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E-mail: Jack.Smith@cliftonlaboratories.com
 

 

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Z10010 Coupled Resonator Bandpass Filter

The Z10010 coupled resonator bandpass filter is available. The Z10010 was originally developed to extend the dynamic range of the Z90/91 panadapters when used with an Elecraft K2 transceiver and Clifton Laboratories' Z10000 buffer amplifier.

However, additional interest has been expressed in using the Z10010 when employing a Softrock receiver as a panadapter in order to keep unwanted signals into/out-of the Softrock. To that end, the Z10010 is now available in two models:

  • Z10010-K2 200 KHz bandpass, centered on  4915 KHz
  • Z10010-K3 400 KHz bandpass, centered on 8215 KHz

In addition, a Z10010 may be made in a custom design for frequencies between 500 KHz and 30 MHz. Please contact Clifton Laboratories for a price quotation and feasibility analysis. (I've built custom filters for 10.7 MHz, 28 MHz and 518 KHz with good results. The 518 KHz filter data can be seen at 518 KHz Bandpass Filter.) Coupled resonator filters of this type, using small powdered iron or ferrite inductors, work best when the bandwidth is around 4 or 5% of the center frequency.


I'm reluctant to make these filters available as a kit, as they require the four toroid inductors to be wound and adjusted to the target inductance within ±2%. Even with the inductors within this tolerance, final adjustment requires adjusting four trimmer capacitors to provide the desired center frequency and passband shape. I use an HP4342A Q-meter to adjust the inductors and verify their Q as meeting minimum standards, and an HP8752B vector network analyzer to tune the filter. 

These filter will be supplied as an assembled, tuned and tested assembly, with a tamper seal on the enclosure. Building and aligning a filter is a reasonably laborious process, requiring me to wind the inductors, adjust them to target values, coat them with Q-dope, assemble the PCB, drill the enclosure, tune the filter in a special enclosure and then move the tuned filter assembly to the normal enclosure, re-measuring to verify the performance has not changed. 

A copy of the Z10010 Instruction Manual is available by clicking here or via my Documents page. The manual only covers the K2 version filter at the moment. Additional information can be found on the K2 Filter page and on  the K3 IF Bandpass filter page.

Ordering and Pricing:

Z10010-K2 or Z10010-K3 filter, assembled, aligned with a copy of the bandpass sweep data is $44.95, including postage to domestic US locations. Custom frequencies are quoted individually.

Virginia Sales Tax—If your Z10010 is to be delivered within the Commonwealth of Virginia, don't forget to include 5% sales tax.

To order by PayPal, send the correct funds to orders@cliftonlaboratories.com. Checks should be payable to Clifton Laboratories and sent to the address at the top of this page. Please contact me to obtain a quotation on international shipping if you are outside the USA.
 

Z10010-K2 & K3 Specifications
 

Center Frequency

4.915 MHz nominal (k2) 8.215 MHz nominal (K3)

Dimensions

3.5” X 1.5” X 2”
89mm x 38mm x 51mm

Bandwidth (-3 dB)

200 KHz typical (K2); 400 KHz typical (K3)

Connectors

BNC-female (input and output)

Insertion Loss

3.5 to 4.5  dB typical

Power Rating

Receive Only

Impedance

50 ohms

 

 

 

Z10010 Filter. Photo shows older revision PCB. New board is similar in size and layout but with increased capacitor options.

 
Z10010 Filter in its enclosure.
 
Typical Performance Curves K2 Version
 

Typical Performance Curves, K3 Version
 
Tuning a Z10010 Filter

I thought it might be interesting to learn what is involved in tuning a coupled resonator filter.
 
Because the filter's tuning is sensitive to nearby metallic surfaces, I've made a tuning fixture that permits access to the four trimmer capacitors while in the standard enclosure.

Here's a typical frequency response of a newly built filter before tuning. The trimmers are all at random positions, so the response is far from the expected value.
 

As the four trimmers are adjusted (and they interact) the filter's insertion loss, center frequency and response shape change.
 

After a bit more tweaking, the response is  getting closer to the desired shape.
 

Final tune. The filter has a reasonably flat (within 0.5 dB) over a 200 KHz bandwidth and a 3 dB bandwidth of approximately 350 KHz. Tuning the filter usually takes five to ten minutes from start to finish.