10M4D filters - quick performance plots and impedance matching

A quick performance test of the low cost 10M4D filters obtained from Germany, note loss indicated on plots includes that of resistive matching & ultimate attenuation isn't displayed due to reaching the analyser noise floor.

The indication is that the filter easily meets its published specification, the plots haven't been "frigged" in any way and were made with the interface shown. IMD tests haven't been made.

Centre frequency 10.695MHz

MODEL

NO
of
Pole

Pass
Bandwidth
(dB) (KHz)

Stop
Bandwidth
(dB) (KHz)

Ripple


(dB)

Insertion
Loss
(dB)

Guaranteed
Attenuation
(dB)

Terminating
Impedance
(k//pf)

10M4D

8

6  2.0

80  5

2.0

4.0

90

0.9//10

Published specification

Drawing - 10M4D is type D1 (manufacturer is NTL )

 

Filter response - 10dB division

 

Spurious response

 

Test circuit


Click to view larger image

Integration into STAR

The method I have used to "match" the filter into Pic-A-Star IF is shown above.

L1 is 22 turns 0.25 mm wire wound onto a T50-2 (red) core, T1 is 36 turns of 0.25 mm wire wound onto a T37-2 (red) core tapped at 29 turns from the "cold" end. Put simply there are 29 turns across R5 with another 7 turns connected to the filter via a DC blocking capacitor. T1 is resonated with a 60pF trimmer, note that as I couldn't obtain 100pF trimmers VC3 is 60pF with 33pF in parallel.

Plot of filter response taken using Spectrogram - DSP filter off, spike at 2400Hz is due to lack of screen around IF

 

DSP filter 3 selected

DSP filter 1 selected