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Oshb5
New member
Username: Oshb5
Post Number: 1
Registered: 8-2017
| | Posted on Tuesday, August 15, 2017 - 9:48 am: | 
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Hello All
. Iv just bought a second hand 2016 and I was cleaning it to get it erected and I was trying to work out the connections when I saw that the copper coil was connected to the radial plate. But at the same time saw that the pole mount also bolted to the same radial plate. Which got me thinking so I put the Ohm meter and it came up as a dead short? I could not test capacitance as my meter is ready to be replaced as that part ain't working. So this got me wondering I checked the internet and no matter how much I searched I could not find anything And i would have thought I would have with something such as this.
So as a last resort I asked the guy i got it from who said yes he knew about the dead short But get it up it works and is a great twig. Now not that I dont trust or believe him I think before I connect my new 480sat to this "twig" i need at least one more conformation before I put it up and try it.I mean I dont want to go through the effort or should I say pay for someone to put it up as I can hardly walk due to a triple bypass not working that I had 14 years ago. But thats another tail.
Regards Osh |
Tech237
Moderator
Username: Tech237
Post Number: 1885
Registered: 4-2004
| | Posted on Wednesday, August 16, 2017 - 10:42 am: |
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While I do not know the particular antenna, I can assure you that many antennas show a DC short across the coax. However due to the way RF works, this does not represent a short at RF frequencies - the combination of inductance and capacitance gives it an impedance of around the magic 50 ohms.
I am sure 833 will pop in with a more definitive answer shortly.
Tech237
N7AUS
God made me an athiest, who are you to question his wisdom?
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Tech833
Moderator
Username: Tech833
Post Number: 2385
Registered: 8-2002
| | Posted on Saturday, August 26, 2017 - 4:32 pm: |
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Yes, that is the way it is supposed to be. The coil connects between the ground and the vertical, the coax connects with shield to ground and the center conductor to one tap on that coil between ground and the vertical.
ALL 5/8 wave gain type antenna use some sort of shunt feed scheme to match the 50 ohm coax to the 2,000 or so ohm end of a 5/8 wave.
Your radio 'Mythbuster' since 1998
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