455kHz Filters and Filter Modules
Glossary of Filter Terms
-6 dB Bandwidth This specification determines how much signal will pass un-filtered. The bandwidth is measured in kHz where the response falls 6 dB from the center frequency of 455 kHz. The wider the bandwidth the more high frequencies will pass. The more narrow the filter the less high frequency content. SSB filters typically have a 6 dB bandwidth of 2.1 to 2.7 kHz. A wide bandwidth would range from 4.0 to 8.0 kHz. Filter bandwidths less than 4.0 kHz are useful for listening to SW signals that are plagued with noise and interference or when DXing and trying to pull a signal out of the noise.
Shape Factor This specification is the bandwidth ratio between the -6 dB bandwidth and the -60 dB bandwidth. It is an important specification because it determines how well the filter rejects adjacent frequencies. The ideal filter would pass the desired signal and reject all others. The closer the figure comes to 1.0 the better the Shape Factor. For example, if a filter measured 4.0 kHz for the -60 dB bandwidth and measured 2.0 kHz for the -6 dB bandwidth, then the Shape Factor would be 4.0/2.0 = 2.0. A good filter will have a Shape Factor of 2.0 or less. Many mechanical filters exhibit Shape Factors of 1.8 to 2.0. A good ceramic filter will have a Shape Factor of 1.5 to 1.9. Crystal filters often exhibit Shape Factors of 1.5. The new digital DSP filters have a Shape Factor of 1.15.
Ultimate Rejection This is also called Ultimate Selectivity. This specification determines the limit of the filtering capability. A poor filter will exhibit 40 to 50 dB of Ultimate Rejection. A good filter will exhibit 60 dB of Ultimate Rejection or more. A good mechanical or crystal filter will exhibit 80 to 90 dB of Ultimate Rejection. An exceptional filter will exhibit an Ultimate Rejection of 90 dB or more.
Zero Insertion Loss Most filters will exhibit a signal loss as the signal passes from the input to the ouput. This is typically 6 dB or half the signal voltage. A filter with Zero Insertion Loss will exhibit no signal loss. This can be beneficial for receiving weak signals. Zero Insertion Loss is also helpful when inserting a filter in the IF signal path without disturbing the gain structure.
Blue Dot Filter
Nominal Bandwidth: 6.5 to 7.0 kHz. This filter is identical in size, shape and pinout to the
LFH4S filter. The bandwidth is excellent for general wide band listening.
LFH-4SNominal Bandwidth: 7.2 to 7.9 kHz. This filter has been a popular replacement for many portable and table-top receivers. However, the last remaining LFH4S filters we have in stock have a wider bandwidth (this filter is no longer manufactured). We recommend this filter for more Hi-Fi applications. NOTE: for general wide band listening, the blue dot filter is a better choice. It is a pin per pin replacement to the Murata CFW-455 type of filters.
LFH-6SNominal bandwidth is 8.2 kHz. This filter is a Hi-Fi bandwidth for excellent fidelity while maintaining moderate rejection to 5 kHz hetrodynes when listening to SW broadcast stations. It is a pin per pin replacement to the Murata CFW-455 type of filters.
Available bandwidths (Please note that we are currently out of stock of narrow filters): 6.0, 6.5, 7.0, 8.0 and 10.0 kHz.
Standard Filter Module Specifications
Operating Frequency: 455 kHz
Insertion Loss: 0 dB
Input Impedance: 10 kohm
Output Drive Impedance: 100 ohms
Shape Factor: <1.8 (typ 1.65)
Ultimate Rejection: minimum 63 dB - typically 68-73 dB
Operating Voltage 4.5 to 36 VDC @ 10 ma
Dimensions: 0.9in w x 1.9in l x 0.75in h (23mm w x 45mm l x 19mm h)
The Standard Filter Module should be ordered as FM___ , with the suffix as the desired bandwidth. For example, a FM 3.5 would be a Standard Filter Module with a -6 dB bandwidth of 3.5 kHz. By adding the /S to the end, the Filter Module can be modified to operate from 4.5 to 15 VDC. This is helpful when installing the Filter Module in low voltage portable receivers such as the Sony ICF-2010/2001D. For example, a FM3.5/S would be a Standard Filter Module with a 3.5 kHz bandwidth capable of operating at 4.5 VDC.
FM____ Price $60.00
Shipping and Handling for one Filter Module within
North America $8.00
Shipping and Handling for two Filter Modules
within North America $10.00
Shipping and Handling for one Filter Module within North America $8.00
Shipping and Handling for two Filter Modules within North America $10.00
The Premium Filter Module is similar to the standard Filter Module but with improved performance. The Premium Filter Module is very quiet. It will not contribute any measureable noise to low level IF signals. These low IF signals are found in the Lowe receivers and more recently in the AOR AR7030 receiver. It will also work well in the JRC 525/535 receivers.
The Premium Filter Module exhibits exceptional Ultimate Rejection. The filter typically exhibits over 100 dB of Ultimate Rejection (upper sideband - see graph below). To achieve this performance, each module requires extensive on-board shielding and the entire module is housed in a metal enclosure that is solder sealed to provide maximum shielding.
Unlike the Standard Filter Module, The Premium Filter Module does exhibit a nominal 6 to 8 dB insertion loss. It must also see a 1.5 to 2 k ohm input and output impedance. This is not a problem when the Premium Filter Module is used for replacement. The circuitry designed within the receiver for ceramic filters (and the new Collins filters) will provide the required impedance match. All that is required is attachment of the input and output coax leads to the appropriate solder pads. Like the Standard Filter Module, the Premium Filter Module is active and requires a DC voltage. Any supply voltage from 4.5 VDC to 15 VDC will suffice. The same voltage that supplies power to the IF board can also supply power to the Premium Filter Module. The Premium Filter Module can be secured to the chassis or pc board with the supplied velcro.
PFM 3.4 kHz Filter Measurements - as plotted on the graph above.
Frequency kHz Attenuation dB
445.0 -95 dB
446.0 -94.5 dB
447.0 -90 dB
448.0 -89 dB
449.0 -86 dB
450.0 -81 dB
451.0 -73 dB
452.0 -48 dB
453.55 -6 dB
454.0 +2.5 dB
454.5 +1.8 dB
455.0 +/- 0 dB reference
455.5 +.8 dB
456.0 +.2 dB
457.0 -6 dB
457.5 -23 dB
458.0 -42 dB
459.0 -78 dB
460.0 -85 dB
461.0 -96 dB
462.0 -120 dB
463.0 -102 dB
464.0 -102 dB
465.0 -103 dB
The available bandwidths will depend on the filters in stock. At present we can create bandwidths with the following ranges (Please note that we are currently out of stock of narrow filters):
6.4 to 7.1 kHz
The easiest way to use the Premium Filter Module is to remove an existing filter from the printed circuit board. The input and output coax leads of the Filter Module are soldered to the appropriate input and output solder pads. Each Filter Module has a red and black power lead that attaches to a DC location on the printed circuit board. The Filter Module is secured to the chassis with self adhesive velcro which we supply.
Premium Filter Module Specifications
Operating Frequency: 455 kHz
Premium Filter Modules should be ordered as PFM___ , with the suffix as the desired bandwidth. Please specify the desired bandwidth and we will try to match it as close as possible. For example, a PFM6.2 would be a Premium Filter Module with a -6 dB bandwidth of 6.2 kHz.
Module Price $85.00 Shipping for one Premium Filter Module within
North America $8.00
Shipping for two Premium Filter Modules within
North America $10.00
Shipping for one Premium Filter Module within North America $8.00
Shipping for two Premium Filter Modules within North America $10.00