In regards to "capacitance"?
Think of the circuit - the Bias breakpoint being the Input Cap, and the Gate being the other "crude" cap.
Now, once you understand the concepts of one cap working a lot like a pass-thru filter cap - then the issue of driving it becomes more understood.
Amp Builders use a similar design
for filtering the power supply feeds...
The effort in finding a Gate Capacitance that is tunable for the RF spectrum you'll be in, is far more important than the wattage. Got Gain? We're not talking Fabric Softener here, but it can make a stink of you don't pay attention to the details.
So if the ERF 2030+ takes a required 1,100pF or 1.1nF or 0.001uF - yes those are the converted values, then you can translate to what is needed in DRIVE to make this work.
But for Gain, the 13N10's or IRF520's make better mates for paring the Driver and Final in drive levels and symmetrical gain values that are workable. (400pF to as much as 600pF) are useable, tunable and working values used in most CB's and even into the VHF range for tuning and output networks.
If you remember the Xtal thread about pF - the higher values require more effort to "bend" their tuning - same is said for the Gate regions of the various FETs' we use in CB's - try to find ones that work within the confines of the board design and the values used to couple the originals together - higher values you get into more troubles with trying to make them work in the region or band of RF spectrum we want.
So think of the Gate as one cap, the Input Cap as the other and then you begin to see the issue of Ohms law when it comes to working with capacitor values versus Resistor or even inductor.
In series - Resistors add up...
Capacitors don't - treat them more like Parallel Resistor theory and practice - the LOWEST value is usually the parallel value you should work with or calculate. So if you have an input cap of 470pF - it simply can't transfer enough Coulombs of energy (Joules) to force the larger Gate plate and its' capacitance to transfer charge - very much.
Remember too, you are also dealing with a "static" DC value that will begin to change into a Dynamic impedance once the switching events occur - refer to the Rudder reference earlier - because if you can't keep the threshold steady, you lose steering ability to control the rudder and switching events.
So hope this helps - sorry to see the ERF's are taking on more of a challenge to change of charge rates that make some radios seem to work, while others won't put out, or simply don't work - again this goes back to what I've discussed with the boss to help us in making sense of the changes going on in Semiconductor industry in general.
