A very short High Power 5th Chebyshev type Bandpass filter specification:
- 10, 20 meter band BPF band Isolation > 60dB
- 15 meter BPF band Isolation > 56dB
- 40 meter band BPF Isolation > 60dB
- 80 meter band BPF Isolation > 65dB
- 160 meter band LPF Isolation > 65dB
- PEP output power up to 3500 watts (a few HAMs used it with OM3500 amplifier)
Please, see BPF specifications and graphs here.
Insertion Loss (dB)
Return Loss (dB)
UP Band Attenuation (dB)
DOWN Band Attenuation (dB)
|160||< 0.12||> 26||> 65||–|
|80||< 0.4||> 26||> 70||> 65|
|40||< 0.32||> 26||> 70||> 60|
|20||< 0.32||> 26||> 60||> 65|
|15||< 0.37||> 26||> 55-57||> 60|
|10||< 0.3||> 26||–||> 65|
BPFs designed to be used after amplifier with kilowatts of applied power and this requirements defined the design criteria.
15M BPF band isolation is lower among all band BPFs because 10 and 15 meter bands are closest located bands (by frequency ratio). The same -60dB could be achieved for the price of a higher insertion loss.
I would like to start explaining what happens if some capacitor gets broken (electrically or mechanically). The Chebyshev type BPF is very good for this matter. If any capacitor failure happens the band Isolation is still high but Insertion Loss and VSWR would go up right away.
- It means 2nd RX radio still protected and if you have a SWR protection built-in into your amplifier you will knew the problem right the next second. If you do not have such a protection it is highly recommended to use some SWR/Power meter with SWR using PTT line protection, like this one : PowerMonitorIII_v4.
- You can buy it directly from website below : https://ikr.andys.ru/proizwodstvo/powermonitor/
- The achievable BPF adjacent band isolation could be a very high number and it sounds like “the more isolation the better” but the price for it will be a higher Insertion Loss and more difficult to get a low VSWR.
Insertion Loss is a heat which dissipated on BPF parts, such as capacitors and coils. Q-factor of coils much lower than that of capacitors that is why the most heat will be dissipated on coils. Larger wire/tube diameter and a fan cooling should be planned for a high power BPF above 1500 watts of output power.
- It is a nice idea to use a radio band decoder, like this one from RemoteQTH.com or any other with a relay output, to turn ON a required High Power BPF cooling fan only when band chosen. This approach will decrease a fan noise and will allow all cooling fans last longer. With SO2R setup only two BPF’s cooling fans will be running simultaneously.
It is hard to melt a copper wire to destroy the filter but with temperature goes up the coil changes its dimension if not built on a ceramic core. Yes, it is a very good idea to use ceramic cores for coils inside the BPF, but it is an expensive and hard to find part today.
I ran a few tests with an extreme hot and cold temperature to see how much BPF’s parameters would be changed. The graphs shifted left/right when temperature changed with band attenuation up or down 3-5dB. As BPF’s VSWR below 1.1 is quite wide by frequency range, it’s never been above 1.2 with an extreme temperature change tests. It is an acceptable result but a room temperature considered as a normal usage requirements.
-0.4 dB of Isolation Loss is 10% loss of applied power. For 1500 watt output power this is 150 watt dissipation inside the BPF with 100% cycle. Of course, our CW/SSB TX cycle is not 100 % . We can consider this 150 watt dissipation an average between 65-100 watts. The -0.3 dB loss brings that level below 50 watt.
BPFs can work without air cooling for 1000-1500 watts depending on a band. For a low bands, such as 40-80 meter bands, all coils have more wire turns than those for a high bands, especially for a 10 meter band and such coils are easier to cool off.
The longer the coil wire the easier to cool a coil wire off. If we compare 40 meter band BPF with 10 meter band BPF, the first could be used without cooling up to 1500 watt CW/SSB but with 10M small 3 turn coils this power level will make coils very hot and that is why a lower output power without fan cooling recommended.
- BPF Impedance should be as close to 50 Ohm as possible. If BPFs used with triplexer, both have to have as close Impedance to 50 Ohm as possible.
If BPFs connected between Amplifier and Antenna than it makes some sense to increase Isolation level if required. That is why I build my 40 and 80 meter band BPFs with higher adjacent band isolation and 10-15-20 meter bands used with triplexer with lower numbers.
- The total band isolation of the 3000W triplexer with BPFs is better than -80 dB and this level is a sufficient level of band isolation up to 5000-6000 watts to the tribander antenna.
Military specification doorknob capacitors have a specified nominal reactive power. All capacitors used at least two in parallel with minimum reactive power of 6 Kvar each. Those capacitors should handle a power up to 4000 watt level without any problems.
Please, see all detailed information about BPFs on a related webpages.