Maker Pro
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antenna length for video xmtr

E

Eric R Snow

Jan 1, 1970
0
Greetings Folks,
I have a video camera/transmitter unit that transmits in the 900 MHz
to 1200 MHz range according to the spec sheet. It currently has a
wire for the antenna that's 3.5 inches long. For optimum transmitting
doesn't the antenna length need to be a length that divides evenly
into wavelength? I will be enclosing the camera in a small plastic
waterproof enclosure with batteries and a light. Then it will be
lowered 70 feet down a 6 inch diameter iron pipe. It will be used to
inspect the well casing and pump as well as to watch the water as it
is being pumped. I want the best signal possible and was wondering how
long to make the antenna if the present one doesn't work. Right now,
in open air, a good signal is present at 100 feet. But I don't know
how well it will work when lowered down the iron pipe.
Thank You,
Eric R Snow
 
B

Bob Myers

Jan 1, 1970
0
Eric R Snow said:
I want the best signal possible and was wondering how
long to make the antenna if the present one doesn't work. Right now,
in open air, a good signal is present at 100 feet. But I don't know
how well it will work when lowered down the iron pipe.

If you're going to be lowering the thing down
an iron pipe, I would think you would do FAR
better simply running the signal over a cable than
you ever will with a wireless link.

Bob M.
 
E

Eric R Snow

Jan 1, 1970
0
If you're going to be lowering the thing down
an iron pipe, I would think you would do FAR
better simply running the signal over a cable than
you ever will with a wireless link.

Bob M.
That's what I'm afraid of. But it's much easier to keep the camera dry
and to maneuver it around if it's only connected by a rope. So I'm
gonna try it first.
ERS
 
B

Bob Myers

Jan 1, 1970
0
That's what I'm afraid of. But it's much easier to keep the camera dry
and to maneuver it around if it's only connected by a rope. So I'm
gonna try it first.

There's a problem with the "rope" being a coaxial
cable, or at least having a mini-coax wrapped around
it?

You're going to have REAL problems with an RF link
in this case, trust me...


Bob M.
 
S

Si Ballenger

Jan 1, 1970
0
Greetings Folks,
I have a video camera/transmitter unit that transmits in the 900 MHz
to 1200 MHz range according to the spec sheet. It currently has a
wire for the antenna that's 3.5 inches long. For optimum transmitting
doesn't the antenna length need to be a length that divides evenly
into wavelength? I will be enclosing the camera in a small plastic
waterproof enclosure with batteries and a light. Then it will be
lowered 70 feet down a 6 inch diameter iron pipe. It will be used to
inspect the well casing and pump as well as to watch the water as it
is being pumped. I want the best signal possible and was wondering how
long to make the antenna if the present one doesn't work. Right now,
in open air, a good signal is present at 100 feet. But I don't know
how well it will work when lowered down the iron pipe.
Thank You,
Eric R Snow

You need to run your video and power over a cable (easy to do
using 4 conductor telephone wire). The below cams would be easy
and cheap to use with a little tweeking/modding.

http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=91309
http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=47546
 
E

Eric R Snow

Jan 1, 1970
0
There's a problem with the "rope" being a coaxial
cable, or at least having a mini-coax wrapped around
it?

You're going to have REAL problems with an RF link
in this case, trust me...


Bob M.
Yeah Bob, I tried the cable as rope thing and the cable wrapped around
the rope and had problems with manipulation and strength problems. I
guess I'll lower tthe camera down and if there are problems then go to
the extra trouble to make a case with sealed leads coming through. .
ERS
 
C

Captain

Jan 1, 1970
0
Eric R Snow said:
Greetings Folks,
I have a video camera/transmitter unit that transmits in the 900 MHz
to 1200 MHz range according to the spec sheet. It currently has a
wire for the antenna that's 3.5 inches long. For optimum transmitting
doesn't the antenna length need to be a length that divides evenly
into wavelength? I will be enclosing the camera in a small plastic
waterproof enclosure with batteries and a light. Then it will be
lowered 70 feet down a 6 inch diameter iron pipe. It will be used to
inspect the well casing and pump as well as to watch the water as it
is being pumped. I want the best signal possible and was wondering how
long to make the antenna if the present one doesn't work. Right now,
in open air, a good signal is present at 100 feet. But I don't know
how well it will work when lowered down the iron pipe.
Thank You,
Eric R Snow

1/4 wavelength is the best length. L=C/F (C=3E8) For 900 MHz this is 333
cm. Cut the antenna a bit longer and trim until you get best signal
strength. If it will fit, silver plated narrow gauge welding rod works
well.

Actually, with the transmitter down a metal pipe you could get a wave guide
effect, in which case the signal will boom out.

Cap
 
R

Robert Monsen

Jan 1, 1970
0
Captain said:
1/4 wavelength is the best length. L=C/F (C=3E8) For 900 MHz this is 333
cm. Cut the antenna a bit longer and trim until you get best signal
^^ ?

No, 3e8/9e8 = 1/3m. Thats the wavelength in meters.

1/4 of that is 8.33cm, or 3.28 in. Your antenna is already close to 1/4
of a wavelength.
strength. If it will fit, silver plated narrow gauge welding rod works
well.

Actually, with the transmitter down a metal pipe you could get a wave guide
effect, in which case the signal will boom out.

Cap

Regards,
Bob Monsen
 
E

Eric R Snow

Jan 1, 1970
0
^^ ?

No, 3e8/9e8 = 1/3m. Thats the wavelength in meters.

1/4 of that is 8.33cm, or 3.28 in. Your antenna is already close to 1/4
of a wavelength.


Regards,
Bob Monsen
Greetyings Bob,
It's interesting that the calculations comes so close to the length.
Since the thing transmits anywhere in the 900 to 1200 range the
antenna being 3.5 inches long would seem to be covering that range.
If the antenna needs to be extended and a shielded wire is used until
the last 3.5 inches of wire will the effect be the same as the antenna
being connected directly to the circuit board as it is now?
Thanks,
eric
 
R

Rich Grise

Jan 1, 1970
0
Yeah Bob, I tried the cable as rope thing and the cable wrapped around
the rope and had problems with manipulation and strength problems.

What strength problems? If the rope will hold the camera without
the cable, what makes the rope becomes weaker when there's a cable
dangling alongside it? You leave some slack at the camera end, and
let the cable support only its own weight. You could keep them at
the same length with some kind of capstan.

Good Luck!
Rich
 
C

Captain

Jan 1, 1970
0
Robert Monsen said:
^^ ?

No, 3e8/9e8 = 1/3m. Thats the wavelength in meters.

1/4 of that is 8.33cm, or 3.28 in. Your antenna is already close to 1/4
of a wavelength.


Regards,
Bob Monsen

Mea culpa! I thought a foot was a bit long for the frequency!
Cap
 
E

Eric R Snow

Jan 1, 1970
0
What strength problems? If the rope will hold the camera without
the cable, what makes the rope becomes weaker when there's a cable
dangling alongside it? You leave some slack at the camera end, and
let the cable support only its own weight. You could keep them at
the same length with some kind of capstan.

Good Luck!
Rich
Rich,
The video cable by itself was too weak. Wrapped arond the rope it was
a mess.
ERS
 
S

Si Ballenger

Jan 1, 1970
0
The video cable by itself was too weak. Wrapped arond the rope it was
a mess.

How much weight are you trying to drop down your well? Most cams
small enough to drop down the well casing with the pump still
installed weigh only a couple of ounces at most. Bullet types of
cams usually have a threaded fitting on the rear in which a ~1'
length piece of threaded rod can be attached. Tape the cam cable
to the threaded rod so all hangs vertically. You can see the
threaded hole on the rear of the little IR cam on the below page
(this cam is small, but the bullet cams are even thinner). The
cable with this cam probably could withstand a 50lb pull if it
got stuck. The rear of the cam would need to be tapered to the
threaded rod so the edge wouldn't catch on a casing misalignment
and such. Sounds like you are trying to put too large a cam setup
down your casing.

http://www.geocities.com/zoomkat/ezservo.htm
 
E

Eric R Snow

Jan 1, 1970
0
How much weight are you trying to drop down your well? Most cams
small enough to drop down the well casing with the pump still
installed weigh only a couple of ounces at most. Bullet types of
cams usually have a threaded fitting on the rear in which a ~1'
length piece of threaded rod can be attached. Tape the cam cable
to the threaded rod so all hangs vertically. You can see the
threaded hole on the rear of the little IR cam on the below page
(this cam is small, but the bullet cams are even thinner). The
cable with this cam probably could withstand a 50lb pull if it
got stuck. The rear of the cam would need to be tapered to the
threaded rod so the edge wouldn't catch on a casing misalignment
and such. Sounds like you are trying to put too large a cam setup
down your casing.

http://www.geocities.com/zoomkat/ezservo.htm
The camera is small. The casing with batteries and LED lights is the
big part.
ERS
 
P

Peter Bennett

Jan 1, 1970
0
The video cable by itself was too weak. Wrapped arond the rope it was
a mess.
ERS

Cable TV companies use a cable consisting of a coax and a stronger
support wire for the drops from a utility pole to a house - perhaps
you could use that... (Belden 7983A, for example)





--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca
 
S

Si Ballenger

Jan 1, 1970
0
The camera is small. The casing with batteries and LED lights is the
big part.

I've only pulled a couple of well pumps, but I wouldn't be
putting all that stuff down the well casing. You are just asking
for trouble. Go to google search to see what the well inspectors
use. An IR bullet cam on the end of cheap cat5 cable will be
plenty strong enough to support the cam and pull back out if it
gets in a bind. Below is a cam you might want to look into. YMMV!

http://www.supercircuits.com/store/prodinfo.asp?number=PC136UW1&variation=&aitem=7&mitem=11
 
R

Rich Grise

Jan 1, 1970
0
Rich,
The video cable by itself was too weak. Wrapped arond the rope it was
a mess.
ERS

What part of "alongside" don't you understand?

Thanks,
Rich
 
R

Rich Grise

Jan 1, 1970
0
I've only pulled a couple of well pumps, but I wouldn't be
putting all that stuff down the well casing. You are just asking
for trouble. Go to google search to see what the well inspectors
use. An IR bullet cam on the end of cheap cat5 cable will be
plenty strong enough to support the cam and pull back out if it
gets in a bind. Below is a cam you might want to look into. YMMV!
http://www.supercircuits.com/store/prodinfo.asp?number=PC136UW1&variation=&aitem=7&mitem=11

And leave the batteries topside, of course.

Cheers!
Rich
 
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