The ft of the 2SC5551 is 3.5 GHz.? This should show absolutely no gain slump at 30 MHz.? But,being in the GHz range, it will be far more difficult to "tame".? Good ?W layout techniques will be required.
As for the size of the NanoVNA and the 1:1 "balun", yes, the Nano is small enough that the balun is not necessary at HF frequencies so long as short leads are used in the test setup.? I can not use my 8753C for such measurements!! ??
