Zener_Diode said:
I understand, and if I need if=11-12Mhz with sensitivity 0.5uV, for 50ohm antena.
what chip do I need to use????
The standard IF for VHF radio is 10.7MHz, and ceramic filters (and conventional IF transformers) are freely available for those frequencies.
As I mentioned earlier, the TDA7000 doesn't appear to have a 75 ohms input impedance, it's not mentioned anywhere in the specs, nor would I expect the input of a chip to do so.
You appear to be wanting a very high spec VHF receiver, as such I would recommend a 'proper' superhet design, with at least one tuned RF stage (preferably more), a seperate mixer, a seperate oscillator - all using discrete devices. Then follow this by a 10.7MHz FM IF strip, using a chip, which could also contain the FM demodulator - I can't remember the number off hand, but there's an excellent one that's been used in FM radio projects for years.
As you have a requirement for 50 ohm input impedance, I presume this isn't for a broadcast receiver?, as such it's more likely an NBFM (Narrow Band FM) receiver, in which case you should do a second conversion down to a 455KHz second IF, to get a decent level of audio out.
The aerial input impedance is completely down to your own design, simply on the tuned circuit at the front end - you tap the coil for the impedance you require.
What EXACTLY are you trying to do?.