In message , John Smith
writes
On 8/7/2010 9:56 AM, spamhog wrote:

I am rebuilding my 15+ yr old longwire+MLB antenna due to broken coax
etc etc.

I checked the DC resistance between the 3 terminals of the MLB:
IN - high impedance longwire tiepost
OUT - low impedance coax center conductor
SHIELD - coax shield.
Weird results:
IN-OUT = 2 ohm
IN-SHEILD = OUT-SHIELD = ~50 ohm (can't really notice a difference)

Inverting + and - does not change result, hence not an obvious
semiconducting corrosion cell.

AFAIK
- the circuit is just a very broadband impedance transformer
- there should be no resistor
...however I don't remember what the normal resistance might have
been.

QUESTIONS
1- what would be normal resistance values?
would near zero be reasonable?
2- guesses on what might have happened?
is 50 ohm compatible with a poor contact
3- did anybody crack it open?
suggestions for repair?

Thanks for any wisdom on this matter!

N1JPR

What many call a balun is not, it is an RF auto-transformer; The common
schematic on the net uses a 10 turn primary with a 29-30 turn
secondary; This is an auto-transformer, but it works fine in matching
an an antenna in place of a 9:1 balun, for general SWL.

A 9:1 auto-transformer:
http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=12673

A true 9:1 balun (schematic down on the page):
http://users.belgacom.net/hamradio/s...0Balun_MLB.htm

One importance difference you will notice, the auto-transformer has two
windings, the cold ends of the two windings running to gnd/coax-braid.
The balun has three windings, or a trifilar winding, these 3 windings
are connected in series with the 50 ohm connection across one winding,
the high impedance connection is made across all 3 windings.
Transmission Line Transformer is also used to describe some types of
baluns. Baluns are frequently wound using coax for the windings ... etc.

In the above, I have made no difference between balun and unun, there
is a difference, and most often you find ununs employed in SWL, with
monopoles--unbalanced antennas. Baluns are utilized with
dipoles--balanced antennas.

Regardless of whether you use the 9:1 impedance transformer as a, 'unun'
or a balun, the obvious way of winding it is to wind it trifilar by
filling the ring with N turns, then interwinding with a further N turns
(so the wires never cross), then finally interwinding a further N turns.
That isn't made clear in the DXzone article.

The ON6MU balun seems to be wound with purpose made trifilar wire,
rather than ordinary off-the-shelf single wire, interwound. [Or maybe
it's just wound very, very carefully!] Some Cable TV equipment used to
use ready-made wire (both bifilar and trifilar) for the windings of
their miniature wideband torroidal 'transmission line' RF transformers.
There were typically 5 turns around the ring, and they were normally
connected as 2:1 turns ratio (4:1 impedance) or 3:2 turns ratio (2.25
impedance).

Whether the transformer ends up as a balun or an unun simply depends on
how you connect the windings, and where you make the external
connections.
--
Ian

On Sep 6, 5:41*am, John Smith wrote:
On 9/6/2010 5:18 AM, RHF wrote:

...
"IJ",

Many/most SWLers are simple DIYers
and not Ham-Techies : "KISAP"
...
Just "KISAP" = Keep It Simple And Practical - iane ~ RHF
* .
* .

- Yes, well, "ignorance is bliss"
- (related to KISS), as a motto,
- is a usable tool, I suppose ...

JS - Don;t like "KISS" -cause-
'Keep It Simple Stupid'
has you calling someone 'Stupid'.

That's Why the "KISAP" is better
'Keep It Simple And Practical'
has you Being Helpful by :
1 - Making It Easy to Understand
2 - Providing a Useful Way of Doing Something

JS - 'kisap' goes to motive and motivation ~ RHF

Can 'We' Getting back to the Subject Being Discussed :

Magnetic Longwire SWL Antenna {Balun}
9:1 Matching Transformer "KISAP"
http://groups.google.com/group/rec.r...0018d6b7524b37

On Sep 6, 8:51*pm, John Smith wrote:
On 9/6/2010 4:58 PM, RHF wrote:

...
JS - it sounds like you are . . .
still stuck on "17" - pal ~ RHF
* .

I can't believe they can take my tax dollars, good money, and have the
school system turn out witless idiots ...

Regards,
JS

Unfortunately- more often than we hope our hard earned (read blood)
money collected by the taxman goes to waste. From what I see the
entire educational system has become a complete farcicle. How about
sending men to Mars? That can be much more beneficial- at least it
might revive NASA and create some jobs. May be...

RHF wrote:
On Sep 6, 8:27 pm, wrote:
On Sep 6, 8:51 pm, John wrote:

On 9/6/2010 4:58 PM, RHF wrote:

...
JS - it sounds like you are . . .
still stuck on "17" - pal ~ RHF
.

I can't believe they can take my tax dollars, good money, and have the
school system turn out witless idiots ...

Regards,
JS

Unfortunately- more often than we hope our hard earned (read blood)
money collected by the taxman goes to waste. From what I see the
entire educational system has become a complete farcicle.
- How about sending men to Mars?
- That can be much more beneficial- at least it
- might revive NASA and create some jobs.
- May be...

-wrt- NASA Sending Men to Mars :

How about we spend all that time and money
on 'fixing' our Education System first.

What good is it to send Men to Mars . . .
-if- The People back on Earth can't spell M-a-r-s
-and- Don't know that Mars exists or anything
about it . . .

Why train American engineers when S. Asian engineers are more
cost-effective? That makes no business sense.

"You want fries with that?"

On Sep 7, 9:30*am, dave wrote:
RHF wrote:
On Sep 6, 8:27 pm, wrote:
On Sep 6, 8:51 pm, John *wrote:

On 9/6/2010 4:58 PM, RHF wrote:

...
JS - it sounds like you are . . .
still stuck on "17" - pal ~ RHF
* *.

I can't believe they can take my tax dollars, good money, and have the
school system turn out witless idiots ...

Regards,
JS

Unfortunately- more often than we hope our hard earned (read blood)
money collected by the taxman goes to waste. From what I see the
entire educational system has become a complete farcicle.
- How about sending men to Mars?
- That can be much more beneficial- at least it
- might revive NASA and create some jobs.
- May be...

- - -wrt- NASA Sending Men to Mars :
- -
- - How about we spend all that time and money
- - on 'fixing' our Education System first.
- -
- - What good is it to send Men to Mars . . .
- - -if- The People back on Earth can't spell M-a-r-s
- - -and- Don't know that Mars exists or anything
- - about it . . .

- Why train American engineers when S. Asian
- engineers are more cost-effective?
- That makes no business sense.
-
- "You want fries with that?"

Ah Dave you come from Planet Jack-in-the-Box
in the Solar System of Walmart. - wass ~ RHF

Ian Jackson wrote:


And I can confirm that, with a transmitter-side (shack end)
matcher/tuner, and good, low-loss coax, you can do away with the
transformer.

All that does is match the 50 Ohm transmitter to the 50 Ohm (or less)
transmission line. It doesn't address the mismatch between the
transmission line and the antenna at all.

On Sep 15, 9:09*am, dave wrote:
Ian Jackson wrote:

And I can confirm that, with a transmitter-side (shack end)
matcher/tuner, and good, low-loss coax, you can do away with the
transformer.

- All that does is match the 50 Ohm transmitter
- to the 50 Ohm (or less) transmission line.
- It doesn't address the mismatch between the
- transmission line and the antenna at all.

Isn't there a little factors like cutting the Antenna
Wire to the 'right-length' and having the 'correct
length' of Coax Cable that contribute to a good
"Match" : At least for one SW Band ? ~ RHF

On 9/15/2010 6:48 AM, spamhog wrote:


...
ha ha ha! And I'd like to add that I hadn't asked any question even
remotely related to the pros and cons of the concept of broadband
impedance matching between coax and random wire, how good this
specific RF-System MLB un-un implementation was, detailed instructions
for DIY alternatives, and the semantics of calling magnetic "balun"
something that isn't so. Such replies push (s+n)/n to unity.

Yeah, I was too wordy, should have been, "Toss the piece of cr*p and
get/wind something decent ...

Regards,
JS

On 9/15/2010 6:48 AM, spamhog wrote:

...
ha ha ha! And I'd like to add that I hadn't asked any question even
remotely related to the pros and cons of the concept of broadband
impedance matching between coax and random wire, how good this
specific RF-System MLB un-un implementation was, detailed instructions
for DIY alternatives, and the semantics of calling magnetic "balun"
something that isn't so. Such replies push (s+n)/n to unity.

Funny, your very first post contained, "I am rebuilding my 15+ yr old
longwire+MLB antenna due to broken coax etc etc. ... "

Then, you just shoot a lot of amps though wire that was NEVER meant to
take the amps, this is obvious by the manufacturer saying not to run 5
watts though it. And, I have never ran a heavy, magnetizing current,
though a toroid to see attempting to turn my core into a magnet would
suddenly be "a good idea."

Etc., etc. But, I will agree you didn't ask ... you just did a lot of
pretty nutty stuff ... so now you have an old corroded balun which you
have exceeded current on, heated the winding and their insulating
coating to gawd knows what temp, are counting on all this making good
contact on corroded joints, etc., etc.

And then you are afraid what someone said may "sound nuts?" ROFLOL
Now, let me see if I see anything wrong with all that?

I think rebuild it properly, or buy a new one, or build a new one, etc.,
etc. are all better than what you seem to be proud of ... but hey, that
is just me ... and I admit it ...

Regards,
JS