Michael Coslo wrote:

I've always wondered, when people take these antennas that are likely to
have feedline radiation, and try as they may to stop it, isn't it likely
that they are making the antenna not work as well as it might have if we
just left the feedline radiate as it would? You might be taking away a
major part of the antenna performance?

I have to expect that a radiating feedline would have to be a pretty
inconsistent sort of antenna from one installation to another.

- 73 de Mike N3LI -

Absolutely. A radiating feedline is part of the antenna, as is the
entire path to the Earth along the outside of the rig, through the mains
power system or whatever other path it can take. So two people thinking
they have the same "antenna" can really have very different radiating
systems.

Sometimes the radiation from the feedline, mains wiring, and stuff in
the shack can be beneficial -- it might, for instance, fill in deep
nulls in the main antenna's pattern and result in a spectacular signal
strength improvement in particular directions. On the other hand, it can
cause lots of problems. For example, when I was testing an OCF dipole a
while back, on one band my electronic keyer would lock up after the
first "dit" due to RF in the shack and on all the station connecting
wires. And having the power wiring be part of your antenna system can
lead to trouble with telephone, TV, and other kinds of interference. But
then you might get lucky and get away with it.

Probably because of the same personality quirk that led me to become an
engineer, I prefer to be able to predict and understand how my antenna
system will work, and design it to work as I want, rather than making it
a crap shoot. But that's surely not the only, or necessarily the best,
way to get on the air and talk to people.

Roy Lewallen, W7EL

On 15 fév, 19:22, Roy Lewallen wrote:

Sometimes the radiation from the feedline, mains wiring, and stuff in
the shack can be beneficial -- it might, for instance, fill in deep
nulls in the main antenna's pattern and result in a spectacular signal
strength improvement in particular directions.

I am slightly OT here, but the same argumentation could be used about
non-resonant antennas like the G5RV. Yes, ATU needed, but L-type
autotuners for example have very small insertion loss.

I am wondering about the real advantage of a razor cut dipole
(resonant anyway on a small region around a freq) versus a multi-band
dipole using a length of feed line matching section like the G5RV or
ZS6BKW/G0GSF Antenna System...

73 de Pierre VE2PID

ve2pid wrote:
On 15 fév, 19:22, Roy Lewallen wrote:
Sometimes the radiation from the feedline, mains wiring, and stuff in
the shack can be beneficial -- it might, for instance, fill in deep
nulls in the main antenna's pattern and result in a spectacular signal
strength improvement in particular directions.

I am slightly OT here, but the same argumentation could be used about
non-resonant antennas like the G5RV. Yes, ATU needed, but L-type
autotuners for example have very small insertion loss.

I am wondering about the real advantage of a razor cut dipole
(resonant anyway on a small region around a freq) versus a multi-band
dipole using a length of feed line matching section like the G5RV or
ZS6BKW/G0GSF Antenna System...

73 de Pierre VE2PID

No, the phenomenon I'm talking about is feedline radiation, which is
very difficult to prevent with a non-symmetrical antenna like an OCF
dipole because of their asymmetry. It has nothing to do with resonance
or non-resonance, or wideband or narrowband characteristics. You can, of
course, cause feedlines of symmetrical antennas to radiate by imbalanced
feeding. But this is as true of a resonant dipole as a random length
symmetrical antenna.

Roy Lewallen, W7EL

On 15 f v, 19:22, Roy Lewallen wrote:
Sometimes the radiation from the feedline, mains wiring, and stuff in
the shack can be beneficial -- it might, for instance, fill in deep
nulls in the main antenna's pattern and result in a spectacular signal
strength improvement in particular directions.

I am slightly OT here, but the same argumentation could be used about
non-resonant antennas like the G5RV. Yes, ATU needed, but L-type
autotuners for example have very small insertion loss.

I am wondering about the real advantage of a razor cut dipole
(resonant anyway on a small region around a freq) versus a multi-band
dipole using a length of feed line matching section like the G5RV or
ZS6BKW/G0GSF Antenna System...

73 de Pierre VE2PID

On Feb 16, 4:48*am, ve2pid wrote:
On 15 f v, 19:22, Roy Lewallen wrote:

Sometimes the radiation from the feedline, mains wiring, and stuff in
the shack can be beneficial -- it might, for instance, fill in deep
nulls in the main antenna's pattern and result in a spectacular signal
strength improvement in particular directions.

I am slightly OT here, but the same argumentation could be used about
non-resonant antennas like the G5RV. Yes, ATU needed, but L-type
autotuners for example have very small insertion loss.

I am wondering about the real advantage of a razor cut dipole
(resonant anyway on a small region around a freq) versus a multi-band
dipole using a length of feed line matching section like the G5RV or
ZS6BKW/G0GSF Antenna System...

73 de Pierre VE2PID

As far as I know, the key advantage of a resonant half-wave dipole is
that its feedpoint impedance is a pure resistance, and generally low
enough to provide a decent match to a coaxial feedline. The radiation
pattern of a dipole changes very little with fairly large changes in
frequency, until it becomes somewhat longer than one wavelength. Even
then, it doesn't become inefficient; it just develops lots of lobes
and nulls as its length in wavelengths increases (which may or may not
be a disadvantage). Reading between the lines of what Roy wrote, a
bit of feedline radiation will at least change where those lobes and
nulls are. But even a relatively short antenna (e.g. a dipole that's
only 0.1 wavelength long) can be quite efficient--the loss is
typically mainly in the network (including the feedline) used to feed
power to it. Another factor to consider for electrically short
antenna is that you have to tune out a reactance that's large compared
with the radiation resistance, and that makes them narrow-band if the
matching network is efficient. You have to re-tune for even small
changes in frequency.

Cheers,
Tom

Something that hasn't been mentioned is that common-mode energy forms
into standing waves, e.g. on the outside braid of the coax. An
isolator (choke), as exists on a Carolina Windom, may only change that
point to a current minimum while simply moving the current maximum
point to a different location. Has anyone actually measured the common-
mode current on a Carolina Windom on all bands up and down the coax on
the shack side of the isolator?
--
73, Cecil, w5dxp.com