Hello Stefan,


Thanks for the reply. The filter is shown here:

http://www.w1vd.com/LPF.html

and the schematic here:

http://www.w1vd.com/LPF.pdf


Jay (W1VD) did say it was critical. This is on the amp page of his web
site : "Low pass filters for 137 and 500 kHz used after the kilowatt
deck have been previously described and can be found at LF and MF
Kilowatt+ Low Pass Filters. "T" type low pass filters (not pi type)
must be used with Voltage Mode Class D (VMCD) transmitters. "


When, as an experiment, I tried my G3YXM
amp LPF on the output of the W1VD amp on low voltage, the drain
waveforms went to pot, and the waveforms from out of the LPF as seen
using my Scopematch were distorted, too. I believe the G3YXM LPF is 59
turns on two T200-2 cores.

Without  nearly doubling the power through the W1VD filter the centre
toroid  stays just warm, the outer two are near as damn it cold. #



I was wondering if the #3 material which is rated for use from 0.05 to
0.5 MHz, and has several times the permeability would be a better
choice for more power through it? It probably gives a higher Q with
fewer turns, allowing the use of larger wire without having
overlapping layers in the winding?

Another alternative is perhaps the #15 material, rated for 100 kHz to 2 MHz?

Thanks Stefan.





Wednesday, May 24, 2017, 4:06:19 PM, you wrote:

> Hi Chris,

> 115 uH appears to be very much for 137 kHz. Not sure what type of filter
> you are using but the standard filters use j50 Ohm which is 59 turns on
> a T200-2 if i remember correctly. I passed 1.5 kW through such type of
> filters and the caroe became maybe just 60 C warm.
> So with a T225-2 you should have no problems at 2.5 kW :-)
> For an air coil you will need more wire and will have more losses unless
> you choose a big RF litz wire. But the size will be extreme and there 
> should be no lossy things in a radius of the length of the coil.
> I would build a LPF based on j50 Ohm coils and -j50 Ohm Cs (~ 22 nF at
> LF) and use the T225-2 cores.

> 73, Stefan


>




-- 
Best regards,
 Chris                            mailto:[email protected]