Frequency meter with 0.1ppm resolution

[Picuino]

I'm trying to simulate the input stage and shows certain problems in higher frequencies. I've also tested with an ADF4112 as a Gigahertz prescaler and it works fine, but with some issues.
I think the entry stage is a new challenge with relative complexity.

I don't want to greatly increase the cost and complexity of the frequency counter, so I'm going to separate everything into three projects with three PCBs:
 - Input stage and prescaler
 - Control panel with LCD and buttons
 - Frequency counter

So that the frequency counter can be autonomous, without the other boards.

[Picuino]

The old references 2N5485 (JFET) and 2N4403 (PNP) are now obsolete and unavailable.
Their counterparts in the smd version are readily available
2N5485 --> MMBF5485
2N4403 --> MMBT4403

The simulated input stage shows several problems. At 40Mhz the signal is attenuated too much. And at medium frequencies the PNP saturates. An adjust of R5 is needed.
I do not trust the simulations so I will have to wait to order these transistors at Mouser to be able to do the necessary tests on the prototype board.

Regards.

[mino-fm]

Simply use a TLV3501 with additional input protection.
Or an JFET followed by MAX961 or something like that and don't forget frequencies as low as 0,01 Hz.
Two examples: http://www.mino-elektronik.de/fmeter/eingangsstufe.htm

[Picuino]

Now I'm looking for Amplifier ICs to replace the transistor stage.
MC10216 is unavailable, but the market is plenty of options with a lot of amplifiers like the BGA2851.

MAX961 is another option not previously considered. It is an ultra-fast comparator capable of seamlessly switching to 50MHz.
I'm going to study that idea more. Thanks.