Re: Dual gate mosfet

On Wed, 22 Mar 2006 12:32:09 GMT, Allison-nospam@xxxxxxxxxxxxxxxxxxxxxx
wrote:

On Wed, 22 Mar 2006 10:24:49 +0000, John Wilkinson
<john.wilkinson@xxxxxxxxxxx> wrote:

Hi,
Is there any problem using a 50 Ohm resistor to set the input impedance of
a BF998 dual gate mosfet, at 45MHz.
Will this degrade noise etc?

Thanks,
John.

Yes, 50 ohms is well below optimum for gain and noise.
For best noise and gain the fet seems to be in the 2k region.

Allison

Thanks for the help so far.
So, I was hoping to make this a good 50 Ohms input match. Looking at the
Philips datasheet for the BF998, for the agc and cross mod test, they show
a fully biased Mosfet, and an ac coupled 50 Ohm resistor across the input.
the input is from a 50 Ohm sig gen.

So does this mean if I set the gate resistance to say 2K, and ac couple a
50 Ohm input resistance, is that better? If so why?

Best regards,
John.
.

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