Why use perpendicular feedline?
 

Hello,

I'm running stock power on my radio. I'm using a vertical dipole
mounted in a tree. The bottom of the dipole is about 8 feet (1/4
wavelength) off the ground. The feedline is going down at about a 45
degree angle from the antenna. My SWR is 1.5 which is the best it'll
get.

I'm using a mobile base, with a AC - DC power supply. I receive fine.
Regardless if my noiseblocker is on or not. However, when I transmit,
it sounds god aweful. Others can't understand what I'm saying. I've
used another radio with earphones, and listened to myself talk, and it
sounds like 5 layers of tin foil on my microphone. If i take this same
radio and microphone, and mount it in my truck, it works fine.

I'm thinking the power supply, but don't have a way to verify this yet.
I'm also wondering if there's a chance that this could be because of my
antenna radiating back into my feedline, and creating a feedback loop
or some other type of noise.

My main question is. why is it recommended to run feedline
perpendicular to a dipole?

Why use perpendicular feedline?
 

"SparkySKO" wrote in message
oups.com...
My main question is. why is it recommended to run feedline
perpendicular to a dipole?

It helps to prevent RF currents from flowing on the outside of your coax
cable. A dipole antenna is normally a "balanced" type of antenna relative
to earth ground were as coax cable is not. Running the coax at 90 degrees
greatly reduces the antenna coupling to the ouside of the coax but doesn't
eliminate completely enough in some cases.

There are several things you can do to help decouple the feedline, coax,
from the antenna.

1. Spool up several loops of your feedline right at the dipole feed point.
Use a loop diameter of 6 to 8 inches and try around 5 to 6 loops. Hold the
loops in place using some tape or plastic cable ties. What you want to watch
out for is not to make a resonate circuit from the loop inductance and the
stray capacitance between the loops. I guess the way you'll know if this
happens is the SWR will get really screwy and the RF feedback will increase.

2. You can slip a bunch of ferrite ring cores over the feedline right at the
dipole's feed point. You'll have to check for RF heating of the cores, but
at the low 4 watt level you're talking about it likely won't be a problem.

3. You can use a "balum" to convert from an unbalanced feedline to a balance
load, your dipole antenna. You should be able to do a Google search on
"balum" and find something that looks suitable that you can build.

http://www.arrl.org/qex/2005/qx9roos.pdf
http://eznec.com/Amateur/Articles/Baluns.pdf
http://www.qsl.net/iz7ath/web/02_bre.../pag01_eng.htm

Another antenna idea too.

http://www.signalengineering.com/ult...na_basics.html

The URL above has a design for another type of dipole antenna, at the very
bottom of the web page, that should work good for you as well as eliminating
the RF feedback problem. The point here is note the coax is routed through
the inside of the bottom dipole element. This also helps to shield the coax.

--
Regards,
Leland C. Scott
KC8LDO

Why use perpendicular feedline?
 

"LeIand C. Scot" wrote:
-snip some good advice for brevity-
Another antenna idea too.

http://www.signalengineering.com/ult...na_basics.html


Hi Lee, good job man. It's weird, I booked my woodward cruise motel room
today around lunch time or a bit after that, and now I see your post today.
Are you going to it? (you almost have no choice as close as you are) :P

These years are going by like months now, ain't they? It's hard to believe
it's time for that show again already ain't it? dang

ps. the Tigers look tuff, are you a fan?

Why use perpendicular feedline?
 

Steveo wrote:
"LeIand C. Scot" wrote:
-snip some good advice for brevity-
Another antenna idea too.

http://www.signalengineering.com/ult...na_basics.html


Hi Lee, good job man. It's weird, I booked my woodward cruise motel room
today around lunch time or a bit after that, and now I see your post today.
Are you going to it? (you almost have no choice as close as you are) :P

These years are going by like months now, ain't they? It's hard to believe
it's time for that show again already ain't it? dang

ps. the Tigers look tuff, are you a fan?
We heard you are going up to be some Motown keyclowns' butt buddy. If
your car is there we will see you. However, in advance you are reminded
that all AKC are hetero, so your fantasies are doomed.

Why use perpendicular feedline?
 

At least this was somewhat on topic.

As it turns out, the noise experienced while transmitting was from a
fried frontend on the radio, and was not related to the antenna.

You may now continue your weird usenet mating rituals.

Why use perpendicular feedline?
 

"Steveo" wrote in message
...
"LeIand C. Scot" wrote:
-snip some good advice for brevity-
Another antenna idea too.

http://www.signalengineering.com/ult...na_basics.html


Hi Lee, good job man. It's weird,

It's not realy that weird. If you do some research you'll find it's a bit
more common than you think.

I booked my woodward cruise motel room
today around lunch time or a bit after that, and now I see your post
today.
Are you going to it? (you almost have no choice as close as you are) :P

Not sure if I'm going. I've been traveling so much lately for work I don't
know when I'll be around town. Been every where from Mexico, Raynosa, to
Canada, Guelph, with some points in between like Missouri in just the past 5
to 6 weeks alone. If I am in town I do plan to hang out and watch the cars.

These years are going by like months now, ain't they? It's hard to believe
it's time for that show again already ain't it? dang

Yeah summer is almost shot again and I hardly even noticed it slipping by.

ps. the Tigers look tuff, are you a fan?

Not much of one. I like hockey a lot more.

--
Regards,
Leland C. Scott
KC8LDO

Why use perpendicular feedline?
 

SparkySKO wrote:
Hello,

I'm running stock power on my radio. I'm using a vertical dipole
mounted in a tree. The bottom of the dipole is about 8 feet (1/4
wavelength) off the ground. The feedline is going down at about a 45
degree angle from the antenna. My SWR is 1.5 which is the best it'll
get.

I'm using a mobile base, with a AC - DC power supply. I receive fine.
Regardless if my noiseblocker is on or not. However, when I transmit,
it sounds god aweful. Others can't understand what I'm saying. I've
used another radio with earphones, and listened to myself talk, and it
sounds like 5 layers of tin foil on my microphone. If i take this same
radio and microphone, and mount it in my truck, it works fine.

I'm thinking the power supply, but don't have a way to verify this yet.
I'm also wondering if there's a chance that this could be because of my
antenna radiating back into my feedline, and creating a feedback loop
or some other type of noise.

My main question is. why is it recommended to run feedline
perpendicular to a dipole?

Your power supply is regulated, right? What kind? Hook an auto battery
to the radio to test it from a clean 12 vold dc supply and see if it
cures your problem, or proves the source of trouble is the power supply.

Why use perpendicular feedline?
 

On 10 Aug 2006 12:17:14 -0700, "SparkySKO" wrote
in .com:

At least this was somewhat on topic.

As it turns out, the noise experienced while transmitting was from a
fried frontend on the radio, and was not related to the antenna.


That doesn't make sense. If it works fine on the truck like you said
then there isn't anything wrong with the radio.

Why use perpendicular feedline?
 

3. You can use a "balum" to convert from an unbalanced feedline to a balance
load, your dipole antenna. You should be able to do a Google search on
"balum" and find something that looks suitable that you can build.

Look up "balun" not "balum"

It's balanced to unbalanced, not balanced to umbalanced.

Does your stereo have imputs or inputs?