On Tue, 18 Jul 2006 21:32:13 +0100, "David" nospam@nospam wrote:

Agreed, the centre junction of the radials is not always at 0V.

Hi David,

In isolation, this statement offers nothing at all, unless, of course,
you are talking about an unexcited system. The notion that 0V
inhabits some greater portion of the antenna, or its radials, or its
junction is a strange concept to its normal operation.

David, AE6EO, has similar concerns that you are presenting what I
would call a naive representation of radiators.

Current
flows along the coax braid on the inside, meaning that the inside part of
the coax braid and radials junction can be any voltage. The radials have a
voltage gradient along them because of the standing wave.

In that sense, 0V does reside at some favored points, but this is not
an explanation of anything.

Because the return
current flows on the inside of the coax braid, it is normally safe to touch
or go near the outside of the braid. For permanent low installations in a
public area, coax should be used instead of twin feeder. The fact that the
return current flows on the inside of the braid gives coax its shielding
properties.

Is this germane to a particular point? Again, these are simply
statements, and they appear unconnected to any kind of dialog.

73's
Richard Clark, KB7QHC

wrote:
But there's no way for me to separate the vertical
radiation of the radials from the vertical radiation of the
monopole.

That's not true.

I make a statement about my personal abilities and you have
the audacity to tell me it is not true????
--
73, Cecil, http://www.qsl.net/w5dxp

However, I still think that with only the vertical element connected to the
centre conductor, the vertical element radiates although not very well. With
only the radials connected to the outer braid, the radials do not radiate.
The RF live of the transceiver is normally connected to centre conductor,
and the RF ground side (the 0V side) is normally connected to the braid. The
outer of the connector on the transceiver is possibly connected internally
to the case and mains Earth.

On Wed, 19 Jul 2006 20:33:29 +0100, "David" nospam@nospam wrote:

However, I still think that with only the vertical element connected to the
centre conductor, the vertical element radiates although not very well. With
only the radials connected to the outer braid, the radials do not radiate.
The RF live of the transceiver is normally connected to centre conductor,
and the RF ground side (the 0V side) is normally connected to the braid. The
outer of the connector on the transceiver is possibly connected internally
to the case and mains Earth.

Hi David,

Only the slimmest margin of this comes close, and not enough to
explain anything. 0V, ground, live, dead, hot, cold, or whatever you
want to call it has long since disappeared from the scene at the other
end of a cable or twin lead. Radials do not mimic these terms even if
the illusion of continuity suggests otherwise. There is no "rf side"
nor is there a "ground side" to appeal to. Such distinctions are
reserved for very untechnical allusions.

73's
Richard Clark, KB7QHC

I agree that in the coax side, there is no real 0V because the current has a
standing wave. But the transceiver has a DC power supply (normally 12V) that
is controlled or modulated. One side of the power supply is regarded as 0V
and connected to 0V rail of circuits. The modulated side is the RF live that
is connected to the centre contact of transceiver output connector.

In theory, while transceiver is transmitting, if I touched the outer of the
output connector, I would not expect to get a shock or RF burn. If I touched
the centre contact of output connector, then I would expect to get a shock
or RF burn. Admittedly, I could touch the outer and find that I am close
enough to the centre contact for RF to capacitively couple into me. In real
life, I would never touch the output connector while the rig is
transmitting.

Does RF live and ground not exist on the output connector of the
transceiver?

I agree that in the coax side, there is no real 0V because the current has a
standing wave. But the transceiver has a DC power supply (normally 12V) that
is controlled or modulated. One side of the power supply is regarded as 0V
and connected to 0V rail of circuits. The modulated side is the RF live that
is connected to the centre contact of transceiver output connector.

In theory, while transceiver is transmitting, if I touched the outer of the
output connector, I would not expect to get a shock or RF burn. If I touched
the centre contact of output connector, then I would expect to get a shock
or RF burn. Admittedly, I could touch the outer and find that I am close
enough to the centre contact for RF to capacitively couple into me. In real
life, I would never touch the output connector while the rig is
transmitting.

Does RF live and ground not exist on the output connector of the
transceiver?

"Live" and "ground" aren't absolute, universal things. These terms
exist only in relation to a specific reference point, which you must
choose.

Yes, it's true that the outer rim of the coaxial connector is usually
tied to the chassis of the transceiver, and that this chassis is also
tied to your DC ground. So, the potential voltage between the
connector and your body is usually low and it's not all that likely to
shock you.

However, this doesn't mean that this same thing is true at the other
end of the coaxial cable (i.e. up at the antenna)! Although the far
end of the coax braid is at (or very close to) DC ground, it's far
enough away in RF terms (that is, in terms of wavelengths) that its
voltage is going to be very different much of the time.

Consider also the case in which your transceiver isn't "grounded" at
all... it's sitting on a wooden table, powered by a battery, and the
coax cable runs directly from it to the antenna. There's no "third
wire" in the power cord, or other grounding wire connecting the
transceiver to a water pipe or electric outlet or a grounding rod or
anything like that. Let's further assume that your antenna is a
vertical, with radials, elevated up on an insulated mast.

Now, when you transmit - what's the voltage present at the base of
each radial? If it's "0V", then why, and with respect to what?

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

On Wed, 19 Jul 2006 23:14:33 +0100, "David" nospam@nospam wrote:

I agree that in the coax side, there is no real 0V because the current has a
standing wave.

Hi Dave,

This doesn't really make much sense. Even discounting that and trying
to extrapolate your response, it isn't even 0V then and not true for
SWR in general.

But the transceiver has a DC power supply (normally 12V) that
is controlled or modulated.

A modulated power supply? Even if you mean regulated, it bears no
resemblence to the topic.

One side of the power supply is regarded as 0V
and connected to 0V rail of circuits. The modulated side is the RF live that
is connected to the centre contact of transceiver output connector.

It will, then, come as a surprise to you that the output of the
transmitter comes from an AC coupled link. You may choose either wire
in that link to go to any part of a ground system, or conversely, to
what you consider to be the radiator. It makes no difference because
there is no
Ground
Hot
Cold
Dead
Live
or any other distinction until you plant that wire. You can paint
that wire turquoise in the belief that it is safe, and grab it at a
later time to fry you.

In theory, while transceiver is transmitting, if I touched the outer of the
output connector, I would not expect to get a shock or RF burn.

Expectations here are a belief system, not a proof. I suggest you
stay away from situations that encourage such lethal presumptions.

If I touched
the centre contact of output connector, then I would expect to get a shock
or RF burn. Admittedly, I could touch the outer and find that I am close
enough to the centre contact for RF to capacitively couple into me. In real
life, I would never touch the output connector while the rig is
transmitting.

Does RF live and ground not exist on the output connector of the
transceiver?

There are no absolutes as you might expect. Plenty of correspondents
here complain daily of problems stemming from what you might deny. If
you worked your rig on 10M or 20M from the second story window, you
are so far from ground, electrically, that its apparent proximity is
only an illusion.

73's
Richard Clark, KB7QHC

David wrote:
I agree that in the coax side, there is no real 0V because the current has a
standing wave. But the transceiver has a DC power supply (normally 12V) that
is controlled or modulated. One side of the power supply is regarded as 0V
and connected to 0V rail of circuits. The modulated side is the RF live that
is connected to the centre contact of transceiver output connector.

In theory, while transceiver is transmitting, if I touched the outer of the
output connector, I would not expect to get a shock or RF burn. If I touched
the centre contact of output connector, then I would expect to get a shock
or RF burn. Admittedly, I could touch the outer and find that I am close
enough to the centre contact for RF to capacitively couple into me. In real
life, I would never touch the output connector while the rig is
transmitting.

Does RF live and ground not exist on the output connector of the
transceiver?

Begin with a self-contained, battery-powered transmitter. Put a large
metal plate on the ground, stand on the plate, and set the radio on the
plate. Touch the radio. No burn. Touch the center conductor. Burn. Just
like you said.

But now put the radio on top of an insulator, and connect the center
conductor of the antenna connector to the metal plate. Touch the center
conductor. No burn. Touch the radio. Burn. Whoa -- you got burned from
"0V" -- the "cold" side! No fair!

Finally, insulate the radio and disconnect the center conductor from the
plate. Hold on to the radio and touch the center conductor. Burn. Hold
on to a wire going to the center conductor. No burn. Touch the radio
while you're holding the wire. Burn.

You don't prevent a shock by declaring or "regarding" something to be
ground or "0V". You do it by connecting it to the same potential as your
body. And declaring it to be "live" doesn't cause the burn -- what
causes it is that you're touching something that's at a different
potential than your body.

Roy Lewallen, W7EL