On Aug 8, 3:07*am, RHF wrote:
On Aug 7, 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

N1JPR - OK - What Brand ? Model ? of MLB ?

=WRT= Shortwave Radio Listener {Receive Only}
-so-called- Magnetic Longwire Baluns [MLBs]

Let's say you have a 'classic' 10-Turn Secondary
Winding Coax-Shield-to-Radio-Input that is couple
with a 30-Turn Primary Coax-Shield-to-Antenna.
* Using a Common Coax Shield Ground Point
for both Windings.

Using #24 AWG Solid Copper Wire
-note- Wire Gauge Resistance per foot #24 = 0.03 Ohms/Ft
* #14 = 0.003 Ohms/Ft
* #20 = 0.012 Ohms/Ft
* #36 = 0.4 Ohms/Ft
* #40 = 1.0 Ohm/Ft

Using a Small 1-Inch OD Ferrite Toroid "Donut" Core
with 1/2" ID and 1/2" Thick/Wide.http://www.goldmine-elec-products.co...er=G6683&varia...

Each Turn is about 2.4 Inches of #24 Copper Wire
* 10 Turns ~ 24 Inches ~ 2 Feet = 0.06 [~1/10th] Ohm
* 30 Turns ~ 72 Inches ~ 6 Feet = 0.18 [~1/5th] Ohm

Wire Gauge Resistance per foot #24 = 0.03 Ohmshttp://www.epanorama.net/documents/wiring/wire_resistance.html

With Common Ground Un-Uns -aka- Magnetic
Longwire Baluns [MLBs] that are 'suspect'
* Simply Replace with a New MLB
* Build a New MLB from scratch
* Tear-down and re-build the old MLB into a
New MLB using the same Core -if- not damaged
{cracked or discolored}. *Use New Wire and if
needed New Hardware too.

However before you suspect and replace the MLB :
1 - Check-out your Connections at the MLB
2 - Check-out your Coax Cable
3 - Checkout your Antenna Wire
4 - Checkout your Ground Wire and Ground Rod
More often then not it is the 'Connections' and a
Damaged/Broken Coax Cable where the problem
is and nothing internal to the MLB.

hope this helps - iane ~ RHF
*.
*.

Follow-up . . .

Magnetic Longwire Balun : a Con or Not ?
http://www.hard-core-dx.com/nordicdx...d/magbal1.html