It's probably worth spending a couple of minutes making the joint as 'nice' as
possible. A discontinuity in a TV feed could produce a reflection which could
give a ghost on the telly image.
(a the small refelction that has been demonstrated = 20dB
(b teh fact that teh distances involved are small. you need a fair few
meters to give a discernile ghost.
a line is 60Us long, roughly, so for 600 dots per line rough image
quality, 100ns or less is indiscernible.
That equates to 3meters of cable. Quite a bit
Good points. However, just to clarify, the 20dB return loss was for the
reasonably good joint. The bad joint had a return loss of about 11.6 dB. That's
about 7% of the power being reflected. (20dB reflection corresponds to 1%). I'm
not sure how noticable that ghost would be.
Also, don't forget that signals travel more slowly down cable than in air, by a
factor of (say) 0.5 to 0.7 (.) So, it would only take 2m of cable to give a
discernable ghost (by your test).
I added the note about reflections after a colleague's account of a bad ghost
which was traced to a cable joint made using a 30A mains junction box. Who ya'
In fact there a very well written article on a subject called pre echo
where there is a possibility of direct pick up off poor cables directly
from the transmitter and the delayed signal via a distribution system.
Very good site this is if you're into TV etc...
3db is about 50% reflection, so probably less than 1db
I don't think its that much reduction.
I never advocated a bad joint in a 30A mains junction box :-)
Its been a long time, but certainly one TV installation I saw, had lost
the entire connection to the aerial earth lead...it worked, but certain
stations were vastly better than others - big drop - 10 meters plus.
No ghosts tho - or very few. Possibly because the discontinutity was at
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