[Amps] 160M PI network Toroidal Coil

[peter chadwick]

Manfred,

it is interesting to look at the WW2 German radio equipment - obviously designed pre-1939. The use of ceramics, especially in capacitors, and iron cores is interesting, to say the least.

>Nowadays of course I use DDS chips instead of VFOs, so that problem has 
 been solved<

Has it? unless all the spur and noise  powers summed in a 1 MHz bandwidth are at least - IN THAT 1MHZ- average -110dBc/Hz - from 
100Hz away from the frequency. You don't meet the requirements ot the Radio Regulations.

73

Peter G3RZP

=======================================
 Message Received: Oct 08 2013, 07:26 PM
 From: "Manfred Mornhinweg" <manfred at ludens.cl>
 To: g8on at fsmail.net
 Cc: amps at contesting.com
 Subject: Re: 160M PI network Toroidal Coil
 
 Peter,
 
 > The numbers I've seen for flux density suggest that at 160m, you
 > should be at no more than 100 gauss or 10 mT for reasonable losses
 > and linearity.......and preferably a bit less.
 
 Yes, that's about correct. The exact value varies a bit with core 
 material, size, and so on, but will be close to 10mT.
 
 This tends to require long, relatively slender cores, or very low 
 permability ones.
 
 > So even if you cool the toroid, I'm still a bit doubtful about
 > linearity.
 
 So am I. But the emphasis is on "doubtful". I would have to try it, as I 
 don't have good data about that material's linearity. Real saturation 
 anyway only starts at much higher flux density levels. But hysteresis 
 effects have a good chance to cause significant nonlinearity.
 
 > Plus there's the temperature coefficient to consider, too.
 
 As long as the loaded Q is low enough, that shouldn't become a real 
 problem in a tank circuit. It's much worse when you are trying to make a 
 VFO coil on an powdered iron core, as is often suggested in ARRL 
 literature! In my youth I built several radios with "automatic built-in 
 scanner" that way, until I figured out that nice big air core coils are 
 far more stable!
 
 Nowadays of course I use DDS chips instead of VFOs, so that problem has 
 been solved!
 
 > Fortunately, dust iron has a fairly high Curie temperature, but that
 > needs to be given some consideration - I suspect Amidon don't have a
 > figure for it.
 
 I think that the Curie temperature is probably high enough, so that 
 insulation failure of the wire, or binder degradation of the core, are 
 the limiting factors.
 
 > For some reason, I've never been a big fan of toroidal dust iron
 > inductors....
 
 They have their uses, where they provide some worthwhile advantage over 
 other solutions. But they are certainly not an essential type of 
 component. If all iron dust cores disappeared from this world, I could 
 still design all my circuits, with only minor limitations, using either 
 air core coils or ferrite cores, depending on the case. Instead if 
 ferrite was taken away from this world, life would be much harder! Some
 kinds of circuits we are used to just couldn't be built.
 
 Manfred
 
 ========================
 Visit my hobby homepage!
 http://ludens.cl
 ========================