
Ltp: tft025
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VI
TELEFILTER
Application Note
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1. General
The filter is symmetrical, i.e. input and output are exchangeable with each other. But the
external coupling coil has to be connected to pin 3 in any case.
The filter can be driven balanced only.
To get a balanced signal for test measurements with the network analyzer we use two
wideband 1:1 transformers at each port:
SMT 4, vendor NEOSID, PN 88 8529 10
The calibration for the plots was made at the 50 Ohm ports. Thus, the measured characteristics
include the losses of the two transformers (about 0.7 dB each).
The termination impedances are :
500
|| - 1 pF
This impedance is equal for the input and the output. It has to be realized at the point were the
filter is mounted. To match this impedance to the impedance of the system a matching circuit
is required.
2. Theoretical matching
For the matching of termination impedances to 50 Ohm there can be used two different
matching circuits:
50 Ohm test circuit 1
6
LB-IN
version 1.0
01.11.00
TFS 400C1
1/2
VI TELEFILTER
Potsdamer Strae 18
D 14 513 TELTOW / Germany
Tel: (+49) 3328 4784-52 / Fax: (+49) 3328 4784-30
E-Mail: tft@telefilter.com
VI TELEFILTER reserves the right to make changes to the product(s) and/or information contained herein without notice. No liability is
assumed as a result of their use or application. No rights under any patent accompany the sale of any such product(s) or information.
Vectron International, Inc.
267 Lowell Road
Hudson, NH 03051 / USA
Tel: (603) 598-0070 Fax: (603) 598-0075
E-Mail: vti@vtinh.com
2
1
5
4,7,8,
LB-OUT
SAW
C1
L1
C2
L4
L2
L5
L3
3
L1 = L2 =L3 = L4 = 29.84 nH
C1 = C2 = 1.39 pF
L5 = 56 nH