View Single Post
Old 27-Oct-2016, 11:20 PM   #12
rabbit73
Retired A/V Tech
 
Join Date: Aug 2012
Location: S.E. VA
Posts: 2,747
Quote:
Originally Posted by Nascarken View Post
Yes that' could be varrey TRUE I have read some thing like THAT happens TACK an ohm meter and test it out it should be 75,ohm
You were correct, Nascarken. That was a good idea to suspect the balun.

Sometimes an ohmmeter can help, sometimes not. Not all baluns are wired the same way.

Quote:
Originally Posted by holl_ands View Post
Modern Baluns typically use PAIRS of wires wound either in air or on Ferrite Cores as Transmission Delay Lines. PCB Baluns do the same thing via sinuous circuit board etches and "Coax Baluns" via different lengths of Coax. These Delay Lines have different delays so that when summed together they "Transform" from one impedance to another (unfortunately......it's all in the math).

OUTDOOR TV Baluns usually have DC Continuity between the 300-ohm wire(s) and 75-ohm outer Coax connector in order to discharge the static electricity that builds up on the (ACTIVE ONLY) Antenna Elements due to wind passing across them (like shuffling your feet across a carpet)....which will ALSO protect the Balun against voltage arc-over, thereby avoiding user complaints. Whether there is DC Continuity between the two 300-ohm twinleads depends on choices by the design engineer such as how to use those pesky frequency compensation capacitors...or not...and the chosen interconnection between the Delay Lines.

Since the ACTIVE Elements are NOT connected to the grounded Mast, the leakage path through the Balun is the ONLY way to discharge static electricity buildup on those element. The PASSIVE Elements can (Optionally) be connected to the grounded mast, such as in typical Yagi designs, but if they "float" it's usually unlikely they will spark over due to the distances involved....probably...YMMV....

I as far I as can determine, the Philips and Channel Master OUTDOOR Baluns are known to be high performers....and indeed have DC Continuity between 300-ohm wires and 75-ohm outer Coax connector.
http://www.avsforum.com/forum/25-hdt...l#post23942435
__________________
If you can not measure it, you can not improve it.
Lord Kelvin, 1883
http://www.megalithia.com/elect/aeri...ttpoorman.html

Last edited by rabbit73; 27-Oct-2016 at 11:46 PM.
rabbit73 is offline   Reply With Quote