[Amps] Lowpass filter inductor cores

Jim Thomson jim.thom at telus.net
Mon Aug 21 14:58:28 EDT 2017

Date: Sun, 20 Aug 2017 17:46:14 +0000
From: Manfred Mornhinweg <manfred at ludens.cl>
To: amps at contesting.com
Subject: [Amps] Lowpass filter inductor cores

<Hi all,

<I'm puzzled by seeing many low pass filter boards offered on eBay and 
<elsewhere, that are rated for 1kW, 1.5kW and even more, with some 
<sellers stating that their filters can work in CW without requiring 
cooling; and these filters all seem to use T-130-2 and T-130-6 toroids. 
With the 10m coils having 5 turns on a T-130-6 toroid, and the 6m coils 
4 or even 3 turns.

I just did a small calculation, and if I'm not mistaken I get a flux 
density of around 30mT on the 30m band. Extrapolating the loss data 
given by Micrometals and Amidon for that iron powder material, it turns 
out that at 1500W output the core loss would be around 100W!!! And on 6m 
of course it would be worse. The inductors would get hot enough to 
unsolder themselves.

Either I did a mistake in my calculations, or it's simply not true that 
those filters can work at this power level, maybe not even with forced 
air cooling!

So my question is: Has anybody here actually used any of those filters, 
or the mentioned cores, at legal-limit RTTY, on the highest bands? How 
hot do the toroids get? With how fast air flow?


##  something is amiss.  I have yet to see any of these LP filters that even use
powdered Iron Toroids on the upper bands.  The toroids are only used on 160-80-and
maybe 40 m.  
Never seen toroids ever used on 20- 17 – 15-12-10-6 m  bands... they all 
use air wound coils.    On  20-6m, they all appear to use heavy gauge magnet wire. 
This is on the various  commercial 1.5 kw SS amps..and also kits. 

##  Those mono band  1.5 kw CCS rtty band pass  filters made by 4o3A  are the same deal,
toroids only used on 160-80m.  40-10m are air wound coils.   His  160m filter is a LP filter.....all
other bands are a band pass filter. 

Jim   VE7RF

More information about the Amps mailing list