On Mon, 19 Jan 2009 01:33:32 GMT, "Jerry"
wrote:

At 137 MHz, the insertion loss was about 2.5 dB for
two baluns connected in series, back to back.

OUCH!

I know that seems high, but
the units are really not well built.

Hi Jerry,

So it would seem.

73's
Richard Clark, KB7QHC

On Jan 18, 10:32*pm, Jeff Liebermann wrote:
On Sat, 17 Jan 2009 12:44:05 -0800 (PST), JIMMIE

wrote:
I was considering using a TV type 4:1 balun on 2 meters. Does anyone
know how much power these can handle? I remember a guy doing this when
I was a teenager(long ago) but I think the baluns were built a little
stouter back then than they are now.

May I suggest using a coaxial cable 4:1 balun instead of ferrite core
type. *A 1/2 wave electrical length of coax cable, some soldering, and
you're done. *For just 2 meters, the bandwidth is just fine and the
loss is no more than that of the coax cable. *For low power, small
diameter RG-174 type coax is fine. *I use 4:1 coax baluns for matching
300 ohm folded dipole antennas:
http://users.belgacom.net/hamradio/schemas/14balun.gif

The common TV balun has two xfomers inside, which are sometimes
combined on a single core. *See schematics at:
http://members.tripod.com/rclindia/trans.html
http://www.electronics-tutorials.com/basics/baluns.htm

However, if size is an issue, I guess the coax balun is a bit large.
For just 2 meters, the ferrite core is not necessary. *Just find a
block of PTFE (Teflon) or plastic, and drill it to resemble the TV
balun core, use 2 PTFE toroid cores (if you can find them), or
simulate a torroid with a stack of nylon washers. *Then wind the 2
pairs of 2 wires through the holes and bring out the connections.

--
Jeff Liebermann * *
150 Felker St #D * *http://www.LearnByDestroying.com
Santa Cruz CA 95060http://802.11junk.com
Skype: JeffLiebermann * * AE6KS * *831-336-2558

Jeff, Apparently TV matching transformers used to be air core and
their use was quite common on 6 and 2 meter antennas.I knew the ones
built into the old tuners were but I hadnt thought the old line
transformers also being air core.They were per some of the locals on
2m repeater. If they aare the ones I am thinking of(big fat ones) I
have a few at home.

Jimmie

On Mon, 19 Jan 2009 08:10:07 -0800 (PST), JIMMIE
wrote:

Jeff, Apparently TV matching transformers used to be air core and
their use was quite common on 6 and 2 meter antennas.

Not on any 2m or 6m antenna I've seen or build. Most of what I've
seen used T-match, hair-pin match, gamma match, or something similar.
For the vertical collinears, I used a tapped coil. If I wanted lots
of bandwidth, perhaps a ferrite core might be useful, but for single
VHF band antennas, it's a lossy waste.

I knew the ones
built into the old tuners were but I hadnt thought the old line
transformers also being air core.

The over-simplified idea behind the ferrite (or powdered iron for HF)
cores is to increase the inductance of the windings so the xformer
works at lower frequencies. At VHF and UHF frequencies, the core
mostly disappears and you're relying totally on the coupling between
the bifilar windings.

They were per some of the locals on
2m repeater. If they aare the ones I am thinking of(big fat ones) I
have a few at home.


Jimmie
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Mon, 19 Jan 2009 09:43:27 -0800, Jeff Liebermann
wrote:

The over-simplified idea behind the ferrite (or powdered iron for HF)
cores is to increase the inductance of the windings so the xformer
works at lower frequencies. At VHF and UHF frequencies, the core
mostly disappears and you're relying totally on the coupling between
the bifilar windings.

Actually that is not the mechanism at all, simplified or complexified.

Ferrite compounds for BalUn application principally add resistance to
the common mode path and have (as a design goal) absolutely no
magnetic influence whatever. The increase of inductance is haphazard
at best, and some ferrite compounds actually increase the capacitive
reactance. As such, ferrites are not principally employed in building
inductors. Further, iron cores don't serve much purpose for choking
which is the principle requirement for BalUn input to output
isolation.

If you want to build an iron core, magnetic linkage transformer (AKA
audio or power transformer), this is a very different beast from a
BalUn, and a miserable replacement.

73's
Richard Clark, KB7QHC

Richard Clark wrote:
On Mon, 19 Jan 2009 09:43:27 -0800, Jeff Liebermann
wrote:

The over-simplified idea behind the ferrite (or powdered iron for HF)
cores is to increase the inductance of the windings so the xformer
works at lower frequencies. At VHF and UHF frequencies, the core
mostly disappears and you're relying totally on the coupling between
the bifilar windings.

Actually that is not the mechanism at all, simplified or complexified.

Ferrite compounds for BalUn application principally add resistance to
the common mode path and have (as a design goal) absolutely no
magnetic influence whatever. The increase of inductance is haphazard
at best, and some ferrite compounds actually increase the capacitive
reactance. As such, ferrites are not principally employed in building
inductors. Further, iron cores don't serve much purpose for choking
which is the principle requirement for BalUn input to output
isolation.

If you want to build an iron core, magnetic linkage transformer (AKA
audio or power transformer), this is a very different beast from a
BalUn, and a miserable replacement.

73's
Richard Clark, KB7QHC

When designing any transformer, be it audio, power, or RF, you usually
want to accomplish three things:

1. Maximize the winding impedance.
2. Minimize the leakage impedance. This is another way of saying you
want to maximize the coupling between the windings.
3. Realize an acceptably low loss.

At low frequencies, most cores primarily provide inductance, so most
literature dealing with transformers speaks of "inductance" rather than
"impedance" when discussing the basic goals. But low frequency
transformers could be made and would function just fine using resistive
core materials if they were available. The third goal can be achieved
with resistive materials as long as the first and second goals are
accomplished well enough. That is, if the winding impedance is high
enough, the magnetizing current will be low, so I^2*R loss will be low.
And if coupling is good, increasing the current in one winding won't
appreciably increase the core flux and incur extra loss.

But at RF, as Richard says, many ferrite cores are more resistive than
inductive. Not all are -- there are high frequency ferrites that remain
inductive at very high frequencies. However, for the HF range and above,
the best choice is usually "low frequency" ferrites which are primarily
resistive in that frequency range. They're best for two reasons --
first, they provide much more impedance per turn squared than high
frequency ferrites, making the first two goals much easier to achieve;
and second, there are no resonance effects. An inductive winding will
resonate with stray capacitance at some frequency. The impedance drops
above that frequency, limiting the upper range of the transformer. The
winding and leakage inductances can also resonate with external
capacitance and cause ringing in some applications. A properly designed
transformer using an essentially resistive core can operate very well
over several decades of frequency.

For most RF applications, it's not hard to design a transformer or balun
that will have well under 1 dB of loss, which is negligible again in
most applications. But if high power is involved, even a fraction of a
dB might represent several or may watts of power, resulting in
intolerable core heating. In those applications, lower loss, i.e., more
inductive and less resistive, cores have to be used, often resulting in
more difficult design and/or reduced performance in other respects.

Resistive ferrites are also often good choices for RF chokes for the
same reasons that they make good transformers.

High-Q inductors and tuned transformers are a different critter, though.
For those applications you want to use very low loss, that is, inductive
and not resistive, core materials. This often leads to confusion, since
ferrite manufacturers have traditionally specified a "recommended"
frequency range for various materials which refers to the best range for
these applications. The best material for an RF transformer is usually
one with a "recommended" (for high-Q inductor applications) frequency
range well below the transformer operating frequency.

Roy Lewallen, W7EL

Roy Lewallen wrote in
treetonline:

....
But at RF, as Richard says, many ferrite cores are more resistive than
inductive. Not all are -- there are high frequency ferrites that
remain inductive at very high frequencies. However, for the HF range
and above, the best choice is usually "low frequency" ferrites which
are primarily resistive in that frequency range. They're best for two
reasons -- first, they provide much more impedance per turn squared
than high frequency ferrites, making the first two goals much easier
to achieve; and second, there are no resonance effects. An inductive
winding will resonate with stray capacitance at some frequency. The
impedance drops above that frequency, limiting the upper range of the
transformer. The winding and leakage inductances can also resonate
with external capacitance and cause ringing in some applications. A
properly designed transformer using an essentially resistive core can
operate very well over several decades of frequency.

Hams have a affinity for powdered iron cores in RF applications, mislead
by the thought that low loss material naturally produces a better
solution. Thing is that it is a huge leap from low loss *material* to a
low loss *solution*.

Here is a recent design for a Guanella 1:1 balun for 6m and 2m on a #61
ferrite co http://www.vk1od.net/balun/G1-1-FT140-61/index.htm .

The article contains a graph of the material characteristics, which
shows that at 2m, µ' has fallen to 10% or so of µi, and µ'' has risen,
so an inductor will be more resistive than inductive.

But, does that make it a poor TLT? Not at all, it has very high common
mode or choking impedance (a critical performance parameter that is
rarely reported for commercial baluns).

Would such a balun wound on a powdered iron core work better? Probably
not. I say probably because I have been unable to find manufacturer's
loss data for powdered iron materials above about 5MHz. The probability
is that a powdered iron core would yeild a balun with a choking
impedance that is lower and more inductive than resistive and may likely
be *more* lossy. (I have a prospective project to measure a couple of
powdered iron cores at 6m to further explore this, but they will not be
lab grade measurements.)

The key is in thinking about I^2*R. The lossy ferrite balun has very
high Z, so very low I, very high R, and the product of I^2*R is
relatively low. A powdered iron choke will have lower Z, so higher I,
low R, and the product I^2*R may be quite higher than the ferrite.

Higher choking impedance can reduce loss, even if the higher choking
impedance is by way of a lower Q inductor. The characteristic is a
curve, concave down and the trick is to choose a design (whether it is
powdered iron, air cored, or ferrite cored) for acceptable loss, and
that often means an operating point that is well on the right hand side
or the left hand of the curve maximum.

Another facet of ferrite TLTs operated in their lossy region, is that
they remain useful well above the device self resonance, whereas when
choking depends on a high Q impedance, it rapidly falls above resonance.
(Self resonance is ignored in most models of balun performance that I
have seen.)

Owen

Owen Duffy wrote:

Hams have a affinity for powdered iron cores in RF applications, mislead
by the thought that low loss material naturally produces a better
solution. Thing is that it is a huge leap from low loss *material* to a
low loss *solution*.

. . .

Would such a balun wound on a powdered iron core work better? Probably
not. I say probably because I have been unable to find manufacturer's
loss data for powdered iron materials above about 5MHz. The probability
is that a powdered iron core would yeild a balun with a choking
impedance that is lower and more inductive than resistive and may likely
be *more* lossy. (I have a prospective project to measure a couple of
powdered iron cores at 6m to further explore this, but they will not be
lab grade measurements.)

. . .

Like ferrites, powdered irons come with a wide range of characteristics.
Micrometals (http://micrometals.com) makes the popular -2 (red), -6
(yellow), and other cores which are very suitable for high-Q inductors
at HF, as well as lower frequency mixes. I have a book of "Q curves"
they published which characterizes a number of inductors to fairly high
frequencies. But for most of my work I've simply wound inductors and
measured their Qs with a simple home made Q meter. I use -6 and to a
lesser extent -2 cores for inductors in nearly all HF filter and
matching applications. I've used lower frequency powdered iron cores for
RF chokes. They behave a lot like low frequency ferrites, but are
characterized by tolerance of very high flux densities. I'm sure that
some low frequency powdered iron cores would be fine for baluns and
broad band transformers, but they're not nearly as available as ferrites
and high frequency powdered iron cores.

I highly recommend that anyone anticipating using ferrite or powdered
iron cores invest in an "antenna analyzer". It allows a very quick and
easy characterization of cores at the frequencies of interest.

Roy Lewallen, W7EL

Owen Duffy wrote:


Hams have a affinity for powdered iron cores in RF applications, mislead
by the thought that low loss material naturally produces a better
solution.

All hams?

Dave wrote in
m:

Owen Duffy wrote:


Hams have a affinity for powdered iron cores in RF applications, mislead
by the thought that low loss material naturally produces a better
solution.

All hams?


Your words, not mine.

Owen

On Tue, 20 Jan 2009 20:15:38 GMT, Owen Duffy wrote:

Hams have a affinity for powdered iron cores in RF applications, mislead
by the thought that low loss material naturally produces a better
solution. Thing is that it is a huge leap from low loss *material* to a
low loss *solution*.

Here is a recent design for a Guanella 1:1 balun for 6m and 2m on a #61
ferrite co http://www.vk1od.net/balun/G1-1-FT140-61/index.htm .

The article contains a graph of the material characteristics, which
shows that at 2m, µ' has fallen to 10% or so of µi, and µ'' has risen,
so an inductor will be more resistive than inductive.

But, does that make it a poor TLT? Not at all, it has very high common
mode or choking impedance (a critical performance parameter that is
rarely reported for commercial baluns).

Would such a balun wound on a powdered iron core work better? Probably
not. I say probably because I have been unable to find manufacturer's
loss data for powdered iron materials above about 5MHz. The probability
is that a powdered iron core would yeild a balun with a choking
impedance that is lower and more inductive than resistive and may likely
be *more* lossy. (I have a prospective project to measure a couple of
powdered iron cores at 6m to further explore this, but they will not be
lab grade measurements.)

The key is in thinking about I^2*R. The lossy ferrite balun has very
high Z, so very low I, very high R, and the product of I^2*R is
relatively low. A powdered iron choke will have lower Z, so higher I,
low R, and the product I^2*R may be quite higher than the ferrite.

Higher choking impedance can reduce loss, even if the higher choking
impedance is by way of a lower Q inductor. The characteristic is a
curve, concave down and the trick is to choose a design (whether it is
powdered iron, air cored, or ferrite cored) for acceptable loss, and
that often means an operating point that is well on the right hand side
or the left hand of the curve maximum.

Another facet of ferrite TLTs operated in their lossy region, is that
they remain useful well above the device self resonance, whereas when
choking depends on a high Q impedance, it rapidly falls above resonance.
(Self resonance is ignored in most models of balun performance that I
have seen.)

Owen

"A Ham's Guide to RFI, Ferrites, Baluns, and Audio Interfacing" is
an very good tutorial written by Jim Brown, K9YC, for understanding
and fixing RFI problems. Chapter 6 (page 23) Includes an excellent
explanation of balun operation and constrution information. A must
read for anyone designing and/or building baluns

http://audiosystemsgroup.com/RFI-Ham.pdf

Danny, K6MHE