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BL-2 Balun Heating

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Gary Winkelman

BL-2 Balun Heating

I recently built a BL-2 Balun. It is connected between my Palstar AT1KM
tuner and my doublet antenna. The antenna consists of a 100' wire up
25' and fed by 95' of 600 ohm open wire feeder. I'm using the 1:1
setting on the balun. There is a 4" section of RG-213 between the balun
and a coax input of the tuner. I'm driving it with 125 watts from a
TS-850. After no more than a few minutes of CW or RTTY transmission,
the balun is too hot to touch, the SWR rises and the power goes down.
The balun is obviously saturated.

Does anyone have an idea how I can reduce the overheating? I've tried
adding a heat sink but it doesn't make any difference.

Tnx for reading!

Gary N2UM
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Don Wilhelm-4

Re: BL-2 Balun Heating

Gary,

Balun heating is normally caused by attempting to feed a very high or
very low impedance.
Have you tried the 4:1 position? It may help, so do try it even though
I would believe the antenna system feedpoint impedance where the balun
is connected may be in the range of thousands of ohms rather than being
in the 'hundreds of ohms' range that a balun can normally handle.
Another thing to look for is a shorted or open feedline or feedline to
antenna connection.

You may want to try adding or subtracting some length to your antenna or
to your feedline.

If you had mentioned the band(s) where this situation occurs, we might
have been able to offer more insight than my generic response provides.

73,
Don W3FPR

Gary Winkelman wrote:

> I recently built a BL-2 Balun. It is connected between my Palstar AT1KM
> tuner and my doublet antenna. The antenna consists of a 100' wire up
> 25' and fed by 95' of 600 ohm open wire feeder. I'm using the 1:1
> setting on the balun. There is a 4" section of RG-213 between the balun
> and a coax input of the tuner. I'm driving it with 125 watts from a
> TS-850. After no more than a few minutes of CW or RTTY transmission,
> the balun is too hot to touch, the SWR rises and the power goes down.
> The balun is obviously saturated.
>
> Does anyone have an idea how I can reduce the overheating? I've tried
> adding a heat sink but it doesn't make any difference.
>
> Tnx for reading!
>
> Gary N2UM
> ______________________________________________________________
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> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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>
>
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>

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P.B. Christensen

Re: BL-2 Balun Heating

In reply to this post by Gary Winkelman

Gary,

What frequency of operation causes the balun overheating? Assuming the
balun was constructed correctly, I would begin looking at trying to optimize
line length if you favor that band of operation.

For example, when using a 100 ft. dipole at 3.8 MHz and 1/4-wave in height
above ground, the optimal feedline length of 450 ohm transmission line
occurs at roughly 27, 143, or 260 feet from the antenna feed point. The
50-ohm RG-213 or 1:1 balun would couple at one of these distances. At these
lengths, the 50-ohm line VSWR on your RG-213 would approach 1:1 while using
any 50-ohm line length although the balanced open line VSWR is always
determined by the line to antenna mismatch and not considering line loss,
VSWR on that section of the line is constant irrespective of line length.

When coupling the 50-ohm line (or balun) to the balanced line at a
line-current maximum point, a tuner is generally no longer necessary. Worst
case is that the tuner is used as a touch-up device to ensure full band
coverage but at least the balun is no longer seeing wildly outrageous Z
values since the change in line length functions as a variable RF
transformer to achieve Z values reasonably close to 50-ohms at the balun.

Paul, W9AC

----- Original Message -----
From: "Gary Winkelman" <[hidden email]>
To: <[hidden email]>
Sent: Thursday, November 19, 2009 10:02 PM
Subject: [Elecraft] BL-2 Balun Heating

>I recently built a BL-2 Balun. It is connected between my Palstar AT1KM
> tuner and my doublet antenna. The antenna consists of a 100' wire up
> 25' and fed by 95' of 600 ohm open wire feeder. I'm using the 1:1
> setting on the balun. There is a 4" section of RG-213 between the balun
> and a coax input of the tuner. I'm driving it with 125 watts from a
> TS-850. After no more than a few minutes of CW or RTTY transmission,
> the balun is too hot to touch, the SWR rises and the power goes down.
> The balun is obviously saturated.
>
> Does anyone have an idea how I can reduce the overheating? I've tried
> adding a heat sink but it doesn't make any difference.
>
> Tnx for reading!
>
> Gary N2UM
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

Jim Dunstan

Re: BL-2 Balun Heating

In reply to this post by Gary Winkelman

At 10:02 PM 11/19/2009 -0500, you wrote:

Hi Gary,

You could place the balun (in the 1:1 configuration) on the other side of
the tuner ... that is between the xcvr and the tuner. One side of the
balun output would connect to the center pin of the input coax connector
and the other side of the balun output connects to the tuner ground
(frame). The tuner frame would of course be isolated from any ground
especially the radio. The output of the tuner (no balun on the output)
would connect directly to the 600 ohm feed line .... one side of the line
connects to the center of the coax output center pin and the other side of
the line connects to the tuner ground.

The arrangement will work perfectly as a balanced tuning arrangement for
the feed line and at the same time place the balun where it should be ....
in the low impedance 1:1 circuit point ... with the result it will operate
with efficiency and be cool as cucumber. At the moment it is not a 'balun'
problem ... but a circuit problem.

Jim, VE3CI

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Jim Dunstan

Re: BL-2 Balun Heating

PS

I believe the BL-2 is rated at 150 watts .... so running at 125W is already
at the limit .... even when it is placed in the ideal point in the circuit
... (50 ohms resistive). Place it in a point in the circuit where the
resistance varies up or down from the ideal of 50 ohms and then make it
complex with added reactance and the unit could make like a toaster
element. Of course if you operate QRP you will be just fine as long as you
tolerate the RF power loss in the balun. Just imagine trying to make the
circuit work at 1KW. Nothing like power to illustrate weakness.

Jim, VE3CI

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AC7AC

Re: BL-2 Balun Heating

In reply to this post by Gary Winkelman

CONTENTS DELETED

The author has deleted this message.

Steve Ellington

Re: BL-2 Balun Heating

I have the AT1KM. It has a nice big 4:1 balun built in. Have you tried it to
see if it gets hot too? That little BL2 may be rated for 250 watts but this
is for a resistive load or 200 ohms. It's not going to be able to handle the
extreme reactance of that antenna system. Even 25 watts would be asking a
lot of it.
I quote the BL2 manual:
"Power Rating 250 watts with a MATCHED LOAD". Your load is far from matched.
73

Steve
N4LQ
[hidden email]
----- Original Message -----
From: "Ron D'Eau Claire" <[hidden email]>
To: <[hidden email]>; <[hidden email]>
Sent: Thursday, November 19, 2009 11:32 PM
Subject: Re: [Elecraft] BL-2 Balun Heating

> Yes, you are reaching the "curie temperature" of the core. At that point
> it's magnetic properties change dramatically.
>
> Of course that heat comes from RF that is becoming heat instead of being
> radiated by the antenna. A bigger core isn't the answer. You'd still be
> losing the same amount of power even if a much larger core felt cooler.
> Same
> with a heat sink.
>
> You didn't say what band you are using. Heating a balun is usually a sign
> of
> excessive current flowing -that is you are at a current loop. You can
> change
> that by changing the length of the feedline or just do away with the balun
> and connect one side of the open wire feeders to the center pin of the
> tuner
> output and the other to the case. That does not introduce anything like
> the
> degree of "unbalance" that some suggest. Indeed, the balance in the
> feedline
> is much more strongly affected by the antenna than the source.
>
> Ron AC7AC
>
>
> -----Original Message-----
> I recently built a BL-2 Balun. It is connected between my Palstar AT1KM
> tuner and my doublet antenna. The antenna consists of a 100' wire up
> 25' and fed by 95' of 600 ohm open wire feeder. I'm using the 1:1
> setting on the balun. There is a 4" section of RG-213 between the balun
> and a coax input of the tuner. I'm driving it with 125 watts from a
> TS-850. After no more than a few minutes of CW or RTTY transmission,
> the balun is too hot to touch, the SWR rises and the power goes down.
> The balun is obviously saturated.
>
> Does anyone have an idea how I can reduce the overheating? I've tried
> adding a heat sink but it doesn't make any difference.
>
> Tnx for reading!
>
> Gary N2UM
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

--------------------------------------------------------------------------------

No virus found in this incoming message.
Checked by AVG - www.avg.com
Version: 9.0.707 / Virus Database: 270.14.73/2514 - Release Date: 11/19/09
14:42:00

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Gary Winkelman

Re: BL-2 Balun Heating

In reply to this post by Gary Winkelman

Thanks to everyone that replied to my situation. Looks like I'll be
busy doing a lot of testing and experimenting today. I'll get back with
the results later.

Gary N2UM
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Parker Buckley

Re: BL-2 Balun Heating

In reply to this post by Gary Winkelman

"Thanks to everyone that replied to my situation. Looks like I'll be
busy doing a lot of testing and experimenting today. I'll get back with
the results later."

Gary N2UM

I hope that will include the suggestion of placing the balun between the rig
and tuner, just so you can report back on it. K7EL of EZNEC fame wrote
pretty extensively on this several years ago. I've tried it, and it seems
to work, but I was never quite comfortable not grounding the tuner (not sure
why). But if you look at Palstar's balanced tuner, that's exactly what he
does. There are similar balance-L circuits out there, so it's probably
worth a try if you don't want to spend a lot of time trying to find a
combination of feedline and antenna length that will make your balun happy
on several bands.

Let us know!

73,
Parker WD8JOL
K2 #2636

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Gary Winkelman

Re: BL-2 Balun Heating

In reply to this post by Gary Winkelman

Thanks for all the advise! I've been running tests all day to which I
have a nice Excel spreadsheet. I've run the tests on 160 thru 10 meters
using my trusty MFJ-259B (couldn't live without it). I ran AT1KM - no
balun, BL-2 1:1, BL-2 4:1 and a W2AU bead balun 1:1, all thru the
AT1KM. All SWR, R & X values jived. I did not try running 125 watts
thru the balun during the tests. If it heated up, I'd have to let it
cool to get an accurate reading the next frequency. The test would take
2 weeks!

Finally, I took the advise to put the balun between the tuner and the
transmitter. Tuned fine so I added power. It stays cool as the
proverbial cucumber! One slight problem, the tuner is now RF hot. and
there's RF getting into my computer. If I reduce the power to 75 watts,
the computer functions. The transmitter is not bonded to the tuner.
Because of my circumstances, I am not able to use an RF ground rod. I
have two 80 foot counterpoises that run next to our house on the ground.

Thanks everybody for all your help!

73, Gary N2UM
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Don Wilhelm-4

Re: BL-2 Balun Heating

Gary,

Those two 80 foot 'counterpoises' are doing you no good at all.
run some wires off the ground and insulate the ends, cut each one to be
a 1/4 wavelength at a band of interest. If you have to run them in a
bundle, keep the ends of the shorter ones separated from the rest of the
wires by at least 2 feet.
Those wires have a high impedance at the far ends and thus may have a
high RF voltage. The near end (in the shack) will be a low impedance
for RF at the frequency where it is an electrical 1/4 wavelength long.
In your case, the best place to connect the wires is at the place where
the coax shield meets the input of the balun.

If your tuner is actually radiating given the current configuration,
there will be little that you can do other than switching to a balanced
tuner. I believe radiation from the tuner is probable since it is an
unbalanced tuner feeding a balanced line. Yes, a tuner chassis used
like you are using it will be hot with RF and adequate protection
measures to prevent anyone touching the tuner chassis while transmitting
are necessary.

73,
Don W3FPR

Gary Winkelman wrote:

> Thanks for all the advise! I've been running tests all day to which I
> have a nice Excel spreadsheet. I've run the tests on 160 thru 10 meters
> using my trusty MFJ-259B (couldn't live without it). I ran AT1KM - no
> balun, BL-2 1:1, BL-2 4:1 and a W2AU bead balun 1:1, all thru the
> AT1KM. All SWR, R & X values jived. I did not try running 125 watts
> thru the balun during the tests. If it heated up, I'd have to let it
> cool to get an accurate reading the next frequency. The test would take
> 2 weeks!
>
> Finally, I took the advise to put the balun between the tuner and the
> transmitter. Tuned fine so I added power. It stays cool as the
> proverbial cucumber! One slight problem, the tuner is now RF hot. and
> there's RF getting into my computer. If I reduce the power to 75 watts,
> the computer functions. The transmitter is not bonded to the tuner.
> Because of my circumstances, I am not able to use an RF ground rod. I
> have two 80 foot counterpoises that run next to our house on the ground.
>
> Thanks everybody for all your help!
>
> 73, Gary N2UM
>
>

Steve Ellington

Re: BL-2 Balun Heating

In reply to this post by Gary Winkelman

Gary
I still don't understand why you don't use the balun in the tuner. That's
what those big ceramic insulators on the back are for. Why are you messing
with that little Elecraft balun?
Steve
N4LQ
[hidden email]
----- Original Message -----
From: "Gary Winkelman" <[hidden email]>
To: <[hidden email]>
Sent: Friday, November 20, 2009 4:24 PM
Subject: Re: [Elecraft] BL-2 Balun Heating

--------------------------------------------------------------------------------

No virus found in this incoming message.
Checked by AVG - www.avg.com
Version: 9.0.709 / Virus Database: 270.14.74/2515 - Release Date: 11/20/09
03:02:00

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