Hi Paul, Stefan !
As Stefan wrote, the Amidon T106-2 iron powder cores do a good job at
475 kHz and 100W out. See attached foto of my lowpass filter.
Data : 3 x T106-2, 6 x 6800pF capacitor Wima FKP1/1250 Volt, 7 pole
Chebychev lowpass filter.
input, 6800pF to ground, serial coil(=toroid) 19.5 µH, 13600pF
(=6800+6800) to ground, serial coil 21.6 µH, 13600pF to ground, serial
coil 19.5µH and 6800 pF to ground, output.
toroid 1+3 : 38 Turns on T106-2 = 19.5µH,
toroid 2 : 40 Turns on T106-2 = 21.6µH, all 0.85mm magnet wire =AWG #20
= SWG #21.
measured attenuation (VNWA3) : 0.16dB at 475kHz,30dB at 758kHz, 60dB at
1125kHz. Does not get warm at continuous 100W out on 475kHz.
73 de dg3lv Tobias
Am 10.03.2016 um 23:59 schrieb DK7FC:
Hi Paul,
Am 10.03.2016 23:29, schrieb Paul Nicholson:
The coils of the T filter wound on ferrite toroids get very
hot very quickly. It's the ferrite producing the heat not
the wire. I must have the wrong flavour of ferrite so I
ordered some different ones (nice blue EPCOS ones) but they
wont arrive till Monday. Meanwhile I'll wind some air cored
coils for the filter.
The ferrite seems to saturate.
I recommend using iron power cores of -2 type (everywhere available,
cheap, well working world wide). For your power level, T106-2 or maybe
*T130-2* types are suitable. A T200-2 can be used for 1 kW when wound to
j50 Ohm at LF.
73, Stefan
LPF475_7poleCheby_001.jpg
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