"stan" <stan.winikoff.RemoveThis@comcast.net> wrote in
news:1126558526.670755.222670@g44g2000cwa.googlegroups.com:
> works or not.
Anything metal is an antenna. They all "work". But, alas, it's how WELL
they work that makes the difference....
The military has an antenna that's a big H they BURY in the sand. It works
quite well, actually. Sand is a rotten conductor, but a fairly good
camoflage.
Still, the best HF antenna is a long, insulated backstay. Lionheart's is
naturally resonant around 8 Mhz. No tuner is necessary. It's too bad I
can't add a center inductor below that frequency to improve her H-field
when the antenna is so short on the lower bands.... Tuned to 12 Mhz, the
backstay is actually 5/8 wave, which gives her a little gain. 5/8 wave VHF
mobile antennas have been used with end-fed matching since Motorola was in
a garage. 3db gain is the result, but I doubt it's anything like that with
all the rigging loading it all down. Sailboat rigging, metal masts, etc.,
all cost you LOTS of signal by absorption so close to the radiating
backstay. Lionheart is worse with the backstay between main and mizzen
aluminum masts with many shrouds.
I have used my own designed HF mobile antenna for 20 years. It uses one or
two loading coils under a fairly large capacitor hat made of 8 spokes of
stainless welding rod about 36" in diameter. This raises the current
up the antenna to create a larger H field most mobile antennas lack. This
antenna, with a good ground, would make a great marine HF antenna on the
stern of a boat. Tuning it is done by moving a tap on its coil(s), which
are easily swapped and added to with 1/4 turn twist-lock devices that lock
all the components together. Two nylon lines to the handrails forward of
the stern would hold it upright in awful weather. It's 15 feet high, just
low enough to go under standard wires and bridges on the highway....same
height as a tractor trailer.
|
|
|
|
|
|
|
| <cut down 102" CB whip to limit height to 15'
QUICK CONNECTOR> ^
-----------|----------- <capacitor hat 36" diam, 8 spokes
| no outside ring
|
| <4 ft stainless rod threaded 3/8-24 male on both ends
|
QUICK CONNECTOR> ^
|-|
| |
| | <Henry Allen's largest 6" diam #10 coil
|-| (coil #680)
|
|
| <3 ft stainless rod threaded 3/8-24 male both ends
|
- <3/8-24 base mount on trailer hitch
|=| <10T #10 solid copper wound on fiberglass-insulated
ferrite core tapped with banana-jack at each turn.
coax input shield and one end of the coil go to
chassis ground of car. Coax hot and a jumper strap
from the insulated antenna base have banana plugs
on them so they may tap the coil. This broadband
matches the 17 ohm vertical Z to the 50 ohm coax Z.
Henry Allen's coils are on:
http://www.texasbugcatcher.com/cata/tbcspec.htm#6inch
I use a 680 and 480 coils
This antenna is naturally resonant (big coil shorted out by a strap with a
clip all the way from top to bottom) on 14.250 Mhz. The capacitor hat was
trimmed to resonate it on this frequency of my favorite ham band. Tuned
with only the capacitor hat, the antenna SWR is below 1.4:1 from 14.01 to
14.35 Mhz, the entire ham band. No extra tuning is necessary.
To resonate below 14 Mhz, the strap that is hard connected to the bottom of
the coil has a big clip that taps down the coil to add more inductance.
With the whole coil in the circuit, it resonates at 2.8 Mhz. Any frequency
between 2.8 and 14.35 Mhz is simply a tap change. plastic tabs are glued
to the coil with certain frequencies engraved on them, making tuning a
snap. Even on 75 meters, the antenna is 50 Khz bandwidth to 2:1 SWR
points, making stopping the car unnecessary just to move frequency a ways.
The antenna in this configuration will not resonate above 14.25 Mhz. To
use frequencies above, the antenna is disassembled above the coil and at
the other quick connector above the capacitor hat, removing the 4'
stainless rod section and its capacitor hat. The CB whip now plugs into
the top of the coil for the upper end of HF. The shorted out, natural
resonant frequency WITHOUT the 4' section and capacitor hat is 29.0 Mhz
with the big coil again shorted out completely. It's bandwidth is from
27.8 to over 32 Mhz making this how you tune 10 meters, the whole band. To
get the other upper HF bands, the tap is again moved down the coil to a
single tab marking the position of the tap for each whole ham band. No
further adjustment is necessary as the antenna is very broadbanded up here.
An extra coil, Allen #480XL, is added directly to the top of the 6" coil to
increase loading inductance for use on the 1.8-2.0 Mhz ham band only. The
coil is added and the 6" coil's shorting tap is adjusted to tune the
antenna on a 30 Khz bandwidth of this band. This extra coil has quick
connectors on both ends to mate with the quick connectors (symbol ^ on my
graphic) on top of the big coil. Just disconnect the whole top of the
antenna and insert this coil.
An additional base toroid transformer is also swapped out. It has 30
turns, instead of the 10 turns used above 3 Mhz. Input is across all 30
turns. Antenna plugs into turn 8 or 9 to get a perfect match.
I feed this antenna with an honest 650 watts of RF power from a modified
TenTec Hercules II 12V solid-state HF linear amp in the trunk. It is fed
from a pair of 220AH golf cart beasts also trunk mounted and connected
through a marine ON-OFF switch to the old '73 Mercedes 220D's big
alternator and starting battery up front. Same idea as a boat. The house
battery is in the trunk so I can use it without the engine running. It
only draws 120 amps at full power on RTTY, key-down CW. At 300 watts
carrier on AM, it draws a measily 55 amps. SSB average current is much
lower, of course, at 650W PEP. Transceiver is a Yaesu FT-900, trunk
mounted with its removeable control panel on a flexible stick on the dash
right next to the steering wheel. I use a Heil headset/mic and VOX keying
on phone modes. It even runs 600 watts on 10 meter FM...(c; At this power
level, especially on bands below 7 Mhz, a very large corona appears on the
ends of the capacitor hat spokes (even after we bent them around to get rid
of the "points") and at the top of the CB whip. On 160 meters, this corona
trails out behind the antenna at highway speed as we ionize the air. It
flashes over to low interstate bridges! It also lights flourescent signs
within 15 feet of it...right in their boxes...(c; An old KAM Plus and
Win98SE notebook provide digital service. The notebook also serves as the
VHF portable packet station into a Paccomm Tiny II subminiature TNC and
tiny VHF walkie to carry around hamfests talking to DX stations THROUGH the
KAM Plus' crossband packet repeater and the 650 watt mobile HF packet
station left running in the parking lot, unattended. IF YOU SEE IT PARKED
SOMEWHERE, READ THE SIGN ON THE ANTENNA THAT SAYS "DANGER-RF RADIATION
HAZARD" and DON'T TOUCH IT EVEN IF YOU DON'T SEE ME! Many can't
read....fingers burned appropriately...hee hee.
This mostly-home-made antenna would make a great boat antenna for marine
HF, once you learned how its simple tuning is done. Yeah, it's not
pushbutton automatic from the nav station. But, with its amazing signal
and very strong RF field it produces, other stations cannot believe they
are hearing a MOBILE, driving down the interstate...especially on 160
meters where mobiles rarely tread. Many times I've been called a liar,
well, until they hear a truck pass and my horn blow over the air. As it is
always a RESONANT antenna, not some random length wire with a very lossy
base tuner, like your current boat HF antenna, it just simply radiates a
MUCH stronger RF field. It survives 80 mph, about as fast as a 2.2L 4-cyl
diesel will run that's going on 33 years old. I use two monofilament
fishing lines to the two rear doors to "guy" it against the wind from the
top of the big coil. This keeps it from bending back against the 57hp
diesel's lightning acceleration, too!
--
Larry W4CSC
Ok, guys....Unkey the RTTY until Mike gets into the car. His fingers keep
burning on the door handle...(c;
POWER IS OUR FRIEND!
NNNN
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