4 foot vertical for 1.6mhz 100milliwatt tx?
 

I do sound work at horse shows, and would like to provide my audio source
to vehicles parked at the show. I have a real nice 100 milliwatt input
1.6mhz transmitter which shows about 60 milliwatts of output at 50 ohms.

I would like to build a transmitting antenna that would be 4 feet in length
and having the 3/8 24 thread at the bottom so I can fasten it into my hamstick
mag mount base.

I am thinking a 1 inch diameter wooden dowel 4 feet long, and wrapped evenly
from bottom to top with perhaps #22 wire.

Any idea how much wire it would take to begin to act like a 50 ohm impedance
at the base? Would you solenoid wind it bottom to top, or would it work better
with maybe a 4 inch high multilayered coil at the bottom and 3.5 foot steel
whip antenna.

I am not out to **** off the FCC, and with a mere 60 milliwatts of output
power at 50 ohms, I don't think anyone beyond 300 yards will even here it.
I do however want to be clearly heard on an A.M. car radio anywhere on the
show grounds. There are no local stations on 1600khz, or even anywhere near
it, and since these shows are only in the daytime, I won't be competing with
skywave, or 50kw clear channels.

Any tall light-poles nearby? You could put a tap onto one a couple of feet
up from the base if you have an antenna tuner.
100mW in for 60mW out? Doesn't sound like much of an amplifier!

"gudmundur" wrote in message
...
I do sound work at horse shows, and would like to provide my audio source
to vehicles parked at the show. I have a real nice 100 milliwatt input
1.6mhz transmitter which shows about 60 milliwatts of output at 50 ohms.

I would like to build a transmitting antenna that would be 4 feet in
length
and having the 3/8 24 thread at the bottom so I can fasten it into my
hamstick
mag mount base.

I am thinking a 1 inch diameter wooden dowel 4 feet long, and wrapped
evenly
from bottom to top with perhaps #22 wire.

Any idea how much wire it would take to begin to act like a 50 ohm
impedance
at the base? Would you solenoid wind it bottom to top, or would it work
better
with maybe a 4 inch high multilayered coil at the bottom and 3.5 foot
steel
whip antenna.

I am not out to **** off the FCC, and with a mere 60 milliwatts of output
power at 50 ohms, I don't think anyone beyond 300 yards will even here it.
I do however want to be clearly heard on an A.M. car radio anywhere on the
show grounds. There are no local stations on 1600khz, or even anywhere
near
it, and since these shows are only in the daytime, I won't be competing
with
skywave, or 50kw clear channels.

Any tall light-poles nearby? You could put a tap onto one a couple of feet
up from the base if you have an antenna tuner.
100mW in for 60mW out? Doesn't sound like much of an amplifier!

"gudmundur" wrote in message
...
I do sound work at horse shows, and would like to provide my audio source
to vehicles parked at the show. I have a real nice 100 milliwatt input
1.6mhz transmitter which shows about 60 milliwatts of output at 50 ohms.

I would like to build a transmitting antenna that would be 4 feet in
length
and having the 3/8 24 thread at the bottom so I can fasten it into my
hamstick
mag mount base.

I am thinking a 1 inch diameter wooden dowel 4 feet long, and wrapped
evenly
from bottom to top with perhaps #22 wire.

Any idea how much wire it would take to begin to act like a 50 ohm
impedance
at the base? Would you solenoid wind it bottom to top, or would it work
better
with maybe a 4 inch high multilayered coil at the bottom and 3.5 foot
steel
whip antenna.

I am not out to **** off the FCC, and with a mere 60 milliwatts of output
power at 50 ohms, I don't think anyone beyond 300 yards will even here it.
I do however want to be clearly heard on an A.M. car radio anywhere on the
show grounds. There are no local stations on 1600khz, or even anywhere
near
it, and since these shows are only in the daytime, I won't be competing
with
skywave, or 50kw clear channels.

At 1.6 MHz at 4 foot long helical would be very low impedance - probably
around 1 ohm or so at resonance. You would have to feed it against ground -
ground losses would be 30-50 ohms, depending on your grounding mechanism. So
the antenna might be a good match but radiation efficiency would be only 1-2
% as most of the power will be lost in ground resistance.

Richard

matt wilson wrote in message
...
Any tall light-poles nearby? You could put a tap onto one a couple of feet
up from the base if you have an antenna tuner.
100mW in for 60mW out? Doesn't sound like much of an amplifier!

"gudmundur" wrote in message
...
I do sound work at horse shows, and would like to provide my audio
source
to vehicles parked at the show. I have a real nice 100 milliwatt input
1.6mhz transmitter which shows about 60 milliwatts of output at 50 ohms.

I would like to build a transmitting antenna that would be 4 feet in
length
and having the 3/8 24 thread at the bottom so I can fasten it into my
hamstick
mag mount base.

I am thinking a 1 inch diameter wooden dowel 4 feet long, and wrapped
evenly
from bottom to top with perhaps #22 wire.

Any idea how much wire it would take to begin to act like a 50 ohm
impedance
at the base? Would you solenoid wind it bottom to top, or would it work
better
with maybe a 4 inch high multilayered coil at the bottom and 3.5 foot
steel
whip antenna.

I am not out to **** off the FCC, and with a mere 60 milliwatts of
output
power at 50 ohms, I don't think anyone beyond 300 yards will even here
it.
I do however want to be clearly heard on an A.M. car radio anywhere on
the
show grounds. There are no local stations on 1600khz, or even anywhere
near
it, and since these shows are only in the daytime, I won't be competing
with
skywave, or 50kw clear channels.

At 1.6 MHz at 4 foot long helical would be very low impedance - probably
around 1 ohm or so at resonance. You would have to feed it against ground -
ground losses would be 30-50 ohms, depending on your grounding mechanism. So
the antenna might be a good match but radiation efficiency would be only 1-2
% as most of the power will be lost in ground resistance.

Richard

matt wilson wrote in message
...
Any tall light-poles nearby? You could put a tap onto one a couple of feet
up from the base if you have an antenna tuner.
100mW in for 60mW out? Doesn't sound like much of an amplifier!

"gudmundur" wrote in message
...
I do sound work at horse shows, and would like to provide my audio
source
to vehicles parked at the show. I have a real nice 100 milliwatt input
1.6mhz transmitter which shows about 60 milliwatts of output at 50 ohms.

I would like to build a transmitting antenna that would be 4 feet in
length
and having the 3/8 24 thread at the bottom so I can fasten it into my
hamstick
mag mount base.

I am thinking a 1 inch diameter wooden dowel 4 feet long, and wrapped
evenly
from bottom to top with perhaps #22 wire.

Any idea how much wire it would take to begin to act like a 50 ohm
impedance
at the base? Would you solenoid wind it bottom to top, or would it work
better
with maybe a 4 inch high multilayered coil at the bottom and 3.5 foot
steel
whip antenna.

I am not out to **** off the FCC, and with a mere 60 milliwatts of
output
power at 50 ohms, I don't think anyone beyond 300 yards will even here
it.
I do however want to be clearly heard on an A.M. car radio anywhere on
the
show grounds. There are no local stations on 1600khz, or even anywhere
near
it, and since these shows are only in the daytime, I won't be competing
with
skywave, or 50kw clear channels.

"gudmundur" wrote in message
...
I do sound work at horse shows, and would like to provide my audio source
to vehicles parked at the show. I have a real nice 100 milliwatt input
1.6mhz transmitter which shows about 60 milliwatts of output at 50 ohms.

I would like to build a transmitting antenna that would be 4 feet in
length
and having the 3/8 24 thread at the bottom so I can fasten it into my
hamstick
mag mount base.

I am thinking a 1 inch diameter wooden dowel 4 feet long, and wrapped
evenly
from bottom to top with perhaps #22 wire.

Any idea how much wire it would take to begin to act like a 50 ohm
impedance
at the base? Would you solenoid wind it bottom to top, or would it work
better
with maybe a 4 inch high multilayered coil at the bottom and 3.5 foot
steel
whip antenna.

1) 60 mW RF out for 100 mW DC input sounds like suspiciously high
efficiency.

2) To a VERY rough approximation, I'd aim to put a quarter-wave (at 1600
kHz) of wire on the dowel. That's almost 200 meters / 660 feet. I doubt
that you can fit that much on the dowel. In any case a tophat on the dowel
will partially compensate for too little wire. Even something a foot or two
in diameter might help a little.An example: a broadcast station near 1600
kHz has a tower only 67 degrees tall (less than 90 degrees / 1/4-th wave).
At the top they stick 4 or 6 or 8 10-ft-long rods straight out to the sides.
They claim this top-hat is the equivalent of 10 degrees more tower height,
bringing them up to an equivalent of 77 degrees. With this they claim to
meet the FCC's required minimum antenna radiation efficiency for their class
of station. Top-hats like this are pretty common for AM stations. Sometime
they use the top few feet of the guy wires.

3) Putting the loading coil at the bottom of the antenna is the worst
possible choice. It's the current flowing in the antenna that radiates, and
the current is highest at the feedpoint and zero at the tip, for
quarter-wave and shorter antennas. The high current points would all be
hidden in the loading coil and only the high-voltage/low-current part would
be "visible". Look at the short CB antennas. They will be have most of the
turns of wire near the tip.

4) Your mag mount won't have enough capacitance to the vehicle to be a
really good connection at 1600 kHz if you manage to make the antenna
impedance low, like 50 ohms.

5) In any case, the impedance looking into the base of any antenna _I_ think
you can fit in 4-ft length will be much higher than 50 ohms. You should
build a matching network. The less wire you can fit on the antenna rod, the
higher the input impedance. Look in the ARRL Antenna Book for networks for
feeding short antennas on the 160 meter ham band. The coil in a matching
network should be wound with rather hefty wire for low loss.

"gudmundur" wrote in message
...
I do sound work at horse shows, and would like to provide my audio source
to vehicles parked at the show. I have a real nice 100 milliwatt input
1.6mhz transmitter which shows about 60 milliwatts of output at 50 ohms.

I would like to build a transmitting antenna that would be 4 feet in
length
and having the 3/8 24 thread at the bottom so I can fasten it into my
hamstick
mag mount base.

I am thinking a 1 inch diameter wooden dowel 4 feet long, and wrapped
evenly
from bottom to top with perhaps #22 wire.

Any idea how much wire it would take to begin to act like a 50 ohm
impedance
at the base? Would you solenoid wind it bottom to top, or would it work
better
with maybe a 4 inch high multilayered coil at the bottom and 3.5 foot
steel
whip antenna.

1) 60 mW RF out for 100 mW DC input sounds like suspiciously high
efficiency.

2) To a VERY rough approximation, I'd aim to put a quarter-wave (at 1600
kHz) of wire on the dowel. That's almost 200 meters / 660 feet. I doubt
that you can fit that much on the dowel. In any case a tophat on the dowel
will partially compensate for too little wire. Even something a foot or two
in diameter might help a little.An example: a broadcast station near 1600
kHz has a tower only 67 degrees tall (less than 90 degrees / 1/4-th wave).
At the top they stick 4 or 6 or 8 10-ft-long rods straight out to the sides.
They claim this top-hat is the equivalent of 10 degrees more tower height,
bringing them up to an equivalent of 77 degrees. With this they claim to
meet the FCC's required minimum antenna radiation efficiency for their class
of station. Top-hats like this are pretty common for AM stations. Sometime
they use the top few feet of the guy wires.

3) Putting the loading coil at the bottom of the antenna is the worst
possible choice. It's the current flowing in the antenna that radiates, and
the current is highest at the feedpoint and zero at the tip, for
quarter-wave and shorter antennas. The high current points would all be
hidden in the loading coil and only the high-voltage/low-current part would
be "visible". Look at the short CB antennas. They will be have most of the
turns of wire near the tip.

4) Your mag mount won't have enough capacitance to the vehicle to be a
really good connection at 1600 kHz if you manage to make the antenna
impedance low, like 50 ohms.

5) In any case, the impedance looking into the base of any antenna _I_ think
you can fit in 4-ft length will be much higher than 50 ohms. You should
build a matching network. The less wire you can fit on the antenna rod, the
higher the input impedance. Look in the ARRL Antenna Book for networks for
feeding short antennas on the 160 meter ham band. The coil in a matching
network should be wound with rather hefty wire for low loss.

On Sat, 29 Nov 2003 06:54:01 GMT, "matt wilson"
wrote:

Any tall light-poles nearby? You could put a tap onto one a couple of feet
up from the base if you have an antenna tuner.
100mW in for 60mW out? Doesn't sound like much of an amplifier!

That'd be 100mW *DC* in for 60mW *RF* out! Nothing wrong with that.
--

"I expect history will be kind to me, since I intend to write it."
- Winston Churchill

On Sat, 29 Nov 2003 06:54:01 GMT, "matt wilson"
wrote:

Any tall light-poles nearby? You could put a tap onto one a couple of feet
up from the base if you have an antenna tuner.
100mW in for 60mW out? Doesn't sound like much of an amplifier!

That'd be 100mW *DC* in for 60mW *RF* out! Nothing wrong with that.
--

"I expect history will be kind to me, since I intend to write it."
- Winston Churchill

On Sat, 29 Nov 2003 06:17:53 -0000, (gudmundur)
wrote:

I do sound work at horse shows, and would like to provide my audio source
to vehicles parked at the show. I have a real nice 100 milliwatt input
1.6mhz transmitter which shows about 60 milliwatts of output at 50 ohms.

I would like to build a transmitting antenna that would be 4 feet in length
and having the 3/8 24 thread at the bottom so I can fasten it into my hamstick
mag mount base.

I am thinking a 1 inch diameter wooden dowel 4 feet long, and wrapped evenly
from bottom to top with perhaps #22 wire.

Any idea how much wire it would take to begin to act like a 50 ohm impedance
at the base? Would you solenoid wind it bottom to top, or would it work better
with maybe a 4 inch high multilayered coil at the bottom and 3.5 foot steel
whip antenna.

You need one of Reg Edwards' utilities to work this out for you. He's
written a number of small programs for the PC that handle exactly this
kind of problem and they're available for free download. I can't
recall the URL off hand but just Google for "Reg Edwards" on the
newsgroup sci.electronics.design and that'll bring it up.
--

"I expect history will be kind to me, since I intend to write it."
- Winston Churchill