Wire you saying that?

[cid]

Okay...
Out at the station, and one of the antennas seems to be a bit funky. Antenna lead comes in to patch panel, radio lead goes to patch panel,
run a male/male coaxial cable jumper to connect 'em (this lets you connect any radio to any antenna).
When inserting male jumper center pin into female socket, signals on radio are loud -- but when outside shell of PL259 connector
screws onto SO239 socket, it gets really quiet -- enough to make me think something's wrong.
Have traded jumper cables, and switched antennas. Maybe the jumper change fixed things. But it almost felt/sounded like the center socket
on the SO239 just wasn't making proper connection with the PL259.

Now -- herein's the rub...
I have always been of the opinion that the outbound AND inbound signals travel on the center of the connectors/coaxial cable
(in our case, we're using RG213U 50-ohm coax -- an upgrade (better shield) than the traditional RG8). I always thought the shield was there to
provide a ground/return path for an unbalanced antenna setup, and to prevent interference from other signals impressing themselves
on the cable.
Mein buddy who is in charge of maintenance out here seems to think that the center is for TX and the shield is for RX.
I don't think so...

All you electrogeeks out there chime in. Who's got their connectors screwed on straight here?

[Sigma_Orionis]

According to what little I remember about this kind of stuff, you're right, a coaxial cable is an unbalanced line, the shield is connected to ground and the center conductor is used for signals.

Let's see what the AAP has to say

Edited to correct: the ACA

Damn had to fix the fix, how bad is that?

[FZR1KG]

Sigma's pretty much got it.
A coaxial line is unbalanced but it has a characteristic impedance, usually set to 50ohms.

If you are connecting the center and getting a loud signal then when you connect the shield you get little or no signal it suggests that your antenna lead system has a short from shield to core.
Grab a multimeter and check the center to shield of the main antenna feed and the patch cables.As to why it behaves like this, think about the length of radio waves vs the length of the coax. If you short the coax at any particular point you still can make a very effective antenna depending on the position of the short, hence its length, hence the optimum wave length that it will allow through. You have basically made a tuned antenna by shorting it. The response is usually a pandpass filter and the center frequency will depend on the short position.

To give you an example, a UHF receiver I designed consists of the antenna feed point at the PCB socket that splits two ways. One goes to a PCB trace inductor and to the front end of the receiver. The other goes at 90 degrees and travels about 1cm (a bit over a 1/3inch) then goes directly to ground! If you look at the circuit you see that the core of the receiver is shorted to directly to the ground plane that is under the whole receiver stage. One would think this would just not work at all but what it is in effect is a tuned circuit that was designed by using a form of finite analysis to make the receiver have both a tuned bandpass filter and to match the chatacteristic impedance of the antenna socket on the PCB to 50ohms.

In your case what you are likely getting is an untuned antenna when you connect just the core and when you connect the shield you create a tuned antenna. Untuned antenna are wide band and have a relatively high impedance but in reception that's not usually a big deal. It's basically a long wire.
When the shield connects you have created both a tuned antenna and changed its impedance.
Depending on the short position you may it may be a really good filter for rejecting the band you're listening to or if you change bands it may become a fine tuned antenna or anywhere in between.
If you're using a HF antenna the odds are you've created a bandpass filter high up in frequency so that when you are listening to SW it's effectively a short to ground.

Here's the fun part, if you grab a scanner you can check the peak reception frequency. That would give you a corresponding wavelength. With that you can reverse engineer the approximate point of the short.
I say that in jest as it's far easier to just find the thing with a low ohms meter or by physically checking the cable in most cases.

Another likely scenario is that your actual antenna is missing, at least electrically.
If you have a corroded connection at the antenna your antenna is effectively not connected.
The core will still provide reception through capacitive coupling to the shield so long as you don't ground the shield.
When you ground the shield you effectively change kill that signal.
Since the standard design for noise purposes is a single point ground your antenna cable shield is just a free long wire until you connect the thing to ground by joining the shields.

And your friend is incorrect. Both the shield and the core are used to transmit the signal.
Think of a battery. If you use only one lead to connect a battery, how much power, voltage or current can you get out of it?
When transmitting the actual RF, you need a ground plane as well as the antenna.
If either one is inadequate the system isn't going to be very good.