Like the Wave Bubble's Voltage Controlled Oscillators (VCOs) the MAX2870 has a tuning voltage pin, varying the voltage supplied to this pin changes the frequency. However it only varies the frequency between the sub-band's frequency range.There are 64 sub-bands, selected by bits 31:26 in Register 3, and I *think* that each sub band is 40MHz wide. I calculated this from (6GHz - 3Ghz) / 64 ~ 45MHz. Another way of looking at it is if you were to have a single band the maximum control voltage would be +3.3V and you would get 1MHz of bandwidth for each millivolt on the tuning pin.
So in manual mode you'll need to figure out which sub-band to start in, then ramp the control voltage until max, then go to the next sub-band then ramp the control voltage until max until you get to your upper limit frequency. Luckily most signals seem to only require a bandwidth of 30MHz - 75MHz which would require up to 3 sub-band changes, of course if you wanted to cover multiple bands you'd need to increase that figure.
Another option is to use the auto select state machine to re-tune the VCO every time you hit the limits of the control voltage pin but I'm not sure how well that would work.
The Wave Bubble on the other hand is very simple, a 555 timer generates an continuously resetting ramp signal which is amplified so it can reach the max vtune voltage of +28V for the minicircuits VCOs. Then a digital pot limits the range of this ramp to match the max bandwidth required. A DC offset is added from the microcontrollers PWM pins to set the minimum frequency of the ramp. A PLL chip is used as a glorified frequency matcher to check that lower and upper limits are reached and it's assumed the band is swept by the ramp in between.
In short the MAX2870 cannot be controlled as easily as the Wave Bubble. It can be controlled but it would require a completely different circuit, completely new code and thus would no longer be a Wave Bubble. It also seems to be just as hard as the LMX2433/VCOs to purchase.