There is an inherent trade-off between LO drive level, input RF power and intermodulation distortion. As a minimum, LO power should generally be at least 7 dB higher than the highest expected RF power to avoid mixer compression. This value of 7 dB actually depends on the specific mixer (i.e. T3 mixers relax this tolerance to about 4 dB), but 7 dB can always be used as a conservative estimate. Thus, if you have RF powers not to exceed +5 dBm, then you can use medium barrier (“M-type”) diodes with LO drive around +10 to +13 dBm. If a higher LO drive is available in the system, then a better choice may be to use a high barrier diode because the intermodulation distortion generated during the mixing process will be suppressed more fully. Keep in mind that under normal operation, the greater the difference between the LO and RF power, the lower the intermodulation products.
- You must login to post comments
Please login first to submit.