Me wrote:
In article ,
Dave Bushong wrote:


That is actually not quite true. On an HT, the transmission line ends
somewhere inside the radio. The SMA/BNC connector is part of the
antenna proper. If you add a sleeve (as the previous poster, "dixon",
says), you will be changing the antenna itself. ASCII schematic follows:

befo


I have been in the communications field for 35 years, and I have NEVER
seen a SMA/BNC antenna connector on a Handheld Radio that didn't
have a the RF Ground connected to the ground side of the connector.
there are some that use different antenna connectors than SMA/TNC?BNC
that are singleended but I have never seen one used that way.
CFR (Call for Rference) Tell us all which radios your talking about.
Make, Model, Version.


Me

You missed my point, I think. The counterpoise is the (poor) metal of
the radio and of the user's hand. Any connector/adapter will be coaxial
and probably low loss, but the counterpoise stays put. The feedpoint
rises but the "ground" plane does not. For an SMA adapter, it might not
be enough to hear a difference, but the radiated signal will be worse
when using such an adapter.

73,
Dave

A few themes have shown up on this thread that seem to reinforce some
misconceptions about antennas. They might not have been meant that way,
but I think it's a good idea to clarify them in case a casual reader
might drop by and be misled.

The first one is about where the "transmission line" ends and where the
"antenna" starts. The antenna starts at the point where the two current
carrying conductors move far enough apart for significant radiation to
take place. By way of illustration, let's take the example of a simple
vertical mounted on a perfect ground plane. We'll feed it at the bottom
via a piece of coax. It doesn't matter where the coax is, above or below
the ground plane. Inside the coax, there's current on the outside of the
inner conductor, and an equal amount, flowing the opposite direction, on
the inside of the outer conductor. The fields from these two currents
cancel everywhere outside the coax, so it doesn't radiate.

At the point where the coax connects to the antenna, the current from
the inner conductor flows up the antenna. The (equal) current from the
inside of the shield flows over the ground plane, spreading out from the
point where the shield connects to the ground plane. The currents are
now physically separated, so their fields no longer cancel, and net
radiation can result.

An important feature of this setup is the effect of the current flowing
along the ground plane. For every bit of current flowing outward in one
direction, there's an equal bit flowing outward in exactly the other
direction. The fields from these two bits of current cancel at right
angles to the directions of flow. When you look at all the bits of
current, you find that the net field from the whole amount of current is
zero. So the current on the ground plane doesn't result in any
radiation. (By contrast, the current on the antenna wire doesn't have
any cancelling current, so it radiates.) A conductor which carries
current but doesn't radiate (significantly) is often called a
"counterpoise". Misuse of this term is another problem with some of the
postings, and I'll address it in a minute. The important thing to
remember is that a "counterpoise" doesn't radiate significantly. If it
does, it's not a "counterpoise" but a part of the antenna.

What happens if we put a piece of pipe around the bottom, say, 1/4 of
the antenna, weld it to the ground plane, and connect the coax shield to
its inside? Now the pipe is an extension of the transmission line. The
portion of the antenna inside the pipe is the center conductor, and the
pipe is the shield. So the portion of the antenna inside the pipe can't
really be called an "antenna" any more, since it doesn't radiate.

The current on the inside of the pipe reaching the top of the pipe flows
over the edge and down the outside to the ground plane. Here's a very
important point: *This current radiates just like the current on the
antenna wire*. What we have now is a lopsided dipole. The antenna wire
protruding from the top of the pipe is one side of the dipole, and the
outside of the pipe is the other. The "feedpoint" is where the wire
sticks out of the pipe. Once the current along the outside of the pipe
hits the ground plane, it spreads as before. The current on the outside
of the pipe radiates, the current on the ground plane doesn't.

A statement was made about a situation sort of like this "shielding" the
"high current" part of the antenna. This isn't what happens at all. What
happens is that the portion of the original antenna wire inside the pipe
is no longer an antenna at all, but part of a transmission line. The
current on it isn't the same as before the pipe was put there. The
radiating antenna is now the portion sticking out of the pipe, and the
current at its bottom, all other things being equal, will now be greater
than before the pipe was added. No signal or power is lost due to
"shielding". All you've done is shortened the antenna a bit, just as
though you'd cut a bit off the top.

Now let's remove the pipe and bend the ground plane downward into a
cone, with the antenna sticking out of the cone's apex. Here we'll find
that the current flowing on the ground plane does indeed radiate.
There's no net radiation straight up, but it radiates horizontally and
in all other directions. The ground plane is no longer a "counterpoise",
but simply a conically-shaped dipole half. If the ground plane radius
was about the same as the "antenna" length, and the ground plane is bent
downward at a reasonably sharp angle, the radiation from the conical
ground plane will be about the same as the radiation from the "antenna".
Calling it a "counterpoise" doesn't give it magical properties so we can
ignore it -- it's every bit as much a part of the antenna as the "antenna".

Finally, consider an HT. Here, one half of the antenna is the rubber
ducky or other "antenna". If you put a sleeve over part of the outside
of it, the real radiating top part of the antenna is the part sticking
out of the sleeve. The other half of the antenna -- NOT a
"counterpoise", but a real part of the antenna of at least equal
importance to the intended part -- is the outside of the sleeve, and the
outside of the HT, your hand, and your body. Whatever current flows up
into your "antenna" also flows along the other half -- that is, along
the HT and your body -- and radiates.

Roy Lewallen, W7EL

In article ,
Dave Bushong wrote:

That is actually not quite true. On an HT, the transmission line ends
somewhere inside the radio. The SMA/BNC connector is part of the
antenna proper. If you add a sleeve (as the previous poster, "dixon",
says), you will be changing the antenna itself. ASCII schematic follows:

befo

I have been in the communications field for 35 years, and I have NEVER
seen a SMA/BNC antenna connector on a Handheld Radio that didn't
have a the RF Ground connected to the ground side of the connector.
there are some that use different antenna connectors than SMA/TNC?BNC
that are singleended but I have never seen one used that way.
CFR (Call for Rference) Tell us all which radios your talking about.
Make, Model, Version.


Me

In article ,
Dave Bushong wrote:

That is actually not quite true. On an HT, the transmission line ends
somewhere inside the radio. The SMA/BNC connector is part of the
antenna proper. If you add a sleeve (as the previous poster, "dixon",
says), you will be changing the antenna itself. ASCII schematic follows:

befo

I have been in the communications field for 35 years, and I have NEVER
seen a SMA/BNC antenna connector on a Handheld Radio that didn't
have a the RF Ground connected to the ground side of the connector.
there are some that use different antenna connectors than SMA/TNC?BNC
that are singleended but I have never seen one used that way.
CFR (Call for Rference) Tell us all which radios your talking about.
Make, Model, Version.


Me

A few themes have shown up on this thread that seem to reinforce some
misconceptions about antennas. They might not have been meant that way,
but I think it's a good idea to clarify them in case a casual reader
might drop by and be misled.

The first one is about where the "transmission line" ends and where the
"antenna" starts. The antenna starts at the point where the two current
carrying conductors move far enough apart for significant radiation to
take place. By way of illustration, let's take the example of a simple
vertical mounted on a perfect ground plane. We'll feed it at the bottom
via a piece of coax. It doesn't matter where the coax is, above or below
the ground plane. Inside the coax, there's current on the outside of the
inner conductor, and an equal amount, flowing the opposite direction, on
the inside of the outer conductor. The fields from these two currents
cancel everywhere outside the coax, so it doesn't radiate.

At the point where the coax connects to the antenna, the current from
the inner conductor flows up the antenna. The (equal) current from the
inside of the shield flows over the ground plane, spreading out from the
point where the shield connects to the ground plane. The currents are
now physically separated, so their fields no longer cancel, and net
radiation can result.

An important feature of this setup is the effect of the current flowing
along the ground plane. For every bit of current flowing outward in one
direction, there's an equal bit flowing outward in exactly the other
direction. The fields from these two bits of current cancel at right
angles to the directions of flow. When you look at all the bits of
current, you find that the net field from the whole amount of current is
zero. So the current on the ground plane doesn't result in any
radiation. (By contrast, the current on the antenna wire doesn't have
any cancelling current, so it radiates.) A conductor which carries
current but doesn't radiate (significantly) is often called a
"counterpoise". Misuse of this term is another problem with some of the
postings, and I'll address it in a minute. The important thing to
remember is that a "counterpoise" doesn't radiate significantly. If it
does, it's not a "counterpoise" but a part of the antenna.

What happens if we put a piece of pipe around the bottom, say, 1/4 of
the antenna, weld it to the ground plane, and connect the coax shield to
its inside? Now the pipe is an extension of the transmission line. The
portion of the antenna inside the pipe is the center conductor, and the
pipe is the shield. So the portion of the antenna inside the pipe can't
really be called an "antenna" any more, since it doesn't radiate.

The current on the inside of the pipe reaching the top of the pipe flows
over the edge and down the outside to the ground plane. Here's a very
important point: *This current radiates just like the current on the
antenna wire*. What we have now is a lopsided dipole. The antenna wire
protruding from the top of the pipe is one side of the dipole, and the
outside of the pipe is the other. The "feedpoint" is where the wire
sticks out of the pipe. Once the current along the outside of the pipe
hits the ground plane, it spreads as before. The current on the outside
of the pipe radiates, the current on the ground plane doesn't.

A statement was made about a situation sort of like this "shielding" the
"high current" part of the antenna. This isn't what happens at all. What
happens is that the portion of the original antenna wire inside the pipe
is no longer an antenna at all, but part of a transmission line. The
current on it isn't the same as before the pipe was put there. The
radiating antenna is now the portion sticking out of the pipe, and the
current at its bottom, all other things being equal, will now be greater
than before the pipe was added. No signal or power is lost due to
"shielding". All you've done is shortened the antenna a bit, just as
though you'd cut a bit off the top.

Now let's remove the pipe and bend the ground plane downward into a
cone, with the antenna sticking out of the cone's apex. Here we'll find
that the current flowing on the ground plane does indeed radiate.
There's no net radiation straight up, but it radiates horizontally and
in all other directions. The ground plane is no longer a "counterpoise",
but simply a conically-shaped dipole half. If the ground plane radius
was about the same as the "antenna" length, and the ground plane is bent
downward at a reasonably sharp angle, the radiation from the conical
ground plane will be about the same as the radiation from the "antenna".
Calling it a "counterpoise" doesn't give it magical properties so we can
ignore it -- it's every bit as much a part of the antenna as the "antenna".

Finally, consider an HT. Here, one half of the antenna is the rubber
ducky or other "antenna". If you put a sleeve over part of the outside
of it, the real radiating top part of the antenna is the part sticking
out of the sleeve. The other half of the antenna -- NOT a
"counterpoise", but a real part of the antenna of at least equal
importance to the intended part -- is the outside of the sleeve, and the
outside of the HT, your hand, and your body. Whatever current flows up
into your "antenna" also flows along the other half -- that is, along
the HT and your body -- and radiates.

Roy Lewallen, W7EL

A few themes have shown up on this thread that seem to reinforce some
misconceptions about antennas. They might not have been meant that way,
but I think it's a good idea to clarify them in case a casual reader
might drop by and be misled.

The first one is about where the "transmission line" ends and where the
"antenna" starts. The antenna starts at the point where the two current
carrying conductors move far enough apart for significant radiation to
take place. By way of illustration, let's take the example of a simple
vertical mounted on a perfect ground plane. We'll feed it at the bottom
via a piece of coax. It doesn't matter where the coax is, above or below
the ground plane. Inside the coax, there's current on the outside of the
inner conductor, and an equal amount, flowing the opposite direction, on
the inside of the outer conductor. The fields from these two currents
cancel everywhere outside the coax, so it doesn't radiate.

At the point where the coax connects to the antenna, the current from
the inner conductor flows up the antenna. The (equal) current from the
inside of the shield flows over the ground plane, spreading out from the
point where the shield connects to the ground plane. The currents are
now physically separated, so their fields no longer cancel, and net
radiation can result.

An important feature of this setup is the effect of the current flowing
along the ground plane. For every bit of current flowing outward in one
direction, there's an equal bit flowing outward in exactly the other
direction. The fields from these two bits of current cancel at right
angles to the directions of flow. When you look at all the bits of
current, you find that the net field from the whole amount of current is
zero. So the current on the ground plane doesn't result in any
radiation. (By contrast, the current on the antenna wire doesn't have
any cancelling current, so it radiates.) A conductor which carries
current but doesn't radiate (significantly) is often called a
"counterpoise". Misuse of this term is another problem with some of the
postings, and I'll address it in a minute. The important thing to
remember is that a "counterpoise" doesn't radiate significantly. If it
does, it's not a "counterpoise" but a part of the antenna.

What happens if we put a piece of pipe around the bottom, say, 1/4 of
the antenna, weld it to the ground plane, and connect the coax shield to
its inside? Now the pipe is an extension of the transmission line. The
portion of the antenna inside the pipe is the center conductor, and the
pipe is the shield. So the portion of the antenna inside the pipe can't
really be called an "antenna" any more, since it doesn't radiate.

The current on the inside of the pipe reaching the top of the pipe flows
over the edge and down the outside to the ground plane. Here's a very
important point: *This current radiates just like the current on the
antenna wire*. What we have now is a lopsided dipole. The antenna wire
protruding from the top of the pipe is one side of the dipole, and the
outside of the pipe is the other. The "feedpoint" is where the wire
sticks out of the pipe. Once the current along the outside of the pipe
hits the ground plane, it spreads as before. The current on the outside
of the pipe radiates, the current on the ground plane doesn't.

A statement was made about a situation sort of like this "shielding" the
"high current" part of the antenna. This isn't what happens at all. What
happens is that the portion of the original antenna wire inside the pipe
is no longer an antenna at all, but part of a transmission line. The
current on it isn't the same as before the pipe was put there. The
radiating antenna is now the portion sticking out of the pipe, and the
current at its bottom, all other things being equal, will now be greater
than before the pipe was added. No signal or power is lost due to
"shielding". All you've done is shortened the antenna a bit, just as
though you'd cut a bit off the top.

Now let's remove the pipe and bend the ground plane downward into a
cone, with the antenna sticking out of the cone's apex. Here we'll find
that the current flowing on the ground plane does indeed radiate.
There's no net radiation straight up, but it radiates horizontally and
in all other directions. The ground plane is no longer a "counterpoise",
but simply a conically-shaped dipole half. If the ground plane radius
was about the same as the "antenna" length, and the ground plane is bent
downward at a reasonably sharp angle, the radiation from the conical
ground plane will be about the same as the radiation from the "antenna".
Calling it a "counterpoise" doesn't give it magical properties so we can
ignore it -- it's every bit as much a part of the antenna as the "antenna".

Finally, consider an HT. Here, one half of the antenna is the rubber
ducky or other "antenna". If you put a sleeve over part of the outside
of it, the real radiating top part of the antenna is the part sticking
out of the sleeve. The other half of the antenna -- NOT a
"counterpoise", but a real part of the antenna of at least equal
importance to the intended part -- is the outside of the sleeve, and the
outside of the HT, your hand, and your body. Whatever current flows up
into your "antenna" also flows along the other half -- that is, along
the HT and your body -- and radiates.

Roy Lewallen, W7EL

Me wrote:
In article
,
Bob Dixon wrote:


Adding any adaptor would seem to significantly move the radiating
portion of the antenna further away from the "ground plane" of the radio.
This should affect the operation of the antenna adversely. Comments?

Bob



Adding an adapter to a Transmission Line will have no effect, except to
add insertion loss of the adapter. Adding an adapter to the antenna
itself MAY cause the antenna charactoristics to change. Most SMA and BNC
connecters are used in Transmission Lines, and not antennas themselves.
The OP doesn't really explain where the adapter is to be used. Most
small handheld devices with external antenna connections have those
connection in the Transmission Line and not in the antenna itself.

Me

That is actually not quite true. On an HT, the transmission line ends
somewhere inside the radio. The SMA/BNC connector is part of the
antenna proper. If you add a sleeve (as the previous poster, "dixon",
says), you will be changing the antenna itself. ASCII schematic follows:

befo


|
| antenna
|
|
_ ground + bnc/sma
||
|| coax from PA strip
||
||

after

|
| antenna
|
|
||
|| shielded antenna (adapter)
||
_ ground (bnc
||
|| coax from PA strip
||
||

And as we remember, "maximum radiation at the current maximum" (that is,
the base of a classic 1/4 wave antenna), you are shielding the point of
maximum radiation.

From a practical standpoint, you will probably be using a gain-retarded
rubber duckie, and the 1 or 2 dB loss from even the worst adapter will
be swamped by the -10 dB gain of the duck (that is "minus 10 dB gain").
The rubber-duck will make a 5 watt transmitter sound like a 1/2 watt
one. Having another 1 dB of loss will make that 5-watt radio sound like
0.4 instead of 0.5. No big deal.

If you can keep your radio from being broken by using a quality adapter,
and with a negligible loss in performance, I say, "do it."

If you are talking about squeaking out every last bit of signal, such as
EME, the answer is "no". But if you are talking about walking around a
hamfest on 2m, then spend a few extra bucks to keep from fracturing your
antenna connector connection, which these days, most hams can't, or
don't know how to, fix. flames invited

Your mileage may vary.

Dave
KZ1O

Me wrote:
In article
,
Bob Dixon wrote:


Adding any adaptor would seem to significantly move the radiating
portion of the antenna further away from the "ground plane" of the radio.
This should affect the operation of the antenna adversely. Comments?

Bob



Adding an adapter to a Transmission Line will have no effect, except to
add insertion loss of the adapter. Adding an adapter to the antenna
itself MAY cause the antenna charactoristics to change. Most SMA and BNC
connecters are used in Transmission Lines, and not antennas themselves.
The OP doesn't really explain where the adapter is to be used. Most
small handheld devices with external antenna connections have those
connection in the Transmission Line and not in the antenna itself.

Me

That is actually not quite true. On an HT, the transmission line ends
somewhere inside the radio. The SMA/BNC connector is part of the
antenna proper. If you add a sleeve (as the previous poster, "dixon",
says), you will be changing the antenna itself. ASCII schematic follows:

befo


|
| antenna
|
|
_ ground + bnc/sma
||
|| coax from PA strip
||
||

after

|
| antenna
|
|
||
|| shielded antenna (adapter)
||
_ ground (bnc
||
|| coax from PA strip
||
||

And as we remember, "maximum radiation at the current maximum" (that is,
the base of a classic 1/4 wave antenna), you are shielding the point of
maximum radiation.

From a practical standpoint, you will probably be using a gain-retarded
rubber duckie, and the 1 or 2 dB loss from even the worst adapter will
be swamped by the -10 dB gain of the duck (that is "minus 10 dB gain").
The rubber-duck will make a 5 watt transmitter sound like a 1/2 watt
one. Having another 1 dB of loss will make that 5-watt radio sound like
0.4 instead of 0.5. No big deal.

If you can keep your radio from being broken by using a quality adapter,
and with a negligible loss in performance, I say, "do it."

If you are talking about squeaking out every last bit of signal, such as
EME, the answer is "no". But if you are talking about walking around a
hamfest on 2m, then spend a few extra bucks to keep from fracturing your
antenna connector connection, which these days, most hams can't, or
don't know how to, fix. flames invited

Your mileage may vary.

Dave
KZ1O

"Bob Dixon" wrote in message
...
Adding any adaptor would seem to significantly move the radiating
portion of the antenna further away from the "ground plane" of the radio.
This should affect the operation of the antenna adversely. Comments?

What makes you think the effect should be adverse? When you consider all
the different radios that a given antenna could be connected to, the change
from radio to radio is going to be far greater than what a 3/8" adapter is
going to do (consider its electrical length at 2m...). In fact, I would
hope that most HT antennas weren't meant to be used with counterpoises, but
now that I think about it, I don't really know whether or not that's the
case. Anyone?

I mean... the radiation pattern of a wire cut 'to length' stuck into a BNC
connector on the top of an HT is going to be very seriously distorted
relative to the same wire above a near-infinite ground plane.

Cell phones often use sleeve dispole antennas to avoid the need for a
counterpoise...

---Joel

In article
,
Bob Dixon wrote:

Adding any adaptor would seem to significantly move the radiating
portion of the antenna further away from the "ground plane" of the radio.
This should affect the operation of the antenna adversely. Comments?

Bob


Adding an adapter to a Transmission Line will have no effect, except to
add insertion loss of the adapter. Adding an adapter to the antenna
itself MAY cause the antenna charactoristics to change. Most SMA and BNC
connecters are used in Transmission Lines, and not antennas themselves.
The OP doesn't really explain where the adapter is to be used. Most
small handheld devices with external antenna connections have those
connection in the Transmission Line and not in the antenna itself.

Me