Ispired by a relatively old paper titled
"Low Cost Electronically Steered Antenna and Receiver System for Mobile Satellite Communications"
and attached, I was wondering if it would be possible to use the AD8346 as phase shifter for GPS.
The part originally used was a HPMX-2001 and the LO 0/90 were fed with an active GPS antenna feed (25dB gain and 2dB noise figure) passing through a 90 deg coupler.
Obviously the datasheet states that a LO drive of -10dB is optimal for these quadrature modulators.. but I was wondering what would happen if I would connect a "noise like" at roundabout -100dBm
I hope this intrigues someone wiser than me!
I am not wiser than you, but I guess the problem would be the additive noise. The data sheet of the 8345 is the most communicative about the LO input. The equivalent circuit (Figure 24. Circuit B) should work at lower level,
but it could be noisy because of the resistive components. It says on P12, "Higher levels degrade linearity while lower levels tend to increase the noise floor slightly. For example, reducing the LO power from −2 dBm to −10 dBm increases the noise floor by approximately 0.3 dB (see Figure 21)." It would be hard to extrapolate down to
-100dBm, but I am affraid the noise floor could be higher than the noise from the antenna. Using hybrid as phase spitter is more adequate choise in this case (as in the paper), because it is non-resistive.
Best regards, vili
There are two mixers in IQ Modulator like AD8345/6/9 and these mixers ask certain minimum level on LO input to work properly even though there are amplifier stages on LO path. It may work under -10dBm ,may be at around -20dBm. However, it will not work at -100dBm. I would recommend vector modulator such as AD8340/1,ADL5390 to do phase shifting in a linear.
Ah.. interesting I could not find the AD8340/1 on the website..
I guess I will have to decide on some DAC to drive the BB gain controls
Thanks all for the suggestions!