A very short High Power 5th Chebyshev type Bandpass filter specification:
- 10, 20 ,15, 40, 80 meter band BPFs
- 160 meter band LPF
- 160 meter band BPF
- 40, 80, 160 in a smaller enclosures
- 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||< 0.35||> 26||> 65||> 65|
|40||< 0.3||> 26||> 70 ( >82)*||> 60|
|20||< 0.3||> 26||> 62||> 65|
|15||< 0.35||> 26||> 55-57**||> 60|
|10||< 0.25||> 26||–||> 65|
* -82dB Isolation level in 40M BPF achieved with coupling coils made on Iron Powder coils. Please, see HP 40M band page.
** 15M BPF band isolation is lower among all other 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 which are not a good thing for High Power filters.
All filters are Chebyshev type band-pass filters which can provide a good attenuation level with low insertion loss and passband ripples. All of them an inductor-coupled bandpass filters except 10M band BPF which is a capacitor-coupled type. 160M band is a Low pass filter to eliminate higher harmonics.
BPFs designed to be used after amplifier with kilowatts of applied power and this requirements defined the design criteria.
BPF installed after amplifier is very effective in reducing TX harmonics.
- VE6SV experienced the 2nd 40M TX harmonics interference to 20M band with both 40 and 20 meter antennas located on the same tower. 20M BPF installed on a receiver side (20M band) changed almost nothing but 40M BPF installed on TX side (40M band) removes a wide band 2nd harmonics noise on 20M band to a zero level.
Coax stubs are not so effective compare to BPFs because of having lower attenuation and because of having much narrower bandwidth (can work on CW but not on SSB section). With a few of them in line, good quality coax cable and some added relays (if required) the coax stubs becomes not a cheap solution as well, but simpler to build compare to HP BPFs.
All designed BPFs are Chebyshev type filters. Cauer (Elliptic) type can be used as well and with LC traps some higher band isolation can be achieved but LC trap inside the BPF can be quite narrow and any failure (or change) of those LC traps can reduce band isolation to a “risky” level. Chebyshev type is much better in this term.
- The 2nd RX radio still protected when BPF failed if you have a SWR protection built-in into your amplifier. If you do not have such a protection it is highly recommended to use some SWR/Power meter with SWR using PTT line protection, something like this one : PowerMonitorIII_v4.
- 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 achieve a good Return Loss (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.
- 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 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 1200-1500 watts depending on a band and a duty cycle. For a low bands, such as 40-80 meter bands, all coils have more wire turns than those for a higher bands, especially for a 10 meter band and larger 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 1800 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 should have as close Impedance to 50 Ohm as possible.
- The total band isolation of the 3000W triplexer with BPFs is better than -85 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.