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Z10020 Medium Wave (AM Broadcast) Band Reject Filter

Table of Contents

The Z10020 Medium Wave (AM Broadcast) Band Reject Filter reduces signals in the 530 - 1700 KHz  range whilst passing frequencies below this range and above this range with minimal attenuation. For a wide range of the AM broadcast band, rejection levels of 80 dB and more are possible.


The Z10020 in an indoor enclosure with BNC connectors (the normal arrangement) is pictured below.

The Z10020 in a weatherproof enclosure, with UHF (SO-239) connectors is shown below.

Inside the Z10020 filter.

Z10020 Specifications
  Parameter Value
  Design 7th Order, 1 dB Chebyshev design
  Impedance 50 Ohms, or 75 Ohms with Option 075.
  Passband Loss Typically 1.25 dB, except 1.8 - 2.0 MHz where loss may be 3.0 dB (1.8 MHz, improving to 1.25 dB at 2.0 MHz).
  Stopband Loss See table below
  VSWR Typically less than 2.5:1 in passband.
  Maximum Power The Z10020 is intended for receive use only. Powers in excess of 100 mW may damage the filter.
  Connectors BNC standard, UHF, Type N or other connectors available as options. Extra charge may apply.
  Enclosure Die-cast box for indoor use (not weatherproof); optional weatherproof die cast enclosures with mounting flange available at extra charge.
  DC power pass No change in  filter performance with up to 100 mA DC current pass through. Maximum recommended voltage is 24V.

The response figures below are typical of a standard design Z10020 filter, but there is some unit-to-unit variation. In addition, if a specific broadcast station is of concern, it may be possible to provide a custom filter with a deep notch at that frequency with lesser attenuation in other portions of the AM band. Attenuation in the upper end of the medium wave band is constrained by the Z10020's 1.8-2.0 MHz loss requirements. If operation on 160 meters is not critical, rejection in  the upper portion of the AM medium wave band may be increased. Please contact Clifton Laboratories for these and other specialized applications.

Four versions of  the Z10020 are available:

  • Standard Design. Maximum AM medium wave band rejection. Unless otherwise stated, the performance figures on this page are for the standard design filter.
  • Improved 160 Meter Design. By sacrificing some attenuation for medium wave frequencies above 1500 KHz, the loss at 1.800 MHz can be improved. The standard design filter exhibits approximately 3 dB loss at 1.800 MHz, rapidly declining as the frequency increases. The "Improved 160 Meter Design" reduces the 1.800 MHz loss to approximately 1.5 to 2 dB.
  • NDB/NAVTEX Design. The Standard Design Z10020 begins to roll off at 450 KHz or so. At the request of customers interested in chasing non-directional beacon DX, or monitoring 518 KHz NAVTEX operations, or wishing to listen to the  500 KHz amateur radio experimental operations, the NDB/NAVTEX Design moves the low frequency cutoff point up to approximately 530 KHz. As may be expected, there is some sacrifice of medium wave rejection at the bottom end of the MW band.
  • "I don't care about 160 meters" Design. A recent special design for a customer who wanted maximum rejection of the upper end of the AM medium wave band, and is not interested in 160 meter coverage. The upper -3 dB point is moved to 2.0 MHz and the lower -3 dB point to 440 KHz. This provides maximum rejection of AM medium wave signals, over the range 530 KHz - 1600 KHz. Measured attenuation 45 dB at 550 KHz and 50 db at 1560 KHz.

When ordering your Z10020 filter, please indicate which design you wish to purchase.

I've made available, with the consent of Warren, K2ORS, a detailed performance report on a Z10020 NDB/NAVTEX filter I recently built for him. Click here to read the report. It's a 300 kB PDF file. The standard performance documentation option does not include this level of detail.)

  Attenuation Frequency Range
  Full AM medium wave range 530 KHz: 23 dB
1690 KHz: 17 dB
  > 30 dB 545 KHz to 1600 KHz
  > 40 dB 575 KHz to 1520 KHz
  > 60 dB 635 KHz to 1375 KHz
  > 70 dB 670 KHz to 1315 KHz
  > 80 dB 720 KHz to 1225 KHz

Typical Performance Plots

The data below is from a 50 ohm production filter and represents the typical performance of a Z10020 filter.

Insertion loss

Expanded resolution view of passband loss.

Expanded View of AM Medium Wave Rejection

Note the ultimate rejection is 100 dB or more.

Input SWR

The two plots below compare standard and NDB/NAVTEX responses of the Z10020 band-reject filter.
Pricing and Options

Pricing for the standard Z10020 BC band rejection filter (50 ohm / BNC connectors / Indoor enclosure) is:

1. Full kit - builder is responsible for winding cores and adjusting windings to resonate with the supplied capacitors. Enclosure is drilled and all electronic and mechanical parts are provided.

2. Semi-kit - inductors are wound and the capacitors are measured and selected. Builder has to solder in parts and mechanically assemble.

3. Assembled and tested.

4. Optional swept measurement documentation (insertion and return loss) for an assembled filter or one built as a kit (plus return postage if an assembled kit is to be measured)

Prices are:

1. $49.95
2. $67.50
3. $77.50
4. $10.00

Option 1 requires the  builder to measure inductance and capacitance accurately at RF frequencies.

I've now built a dozen of these filters and I do not recommend Option 1 unless the builder is up to the task. It takes me about three hours to wind the inductors and hand-select the appropriate capacitors using an HP 4192A LF Impedance Analyzer, and a General Radio 1658 digital capacitance bridge.

Domestic US shipping via Priority Mail is $7.50. Please contact Clifton Laboratories for international shipping.

If the Z10020 is to be shipped to a location within the Commonwealth of Virginia, please add 5% sales tax.

Construction Options:

Opt U: UHF connectors, silver/Teflon (import) with interior hoods: $12.50
Opt U*: UHF connectors, import, nickel plated, no hoods: $8.00 (Filter performance is not guaranteed with this option.)
Opt N: Type N connectors, with interior hoods $12.50
Opt S: SMA connectors. $12.50
Opt WSFL: Hammond 1590WSFL flanged weatherproof enclosure $14.00
Opt WSF: Hammond 1590WSF flanged weatherproof enclosure $18.00
Opt 75: 75 ohm impedance instead of 50, built with 50 ohm connectors--no extra charge.
Opt 75N: 75 ohm impedance with 75 ohm Type N connectors: $22.50

Design Options:

Standard: Standard upper and lower 3 dB points
160 Meter: Reduced loss at 1.8 MHz, but lesser rejection in the medium wave band above 1500 KHz
NDB/NAVTEX: Lower 3 dB point moved to 530 KHz, with lesser rejection in the lower frequency portion of the medium wave band.

There is no price difference for the three Design Options.

The difference between Option WSFL and WSF is the flange location. Option WSFL has the flange on the enclosure lid and option WSF has the flange on the enclosure base. The weatherproof enclosure photograph at the top of the page is of the WSFL enclosure.

Options WSFL and WSF come with gasketed hardware - the 6-32 and 4-40 screws have recessed grooved heads with a Buna-S gasket to reduce water ingress.

These filters are assembled as orders arrive and most options will require an additional order interval. Normal order interval is one week.

Payment may be made with a check or money order payable to Clifton Laboratories at the address on the top of this page, or via PayPal to If ordering a filter, please also send a separate E-mail with your order specifics and contact information.

Effectiveness of Filter

To illustrate the effectiveness of the Z10020 Band Reject filter, the following spectrum analyzer shows the spectrum over the  range 0 - 2 MHz at Clifton VA. The antenna is a Clifton Laboratories Z1501C Active Antenna.

The blue trace is with the Z10020 out of the circuit, and the magenta trace is with the filter connected.

The AM medium wave environment at Clifton VA is not too extreme, as the strongest signal is 1460 KHz, at an amplitude of around -25 dBm. 

Ron, K8AQC, in contrast, is located in suburban Detroit in a location with many very strong medium wave signals. Ron has a Z10020 NDB/NAVTEX band-reject filter and kindly supplied a similar spectrum analyzer image. (Ron is also using a Z1501C Clifton Laboratories Active Antenna.)

The blue trace is direct and the magenta is with the Z10020 NDB/NAVTEX filter in place. Note that one station (WJR, 760 KHz) has been reduced from nearly 0 dBm into the spectrum analyzer noise floor, and the strongest station (1500 KHz) has been reduced from +5 dBm to -39 dBm, well within the range of reasonable signal strength to be handled by a typical receiver.

User Comments


Hi Jack:

 I just wanted to add my name to your long list of testimonials regarding that AM reject filter.  Mine is working fabulously.  I have a software radio from RFSpace that was being totally overloaded as was my Icom IC-7000. (The FT-1000MP was mostly able to overcome the strong AM, but I put the filter in the receive loop and I think it does make a difference there too.)

Anyways, I am now able to use my SDR-14 the way it was intended and to use my IC-7000 again.

You are my hero!

73  Greg KN6MT

From Warren, K2ORS:
Hi Jack,
Received the filter today, it's performance is awesome!
It knocks 50kW locals into the noise.

Let me know when the active antenna and multicoupler are ready, I'm interested in both.

Many thanks!
From Bob, K7KMQ

Kudos to your clerk at the Clifton post office. She knows her business, your filter arrived Friday noon.
What a beautiful filter it is...  It has done everything I expected and more.
Thank you Jack... I love it...   Bob