2005-04-22
The purpose of this webpage is to analyse the RF performance of a standard +7 dBm Doubly Balanced Mixer. A HPF-505 was used but SBL-1, IE-500, IE-800 or similar should show same performance.
The measurements were carried out with the following parameters:
The mixer is the only device involved in the test circuit. Signal generators were used as signal sources.
Only one mixer have been tested.
Mixer output power versus input power (red). Linear line (blue). The 1 dB compression point occurs at POutput equal to -5,2 dBm.
Third order mixer output relative to output PEP.
The mixer is clearly in saturation with input levels exceeding +2 dBm PEP. According to Jørgen, OZ7TA, the the lack of IMD performance at lower levels is most likely coming from imperfections amoung the diodes in the mixer.
IF level fixed at -11 dBm PEP.
| 42 MHz LO [dBm] | 70 MHz IMD relative to PEP [dB] |
| 11 | -61 |
| 10 | -54 |
| 9 | -54 |
| 8 | -53 |
| 7 | -54 |
| 6 | -57 |
| 5 | -62 |
| 4 | -67 |
It seems a bit strange that the IMD is "worst" at nominal LO level. However, according to Jørgen, OZ7TA, the the lack of IMD performance at lower levels is most likely coming from imperfections amoung the diodes in the mixer. Reducing the LO below 4 dBm reduces the IMD performance.
"Normal mode" means that the LO drive at +7dBm and at 42 MHz is applied to pin 8 (LO port) and the output signal RF signal is found on pin 1 (RF port). "Revers mode" means that the LO drive at +7dBm and at 42 MHz is applied to pin 1 (RF port) and the output signal RF signal is found on pin 8 (LO port). In both cases the input signal is applied to pin 3 and 4 (IF port).
Normal mode and input power is +3 dBm.
Normal mode and input power is +0 dBm.
Normal mode and input power is -15 dBm.
Reverse mode and input power is +3 dBm.
Reverse mode and input power is +0 dBm.
Reverse mode and input power is -15 dBm.
Analyser "IMD" measured using a Mini Circuits MCL ZFSC-2-4 3 dB combiner. 42 MHz LO power is +7 dBm and 28 MHz IF power is 0 dBm. No IMD is seen.
Input level For pure signal mixing the HPF-505 may be supplied with up to 2 dBm. However, if the purpose is signal mixing where the input signal (IF port) is linear the input should not exceed 0 dBm resulting in the third IMD being -32 dB relative to PEP. Taking later stage IMD into consideration an even lower input signal should be applied and more in the range of below -10 dBm PEP.
Normal vs. reverse ports Overall there seems to be only minor differences or none at all if the RF and LO ports are used in "normal mode" or reverse mode." In fact it seems as if close-in performance is slightly better in "reverse mode."
Bo, OZ2M, www.rudius.net/oz2m