Antenna for my Kenwood R-1000 receiver?
 

Hello America and ships at sea,.. I just got a Kenwood R-1000 receiver
and I was wondering if anyone knew what kind of antenna I could rig up
for it. Can I clip something on to the stainless steel backstay and
expect to get a signal? I'm watching the other ssb thread that
suggests you can get a weather fax from it too. Thanks as always.

Antenna for my Kenwood R-1000 receiver?
 

ray lunder wrote in
:

Can I clip something on to the stainless steel backstay and
expect to get a signal?

Lots of sailboats have the neatest little antenna fed right into the main
cabin.....where the chainplate bolts hold the shrouds to the plastic. Most
of them are not grounded at this point. Hell, most of them are not
grounded at all, leaving you with an ungrounded lightning rod sticking up
out of the water just waiting to be hit, killing the family instantly.
It's simply a credit to the conductivity of seawater that it doesn't happen
more often than it does.

So, if you just add another nut to a handy, existing chainplate bolt and
put the hot wire of your receiver to it, you end up with a dandy antenna
just waiting for a lightning hit. If you run a heavy battery cable WITHOUT
those neat right angles boaters love from the bottom of the mast step to
the engine block, it will shunt off MOST, but not all, of the static
buildup that threatens the receiver and everyone aboard. It's not perfect
but it is safer.

Why didn't "they" ground everything? M-O-N-E-Y...same as always.

Larry
--

Antenna for my Kenwood R-1000 receiver?
 

ray lunder wrote:
Hello America and ships at sea,.. I just got a Kenwood R-1000 receiver
and I was wondering if anyone knew what kind of antenna I could rig up
for it. Can I clip something on to the stainless steel backstay and
expect to get a signal? I'm watching the other ssb thread that
suggests you can get a weather fax from it too. Thanks as always.


Hello Ray,

Sure, you can try the lifelines, the backstay, or a random length of
wire you have handy. Try them all. See which works best.

The downside of that sort of antenna is that it is likely to pick up a
lot of unwanted noise as well as signals of interest. Of course, at sea
the noise issue will be less. If you find reception is poor with these
antennas, you can always use an antenna resonant at the frequency of
interest (hopefully you won't have more than one or two of these) or you
can use a simple antenna tuner. For reception only, the tuner can use
very small and inexpensive components.

Keep in mind that we're at the bottom of the 11-year sunspot cycle and
high frequency propagation can be pitiful at times.

Chuck

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Antenna for my Kenwood R-1000 receiver?
 

chuck wrote in news:1173789524_25635
@sp6iad.superfeed.net:

high frequency propagation can be pitiful at times

"Pitiful" can be ZERO at times, recently....it's awful.

Larry
--

Antenna for my Kenwood R-1000 receiver?
 

On Wed, 14 Mar 2007 11:30:57 +0000, Larry wrote:

high frequency propagation can be pitiful at times

"Pitiful" can be ZERO at times, recently....it's awful.

Any sign yet of an upturn in the cycle?

At night the only thing that's working for me on Winlink/Pactor is
80M.

Antenna for my Kenwood R-1000 receiver?
 

On Tue, 13 Mar 2007 07:43:10 -0500, Larry wrote:

ray lunder wrote in
:

Can I clip something on to the stainless steel backstay and
expect to get a signal?

Lots of sailboats have the neatest little antenna fed right into the main
cabin.....where the chainplate bolts hold the shrouds to the plastic. Most
of them are not grounded at this point. Hell, most of them are not
grounded at all, leaving you with an ungrounded lightning rod sticking up
out of the water just waiting to be hit, killing the family instantly.
It's simply a credit to the conductivity of seawater that it doesn't happen
more often than it does.

So, if you just add another nut to a handy, existing chainplate bolt and
put the hot wire of your receiver to it, you end up with a dandy antenna
just waiting for a lightning hit. If you run a heavy battery cable WITHOUT
those neat right angles boaters love from the bottom of the mast step to
the engine block, it will shunt off MOST, but not all, of the static
buildup that threatens the receiver and everyone aboard. It's not perfect
but it is safer.

Why didn't "they" ground everything? M-O-N-E-Y...same as always.

Larry

So what would a proper boat antenna look like? Examples, pictures,
name brands? Thanks as always.

Antenna for my Kenwood R-1000 receiver?
 

Wayne.B wrote in
:

Any sign yet of an upturn in the cycle?

It's an 11 year cycle.... You can watch it on:
http://solarscience.msfc.nasa.gov/predict.shtml

The most fascinating place about it is at:
http://www.spaceweather.com/
Today's sunspot number is ZERO! NO SUNSPOTS! Arrghh.
Sure glad there's Skype...(c;
Spaceweather can EASILY occupy an entire evening exploring.

Canada accurately tracks the Solar Radio flux on 2.8 Ghz:
http://www.drao-ofr.hia-iha.nrc-cnrc...sol_home.shtml

So, from their prediction graph, it looks like a nice peak in 2012. This
is perfect as that is the year my Socialist Security checks start
rollin' in and I can stop working for all my money and live off the kids
at Mickey D's flipping hamburgers.

Who knows. I might just put W4CSC back on the air...(c;


At night the only thing that's working for me on Winlink/Pactor is
80M.


80 and 160M act more like AM broadcast band than shortwaves. They're
pretty predictable as a good nighttime freq with groundwave only on the
sunny side of the planet. 40M up to 10M is what the solar cycle hits so
hard. I have seen 75M SSB totally unusable for nets a few times. Of
course, to become "net control" on an ARRL net, you must NOT own a proper
ANTENNA or BIG LINEAR AMPLIFIER so you don't sound like you're talking on
a wet string with 10 watts, no matter what the conditions...(c;

I used to be active on the SC SSB net on 3915 many years ago. One night
at net time you couldn't hear hardly anyone it was so bad. At that time,
I was running an old Heathkit HW-100 SSB transceiver (tubes, cheap) and a
home brew little amp I made out of some power company parts and a PAIR of
4-1000A tetrodes in a 7 ft tall old navy transmitter rack, about 4' wide.
Using "minimum power to establish communications" that night meant
running 6000 VDC at about 950ma on the little tubes. That's about a
kilowatt, right?....(c; The AM station down the street ran 200W on 1260
at night in a 3-tower directional array over my house. EJ, the chief
engineer and night DJ at the transmitter building used to call me and ask
if I would hold off transmitting until he read the antenna current meters
wildly moving around too far to fill in his log. He joked I had more
current in his towers than he did...hee hee...(c;

Those were fun days....no money, homebrew everything. I carried a melted
2' section of RG-8A/U coax into a ham club meeting and said they just
don't make coax like they used to....my little amp melted it...(c;

Larry
"POWER is our FRIEND!" (Robert Mitchell, AAA Communications, paging)

"You can tell when your ham station is tuned up, easily, by seeing how
dim the lights are in your neighbor's house." - (me)

Antenna for my Kenwood R-1000 receiver?
 

ray lunder wrote in
:

So what would a proper boat antenna look like? Examples, pictures,
name brands? Thanks as always.



Boats have no room for antennas that work good. So, there are two
compromises that work, "sort of".

One is an 18' whip coated in fiberglass to make it "yachtie", tuned from
the bottom against a seawater ground (we hope, or it's going nowhere):
http://www.boatersland.com/sha390.html
Above 15 Mhz, it's somewhat of an antenna. Below 15 Mhz, the further
down you go the worse it gets because it's just TOO SHORT! We put these
awful lossy "tuners" between the bottom of the whip and the radio to
match the impedance, at the cost of losing a lot of power. Being so
short at lower HF frequencies, its radiation pattern looks more like an
inflated hot air balloon, radiating mostly straight up...not out towards
the receivers over the horizon. These antennas at low frequencies have
almost no antenna CURRENT, which makes the required H field (the magnetic
radiation part of the radio wave). They have lots of voltage, E-field,
but E-field cannot exist without H-fields perpendicular to them so they
radiate poorly. You need BOTH.

Some of the "cure", about as much as you'll get, is to use a LONGER
antenna with the tuner doing less of the work. One comes with sailboats.
We call it the "backstay", a nice sloping piece of wire we can insulate
from ground on the bottom (series feeding it's called because the tuner
is installed in SERIES between ground and the bottom of the backstay,
because of the insulator. We insulate the top to keep the antenna
current from continuing up the backstay into the mast and going DOWN the
mast...which makes a wave that CANCELS the wave made by the backstay!
That's what the top insulator does. On "Lionheart", an Amel Sharki 41
ketch, this backstay is about 55' long, which is nicely resonant (where
the length becomes 1/4 wavelength) at 4.4 Mhz. It radiates very well
between 3-5 Mhz..maybe even wider. It also radiates very nicely as a 1/2
wavelength at 8.5 Mhz if you can get everyone away from the bottom of it
and you have a tuner that can tune very high impedances. At 8.5 Mhz, it
becomes a full dipole antenna with the tuner feeding the END of it, not
the middle as a normal dipole is fed at low impedance. There is
CONSIDERABLE voltage at 8.5 Mhz right at the bottom insulator. Keeping
hands off it is easy. Just key the mic, whistle in it and listen for the
cursing near the antenna...(c; Burn the captain and you walk the plank!
Both of these bands are very nicely around some great marine bands.

Unfortunately for sailboaters, they keep making masts, shrouds, topping
lifts, and other lines coming from the top of the masts to the bottom out
of METAL....which becomes passive elements, not directly driven, by your
backstay transmitter. The regenerated waves from any vertical metal,
wire rope, cables, shrouds, are always slightly out of phase and most
assuredly out of place with the main signal on the backstay. This causes
the reasonably nice fat donut you're looking for in a radiation pattern
into something that resembles the outside shape of an 8 leaf Shamrock
(Happy St Patty's Day, everyone!) with peaks in some directions and nulls
in others as the waves support and cancel each other around the azimuth.
These damnable metal things sticking up also absorb a lot of our radiated
signal, but are generally forgiven when the sailboat takes on diesel fuel
for these transgressions against our SSB signal. Again, it's all a
compromise.

http://www.tpub.com/content/et/14092/css/14092_35.htm
Oddly enough, those loud shore stations that haven't gone dead on marine
radio use a mast with shrouds all around it called a "conical monopole"
antenna which is VERY broadband over a wide variety of frequencies! Look
at the conical monopole on this webpage, and compare it to your
mast/shrouds/stays on the sailboat. Your boat is the TOP HALF of this
antenna! So, all is not lost. Too bad yours cannot be totally isolated
from ground and the whole rigging loaded as a giant antenna. On
Geoffrey's former boat, an Endeavour 35 sloop, I used to load the port
shroud through the ungrounded chainplate that lead right into the port
storage cabinet over the settee...and ran a ground wire down under the
cushions to the ground strap back to the engine I installed. This
arrangement SHUNT fed the mainmast, which wasn't grounded properly to
anything at its step. Shunt feeding has been used since the beginning of
radio. We hams have been shunt feeding out "masts" for decades:
http://www.qsl.net/w9rb/webdoc9.htm
Because the feed runs right along side the mast its feeding, there is no
changing phase angle the backstay creates running out from it. A series
capacitor is tuned to balance out the inductance of the shunt wire
running up, and insulated from the mast until it is attached at the top.
Broadcasters also use shunt fed, GROUNDED towers, because the expensive
AM transmitter is NOT in series with the 10 gigaamp lightning blast that
hits the tower and goes straight to the huge ground network that's
attached directly to the bottom of the tower, underground. You can see
which type of feed your local AM stations use on their tower antenna by
looking for the shunt wire running on insulators towards the top of the
tower. Series fed will have a huge insulator at the base and no shunt
wire. Shunt fed towers are firmly grounded at the base, not insulated.

I don't know why more HF-savvy boaters don't fool around with shunt
feeding their mainmast with a shunt wire insulated from the mast on the
port or starboard side under the shrouds. They work great and give you a
fantastic excuse to put a huge ground strap from the mast to ocean
grounding blocks under the hull to protect you from lightning hits.
http://nidxa.org/kb9cry_shunt_fed_tower.htm
http://www.fybush.com/sites/2007/site-070223.html
http://www.earthsignals.com/N6TZ/

Of course, some hams are MOST useful to HF boaters with their obsession
of antennas:
http://www.k7zsd.com/antennas.htm
Very nice, indeed. No restrictive covenants in HIS neighborhood!...(c;


Larry
--
Roll up to the long checkout line....
Yell, "ICE RAID!"
It's your turn to load the grocery belt...(c;

Antenna for my Kenwood R-1000 receiver?
 

Larry wrote:
ray lunder wrote in
:

So what would a proper boat antenna look like? Examples, pictures,
name brands? Thanks as always.



Boats have no room for antennas that work good. So, there are two
compromises that work, "sort of".

One is an 18' whip coated in fiberglass to make it "yachtie", tuned from
the bottom against a seawater ground (we hope, or it's going nowhere):
http://www.boatersland.com/sha390.html
Above 15 Mhz, it's somewhat of an antenna. Below 15 Mhz, the further
down you go the worse it gets because it's just TOO SHORT! We put these
awful lossy "tuners" between the bottom of the whip and the radio to
match the impedance, at the cost of losing a lot of power. Being so
short at lower HF frequencies, its radiation pattern looks more like an
inflated hot air balloon, radiating mostly straight up...not out towards
the receivers over the horizon. These antennas at low frequencies have
almost no antenna CURRENT, which makes the required H field (the magnetic
radiation part of the radio wave). They have lots of voltage, E-field,
but E-field cannot exist without H-fields perpendicular to them so they
radiate poorly. You need BOTH.

Some of the "cure", about as much as you'll get, is to use a LONGER
antenna with the tuner doing less of the work. One comes with sailboats.
We call it the "backstay", a nice sloping piece of wire we can insulate
from ground on the bottom (series feeding it's called because the tuner
is installed in SERIES between ground and the bottom of the backstay,
because of the insulator. We insulate the top to keep the antenna
current from continuing up the backstay into the mast and going DOWN the
mast...which makes a wave that CANCELS the wave made by the backstay!
That's what the top insulator does. On "Lionheart", an Amel Sharki 41
ketch, this backstay is about 55' long, which is nicely resonant (where
the length becomes 1/4 wavelength) at 4.4 Mhz. It radiates very well
between 3-5 Mhz..maybe even wider. It also radiates very nicely as a 1/2
wavelength at 8.5 Mhz if you can get everyone away from the bottom of it
and you have a tuner that can tune very high impedances. At 8.5 Mhz, it
becomes a full dipole antenna with the tuner feeding the END of it, not
the middle as a normal dipole is fed at low impedance. There is
CONSIDERABLE voltage at 8.5 Mhz right at the bottom insulator. Keeping
hands off it is easy. Just key the mic, whistle in it and listen for the
cursing near the antenna...(c; Burn the captain and you walk the plank!
Both of these bands are very nicely around some great marine bands.

Unfortunately for sailboaters, they keep making masts, shrouds, topping
lifts, and other lines coming from the top of the masts to the bottom out
of METAL....which becomes passive elements, not directly driven, by your
backstay transmitter. The regenerated waves from any vertical metal,
wire rope, cables, shrouds, are always slightly out of phase and most
assuredly out of place with the main signal on the backstay. This causes
the reasonably nice fat donut you're looking for in a radiation pattern
into something that resembles the outside shape of an 8 leaf Shamrock
(Happy St Patty's Day, everyone!) with peaks in some directions and nulls
in others as the waves support and cancel each other around the azimuth.
These damnable metal things sticking up also absorb a lot of our radiated
signal, but are generally forgiven when the sailboat takes on diesel fuel
for these transgressions against our SSB signal. Again, it's all a
compromise.

http://www.tpub.com/content/et/14092/css/14092_35.htm
Oddly enough, those loud shore stations that haven't gone dead on marine
radio use a mast with shrouds all around it called a "conical monopole"
antenna which is VERY broadband over a wide variety of frequencies! Look
at the conical monopole on this webpage, and compare it to your
mast/shrouds/stays on the sailboat. Your boat is the TOP HALF of this
antenna! So, all is not lost. Too bad yours cannot be totally isolated
from ground and the whole rigging loaded as a giant antenna. On
Geoffrey's former boat, an Endeavour 35 sloop, I used to load the port
shroud through the ungrounded chainplate that lead right into the port
storage cabinet over the settee...and ran a ground wire down under the
cushions to the ground strap back to the engine I installed. This
arrangement SHUNT fed the mainmast, which wasn't grounded properly to
anything at its step. Shunt feeding has been used since the beginning of
radio. We hams have been shunt feeding out "masts" for decades:
http://www.qsl.net/w9rb/webdoc9.htm
Because the feed runs right along side the mast its feeding, there is no
changing phase angle the backstay creates running out from it. A series
capacitor is tuned to balance out the inductance of the shunt wire
running up, and insulated from the mast until it is attached at the top.
Broadcasters also use shunt fed, GROUNDED towers, because the expensive
AM transmitter is NOT in series with the 10 gigaamp lightning blast that
hits the tower and goes straight to the huge ground network that's
attached directly to the bottom of the tower, underground. You can see
which type of feed your local AM stations use on their tower antenna by
looking for the shunt wire running on insulators towards the top of the
tower. Series fed will have a huge insulator at the base and no shunt
wire. Shunt fed towers are firmly grounded at the base, not insulated.

I don't know why more HF-savvy boaters don't fool around with shunt
feeding their mainmast with a shunt wire insulated from the mast on the
port or starboard side under the shrouds. They work great and give you a
fantastic excuse to put a huge ground strap from the mast to ocean
grounding blocks under the hull to protect you from lightning hits.
http://nidxa.org/kb9cry_shunt_fed_tower.htm
http://www.fybush.com/sites/2007/site-070223.html
http://www.earthsignals.com/N6TZ/

Of course, some hams are MOST useful to HF boaters with their obsession
of antennas:
http://www.k7zsd.com/antennas.htm
Very nice, indeed. No restrictive covenants in HIS neighborhood!...(c;


Larry
Larry,
I don't think the OP with an R-1000 has to worry about radiation
pattern, antenna current and tuners. He just needs a good long wire for
his receiver.
krj

Antenna for my Kenwood R-1000 receiver?
 

Larry wrote:

SNIP

Above 15 Mhz, it's somewhat of an antenna. Below 15 Mhz, the further
down you go the worse it gets because it's just TOO SHORT! We put these
awful lossy "tuners" between the bottom of the whip and the radio to
match the impedance, at the cost of losing a lot of power. Being so
short at lower HF frequencies, its radiation pattern looks more like an
inflated hot air balloon, radiating mostly straight up...not out towards
the receivers over the horizon.

Actually, vertical antennas (even very short ones) radiate almost
nothing directly overhead. Over seawater, vertical antennas radiate
better at low angles toward the far horizon than just about any
horizontal antenna.

These antennas at low frequencies have
almost no antenna CURRENT, which makes the required H field (the magnetic
radiation part of the radio wave). They have lots of voltage, E-field,
but E-field cannot exist without H-fields perpendicular to them so they
radiate poorly. You need BOTH.

If the short antenna is matched (i.e., you use a tuner) it will be
nearly as efficient as its longer counterpart. A short vertical antenna
has very HIGH current at its base. Any loss in efficiency is due almost
exclusively to the tuner when operated over seawater. Over land, ground
losses become a more significant factor in reducing efficiency.


Some of the "cure", about as much as you'll get, is to use a LONGER
antenna with the tuner doing less of the work.

Ironically (as is often the case with natu if bread and crackers are
exposed to the same environment, the bread becomes hard and the crackers
soft. Go figure.) at the higher frequencies, a longer vertical antenna
may actually radiate less toward the horizon (low angles). So an antenna
that is the "right" size for 4 MHz may not work as well on 15 MHz as a
shorter one! An antenna "too long" for a frequency will develop lobes
and nulls in the vertical plane which may be detrimental to your desired
propagation path. Yet another need for thoughtful compromise.

One comes with sailboats.
We call it the "backstay", a nice sloping piece of wire we can insulate
from ground on the bottom (series feeding it's called because the tuner
is installed in SERIES between ground and the bottom of the backstay,
because of the insulator. We insulate the top to keep the antenna
current from continuing up the backstay into the mast and going DOWN the
mast...which makes a wave that CANCELS the wave made by the backstay!

Well, if the mast is insulated at the base (some are) what you have is
something like an inverted "V" (end-fed) and there will be some
directionality, but cancellation is far too strong a term to describe
it. Even if the mast base is grounded, the small amount of
directionality would probably not be noticed in normal operation.

SNIP


On Geoffrey's former boat, an Endeavour 35 sloop, I used to load the port
shroud through the ungrounded chainplate that lead right into the port
storage cabinet over the settee...and ran a ground wire down under the
cushions to the ground strap back to the engine I installed. This
arrangement SHUNT fed the mainmast, which wasn't grounded properly to
anything at its step. Shunt feeding has been used since the beginning of
radio. We hams have been shunt feeding out "masts" for decades:
http://www.qsl.net/w9rb/webdoc9.htm

Shunt-feeding the mast (and back- and forestays) doesn't require the
base of the mast to be insulated. I've been shunt-feeding a grounded
mast on a 34' Tartan for years and never felt the need for a better
antenna. Since I use a manual tuner, it was impractical to feed the
bottom of the backstay with a tuner in the cabin. Because the lower ends
of the forestay and backstay are ungrounded, they act as a top hat,
making the mast appear longer (electrically) than it is. Since the stays
are not symmetrical, they doubtless provide some often needed horizontal
radiation.

I must say that on some frequencies, particularly the 40 meter band, the
feedpoint impedance of the system was wildly high. I ended up using
some additional outboard reactances to tame it. Everywhere else, tuning
was reasonable. An autotuner may have handled it OK. A key advantage is
that you can install an SSB in minutes without worrying about insulating
the backstay, etc.


Chuck



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Antenna for my Kenwood R-1000 receiver? EH Antenna
 

Howdy:
Some might be interested in a small, fairly new type of antenna that could be made cheaply, but does take some
effort to tune, but once tuned, you have a small antenna that will work on the lower bands.

The EH Antenna was introduced as small dipole making use of the controversial Crossed Field Theory. One of the conditions for this
mode of radiation is to arrange the magnetic (H) field in phase with the Electric (E) field. The original theory provided by the
inventor was based on feeding the antenna through a 90 degree phase shift network which he claimed shifted the current fed into the
antenna by 90 degrees relative to the voltage across it.


Plans for 40 meter EH antenna:
http://www.qsl.net/vk5br/EHAntenna20_40.htm

80 meter EH antenna:
http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=9346

Some photos of EH antennas:
http://images.google.com/images?hl=e...Images &gbv=2


--

SeeYaa:) Harbin Osteen KG6URO

When American Citizens with dual citizenship pledges allegiance
to the flag, to which flag do they pledge allegiance too?

-

Antenna for my Kenwood R-1000 receiver?
 

chuck wrote in news:1174053226_6783
@sp6iad.superfeed.net:

If the short antenna is matched (i.e., you use a tuner) it will be
nearly as efficient as its longer counterpart. A short vertical antenna
has very HIGH current at its base. Any loss in efficiency is due almost
exclusively to the tuner when operated over seawater. Over land, ground
losses become a more significant factor in reducing efficiency.



Any antenna shorter than 1/4 wavelength has HIGHER impedance and LESS
current. It NEVER has high current at its base. It also suffers from
having so poor an H-field generated without that big current lobe.

A shortened antenna is NEVER anywhere near as efficient as a full 1/4
wave radiator....or more...working against a ground system. Boy, would
AM broadcasters love to have an efficient 50' antenna tower. You'll be
FILTHY RICH if you can make that work!...(c;

If you think running your HF tuner is efficient, you are sadly mistaken.
That tuner is simply a big dummy load on a short whip. It sucks!



Larry
--
Roll up to the long checkout line....
Yell, "ICE RAID!"
It's your turn to load the grocery belt...(c;

Antenna for my Kenwood R-1000 receiver? EH Antenna
 

"Harbin Osteen" wrote in
:

controversial Crossed Field Theory

Oh, ok...Is it made out of lawn furniture like the Gap antennas that
suck?...(c;

We have a ham in town who is a car mechanic. Someone convinced him if
you put this capacitor in series with his 160M long wire it would make a
super antenna. The poor sap bought it, hook, line and sinker and has
built many versions, to my amusement.

I added a second Texas Bugcatcher center loading coil to my 15' mobile
monster with the 4' across capacitor hat on the trailer hitch of my old
Mercedes 220D, the finest HF mobile car ever built....no electronics
noise. It was about 10PM and I was on 160M around 1850 Khz when I heard
this guy talking to some of his buddies over in MS and New Orleans. I
fired up the modified 650W output Tentec Hercules II and said hello.

One of his buddies, or maybe former buddies now, said, "Bob! That mobile
in Charleston is 20 dB LOUDER than you are!" Bob never made another
transmission....(c;

I love to play with antennas. I always have....

Larry
--
Roll up to the long checkout line....
Yell, "ICE RAID!"
It's your turn to load the grocery belt...(c;

Antenna for my Kenwood R-1000 receiver?
 

Larry wrote:
chuck wrote in news:1174053226_6783
@sp6iad.superfeed.net:

If the short antenna is matched (i.e., you use a tuner) it will be
nearly as efficient as its longer counterpart. A short vertical antenna
has very HIGH current at its base. Any loss in efficiency is due almost
exclusively to the tuner when operated over seawater. Over land, ground
losses become a more significant factor in reducing efficiency.



Any antenna shorter than 1/4 wavelength has HIGHER impedance and LESS
current. It NEVER has high current at its base. It also suffers from
having so poor an H-field generated without that big current lobe.


Hmmm. You're thinking about the capacitive reactance of a short antenna,
which can be high, and I'm thinking of the radiation resistance, the
real part of the antenna's impedance. When the short antenna is matched,
the capacitive reactance is cancelled by the tuner and you are left with
a radiation resistance that can be as small as a fraction of an ohm. by
comparison, the radiation resistance of a quarterwave vertical antenna
over seawater is about 35 ohms. The base of the antenna is always a
current node on a short vertical antenna: current is a maximum there.
The high voltages (and low currents!) occur at the tops of these
antennas; not at their bases. Where would the current flow to at the top?

If you deliver 100 watts to a short whip, it will radiate as well as a
quarter-wave vertical, assuming the same ground system, etc. There will
be MORE current at the base of the shorter antenna because power = I
squared x radiation resistance. Radiation resistance of a short antenna
is smaller than that of a quarter-wave antenna, so to keep power at 100
watts, I must INCREASE!

I would not be surprised for a 16- or 23-foot whip on a boat to
outperform a 55-foot, sloping backstay antenna at very low angles of
radiation, even with matching system losses. At 7 MHz, for example. FWIW.

A shortened antenna is NEVER anywhere near as efficient as a full 1/4
wave radiator....or more...working against a ground system. Boy, would
AM broadcasters love to have an efficient 50' antenna tower. You'll be
FILTHY RICH if you can make that work!...(c;


Keep in mind that a decrease in efficiency of 70% (1 dB) is needed
before someone at the other end would even notice it. I would imagine
that with reasonable attention to the matching components, an antenna
could be shortened to 1/8 wavelength without any noticeable drop in
signal strength, and without any noticeable change in the vertical
radiation pattern. A 1/16 wavelength whip over seawater might seem
slightly weaker to a distant station than a full quarterwave vertical
over seawater. No quarter-wave antenna with its base on the ground is
likely to outperform a 1/8 wavelength whip over seawater.

The efficiency of a resonant vertical antenna SYSTEM (even with a
radiator that is a tiny fraction of a wavelength long) is the radiation
resistance (a small number) divided by the sum of the resistances in the
system. These resistances consist of losses in the antenna wire, the
ground system, and the matching circuit (which may be inductors and
capacitive hats) x 100 (to get efficiency in %). Over seawater, "ground"
losses are insignificant, and antenna wire resistance is often
insignificant. There are indeed tuner losses, but these can often be
reduced. The point is that the important sourcea of inefficiency are not
in the antenna but in ground loss and matching circuits.

Eventually, an antenna gets to be so short that the losses (or costs,
broadly defined) incurred in feeding power to it are unacceptably high.
Too much power would be lost in the rest of the system. Nonetheless,
that short antenna will radiate all the power that is delivered to it
with high efficiency.

To maintain balance, I would mention that an antenna that is "too long"
(e.g., your 55' backstay on 15 meters) also requires matching and that
will introduce losses. There are not many antennas that will work on
every HF band without matching. Those that do tend to introduce their
own high losses.

With regard to AM broadcasters, it is not for me to say where the
economics, regulatory, and efficiency curves cross, but capacitive hats
on antennas shorter than a quarter-wave are not unheard of on those
antennas.


If you think running your HF tuner is efficient, you are sadly mistaken.
That tuner is simply a big dummy load on a short whip. It sucks!



Tuner losses are indeed significant at lower frequencies with a short
whip. And on most automobiles, ground losses are also significant. Of
course, a seawater ground and quarter-wave whip are not really
alternatives if you're in a car. ;-)


Chuck

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Antenna for my Kenwood R-1000 receiver?
 

chuck wrote in news:1174139919_4745
@sp6iad.superfeed.net:

Hmmm. You're thinking about the capacitive reactance of a short
antenna,
which can be high, and I'm thinking of the radiation resistance, the
real part of the antenna's impedance. When the short antenna is
matched,
the capacitive reactance is cancelled by the tuner and you are left
with
a radiation resistance that can be as small as a fraction of an ohm.
by
comparison, the radiation resistance of a quarterwave vertical antenna
over seawater is about 35 ohms. The base of the antenna is always a
current node on a short vertical antenna: current is a maximum there.
The high voltages (and low currents!) occur at the tops of these
antennas; not at their bases. Where would the current flow to at the
top?

When a tuner matches a short antenna's reactance and high impedance to,
say, 50 ohm coax, the current to the antenna is very low, in comparison
to the current in the coax at 50 ohms. Most of the current in this
circuit is confined to the series inductance inside the tuner, which
isn't radiated as H-field.

A 1/4 wave vertical over a good ground, like seawater, is closer to 12 to
20 ohms of resistive impedance, if the ground is at the feedpoint where
it should be, not 20' of strap away going down to the bilge. 1/4 wave
verticals have very low impedance, indeed. This makes a very heavy base
current at the feedpoint, if we're lucky, resulting in an impressive H-
field expanding away from the feedpoint at the base, dropping as you go
up towards the open end. A shortened antenna, like an 18' whip on 4 Mhz,
has almost no current at its high impedance feedpoint the tuner must deal
with. H-field suffers awful which causes the E-field to collapse to
match it. It radiates "poorly in all directions", a typical HF mobile
installation.

Many things, some reasonable, some not, can be done to "draw" the current
lobe up the antenna. Some are not practical in a marine environment and
certainly not "boat pretty", so won't be tolerated on yachts. The best
solution is to move the tuning inductor UP the antenna to its middle,
"center loaded". A center-loaded short antenna can be made to exhibit a
very low impedance at its base feedpoint, no where near 12 ohms of a full
1/4 wave vertical, but in the range of 20-30 ohms if the loading coil is
of sufficient size to be efficient, with low capacitance between windings
and low winding resistance, which wastes power turning it into heat. The
antenna appears a little inductive, which is easily balanced by shunt
capacitance at the base. Here's my center loading coil from 80-10
Meters:
http://www.texasbugcatcher.com/cata/tbcspec.htm#6inch
Look at coil #680, which is 6" in diameter on a Lexan form. The white
center insulator is very heavy Teflon. This coil is 4' up a 15' whip
from my feedpoint. I use a large clamp and braided copper strap
connected to the bottom of the coil to tune it by shorting the bottom
turns. Even that creates immense base current at resonance....(c;

On the same webpage, the #480XL coil is inserted in series with the #680,
and the #680 tuning short is used to tune the 15' beast below 3.5 Mhz.
At 1.8 Mhz, this is a VERY short antenna and VERY inductive.

The feedpoint at the car's trailer hitch has two different RF
autotransformers. The HF autotransformer is 10 turns of #10 over a very
heavy ferrite core tapped at every turn. Best impedance match 40-10M
occurs with the antenna tapped 4 turns from ground fed at 6-8 turns, the
coax input tap. 6T at 10M, 8T at 40M. On 80/75M, input is across all
10T, tapped at 5T, an impedance ratio of 4:1, works best. There isn't
enough natural inductance to tune below 3 Mhz, so another ferrite toroid
has 30T of #12, fixed tapped at 22T to operate on 1.8-2.0 Mhz with two
loading coils in series.

The antenna's capacitor hat is 8 stainless steel, about #12 wiresized,
welding rods turned round on the end into a loop to reduce corona, welded
to two stainless washers to hold them tight to a 10-24 whip screwed into
the 3' mast above the one (or two) loading coils. The capacitor hat is
approximately 4' across, and adds capacitive reactance at the top, where
it aids pulling the current lobe up the tuned antenna...instead of at the
base, where it radiates nothing. The capacitor hat and 3' mast above the
coils is removed (1/4 turn quick whip connectors) for operating above 20
meters 14-30 Mhz. Atop the capacitor hat is a cut down stainless CB whip
that creates a resonant antenna on 14.250 Mhz when you short out the
whole 6" coil. The antenna's length and only the capacitor hat resonate
15' to 14.250 by design as that's my favorite ham band. On 20M, VE8RCS
(the northern most amateur station in the world at a Canadian CG base
above the Arctic Circle) reports my mobile in Charleston to be as loud as
any legal ham station they can hear. I used to work them on 20M Packet
quite regularly on 14.105 "Network 105". Their QSL is a prized
posession. Packet, RTTY and the other digital modes are great fun when
traveling with a group of hams to a hamfest...(c;


If you deliver 100 watts to a short whip, it will radiate as well as a
quarter-wave vertical, assuming the same ground system, etc. There will
be MORE current at the base of the shorter antenna because power = I
squared x radiation resistance. Radiation resistance of a short antenna
is smaller than that of a quarter-wave antenna, so to keep power at 100
watts, I must INCREASE!

Nonsense! If it did, every broadcaster on the planet would be buying
50' of Rohn 25 and loading it up at the base....instead of spending
millions on full-sized 1/4 wave radiators like:
http://hawkins.pair.com/wsm/wsmtower.jpg
http://hawkins.pair.com/wcbs_wfan/cbsfan_twr17.jpg
http://hawkins.pair.com/wcbs_wfan/cbsfan_twr14.jpg
(100KW from TWO AM blowtorches is across that insulator)

All you Marine Radio guys need to see this webpage at NSS on Jim
Hawkins' website!
http://hawkins.pair.com/nss.shtml
Take the tour and see why their signal sounds like it does....(c;


Larry
--
Roll up to the long checkout line....
Yell, "ICE RAID!"
It's your turn to load the grocery belt...(c;