BPFs: 1015204080160

Yes, it is not a band-pass filter, it is a low-pass filter(LPF).

The reason to go this way is to fit this filter into a standard size enclosure. The design is LPF with added LC traps for 80 and 40 meter bands.

Recommended BPF Power with antenna VSWR <1.5:

  • 50 CFM fan installed – 3000W CW/SSB (2000W RTTY)
  • Without fan installed -1500W CW/SSB 

Hammond 1444-1773 enclosure can be used :

  • Without Fan – 17″ x 7″ x 3″ (42.5 x 17.8 x 7.6 cm)
  •  With Fan Installed –  17″ x 7.5″ x 3″ (42.5 x 19.5 x 7.6 cm)

Hammond 1411ZU enclosure can be used if more efficient large fan cooling required :

  • Without Fan – 17″ x 4″ x 5″ (42.5 x 10.5 x 12.5 cm)
  •  With Fan Installed –  18″ x 4″ x 5″ (46 x 10.5 x 12.5 cm)

I used Micrometals T200-2 Iron Powder cores for a large coupling coils and this approach allowed me to fit LPF into my desired enclosures.

  • Those coupling coils made on toroids with 2mm copper wire are not under the stress of a large current and can be used up to 3000W of an amplifier output power (At 3000W power level cooling is required).
  • The simulation software shows an acceptable current level in those coils made on Iron Powder cores. The real test confirmed that 160M LPF can be used up to 3000W of output power.
  • Insertion Loss is very low and my test with 1500W of output power without  installed cooling fans showed that nothing overheated and can be used for a higher output power with air cooling.
  • Doorknob capacitors used are in parallel with at least 30KVar of a reactive power and there is no way any HAM radio amplifier can “smoke” them.
  • The picture below is for 160M LPF built in 1444-1773 Hammond enclosure which is only 3″ (7.6cm) tall and built without any cooling fans.
  • As always for all my BPFs and Triplexers only high quality ceramic standoffs used.

The first 160M LPF was built in smaller 1444-1773 enclosure. Please, see some dimensions above.


The results I achieved for the 160M LPF:

  • Insertion Loss < 0.15dB
  • Band Isolation ( 80M > 65 dB, 40M > 80dB)
  • VSWR < 1.1 ( Return Loss > 26 dB)



Later, I build 160M LPF in my standard 1411ZU enclosure. This enclosure is 2″ shorter in depth (but 1″ higher) and with large doorknob capacitors , all parts installed are closer to each other.  Anyway, all numbers are very good.

Please, see 160M LPF in 1411ZU Hammond enclosure below:


The results I achieved for the 160M LPF:

  • Insertion Loss < 0.1dB
  • Band Isolation ( 80M > 65 dB, 40M > 85dB)
  • VSWR < 1.1 ( Return Loss > 26 dB)


The graph below shows Zs (impedance) and VSWR.


I achieved almost the same numbers for both enclosures except Insertion Loss is better and  below 0.1 dB for a larger box. The difference in Insertion Loss is very small and is not going to make any difference in a real application.