Chris,
Diameter of whip or loading rod is not critical. Enter average diameter
over its length.


If not stated, bandwidth is between 3dB points when transmitting. When
receiving, bandwidth is broader, say the 2 dB points, because the receiver
input resistance damps down the very high antenna Q.


Earth electrode resistance depends on size of vehicle and type of soil under
it. For a mobile home enter 3 ohms. For a volkswagon beetle enter 14 ohms.


A larger coil form will give a narrower bandwidth. Double length and height
and for the same inductance (fewer turns), coil Q will also be doubled. You
can't have high efficiency without high Q and narrow bandwidth.


If a flexible whip is used, to reduce overall height it can be curved
backwards in parallel with the vehicle's roof. This also allows fewer turns
of thicker wire on the helix and a higher coil Q with greater efficiency.
There will be an overall gain but not so great as if the whip is vertical
throughout its length.


Leave a gap equal to helix diameter between the bottom of the helix and a
metal roof.


The helix is in fact the L&C Z-matching coil. On 160m, in order to resonate
with its own self-capacitance, it needs a large inductance. There will be
several hundred turns. Therefore, to have a loss as low as possible it has
to be physically large. The only space available is in the antenna - and
that's why it's there.


Ignore silly irrelevant done-to-death arguments about whether the current at
one end of the helix is or is not the same as the other.


The most important dimension of short verticals is overall height. Next
comes physical size of helix. The fatter it is the better. Obesity is not a
problem. Only the wind.
----
Reg, G4FGQ

Reg Edwards wrote:
Chris,
Diameter of whip or loading rod is not critical. Enter average diameter
over its length.


If not stated, bandwidth is between 3dB points when transmitting. When
receiving, bandwidth is broader, say the 2 dB points, because the receiver
input resistance damps down the very high antenna Q.


Earth electrode resistance depends on size of vehicle and type of soil under
it. For a mobile home enter 3 ohms. For a volkswagon beetle enter 14 ohms.


A larger coil form will give a narrower bandwidth. Double length and height
and for the same inductance (fewer turns), coil Q will also be doubled. You
can't have high efficiency without high Q and narrow bandwidth.


If a flexible whip is used, to reduce overall height it can be curved
backwards in parallel with the vehicle's roof. This also allows fewer turns
of thicker wire on the helix and a higher coil Q with greater efficiency.
There will be an overall gain but not so great as if the whip is vertical
throughout its length.


Leave a gap equal to helix diameter between the bottom of the helix and a
metal roof.


The helix is in fact the L&C Z-matching coil. On 160m, in order to resonate
with its own self-capacitance, it needs a large inductance. There will be
several hundred turns. Therefore, to have a loss as low as possible it has
to be physically large. The only space available is in the antenna - and
that's why it's there.


Ignore silly irrelevant done-to-death arguments about whether the current at
one end of the helix is or is not the same as the other.


The most important dimension of short verticals is overall height. Next
comes physical size of helix. The fatter it is the better. Obesity is not a
problem. Only the wind.
----
Reg, G4FGQ


Reg:

Thanks for all the pointers.

I've since found "vertload" as well.. I think I'm going to go that
route. I can make something that will work for my purposes, and that's
the point of all of this.

Thanks for all these great programs. If the "real world" works as
predicted, then I should have something set up for next winter.

Back about 10 years ago, I built an antenna for my CB base (I wasn't a
HAM then), and I was shooting blind. The SWR was, at best, 1.7:1, but
boy did it get out. On the roof of the apartment, (2 stories tall) 3
blocks from the ocean in Oceanside, CA, I was able to hit Escondido on a
legal 4 watts AM, 12 watts SSB, with an S7 or better... That's when I
decided I liked working with building things. I've built every base
antenna for both CB and HAM radio since then... Mobiles seem to act
differently, and everything I've tried for mobile before now has come
with mixed results. These programs you wrote for us will definitely be a
big help.

Thanks again.. I'm gonna play with these and see what I can come up with
for high efficiency, decent bandwidth (10-15KC would be enough!), for
the sizes I have to deal with. Then, when I build it, I'll play with
getting it to behave as designed.

73 de AI8W, Chris

Reg Edwards wrote:
"SideBand" wrote in message
m...

Anyone out there know of any decent solution to getting 160M working in
a mobile? The application is a semi-truck. I've got the Iron Horses for
75, 40, 20, 15, and 10M, but I'd like to work something out for 160
meters that will work on the truck.

I know I'm going to take an efficiency hit, but you're doing that for
everything except 10M on a Semi anyway.. Just so I can get a signal out
there to be heard, in the off chance.

ANY suggestions or ideas would be greatly appreciated.

73 de AI8W, Chris

=============================

For design and performance of a 160 meter band vertical antenna, download
program HELICAL3 from website below. There are other loaded vertical
programs..

Use 1.5" or 2" diameter plastic pipe, with helical winding of thick enamel
insulated wire, mounted on vehicle roof, as tall as possible, stayed, with
short, top caapacitance tuning rod.

Range on 160m with a few hundred watts = 100 miles at noon on groundwave.

1700 miles on very quiet, wiinter nights at midnight via F-layer.
----
.................................................. .........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. .........



Reg, et al:

On the Vertload program, I've been playing with the numbers a bit, and
I've found some things that I have questions from the pro's on..

First, let me explain the situation:

The Truck in question is a Ford LTLA9000. I plan on mounting this
antenna 6-8 inches from the side of the tractor on a mount coming off of
one of the fuel tanks, which are mounted just below the
driver's/passenger's door.

The cab (driving area) of the truck is about 4 feet shorter than the top
of the sleeper. The cab is all steel. I use a mag mount 5/8 wave 2M
antenna on top of the cab, with great results.

The fuel tanks are aluminum. The straps mounting the fuel tanks to the
frame are steel, and mount directly to the frame of the truck under the
cab. The sides of the sleeper are steel, up to the level of the top of
the cab. The top of the sleeper is fiberglass, with steel runner
supports inside.

I plan to mount the antenna off of the fuel tank straps, which will put
it roughly 8" to a foot away from the cab, and the steel sides of the
sleeper. I have several places I can guy the coil to on the side and top
of the cab. I have one or two places I can put PVC standoffs on the cab
and sleeper to keep the antenna away from the cab, and to keep it from
"flying out" while rolling down the road.

This truck, with a trailer on it and a full load (80,000 lbs gross
weight) is capable of traveling at 117 MPH on a straightaway. Faster if
I "turn around" the transmission again (no plans on that.. I'm getting
too old for high speed "chicken truckin" anymore). I usually keep it
down to around 70MPH when the speed limits allow.

So, I've planned on using 1" copper pipe for both the mast and the
"whip" at the top, for ruggedness. Inside the coil, I can use some 1" ID
PVC for support, and put the 3" coil over those supports, with end caps,
etc...

Now, on the antenna, I've found that moving the loading coil up higher
on the whip increases the efficiency. So:

1. Does that efficiency increase come at the cost of bandwidth?
2. Does having the load closer to the base increase the bandwidth, if
all other numbers (coil diameter, coil length, etc) are the same?
3. Would getting the loading coil above the "steel" increase my chances
of making a usable antenna with the bandwidth and efficiency I desire?


I know I'm asking the impossible here; that is a wider bandwidth, higher
efficiency, shortened 160M antenna for mobile operations. Like I said,
I'd like to get about 10-15KC of usable bandwidth, with an efficiency
that'll let me get an ERP of more than a watt or two with 100 watts in.
On top of that, I'd like to build it.

Hope this wasn't too much information, and I hope you all can make sense
of this.

73 de AI8W, Chris

1. Does that efficiency increase come at the cost of bandwidth?

Not sure...Never tested that...But it wouldn't suprise me if it did a
little..

2. Does having the load closer to the base increase the band width, if

all other numbers (coil diameter, coil length, etc) are the same?

Ditto....Not sure....But again, probably a bit...
3. Would getting the loading coil above the "steel" increase my
chances
of making a usable antenna with the bandwidth and efficiency I desire?


Yes, as far as efficiency.

Also using a hat would help a lot, although I know you may not be able
to.
But if you could design a hat, that would help current distribution a
lot.
Take a few turns off the coil too...But the more linear current
distribution
is the main benefit, I think more than any decrease in coil losses....
MK

2. Does having the load closer to the base increase the band width, if
all other numbers (coil diameter, coil length, etc) are the same?
.........


P.S...One reason I've never tested this, is because I've never base fed
my
antenna...MK

Chris:

I see you got lots of answers, but I don't think anyone mentioned the old WW2 approach. Back in the '40s, police radios
were on 1600-1700 kHz, and mobile antennas were bumper mounted 8 or 10 foot bamboo fishing poles wrapped close wound
with as much bell wire as you could put on them. And they worked amazingly well. I've never seen a shootout between
one and a good loaded whip with a capacity hat, but for whatever reasons, I suspect the bamboo pole would come close.
And it meets your other criteria, cheap. And which, now that I think about it, is equivalent to these fiberglass things
they sell for other bands now. Hmmmm.

--
Crazy George
Remove N O and S P A M imbedded in return address
"SideBand" wrote in message m...
Anyone out there know of any decent solution to getting 160M working in
a mobile? The application is a semi-truck. I've got the Iron Horses for
75, 40, 20, 15, and 10M, but I'd like to work something out for 160
meters that will work on the truck.

I know I'm going to take an efficiency hit, but you're doing that for
everything except 10M on a Semi anyway.. Just so I can get a signal out
there to be heard, in the off chance.

ANY suggestions or ideas would be greatly appreciated.

73 de AI8W, Chris