Similarly because of this balance the F1 and F2 signals do not appear at each others port. Some mixers require even higher levels. A pure 50 ohms would be ideal. High quality, high speed diodes which will take the necessary saturating current and large reverse voltages across the non conducting diodes are an absolute must where performance counts. The actual construction will determine the bandwidth.
Diodes make ideal harmonic generators.
Noise figure is rarely an issue in H.F. sets. At V.H.F. and beyond it is likely you would employ a low noise r.f. At H.F. don't even think of using an R.F. amplifier ahead of a mixer unless you know precisely why you are doing it. 2. high local oscillator drive - if you are running portable and using battery power then don't worry about it. A few extra transistors and components won't send you broke and you are after performance after all.