J
[email protected]
- Jan 1, 1970
- 0
I'm working on a homebrewed receiver and am looking at using the
LT5512
as the mixer. I'm not sure of how to arrange an impedance match and
unbalance to balance conversion over a wide range. Perhaps people
can comment on the following so I can see if I'm on the right track.
The LT5512 datasheet says:
Frequency Impedance
10MHz 18.2 + j0.14
240MHz 18.1 + j2.8
450MHz 18.1 + j5.2
One simple approach seems to be:
50 ohm input - ----------- -----------|---------- IN+
) ( ) ( ___
) ( ) (- ground --- 6 pF LT5512
) ( ) ( |
ground - ----------- -----------|---------- IN-
3:1 1:1
Coilcraft Coilcraft
WBC3-1TL WBC1-1TL
The 3:1 transformer converts the unbalanced 50 ohm input to 16.67
ohms.
The 1:1 center tap transformer converts the unbalanced 16.67 ohms to a
balanced 16.67 ohms. The center tap also supplies a DC ground for
biasing the LT5512 inputs. The 6 pF capactor reactance is:
Frequency Reactance
10MHz 2652.58
240MHz 110.52
450MHz 58.95
placing it in parallel with the LT5512 inputs results in:
Frequency Impedance
10MHz 1/(1/(18.2 + j0.14) + 1/2652.58) = 18.21
240MHz 1/(1/(18.1 + j2.8) + 1/110.52) = 17.58
450MHz 1/(1/(18.1 + j5.2) + 1/58.95) = 16.7
Questions:
1) How off base is my simple analysis?
2) Is there a better way to do this?
3) How significant is the 1.6 ohm mismatch at 10 MHz?
-- John
-------------------------------------------------------------------------
| Feith Systems | Voice: 1-215-646-8000 | Email:
[email protected] |
| John Wehle | Fax: 1-215-540-5495
| |
-------------------------------------------------------------------------
LT5512
as the mixer. I'm not sure of how to arrange an impedance match and
unbalance to balance conversion over a wide range. Perhaps people
can comment on the following so I can see if I'm on the right track.
The LT5512 datasheet says:
Frequency Impedance
10MHz 18.2 + j0.14
240MHz 18.1 + j2.8
450MHz 18.1 + j5.2
One simple approach seems to be:
50 ohm input - ----------- -----------|---------- IN+
) ( ) ( ___
) ( ) (- ground --- 6 pF LT5512
) ( ) ( |
ground - ----------- -----------|---------- IN-
3:1 1:1
Coilcraft Coilcraft
WBC3-1TL WBC1-1TL
The 3:1 transformer converts the unbalanced 50 ohm input to 16.67
ohms.
The 1:1 center tap transformer converts the unbalanced 16.67 ohms to a
balanced 16.67 ohms. The center tap also supplies a DC ground for
biasing the LT5512 inputs. The 6 pF capactor reactance is:
Frequency Reactance
10MHz 2652.58
240MHz 110.52
450MHz 58.95
placing it in parallel with the LT5512 inputs results in:
Frequency Impedance
10MHz 1/(1/(18.2 + j0.14) + 1/2652.58) = 18.21
240MHz 1/(1/(18.1 + j2.8) + 1/110.52) = 17.58
450MHz 1/(1/(18.1 + j5.2) + 1/58.95) = 16.7
Questions:
1) How off base is my simple analysis?
2) Is there a better way to do this?
3) How significant is the 1.6 ohm mismatch at 10 MHz?
-- John
-------------------------------------------------------------------------
| Feith Systems | Voice: 1-215-646-8000 | Email:
[email protected] |
| John Wehle | Fax: 1-215-540-5495
| |
-------------------------------------------------------------------------