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Old March 21st 14, 02:54 PM posted to rec.radio.amateur.antenna
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First recorded activity by RadioBanter: Mar 2014
Posts: 16
Default Discone and feedline grounding

Ralph Mowery wrote:

Ok on the vertical dipole. For this antenna you need to run the feedline
horizontal from it for a couple of feet and then down.

The impedance of this antenna should be around 70 ohms and if I were you , I
would use some 70 ohm rg-6 coax back to the receiver.

The 300:75 converter is actually a balun that has a 4 to 1 ratio. It
normally does 2 things, changes a 300 ohm to 75 ohm inpedance such as many
TV antennaas were set for 300 ohms so the twin lead could be used. As
things changed over the years, the newer TV sets had a 70 ohm input for the
coax cable. The 300:70 could be used either way, 300 ohm antenna to coax or
coax to the old 300 ohm input of the TV.

Removing it from the vertical dipole (70 ohm inpedance) and using coax to
the receiver will probably help.



Thanks Ralph, I'll try that this weekend and see what the results are (I
have scads of RG6).

Speaking of cable impedance, will I see much of a difference using 70
ohm cable on an 50 ohm antenna? Assuming less than 50 feed of distance,
does it really matter that much?

The baluns can be used either place. Most often at the antenna if coax is
used and at the transceiver if open wire (twinlead) is used,


I have been using the 70 and 75 ohms without paying much attention. They
are close enough it does not mater.


Jon
 
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