Series XL


These high-power (4,500 W ICAS) Bandpass Filters are to be fitted on the output side of your linear amplifier, filtering out not only harmonics but also broadband noise from the PA.


  • Mitigating intra and inter station interference during contests.
  • Protecting receiver circuitry from damage.
  • Reducing RFI egress and ingress during everyday operation.
  • Enabling full duplex operation (transmitting and receiving simultaneously) on capable transceivers.
  • High power handling capability – up to 4,500 Watts ICAS (100 to 200 W for the other guys).
  • Exceptional out of band rejection, typically > 55 dB and sometimes as high as 75 dB on adjacent ‘contest’ bands thanks to the 5 pole filtering (3 poles are typical elsewhere).
  • For example, the 20m Series XL filter reduces transmitted and received signals on the 40m and 15m bands by approximately 55 dB or more with higher rejection figures on bands further removed from the primary band. See the VNA plots in this section for typical units. Series XL filters are hand tuned and there are small variances between units.

    Full legal amateur power handling within a 3x safety margin ensures that the filters can be safely placed between the linear amplifier and antenna in a station fitted with a linear amplifier. This yields several advantages. First, filtering is in line after final amplification allowing maximum reduction of transmitted broadband noise and harmonic energy. Secondly, station signal routing and switching is greatly simplified vis-a-vis systems that switch low power filters (multiple sets in a SO2R or multi-op configuration) inline between transceivers and amplifiers. Less complex and more reliable. Further, simpler signal routing systems cost less and will substantially offset an investment in a set of Series XL filters. Additional expense offset comes from needing only one Series XL filter per band available to all station transceivers whereas other bandpass filter systems require a complete set of filters for each transceiver.

    The Series XL BPFs are carefully designed for extreme (0.5 dB is typical) insertion loss to avoid overheating and power loss. Balance between each of the five poles of the filter is carefully engineered using high quality high-voltage components to ensure many years of reliable and safe operation.

    A few words about bandpass filter specs. First of all, 55 dB is a lot and 75 dB is, well, incredible! The well regarded (and rightfully so) 3 pole W3NQN BPFs sold by Array Solutions, rated at 200 W ICAS, typically yield about 40 dB rejection on adjacent contest bands (the exact figure varies between 28 & 60 dB depending on the bands compared). The Dunestar BPFs claim 40 dB adjacent band rejection which is to expected from a 3 pole design. The 5 pole 4O3A designs yield significant additional filtering.

    All Series XL filters now have 12 VDC 40 ma cooling fans standard at no extra cost. Generally no additional cooling is needed at amateur power levels however transmit duty cycle, ambient room temperature, humidity and antenna VSWR all factor into the heat dissipation formula. See the Power Derating chart below for guidance on VSWR related power capability.

    Note the 160m Series XL filter is a 5 pole low pass filter, not band pass.

    All 4O3A devices come standard with SO-239 (UHF) female coax connectors. N and 7/16″ DIN connectors available on special order – please contract us for more information.

    Bandpass, low pass, high pass and other filters available for non-amateur frequencies and power levels. Contact us with your requirements for a price quote.

    Series XL filters and other 4O3A Advanced Contest Solutions are helping achieve big scores at some of the world’s greatest contest stations including 4O3A, OH8X, PY5EG, S51A and many others.

    Robust components and construction employing silver-plated high-Q coils, high-current military grade capacitors and heavy duty aluminum enclosures with mounting flanges for secure installation on your bulkhead system or elsewhere in your shack.

    Contest stations operating in SO2R and multi-operator modes will frequently have dedicated antenna systems for each HF contesting band 1. Installing 4O3A Higher Power Band Pass Filters in the antenna line after the linear amplifier and antenna switch means the right filter will always be in circuit on the band/antenna combination in use and the operator will never have to worry about switching filters between transceiver and linear amplifier.

    Contest stations using Triband antennas to cover 20m, 15m and 10m can use the 4O3A High Power HF Triplexer/Combiner in conjunction with Series XL Band Pass Filters to operate simultaneously with a high level of isolation on all three bands with multiple stations sharing the same antenna!

    SO-239 connectors are standard; N and 7/16-inch DIN connectors optional (contact InnovAntennas Sales Team for your special connector order).

    Customer comments:

    With the 4O3A filters our station to station and site to site interaction was negligible across 83,300+ QSOs. We ran 6 stations 24/7 and I don’t recall ever seeing a station not manned. The only time anything was heard was on the exact harmonic and just tuning 5 kHz off that frequency to set the split allowed operation to continue with no impact.

    Jay W2IJ, T33A DXpedition Team Co-Leader

    It is indeed a good feeling when you transmit on one band and can listen even to the weakest signals on the other band, without getting annoyed by interference.

    5B4ADA eHam review

    Typical worst case measurements:


    Insertion loss [dB]

    Input matching [dB]

    Band UP [dB]

    Band down [dB]


    =< 0.35

    => 20

    => 60



    =< 0.47

    => 22

    => 51

    => 52


    =< 0.42

    => 23

    => 56

    => 56


    =< 0.46

    => 25

    => 66

    => 66


    =< 0.4

    => 25

    => 60

    => 51


    =< 0.45

    => 20


    => 65


    =< 0.28

    => 20

    => 65db@144MHz

    => 58db@28MHz

    WARC filters, series XL

    10-10.2 MHz


    =< 20

    45db@14 MHz




    18.05-18.2 MHz

    =< 0.58

    =< 22





    24.89-24.99 MHz

    =< 0.54

    =< 25





    Compared to other filters:


    On the picture above you can see plots of our 20M HP Band pass filter. (dark blue / dark red)
    Our competitors 20M filter is shown in the lighter shades. (light blue / light red)
    Ideally a filter should have a steep sloping curve outside it’s band pass range. It should also have a nominal insertion loss of 0.4dB or less.

    4O3A Signature 20M filter curve has input matching of more then 23dB (dark blue).
    Our competitors filter is about the same in this area.
    Dark red represents the band pass width. Our filters are designed without notch filters and increase attenuation as it moves away from the central frequency. It gives enough attenuation on WARC bands – 34dB on 10MHz and 40dB on 18MHz.
    We measured our competitors filter in house. It’s poorly designed. It uses notch filters to have sufficient attenuation on 7MHz and 21MHz. The filter is very wide and practically doesn’t have attenuation on WARC bands. The attenuation curve is buried at around 40dB. The only upside of this design is lower insertion loss which has no practical purpose. Mechanical design and production is very poor.