Loading inductor Question

[Ken Alexander-2]

Folks,

Given that inductors on toroid cores are used extensively in autotuners, is there any reason (assuming I choose the right size core, made of the correct material for the application and winding it with the right size wire) for not using one as a base loading inductor on a vertical antenna?  I'm talking 100 watts maximum transmitter output here.

Any down side to doing this?

Thanks and 73,

Ken Alexander
VE3HLS
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[Fred Townsend]

Ken:
Toroidal cores have many fine qualities for loading coils. Of course not all
core have the same qualities so be sure you have the right Al rating. You
will want a low rating. Also remember you will lose those fine qualities if
you saturate them so be sure your core is big enough for 250 watts (2.5x
safety margin). I use Teflon wire on mine for lower losses. Finally, it is
very difficult to tap a toroid whereas coil taps are easy on an air core
coil. Don't use toroids if you need taps.
73
Fred, AE6QL

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Ken Alexander
Sent: Monday, April 30, 2012 8:15 AM
To: Elecraft
Subject: [Elecraft] Loading inductor Question

Folks,

Given that inductors on toroid cores are used extensively in autotuners, is
there any reason (assuming I choose the right size core, made of the correct
material for the application and winding it with the right size wire) for
not using one as a base loading inductor on a vertical antenna?  I'm talking
100 watts maximum transmitter output here.

Any down side to doing this?

Thanks and 73,

Ken Alexander
VE3HLS
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[Jim Wiley-2]

Ken -

 A toroidal inductor should work fine,   it is understood that the core
must be of the proper material and size to handle the expected power and
frequency range.  Keep in mind that many of the automatic tuners use
toroidal inductors  in their design.   There is some advantage to having
the loading inductor "out in the air", as it dos radiate somewhat, but
the convenience and practicality of an actual design may dictate that
the inductor (s) be enclosed.  


Being a conservative sort, I would tend to use bigger cores and larger
wire sizes that an absolute engineering solution might dictate, mostly
for safety factor and insurance against core  saturation  when  handling
unusual situations.



- Jim, KL7CC


Ken Alexander wrote:

> Folks,
>
> Given that inductors on toroid cores are used extensively in autotuners, is there any reason (assuming I choose the right size core, made of the correct material for the application and winding it with the right size wire) for not using one as a base loading inductor on a vertical antenna?  I'm talking 100 watts maximum transmitter output here.
>
> Any down side to doing this?
>
> Thanks and 73,
>
> Ken Alexander
> VE3HLS
> _

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[Phil Salas]

Here's a program that will let you compare toroid vs air core losses:

http://www.dl5swb.de/html/mini_ring_core_calculator.htm

Phil - AD5X
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[Jim Brown-10]

On 4/30/2012 8:14 AM, Ken Alexander wrote:
> Any down side to doing this?

Suitable core material is crucial here.  The core materials used for RFI
suppression (including those used for common mode transmitting chokes)
work by adding lots of loss into the common mode circuit because they
are VERY lossy at RF.  The core materials used for inductors are very
different chemical formulations.

73, Jim K9YC
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[Ken Alexander-2]

Many thanks for all the helpful responses!  I do have many toroid cores in stock already but almost all are FT-50-xx and T-50-xx.  I'll do the research and the math and give it a try when antenna building season arrives.  It's still a little too cold and wet for that at the moment.

73 - Ken


From: Ken Alexander <[hidden email]>
To: Elecraft <[hidden email]>
Sent: Monday, April 30, 2012 11:14:33 AM
Subject: [Elecraft] Loading inductor Question
 
Folks,

Given that inductors on toroid cores are used extensively in autotuners, is there any reason (assuming I choose the right size core, made of the correct material for the application and winding it with the right size wire) for not using one as a base loading inductor on a vertical antenna?  I'm talking 100 watts maximum transmitter output here.

Any down side to doing this?

Thanks and 73,

Ken Alexander
VE3HLS
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[Ignacy]

MFJ-902 tuner uses a single toroid with taps. The toroid becomes hot on some frequencies with 100W but survives. I guess losses are small compared to convenience of a very small unit.

From what I understand, the iron cores can have Q in excess of 300 if they are below saturation. How much will they can handle depends on the load. A reactance of 300 will add a resistance loss of 1 Ohm, and a reactance of 3000 will add 100 Ohm.  So the same toroid can handle KW with a longer vertical but could overheat at 100W with a short vertical.

Ignacy

Fred Townsend wrote

Ken:
.... Don't use toroids if you need taps.
73
Fred, AE6QL

[Geoffrey Mackenzie-Kennedy-3]

Ken,

When you do the research and math, worth bearing in mind that powdered iron
(and ferrite) cores can generate intermodulation products.  Usually this
problem will affect the "receive" performance of an antenna matching
network, or a receiver's front end filters, if exposed to strong signals
e.g. SW Broadcast.

The root cause of this IMD problem can be traced back to the magnetic flux
generated in a core by the incoming signals.  The flux density is
proportional to the applied voltage (vector sum of incoming signals), and
inversely proportional  to the core's cross section (area), the number of
turns and the frequency.  Thus the number of active turns should be as large
as possible, the loaded Q of the network should be kept low, the core's mu
low in value, and a large core used.

Sorry to be late with this comment.

73,

Geoff
LX2AO


On May 01, 2012 at 15:23 +0200, Ken Alexander wrote:


Many thanks for all the helpful responses! I do have many toroid cores in
stock already but almost all are FT-50-xx and T-50-xx. I'll do the research
and the math and give it a try when antenna building season arrives. It's
still a little too cold and wet for that at the moment.

73 - Ken



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