[Amps] 160M PI network Toroidal Coil

[Tom Thompson]

The SI570 chip is an interesting alternative for a DDS.  I have measured 
the phase noise at -139 dBc/Hz at 10 kHz away from the carrier.  It does 
require a microprocessor to load the registers but it is a simple chip 
otherwise.  The other advantage is that it does not have the switching 
spurs that a DDS has although the DDS chips are getting better from that 
perspective.  The SI570 does not have the frequency stability capability 
of a DDS, but I am using it at 24 MHz for an LO and it holds within less 
than 10 Hz.

Tom   W0IVJ


On 10/8/2013 1:36 PM, peter chadwick wrote:
> 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
>   
>   ========================
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>   http://ludens.cl
>   ========================
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