Crystal Ladder Filter Board
Generic, 5-Pole Filter,
Crystal Ladder Filter Board,
size-A, 1.2 x 1.2 inch square.
Schematic, in ExpressPCB software.
Printed Wiring Board and Layout, in ExpressPCB software.
The PWB-CLF-5 is a Printed
Wiring Board that will accomode up to 5 series
crystals. It is based on
a generic design that can generate a variety of filter responses.
The response of a Crystal Ladder Filter depends
entirely on the values of components placed on the board.
Therefore, no electrical specifications are assigned to this pwb.
Also, no component values are assigned to this pwb.
However, I will include, at the bottom of this page,
specifications and component values for some different filters.
Each has a different characteristic but uses the same Crystal.
can use the information as a guide for designing
other filters. I highly recommend going to the AADE web site and
downloading their Filter Design and Analysis software. I created
for this generic board using their ladder component references.
However, I use a different topology for impedance transformation.
Here is another crystal ladder filter program.
Although limited in its design capability, it is perfect for the
PWB-CLF-5 topology. Very easy to use. By Horst Steder,
DJ6EV and Jack Hardcastle, G3JIR. To download, go to
http://www.arrl.org/qexfiles and find "11x09_Steder-Hardcastle.zip".
Documentation for Generic,
5-pole Crystal Ladder Filter
for Generic, 5-pole
Crystal Ladder Filter
There are no component values
called out in the schematic. This is because a variety of filters
can be constructed with the same topology, yet have very different
operating characteristic. There is one difference from
the AADE topology. I am using a low-pass impedance transformation
PWB-CLF-5, Master Artwork for Generic, 5-pole Crystal Ladder Filter
You will notice extra components,
not called out in the schematic. It is likely that a required
component value is not
a standard value. The supplemental (x) components can be added to
achieve the proper values. Not all components are used, depending
on the type of Response. Some are replaced with shorts
or zero ohm resistors.
Placements for Generic, 5-pole Crystal Ladder Filter
This view shows component
placement and fence locations. The blue
lines indicate the fences. Each section of the
filter is isolated from the next section. This isolation is very
important to obtain good Ultimate Rejection Ratio. You might
not see this method of fencing in many radio filters. For Single
Sideband or CW filtering, extremely high rejection is not usually
necessary. The human ear can not discern out-of-band signals
that are greater than about 50 dB below the main signal of
interest. However, for a spectrum analyzer, the rejection ratio
must be better than 70 dB. The following screen print shows the
fencing without component placements.
Trace Layer for Generic, 5-pole Crystal Ladder Filter,
The crystals (X3-11) and the RF
connectors (J1, J2) are installed from the bottom side of the
board. The internal fences are installed on the top side of the
trace side. When the module is complete, each section will have
its own separate top cover soldered in place. The perimeter fence
should be about .5 inch high and extend below the bottom of the board
so that it can be soldered on both sides. The internal fences
should also be .5 inches high. This will make them extend about
.1 inch above the perimeter
fence. This makes it much easier to cut and install the top
covers for each section.
I recommend using coffee can lids (tin plated
steel) for fences and covers. It can be cut with scissors,
although I don't suggest using your wife's sewing scissors.
Bottom Ground Layer, as
viewed from the top
Construction Hints for Generic, 5-pole Crystal Ladder Filter:
1. Do not install the fences.
2. Install the components on the top side of the board. Do
not install the attenuators. They will inhibit testing.
3. Install the two connectors on the bottom side of the board.
4. Install the five crystals from the bottom side of the board.
5. Test the filter without variable tuning components. You should
expect very poor Ultimate Rejection Ratio, due to the missing
fences. That is fine. You are concerned only with S11
Magnitude return loss, and S21 bandpass response.
5a. If the filter has respectable S21 and S11 data, install the
internal fences and then install the perimeter fence. Test the
filter again to verify the S11 and S21 data has not changed much.
Expect a minor amount of S11 Magnitude return loss change.
Install the individual top covers.
5b. If the filter has poor response, change the components to variable
components, or you can try adding small amounts of capacitance across
the fixed capacitors to change the response. This is not the best
way to tune a filter because you can add capacitance, but you cannot
Results of a Specific Crystal Ladder
The following are results of a Crystal Ladder Filter
I designed and constructed, using the PWB-CLF-5. I have given it
a preliminary part number of SLIM-CLF-10.11/1.0 The Crystals used
are 10.11 MHz, and the design bandwidth goal was 1.0 KHz. For
actual filter component values, see the Table at the bottom of the
page. These are the average motional characteristics of the 5
crystals, PN: N10.11 PDI.
Fs = 10.11099705 MHz, Fp = 10.12984 MHz, Lm = 20.83468 mH, Cm = .0119
pF, Rm = 10.97 ohms, Cp = 3.182 pF. The 5 crystals were selected
from a batch of 85 that were close in Fs (10 Hz) and Rm (2 ohms).
S21 plot of
completed SLIM filter with shields in place,