A $100 \; \mathrm{MHz}$ carrier of $1 \mathrm{~V}$ amplitude and a $1 \; \mathrm{MHz}$ modulating signal of $1 \mathrm{~V}$ amplitude are fed to a balanced modulator. The output of the modulator is passed through an ideal high-pass filter with cut-off frequency of $100 \; \mathrm{MHz}$. The output of the filter is added with $100 \; \mathrm{MHz}$ signal of $1 \mathrm{~V}$ amplitude and $90^{\circ}$ phase shift as shown in the given figure. The envelope of the resultant signal is
- constant
- $\sqrt{1+\sin \left(2 \pi \times 10^{6} t\right)}$
- $\sqrt{5 / 4-\sin \left(2 \pi \times 10^{6} t\right)}$
- $\sqrt{5 / 4+\cos \left(2 \pi \times 10^{6} t\right)}$