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Old 27 September 2011, 16:29   #1
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Coax and PL259 connectors

Got VHF wired up today but got a few questions about the antenna side of things.

I have the RibRaider antenna connected to the VHF set via a standard PL259 plug with the inner core soldered to the 'pin' of the plug.

When continuity testing the the coax I could get continuity through the inner pin at the antenna through to the inner pin at the plug and similarly continuity from the outside of the plug and outer part of the antenna connector. I'm assuming this is right?

When touching both parts with the meter at the antenna end there was no continuity.

However, when touching both the inner pin and outer part of the plug there was a short. Have I done something wrong?

I could not receive anything whilst the radio was on but I have not tried with a handheld and we are quite a way from anything that would be transmitting.

Help is much appreiciated.

Thanks
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Old 27 September 2011, 16:38   #2
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Might be down to the bottle of wine I drank tonight but I can't quite make headway of what you are saying here. Are you saying on a piece of coax it's good at one end but shorting at the other? If so pass me the corkscrew please........
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Old 27 September 2011, 16:40   #3
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Ok, i'll have another look tomorrow..i'm tired
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Old 27 September 2011, 17:21   #4
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I'm guessing when you tested across the vhf end, you had the other end connected to the antenna? In which case all sounds ok
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Old 27 September 2011, 23:29   #5
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Can't read to the pin if its's connected.

I assume what you meant was with both antenna and radio disconnected, you're reading pin to shield: open at one end, and shorted at the other?

Sounds like you have 2 problems: a shorted pin to shield somewhere, and an open (well, something: Shield to outer connector is probably most likely. Pin to center conductor is harder to screw up.)

You'll most likely need to guess and cut one off, and check the remaining cable, pin to center conductor on the cut end (should short), outer connector to shield on cut end (should short) and pin to outer connector on the remaining connector (should be open.) If it doesn't read correctly, you cut the wrong end. Finished cable should read the same, but substitute "pin" for "center conductor" and "outer connector" for "shield".

Or alternatively, you can simply cut and reterminate both ends, which saves all the troubleshooting.

jky
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Old 28 September 2011, 03:10   #6
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Thanks, I can't get the antenna end off though as its the Rib raider plug.
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Old 28 September 2011, 03:59   #7
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Originally Posted by maxhar View Post
Thanks, I can't get the antenna end off though as its the Rib raider plug.
In which case you cant check the coax, the antenna will show a short - as you have found.
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Old 28 September 2011, 04:20   #8
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So what is supposed to show a short and what isn't?

At the VHF end, is there supposed to be a short from the inner core (pin out top of pug) to the outside of the plug?

Thanks
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Old 28 September 2011, 07:44   #9
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If you disconnect at the antenna and at the radio you can test the cable for continuity, as I understand you have done. In this case you should see no circuit between the centre conductor and any part of the braid or connector casing. You should have continuity from end to end of the centre conductor, and continuity from end to end of the braid.

If you do see a short circuit with both ends of the cable disconnected it is most likely you have made a bad connection at the PL259, probably by having a strand of centre conductor bent back as you pushed the conductor into the PL259. Or you could have a similar problem at that funny connector they use at the antenna end.

If you connect at the antenna end you will now see a short circuit between centre pin of the PL259 and its outer case because that antenna is internally dc grounded. Most vhf antennas are this way.
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Old 28 September 2011, 11:00   #10
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Ok thanks John, that was really helpful. I'm going to have a second look tonight.
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