In article ,
D. Peter Maus wrote:
On 9/8/10 16:29 , bpnjensen wrote:
On Sep 8, 10:30 am, John wrote:
For ferrites commonly used in SWL baluns/ununs:
If you are using type 43 material in an RF transformer, performance will
fall off shortly after 10 Mhz. If the core is wound as a true balun/TLT
(Transmission Line Transformer), I have used it up to 30 Mhz.

Type 61 material is much more suitable for RF transformer from .2 Mhz to
100 Mhz. If wound as a true balun/TLT, it can be pressed into even
broader frequency service.

This page points out the
above:http://www.palomar-engineers.com/Fer...ite_cores.html

With iron:
Type 2, such as T106-2, when wound as an RF transformer is very
satisfactory to a bit beyond 10 Mhz. Wound as a true balun, I have used
it up to 30 Mhz. (it is really too lossy, for me, at 28 Mhz, 10m)

Type 6 material, such as T106-6, is good from 2-30 Mhz when used as RF
transformer (actually, I find the bandwidth to be larger in practice.)
If wound as a balun/unun/TLT, it is quite usable from MW to ~50 Mhz.
When wound as the 16:1/9:1 as I pointed out earlier, I find this to be
THE KILLER BALUN/UNUN (can be used interchangeably.)

This page points out the suitability of the material
above:http://www.palomar-engineers.com/Iro...on_powder.html

Regards,
JS

I am primarily interested in SW listening, not amateur, and really 16
- 160 meters. Would you recommend Type 61 for this application?

Bruce Jensen



Bruce,

The Amidon website has a chart of ferrite materials and their
applicability to various project types. Most of your questions can
be answered there. Including options should you like to build
something specific to your needs, deviating from the intents of an
original design.

And if you're using the Amidon charts, use the line giving useful
frequencies for "broadband transformers". Most of the Amidon frequency
spec. is for tuned circuits, but for broadband use, you're using the
core at frequencies much higher than what the same material is used
for in tuned use.

The first longwire balun I built, inspired by the product review in
a WRTH used, I think, 45 material or something around there. (Not in
the mood to dig out that bag of stuff). It only worked above 15 Mhz,
so was fine for CB listening, but who wants to do that. The transformers
I've done since use the John Bryant recommended type 77, type 75, or
type J. They're good for the range I listen to, 5-17 Mhz and probably
reasonable below that.

Type 77 is speced for tuned use around .1-1 Mhz (as I remember), but
for using it in broadband use, you're trading off some core loss with
much smaller coil windings and the benefits that gives.

Not the same thing as transmitting, where you can accept a more limited
frequency range and don't want your core to melt, or expode, or get
saturated and go nonlinear at that power level.

Mark Zenier
Googleproofaddress(account:mzenier provider:eskimo domain:com)