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Mixer-Measurements.php    10270 Bytes    20-07-2023 11:14:22


Frequency Mixers : Measurements


Some kind of tutorial / leaflet for our Mixer Tinkerboards





ADE-30+





✈ Measuring the Conversion Loss (RF to IF)




Test Setup
Spectrum @ IP-Port (ADE-30+)


Conversion loss is a measure of the efficiency of the mixer.

It is the difference of the RF power and the IF power when LO power is nominal and the mixer is operated in the 'linear' region. For a precise measurement, the cable loss shall not be neglected. Using low-loss cables and having them very short, you mayst get away without loosing too much precision.

As the Conversion loss depends on the LO-power, the measurement shall be repeated with variation of the LO-level.

TEST-SETUP :

SMC100A @ RF-input, level e.g. -30 dBm, frequency e.g. 200 MHz
Marconi 2022E @ LO-input, level e.g. +7 dBm, frequency e.g. 230 MHz
Spectrum Analyzer at IF-output, measuring the level at 230 MHz - 200 MHz = 30 MHz or 230 MHz + 200 MHz = 430 MHz.

We measured at 30 MHz a level of -37.6 dBm, therefore the conversion loss is :
-30 dBm - -37.6 dBm = 7.6 dB. And yes, the conversion loss is frequency dependant. Therefore several measurements mayst be useful.




✈ RF Input Compression Measurement




Test Setup
IF level vs RF level, LO = + 7 dBm (ADE-30+)


The 1-dB Compression Point is a measure of the maximum undistorted input level.

It is the maximum RF power where the IF power shall not deviate more than 1 dB from the linear calculated value. LO power has its nominal value. If you have more than one signal at the RF port, the Intermodulation Measurement mayst be more interesting.

TEST-SETUP :

SMC100A @ RF-input, level variable, frequency e.g. 200 MHz
Marconi 2022E @ LO-input, level e.g. +7 dBm, frequency e.g. 230 MHz
Spectrum Analyzer at IF-output, measuring the level at 230 MHz - 200 MHz = 30 MHz or 230 MHz + 200 MHz = 430 MHz.




✈ Measuring the Isolation




Test Setup
Measurement (ADE-30+)


The Isolation is a measure of the crosstalk between the ports of a mixer.

It is the measured power difference from any Port to the two other Ports.

TEST-SETUP :

SMC100A @ RF-input, -25 dBm, frequency e.g. 200 MHz
Marconi 2022E @ LO-input, level e.g. +7 dBm, frequency e.g. 230 MHz
Spectrum Analyzer at IF-output, measuring the level at 200 MHz and 230 MHz.
LO to IF isolation is + 7 dBm - - 37.21 dBm = 44.2 dB, (48.5 dB says the datasheet)
RF to IF isolation is - 25 dBm - - 54.24 dBm = 29.2 dB




✈ Measuring the Reflections : S11




Test Setup
S11 of RF Port (ADE-30+), Power(NWA) : 0 dBm


Reflection measurements show how good the impedance matching is at a port.

In the RF-field, one usually heads for impedance matching, as this allows for maximum power transfer. (And the power from an antenna is sometimes very small).

TEST-SETUP :

Network Analyzer at the port of interest - hp8753E @ RF-Port.
LO-port terminated with a Source having 50 Ω impedance and delivering + 7 dBm - e.g. SMC100A. Unused port terminated with 50 Ω.

We measured the RF port. We saw, that the result strongly depends on the Test Port Power Level. At lower levels (which deem appropriate for an RF-Input), S11 is far off. (- 15 dBm Test Port Power results in S11 = 0 dB, broadband). Situation improves with (unrealistic) high levels such as + 7 dBm (S11 = 8.5 dB, broadband).




✈ Intermodulation Measurement 3rd Order




Test Setup
IF Spectrum (ADE-30+)


The intercept points or the IM3-products are from interest, because the resulting mixing products fold back into the baseband.
Third order means e.g. 2 * LO + 1 * RF or 2 * LO - 1 * RF.

TEST-SETUP :

SMC100A, -10 dBm, frequency e.g. 200 MHz
SMC100A, -10 dBm, frequency e.g. 201 MHz
As the combiner, we used a Power Split (ZFSC-2-1W-S+, from MCL).
Marconi 2022E @ LO-input, level e.g. +7 dBm, frequency e.g. 230 MHz

Spectrum Analyzer (FSP3) @ IF-Port, measuring the following levels :
-69.13 dBm @ 28 MHz
-19.54 dBm @ 29 MHz
-19.41 dBm @ 30 MHz
-69.18 dBm @ 31 MHz

With that, we can calculate the TOI as follows (values slightly rounded) :

TOI formula




✈ Share your thoughts



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