4:1 balun problems
Jerry Rogich
ants
on 15 Meters. These wire antennas are cut for 40/20Mtrs but used with tuner
on
other higher bands. I found that some commercial 4:1 baluns when lightly
loaded
(about 1K ohm) on high Z side, will show on the mfj analyzer that the R=8
and X=0
on the 50 ohm side at around 21-24Mhz, turning it into a big dummy load. I
do see
some nasty heating effects too. When I load the high Z of the 4:1 to 200
ohms, the
50 ohms side is fine up to 30Mhz and it doesn't heat up.
Is this effect from the ferrite used (rod stock) ? Would toroidal version be
better ?
Different material ? Or is it parasitics from the windings ?
Thanks
Jerry Rogich
Robert Lay (W9DMK)
The effect that you are describing is not an anomaly - it is the norm.
Baluns have the same problems as any transformers. If you don't
operate them at the design impedance, they don't work. A 4:1 balun for
amateur use is designed to operate with 200 +j 0 on the hi side and
will present 50 + j0 on the unbalanced, low side. However, even that
ideal impedance load on the Hi side will only look like 50 + J0 at the
low side over a specific range of frequency. You generally will not
get good performance on 160 meters or on bands above 20 meters -
unless the balun is specifically desgined for one of those bands.
This may be one reason why the choke balun made of ferrites sleeved
over the coax a la Walt Maxwell, W2DU, is so popular.
If you want to see an interesting contrast in performance, measure the
1:1 Current Balun, PRO Balun, Model PB-1-C, by SPI-RO Mfg. Co. against
whatever you are using. You may be surprised.
jerry rogich
one to one. I didn't recognize some of the brands you are referring
to. Any of them have a 4:1 with a wide load/bandwidth/High
Power design ?
AA2T
W6RCecilA
> Any of them have a 4:1 with a wide load/bandwidth/High Power design ?
Hi Jerry, could you share with us why you need a 4:1 balun? Do you
have a 200 ohm load?
--
73, Cecil, W6RCA http://www.bigfoot.com/~w6rca
William Lee
be used to couple 300 or 450 ohm ladder line to 50 ohm coax. I know..... I
know..... you dont need to say it...... That does not compute ...... but
read it for yourself....Page 10 in the MFJ 1999 ham catalog that is sent out
with all orders from MFJ..... MFJ-912 W9INN Balun Box.
I tried one once hoping to get the benefits of both coax in the shack and
450 ohm ladder line outside to the dipole but it never did work anywhere
near as good as ladder line straight to the antenna tuner.
I would think a 9:1 balun would be needed to couple 50 ohm coax to 450 ohm
ladder line but I have never seen one for sale.
William Lee N5WRX
W6RCecilA wrote in message <374B46C9...@IEEE.org>...
Robert Lay (W9DMK)
wrote:
>jerry rogich wrote:
>> Any of them have a 4:1 with a wide load/bandwidth/High Power design ?
>
>Hi Jerry, could you share with us why you need a 4:1 balun? Do you
>have a 200 ohm load?
Forget it Cecil - much too logical.
Robert Lay (W9DMK)
<n5...@mindspring.nospam.com> wrote:
>I could never understand why...but that is the Balun that is recommended to
>be used to couple 300 or 450 ohm ladder line to 50 ohm coax. I know..... I
>know..... you dont need to say it...... That does not compute ...... but
>read it for yourself....Page 10 in the MFJ 1999 ham catalog that is sent out
>with all orders from MFJ..... MFJ-912 W9INN Balun Box.
>
>I tried one once hoping to get the benefits of both coax in the shack and
>450 ohm ladder line outside to the dipole but it never did work anywhere
>near as good as ladder line straight to the antenna tuner.
>
>I would think a 9:1 balun would be needed to couple 50 ohm coax to 450 ohm
>ladder line but I have never seen one for sale.
First of all, you don't want to believe what you read in
advertisements. Second, if you want to understand impedance matching
on transmission lines, get away from baluns for a while and take a
look at some transmission line theory. It's all spelled out in the
ARRL Antenna Book.
The short version of it is this. The impedance seen looking into a 450
ohm transmission line is only 450 ohms under very specific conditions
- either it's infinitely long (no reflections from the far end ever
make it back home) or it is terminated in 450 + j 0 ohms (no
reflections occur at the far end.)
In the real world neither those conditions are likely to exist, so the
transmission line ACTS like a transformer. It transforms the impedance
at the far (load) end into an impedance at the near (sending) end. The
impedance seen looking into the sending end will be something between
near zero and near infinity. Quite a range, eh?
So, if you want to believe in the rather uninformed idea that the 450
ohm line will look like 450 ohms, then continue your search for that
9:1 balun, but if you follow your own experience, you will find that
the balanced tuner is the better approach.
If, on the other hand, that tuner to which you attach your balanced
feed line, is just another unbalanced tuner with a 4:1 balun inside,
(as most are) then all you have done is reduced the total length of
coax in the system.
Jerry Rogich
12Meters with the balun. 15 Meters is completely deaf.
W6RCecilA
> I would think a 9:1 balun would be needed to couple 50 ohm coax to 450 ohm
> ladder line but I have never seen one for sale.
Once again, if the SWR on the 450 ohm ladder-line is not 1:1, the
impedance
seen at the transmitter/tuner will NEVER be 450 ohms. Please, everyone
who
doesn't already understand that, read it over and over until you do. The
only antenna that would need a 9:1 balun would be one with a feedpoint
impedance close to 450 ohms. How many antennas have a feedpoint
impedance
of 450 ohms?
For instance, if the SWR is 7:1 on 450 ohm ladder-line, the impedance
seen at the tuner (depending on the length of the feedline) may be
64 ohms, or 3150 ohms, or 135ąj135 ohms or an infinite number of other
impedances. None of these impedances will require a 9:1 balun. IMO,
the suppliers who offer 4:1 and 9:1 baluns should state that their
baluns were not designed to be used with non-resonant length antennas.
Of course, they will not state such since most of their profit comes
from those very applications.
Here's my opinion: If one doesn't know what impedance to expect at
the unbalanced tuner, use a 1:1 choke. If it won't load properly with
a 1:1 choke, a problem exists that needs to be fixed. The problem
*usually* cannot be fixed by a higher ratio balun and it's a complete
accident if any problem is actually fixed by a higher ratio balun
when used with a non-resonant length antenna.
W6RCecilA
Well, he might have a folded dipole relatively close to the ground.
200 ohms could actually be a possibility.
William Lee
I am going to dig out my ARRL antenna book tonight and read into this a
little.
You know Robert, I think you are correct. My tuner does have a balun on the
balenced outputs.
I never thought about that before.
What tuner would be a true balenced tuner without a balun?
Could you please give an example?
William Lee N5WRX
W6RCecilA
> What tuner would be a true balenced tuner without a balun?
> Could you please give an example?
A link-coupled tuner is balanced. An example is the Johnson
Matchbox.
Dan Richardson
wrote:
Dan Richardson
<wil...@interconnect.net> wrote:
>Thank you Robert Lay and W6RCecilA for your remarks.
>
>I am going to dig out my ARRL antenna book tonight and read into this a
>little.
>You know Robert, I think you are correct. My tuner does have a balun on the
>balenced outputs.
>I never thought about that before.
>What tuner would be a true balenced tuner without a balun?
>Could you please give an example?
>
>William Lee N5WRX
>
There is a good construction article on building a balanced tuner by
Richard Measures in the Feb 1990 QST.
I have built one based on this design and am very happy with it.
Danny, K6MHE
Robert Lay (W9DMK)
<wil...@interconnect.net> wrote:
>Could you please give an example?
Others have already indicated the two types of tuners that I would
have mentioned - the one by Dick Measures and also the Johnson
Matchbox.
Just in case you have trouble getting into those references, it's like
this -
The balanced tuners do NOT use a BALUN in the output. They may well
have one on the input side (Dick Measures uses a choke balun comprised
of some thirty turns of coax coiled on a former on the transmitter
side of the tuner).
The balanced tuner depends primarily on its inherently BALANCED
circuitry. For example, you build a parallel resonant tank circuit. If
you ground one end, it is UNBALANCED. If, on the other hand, you
ground the center tap of the coil, or if you ground the rotor of a
balanced capacitor, then you have a BALANCED tank circuit.
The link coupling of a Johnson Matchbox provides the same function as
the balun. It couples a tank circuit (a parallel resonant L and C) to
other circuits through taps or links. Whenever two circuits are
coupled via a link, the link coupling automatically accomodates the
circuity on either side of the link coupling whether it be balanced or
unbalanced. In those instances where it is very critical, a Faraday
shield between the coupled coils will reduce the common mode or
capacitive coupling.
Dick Measures designed his tuner to have two roller inductors, one in
each side of the balanced line. He has a tuning capacitor in
parallel, across the lines, which can be switched to be at the antenna
side of the inductors or at the transmitter side - whichever is needed
to perform the impedance transformation. The important thing is that
his circuit components are mirror images of each other on the two
sides of the balanced line and they perform the impedance
transformation function. The balun function is provided by a coax
choke on the transmitter side of the tank circuit.
The Johnson Matchbox uses a balanced tank circuit with taps on the
coil and link coupling. I don't have a schematic for it, but I am sure
that it does NOT use a balun, in any form. I'm not sure when Ruthroff
did his pioneering work on baluns, but I think it was prior to 1964,
because I saw his work published in the Bell System Technical Journal
(BSTJ) at about that time.
Roy Lewallen
> . . .
> The Johnson Matchbox uses a balanced tank circuit with taps on the
> coil and link coupling. I don't have a schematic for it, but I am sure
> that it does NOT use a balun, in any form. I'm not sure when Ruthroff
> did his pioneering work on baluns, but I think it was prior to 1964,
> because I saw his work published in the Bell System Technical Journal
> (BSTJ) at about that time.
Ruthroff's classic paper "Some Broad-Band Transformers" was published
in 1959. In it he describes a number of what I call "voltage baluns"
(and others), although I don't believe he mentioned the antenna balun
as a potential use for his transformers. Sevick, W2FMI, credits a man
named Guanella for the invention of the common-mode choke or "current
balun", but I'm not familiar with his work or the time at which it
occurred.
Roy Lewallen, W7EL
Reg Edwards
4:1 toroidal balun can be accurately predicted using
program BALUN4 available by downloading in a few seconds
from my website.
The program uses exact transmission line analysis formulae
adapted by myself and confirms the accuracy of Sevick's
practical measurements of transformer insertion loss. I
have never seen Guanella's work.
--
******************************
Reg, G4FGQ For free software go to:-
http://www.btinternet.com/~g4fgq.regp
******************************
Ken Brown
balanced line to an unbalanced line. It is also and adjustable balun
which can match a 50 to 75 ohm coaxial line to a wide range of
impedances at it's balanced output termenals.
Richard Clark
wrote:
>Robert Lay (W9DMK) wrote:
>> . . .
>> The Johnson Matchbox uses a balanced tank circuit with taps on the
>> coil and link coupling. I don't have a schematic for it, but I am sure
>> that it does NOT use a balun, in any form. I'm not sure when Ruthroff
>> did his pioneering work on baluns, but I think it was prior to 1964,
>> because I saw his work published in the Bell System Technical Journal
>> (BSTJ) at about that time.
>
>Ruthroff's classic paper "Some Broad-Band Transformers" was published
>in 1959. In it he describes a number of what I call "voltage baluns"
>(and others), although I don't believe he mentioned the antenna balun
>as a potential use for his transformers. Sevick, W2FMI, credits a man
>named Guanella for the invention of the common-mode choke or "current
>balun", but I'm not familiar with his work or the time at which it
>occurred.
>
>Roy Lewallen, W7EL
Hi Roy,
Per Sevick's references and from his "Transmission Line Transformers":
"The earliest presentation on transmission line transformers was
by Guanella in 1944 (Ref. 1)"
1) Guanella, G., "Novel Matching Systems for High Frequencies,"
Brown-Boveri Review, Vol 31, Sept 1944, pp 327-329
There are 9 other author citations prior to Ruthroff's work of 1959
for Proc IRE, Vol 45.
73's
Richard Clark, KB7QHC