# Hi, can somebody help to change dual gate jfet in transistor

#### michael1978

Joined Jun 29, 2014
309
Hi, everybody, can somebody help? how to change this 40673, in transistor is that possible, because difficult to find dual jfet and also i undertsand better transist bjt and jfet than dual jfet this is the shematic

#### ebp

Joined Feb 8, 2018
2,332
The 40673 was a dual gate MOSFET, not JFET. I've never encountered a dual gate JFET.

#### michael1978

Joined Jun 29, 2014
309
Hello,

There are quite some dual gate mosfets.
I have used the BF980 and BF981 in the past.
40673
BF980
BF981
BF982

If you really want to change the circuit to a BJT circuit, you could have a look at this post of your other thread:

Inject the signal of the oscillator to the emittor of the BJT.

Bertus
Hi Bertus, is this circuits the same like he show me sir Bordodynov, can i use that circuit in place from this circuits with mosfet, i understand beter.
and more question, normal local oscillator must be from 88-108mhz( i mean with tuning), for fm superheterodyne

Last edited:

#### michael1978

Joined Jun 29, 2014
309
The 40673 was a dual gate MOSFET, not JFET. I've never encountered a dual gate JFET.
Hi, sorry i did not know, i thougt is jfet….

#### michael1978

Joined Jun 29, 2014
309
Hi Bertus, is this circuits the same like he show me sir Bordodynov, can i use that circuit in place from this circuits with mosfet, i understand beter.
and more question, normal local oscillator must be from 88-108mhz( i mean with tuning), for fm superheterodyne
Hello Bertus, i have just this question because now i understand, just local oscillator must 88-108mhz, like i read in internet ? correct

#### bertus

Joined Apr 5, 2008
21,039
Hello,

For an IF of 10.7 MHz, the LO must be 10.7 MHz higher or lower than the frequency to be received.

The frequency of the local oscillator fLO is set so the desired reception radio frequency fRF mixes to fIF. There are two choices for the local oscillator frequency because the dominant mixer products are at fRF ± fLO. If the local oscillator frequency is less than the desired reception frequency, it is called low-side injection (fIF = fRF − fLO); if the local oscillator is higher, then it is called high-side injection (fIF = fLO − fRF).

Bertus

#### michael1978

Joined Jun 29, 2014
309
Hello,

For an IF of 10.7 MHz, the LO must be 10.7 MHz higher or lower than the frequency to be received.

The frequency of the local oscillator fLO is set so the desired reception radio frequency fRF mixes to fIF. There are two choices for the local oscillator frequency because the dominant mixer products are at fRF ± fLO. If the local oscillator frequency is less than the desired reception frequency, it is called low-side injection (fIF = fRF − fLO); if the local oscillator is higher, then it is called high-side injection (fIF = fLO − fRF).

Bertus
Thank you very much Bertus, i understrand, have i nice day...

#### Dodgydave

Joined Jun 22, 2012
9,854
Try SFT210DE