BPFs: 1015204080160

Please, see 80M BPF built with large toroids as a coupling inductors in a smaller enclosure.

80M HP BPF comparison (websites can be opened by links):

Insertion Loss 160M Isolation 40M Isolation
VA6AM  < 0.37 dB > 62  dB > 75 dB
DXEngineering (LBS) < 0.18 dB > 45 dB > 47 dB
4O3A < 0.47 dB > 52 dB > 51 dB


For 80M BPF I used a twice wider enclosure to fit in all large coils.  I have to use MFJ amplifier coils to make up a large inductance for coils. Some large capacitance made of three doorknob capacitors in parallel. All these factors has brought price up.

Two 50 CFM fans installed to get a suffucient air flow to the larger box.

Recommended BPF Power with antenna VSWR <1.5:

  • 3000W CW/SSB (2500W RTTY) 
  • Without fan installed – 1500W 

Enclosure is Hammond 1411ZU :

  • Without Fan – 17 x 10″x 4″ (42.5 x 25 x 12.5 cm)
  • With Fan Installed –  18″x 10″x 4″ (46 x 25 x 12.5 cm)


In general, schematics is the 5th order Chebyshev inductor-coupled BPF.

  • Insertion Loss < 0.40 dB
  • Band Isolation ( 160M > 65dB, 40M > 73dB)
  • VSWR < 1.1 (RL > 25 dB) 


Doorknob capacitors allow to use it up to 6000 PEP output power but I’ve never tested it with this power. For this output power some coils should be made with  a larger wire diameter.

Now, I build all 80M BPFs in a smaller box and with T200-2 toroids as coupling coils. Unfortunately, Ameritron coils sold by MFJ are not available all the time and those coils are too fragile.

The enclosure 1444-1783 used, 17″ x 8″ x 3″ with three 60mm fans installed for a better cooling those coils under the current stress.

80M_LY4L 003