. This has caused WLAN to migrate to 5.7 GHz ISM band. This has raised the need for a testbed which is capable of transmitting and receiving at 5.7GHz in order to analyze the latest in wireless technology. The objective of this project is to design, build and test a portable wireless Transceiver board capable of operating at the following three ISM bands, 915MHz, 2.4GHz and 5.7GHz.

2. Existing 2.4 GHz Transceiver Board

The current RF transceiver board used in the Wireless Research Lab of Stevens Institute of Technology is capable of transmitting and receiving frequencies in the range of 2.4GHz. The initial approach to our project was to understand the functionality of this design so as to come up with a design capable of handling three different frequencies.

2.1 Transmitter End

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The basic components of the transmitter end of the transceiver are the Modulator, Bandpass Filter, Mixer, LO source and Amplifier. This design also uses low pass filters at the IQ end to remove noise from the data acquisition card. The data from the DAQ cards are modulated at 70 MHz with the use of a ZMIQ-70ML modulator. The 70 MHz needed for the modulation is provided by a frequency synthesizer. The modulated signal is passed through a band pass filter with centre frequency of 70 MHz. This removes noise from the modulated signal. The filtered signal is then fed into a mixer, ZAM-42, which accepts the signal at the IF end and a frequency of 2.33 GHz by the frequency source at the Local Oscillator input and produces a carrier signal at 2.4 GHz. This signal is amplified before being transmitted.

2.2 Receiver End

The receiver end of the board reverses the operation of the transmitter end. The received signal is first sent through a low pass filter to remove most of the noise. This signal is then fed into an amplifier before being sent into a mixer which receives a frequency of 2.33 GHz from the LO and subtracts this from the 2.4 GHz signal input to have a signal of 70 MHz generated at the output. A band pass filter is used to filter this signal out and send the signal to the demodulator. The demodulator takes a 70 MHz input from the Local Oscillator to demodulate the signal to have the original data recovered.

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2.3 Noise Figure calculations for 2.4 GHz design

| |Component |NF(dB) |Gain (dB) |NFn |GAINn | |

|1 |SLP 2950 |  |-1 |  |0.794328 | |

|2 |ZKL 2R5 |5 |30 |3.162278 |1000 | |

|3 |ZAM 42 |  |-8.5 |  |0.141254 | |

|4 |SBP 70 |  |-1.5 |  |0.707946 | |

|5 |ZKL 1R5 |3 |40 |1.995262 |10000 | |

| | | |59 | | | |

| | | | | | | |

| | |

| | |

| | |

| | |

| |Nftot = |2.722148 | | | | |

| | | | | | | |

| |NF |4.3491 | | | | |

| | | | | | | |

| |Gain |59 dB | | | | |

| | | | | | | |

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2.4 GHz Wireless Testbed Setup

3. Alternate Designs

Based on the existing 2.4 GHz, several different designs were considered for the tri band receiver.

1. Double Mixer Design

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The modulation of the signal is performed the same as that of the existing 2.4 GHz design. (Refer to section 2.1) The modulated signal is then passed to the mixer. Depending on which frequency you which to transmit the modulated signal at, you pick the mixer. For 900 MHz and 2.33 GHz, only one mixer is used. In the case of the 5.7 GHz section, the signal is first converted to 2.815 GHz using a mixer and this signal is then filtered and passed to a second mixer where it is converted to 5.7GHz. The reason for using two mixers is to avoid the need of an extra frequency source to provide frequency above 5 GHz. This brings the overall cost of the design down by a lot. The downfall of this design is the extra mixer needed which could reduce overall quality of the transmitted signal. The extra mixer and filter also means more board space required.

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2. Single Stage Conversion Design

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This is an expansion of the current 2.4 GHz design where two extra mixers are used working at 915 MHz and 5.7GHz. The major draw back of this design is that we will require LO supplies which are operational at the three different frequencies. This will be both expensive and difficult to obtain. One alternate was to use Voltage Controlled Oscillators as our LO supply. Upon further research on VCOs we came to the conclusion that VCOs will not provide the stability that our system requires. On the receiver end, the same three mixers will be used to down convert the signal. The modulation and demodulation stage are the same as mentioned before.

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3. 900 MHz Modulation

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4. Tripler Design

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5. Three Stage Conversion Design

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The modulation for this design is carried out at 70 MHz as in the case of the existing design. This is then scaled up to 900 MHz using a mixer. If a 900 MHz signal is required this signal is transmitted. If a 2.4 GHz or 5.7 GHz signal is required then the signal is passed onto the respective mixer. And then amplifier is used to amplifier the signal before transmission.

4. Final Design

The final design chosen for the transceiver was based on the Tripler design. This design was picked since it required the least number of components as well as the smallest range of frequency source.

4.1 Transmitter End

The analog signals from the DAC are first passed through a low pass filter to remove noise. These are then modulated at 70 MHz using a ZFMIQ-70ML modulator. This accepts an input of 70 MHz at the LO end and provides a modulated signal of 70 MHz at the RF end. The 70 MHz at the LO end will be provided by the secondary output of a dual output LO Synthesizer from Praxsym Eng. A splitter is used to split the 70 MHz signal for the transmitter and receiver end. The modulated signal is then filtered using a 70 MHz band pass filter. Depending on what frequency is needed, the 70 MHz modulated signal is input into the respective filter.

900 MHz: The 70MHz filtered signal is passed into the IF input of the ZX05-25MH mixer. A frequency of 845 MHz, provided by the primary out of the dual output LO synthesizer is provided at the LO input of the mixer. The frequency from the LO synthesizer is first split into two using a splitter, which one of the signals sent to The output signal at the RF end will be comprised of various signals at different frequencies. One of these is the summation of the two frequencies which is 915 MHz.

2.4 GHz: The 70MHz filtered signal is passed into the same mixer, ZX05-25MH as before. A frequency of 2.33 GHz is supplied to the LO input by the NovaSource G2. The mixer will add the two frequencies together to obtain a signal at 2.4 GHz.

5.7 GHz: The 70 MHz filtered signal is passed into the ZX05-C60 mixer. A frequency of 1.88 GHz from the NovaSource is passed through a Tripler, ATA 1424. This Tripler has a built in amplifier at the front and back end so the signal is amplified twice to minimize power loss. The tripled signal at 5.63 GHz is then input in to the LO end of the mixer where it is added together with the 70 MHz signal to produce a signal of 5.7 GHz at the RF end.

The signal from the RF end of the mixer is amplified using a ZKL-2R5 amplifier before it is transmitted.

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4.2 Receiver End

An antennae is used to receive the signal and the signal is transmitted to the respective filter depending on which frequency the transceiver needs to be operated at.

915 MHz: The received signal is passed through a low pass filter with a cut off frequency of 1000 MHz. This will ensure no frequencies above 1000 MHz get passed through to the rest of the receiver. The filtered signal is then passed to an amplifier before being fed into the RF input of the mixer. A frequency of 845 MHz from the LO synthesizer is fed into the LO input. The difference of these frequencies, 70 MHz is obtained at the IF end.

2.4 GHz: The received signal is passed through a low pass filter with a cut off frequency of 2.9 GHz. The filtered signal is then passed to an amplifier before being fed into the RF input of the mixer. A frequency of 2.33 GHz from the NovaSource G6 is fed into the LO input. The difference of these frequencies, 70 MHz is obtained at the IF end.

5.7 GHz: A low pass filter with a cut off frequency of 6.5 GHz is used after the antennae. The filtered signal is then passed to an amplifier before being fed into the RF input of the mixer. A frequency of 5.63 GHz, which is obtained after tripling the input from the NovaSource G6 is fed into the LO input. The difference of these frequencies, 70 MHz is obtained at the IF end.

The signal obtained at the IF end of mixer is fed into a Band pass filter. This is to filter out the 70 MHz signal and reduce as much noise into the demodulator as possible. The filtered signal is amplifier and passed to the demodulator. A frequency of 70 MHz from the dual output synthesizer is used by the demodulator to separate the signal into the Q and I phase.

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4.3 Calculation of System Specifications

Noise Figure Calculations

|Transmitter End | | | | | |

| | | | | | | |

| |Component |NF(dB) |Gain (dB) |NFn |GAINn |Cummulative NFn |

|1 |ZFMIQ-70M |7.2 |-6.2 |5.248075 |0.239883 |7.20000 |

|2 |SBP 70 | |-1.5 |1 |0.707946 |7.20000 |

|3 |ZX05-C60 | |-6.9 |1 |0.204174 |5.24807 |

|4 |ZKL 2R5 |5 |30 |3.162278 |1000 |18.30004 |

| | | |15.4 | | | |

| | | | | | | |

| | |

| | |

| | |

| | |

| |Nftot = |67.60884 | | | | |

| |NF |18.3000 |dB | | | |

| |Gain |15.4 |dB | | | |

| | | | | | | |

| | | | | | | |

|Receiver End | | | | | |

| | | | | | | |

| |Component |NF(dB) |Gain (dB) |NFn |GAINn |Cummulative NFn |

|1 |LPS50006 |n/a |-1 |0 |0.794328 |#NUM! |

|2 |ZKL 2R5 |5 |30 |3.162278 |1000 |4.3491 |

|3 |ZX05-C60 |n/a |-6.9 |1 |0.204174 |2.7221 |

|4 |SBP 70 |n/a |-1.5 |1 |0.707946 |4.3491 |

|5 |ZKL 1R5 |3 |40 |1.995262 |10000 |4.3629 |

|6 |ZFMIQ-70D |7.2 |-6.2 |5.248075 |0.239883 |4.3629 |

| | | |54.4 | | | |

| | | | | | | |

| | |

| | |

| | |

| | |

| |Nftot = |2.73082 | | | | |

| |NF |4.3629 |dB | | | |

| |Gain |54.4 |dB | | | |

The mixers used for all three frequencies had the same noise figures and gain. Also the three different low pass filters used had the same noise figures and gain therefore, the overall NF and Gain of the transceiver operating at either of the three frequencies were the same. Noise figures and gains weren’t available for all the components hence we could not accurately calculate the values.

Calculations for 915 MHz and 2.4 GHz design

Since the 915MHz and 2.4 GHz design use the same components, the calculations for both are identical.

|Stage |Part |Gain (dB) | Gain |IP3 (dBm) |IP3 (Watts) |

|1 |ZKL-2R5 |30 |1000 |31 |1.258 |

|2 |ZK05-25MH |-9.8 |.1047 |18 |.06309 |

|3 |ZKL-1R5 |40 |10000 |31 |1.258 |

Formula used to convert Gain (dB) to the ratio of powers.

10*Log[pic]= Gain(dB) [pic]

Formula used to convert IP3 (dBm) to IP3(Watts) :

10*Log[pic]=IP3(dBm) IP3(Watts)

Calculation for Minimum Detectable Signal (MDS):

MDS=[-174+NF(system) +10Log(BW(system))] dBm

=[-174 + 4.3491 +10Log(24000000)]

=-95.84 dBm

Calculation of net IIP3 for the receiver system:

[pic]=[pic]+[pic]

which gives IIP3 = 6.27604*(10^-5) Watts

IIP3 (dBm)= 10*log(6.27604*(10^-5))

= -42.03 dBm

Calculation of the Dynamic Range:

DR = [2 (IPs - MDS)/3] dB

= [2(-42.03-(-95.84))/3]

= 35.14 dB

Calculations for the 5.7 GHz system:

|Stage |Part |Gain (dB) | Gain |IP3 (dBm) |IP3 (Watts) |

|1 |ZKL-2R5 |30 |1000 |31 |1.258 |

|2 |ZK05-C60 |-8.5 |.1412 |11 |.012589 |

|3 |ZKL-1R5 |40 |10000 |31 |1.258 |

Calculation of IIP3, using above formula:

= -49 dBm

4.4 Component List

|Part Description |Part Number | Price |Qty |Company |Tel |Total Price | |1 |Low Pass Filter |SLP 15 | $ 34.95 |4 |Minicircuits |1 800 654 7949 | $ 139.80 | |2 |Modulator |ZF MIQ 70ML | $ 89.95 |1 |Minicircuits |1 800 654 7949 | $ 89.95 | |3 |Band Pass Filter |SBP 70 | $ 18.95 |2 |Minicircuits |1 800 654 7949 | $ 37.90 | |4 |Mixer |ZX05-25MH | $ 39.95 |2 |Minicircuits |1 800 654 7949 | $ 79.90 | |5 |Mixer |ZX05-C60 | $ 39.95 |2 |Minicircuits |1 800 654 7949 | $ 79.90 | |6 |Amplifier |ZKL-2R5 | $ 149.95 |3 |Minicircuits |1 800 654 7949 | $ 449.85 | |7 |Low Pass Filter |SLP 2950 | $ 34.95 |1 |Minicircuits |1 800 654 7949 | $ 34.95 | |8 |Low Pass Filter |SLP-1200 | $ 34.95 |1 |Minicircuits |1 800 654 7949 | $ 34.95 | |9 |Low Pass Filter |L0065001 | $ 385.00 |1 |Microwave Circuits |1 800 642 2587 | $ 385.00 | |10 |Amplifier |ZKL-1R5 | $ 149.95 |1 |Minicircuits |1 800 654 7949 | $ 149.95 | |11 |Demodulator |ZF MIQ 70D | $ 89.95 |1 |Minicircuits |1 800 654 7949 | $ 89.95 | |12 |NovaSource G6 |NS3-1700102 | $ 750.00 |1 |Nova Engineering |1 800 341 6682 | $ 750.00 | |13 |Tripler |ATA-1424 | $ 324.00 |1 |Marki Microwave |408 778 4200 | $ 324.00 | |14 |Splitter |ZX10-2-25 | $ 34.95 |1 |Minicircuits |1 800 654 7949 | $ 34.95 | |15 |Splitter |ZX10-2-12 | $ 24.95 |2 |Minicircuits |1 800 654 7949 | $ 49.90 | |16 |Splitter |ZX10-2-98 | $ 39.95 |1 |Minicircuits |1 800 654 7949 | $ 39.95 | |17 |SMA Male Connectors |PE-4112 | $ 4.30 |75 |Pasternack Entp |949 261 1920 | $ 322.50 | |18 |SMA Male Right Angle |PE-4083 | $ 15.95 |20 |Pasternack Entp |949 261 1920 | $ 319.00 | |19 |LO Synthesizer |310-010058-001 | $ 885.00 |1 |Praxsyms |217 897 1744 | $ 885.00 | |20 |Internal Chassis Board |  | $ 35.00 |1 |Staffol Brothers |201 653 6479 | $ 35.00 | | | | | | | | | $ 4,332.40 | |

4.5 Final Layout

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5. System View Simulation

5.1 Background Information

System View provided various RF communication token which allow for the simulation of transceiver designs. Initial simulations did not prove productive and affect consulting with representatives at Elanix, we were given several metafiles for ideal mixer and modulators components. By modifying these design we were able to fairly accurately simulate of design.

5.2 I/O Setup

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Figure 1: I/O Setup Diagram

The same basic I/O setup was used for all simulations. I and Q inputs were simulated using a PN generator to generate a random PN sequence of frequency 10MHz and amplitude 2V. The two inputs are filtered using a 15MHz lowpass filter before being passed onto the QTxRx metafile. The metafile consists of the transmitter end and receiver end components responsible for the modulation and demodulation of the I and Q data. The demodulated data is received as the I & Q output and is filtered using 15MHz low pass filters. The data is displayed for analysis.

5.3 Design Simulation

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Figure 2: QTxRx900.mta

The I and Q input signals are first fed into the TxQMod metafile. This a modified version of the metafile received from Elanix which simulates an IQ modulator. (refer to modulation section for more details on the TxQMod metafile. The modulated data is sent to the TxUpConvMainLib metafile. This metafile simulates a mixer. (Fig.3) The modulated signal is multiplied with a sin wave of desired frequency to produce a signal of that frequency. A band pass filter is used to remove noise from the signal. Two filters were used in this simulation as one wasn’t enough to remove all the noise. (Refer to the Extra filter section for more information)

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Figure 3: Mixer Simulation Setup

The receiver side of the simulation consists of a mixer (Fig.4) which down converts the transmitted signal to 70 MHz. The filter design is identical to that used to in the transmitter end except for the filters used. The band pass filters used which allow only signals in the 70 MHz range to pass through.

[pic]

Figure 4: Mixer Simulation Setup

The 70 MHz signal is passed to the demodulator metafile which will separate the signal into the I an Q components. (Refer to demodulation section for more information.)

5.4 Simulation Results

900 MHz Design

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2.4 GHz Design

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5.7 GHz Design

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5.5 Multiple Filters

A common problem we discovered with the transmitted signal was that some of the signal from the LO had leaked into the transmitted signal. This was identified using by plotting the power spectrum graph of the transmitted signal. In the case of the 915MHz design leakage was noticed at 845 MHz and for the 2.4 GHz design, the leakage was at 2.33 GHz. Both these frequencies are equal to the respective LO frequencies of the designs. The solution to this was found my using multiple band pass filters after the up conversion stage. (Figure 5)

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Figure 5

Simulation Results

900 MHz Tx Signal using one filter

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900 MHz Tx Signal using two filters

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2.4 GHx Tx Signal using one filter

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2.4 GHx Tx Signal using two filters

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2.4 GHx Tx Signal using three filters

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5.6 Simulation using real components

System View provides in its library several RF components. Two of these, passive mixer and amplifier are used in our design and we tried to run simulations using these components. These components are meant to simulate real components taking into account noise figures, conversion loss and other such details not addressed by the ideal components used in the initial simulations. However, working with these components proved to be difficult and results obtained weren’t satisfactory. After several communication with Elanix representatives and other system view users, there was a general consensus that the passive mixer token has numerous flaws and is not ideal for high frequency simulations. Presented below are the results obtained for the 915 MHz design using real components.

915 MHz Simulation Results – Real Components

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Power Spectrum of Tx Signal

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As seen in the results, the Signal is being transmitted at the required frequency, but the input and output signal of the I and Q channels do not match up. We plotted the signal at each stage of the transceiver and it was noted that the signal was being badly distorted after the mixer stage.

After consulting with Elanix, we decided to use the ideal mixer and add an attenuator to simulate the power loss of the mixer. The resulting simulations were much more accurate and the input and output data matched up. The setup for these simulations are as follows:

I/O Setup

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Tx and Rx End

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Mixer Setup

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Simulation Results

900 MHz simulation

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6. Testing

Initial testing of the design was done using the Agilent signal generators and spectrum analyzers present in the wireless research lab. One of the generator was used to generate a 5MHz sine wave which was used as an input into the I channel of the modulator. The spectrum analyzer was used to monitor the signal at various stages in the transmission and reception process. The resulting signal at the I channel of the demodulator in the receiver end was observed using a Cathode Ray Oscilloscope.

915 MHz Test Results

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Input Signal Signal Modulated at 70 MHz

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Transmitted Signal at 900 MHz Down-converted Signal at Receiver Side

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Filtered 70 MHz signal before Demodulation Output Signal at I channel

2.4 GHz Test Results

[pic] [pic]

Input Signal Signal Modulated at 70 MHz

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Up-converted Signal to 2.4 GHz Transmitted Signal

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Down-converted Signal to 70MHz by Rx Filtered and Amplified signal before Demod

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Output Signal

Power Reading Summary from 2.4 GHz Testing

Tx End

Input Signal: Power = -20 dBm

Frequency = 5 MHz

After Modulation: Power = -29.8 dBm

After Filter: Power = -30.2 dBm

Up converted Signal: Power = -53.4 dBm

Amplified Signal: Power = -21.0 dBm

Transmitted Signal: Power = -35.7 dBm

Rx End

Amplified Signal: Power = -14.5 dBm

Down-converted Signal: Power = -33.6 dBm

Amplified Signal: Power = +4 dBm

Working Range of Design

To determine the working range of our design, we used the Agilent Signal generator to generate a signal of frequency 916MHz. This was used as the transmitted signal. The receiver down converts the signal and demodulates it to form a 1 MHz sine wave which was displayed using the CRO. The power of the transmitted signal was varied and the woking range was determined as the power range of transmitted signal for which the signal on the CRO would be displayed. The results of the testing was as follows:

915 MHz Receiver: -32 dBm to -80 dBm

2.4 GHz Receiver: -50 dBm to -90 dBm

5.7 GHz Receiver:

7. Improved Alternate Design

Based on our test results and simulation results, we designed an improved transceiver system, still operating at the three desired frequencies. The major changes in this design were the use of a doubler for the 2.4 GHz portion of the design and using a LO to provide the 5.63 GHz required by the 5.7 GHz mixers. Also, all the lowpass filters in the front end of the receiver were replaced with band pass filters. This is mainly aimed to reduce the LO leakage observed during testing. Since the double we are using is passive, our design also includes an amplifer after the doubler to counter the loss. On the receiver end we have added an extra amplifier to better improve the dynamic range of the system.

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Component List

|Part Description |Part Number | Price |Qty |Company |Tel |Delivery Time |Total Price | |1 |Low Pass Filter |SLP 15 | $ 34.95 |4 |Minicircuits |1 800 654 7949 |2 Weeks | $ 139.80 | |2 |Modulator |ZF MIQ 70ML | $ 89.95 |1 |Minicircuits |1 800 654 7949 |2 Weeks | $ 89.95 | |3 |Band Pass Filter |SBP 70 | $ 18.95 |2 |Minicircuits |1 800 654 7949 |2 Weeks | $ 37.90 | |4 |Mixer |ZX05-25MH | $ 39.95 |2 |Minicircuits |1 800 654 7949 |2 Weeks | $ 79.90 | |5 |Mixer |ZX05-C60 | $ 39.95 |2 |Minicircuits |1 800 654 7949 |2 Weeks | $ 79.90 | |6 |Amplifier |ZKL-2R5 | $ 149.95 |5 |Minicircuits |1 800 654 7949 |2 Weeks | $ 749.75 | |7 |Amplifier |ZKL-1R5 | $ 149.95 |2 |Minicircuits |1 800 654 7949 |2 Weeks | $ 299.90 | |8 |Demodulator |ZF MIQ 70D | $ 89.95 |1 |Minicircuits |1 800 654 7949 |2 Weeks | $ 89.95 | |9 |Splitter |ZX10-2-25 | $ 34.95 |1 |Minicircuits |1 800 654 7949 |2 Weeks | $ 34.95 | |10 |Splitter |ZX10-2-12 | $ 24.95 |2 |Minicircuits |1 800 654 7949 |2 Weeks | $ 49.90 | |11 |Splitter |ZX10-2-98 | $ 39.95 |1 |Minicircuits |1 800 654 7949 |2 Weeks | $ 39.95 | |12 |900MHz Bandpass Filter |B0809253 | $ 350.00 |1 |Microwave Circuits |1 800 642 2587 |3 Weeks | $ 350.00 | |13 |2.4GHz Bandpass Filter |B1523751 | $ 350.00 |1 |Microwave Circuits |1 800 642 2587 | 3 Weeks | $ 350.00 | |14 |5.7GHz Bandpass Filter |B1855001 | $ 350.00 |1 |Microwave Circuits |1 800 642 2587 |3 Weeks | $ 350.00 | |15 |NovaSource M2 |NS2-0065503 | $ 750.00 |1 |Nova Enginnering |1 800 341 6682 |4 Weeks | $ 750.00 | |16 |NovaSource G6 |NS3-0800102 | $ 750.00 |1 |Nova Enginnering |1 800 341 6682 |4 Weeks | $ 750.00 | |17 |NovaSource G6 |NS3-5470102 | $ 750.00 |1 |Nova Enginnering |1 800 341 6682 |4 Weeks | $ 750.00 | |18 |Doubler |PE8600 | $ 369.95 |1 |Pasternack Entp |949 261 7451 |2 Weeks | $ 369.95 | |22 |Internal Chassis Board |  | $ 35.00 |1 |Staffol Brothers |201 653 6479 |2 Days | $ 35.00 | | | | | | | | | | $ 5,396.80 | |

References

[1] The Basics of RF System Design, Mark Hunter, Paper presented at the IEE Training Event - How to Design RF Circuits", 5th April2000.

[2] Noise Figure Measurement, Thomas H. Lee, rev. February 7, 2003;

[3] Introduction to Communication System, Stremler, 3rd Edition, Addison Wesley, 1992

[4]

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Two band pass filters being used.

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