1:1 balun construction
JEFF UK
I am now planning to put up my first dipole for SWL.
I need help with;
1) A sensible length for general SWL.?
I mostly listen between 80 and 20 mtrs.
2) I would like a diagram of a 1:1 balun construction.
I believe this is the correct type for a dipole ?
I have a ferrite rod not rings, will it work the same ?
3) I will be using 75 ohm tv coax to its feed point which
is 90 feet from the house.
Will this be ok ?
4) I will need to bend the legs of the antenna to fit them in the garden.
I think this is ok for receiving ?
All help welcomed
Regards
Jeff
Mark Keith
> Hi.
> I am now planning to put up my first dipole for SWL.
> I need help with;
>
> 1) A sensible length for general SWL.?
> I mostly listen between 80 and 20 mtrs.
Not critical. Anything from 80-120 ft total would be ok.
>
> 2) I would like a diagram of a 1:1 balun construction.
> I believe this is the correct type for a dipole ?
> I have a ferrite rod not rings, will it work the same ?
It would be simple to just make a choke from the coax line at the
feedpoint. Wind a few turns into a choke. Maybe 8 turns with a 6-8
inch form size, and tape it up.
You could use a 1:1 balun, but it's kind of overkill for just SWL. 40m
will be a high Z feed also if you used a 80 dipole... You actually
don't have to use anything, but if you didn't , you might have the
possibility of noise ingress on certain bands. The balun or choke acts
as feedline decoupling.
>
> 3) I will be using 75 ohm tv coax to its feed point which
> is 90 feet from the house.
> Will this be ok ?
Yes.
>
> 4) I will need to bend the legs of the antenna to fit them in the garden.
> I think this is ok for receiving ?
Yes. Transmitting too... MK
RHF
Thinking of a Dipole - Consider the Inverted "L" Antenna for SWLing
The Dipole is not the greatest SWL Antenna.
80 Meter Band 3.5-4.0 MHz
BMP = 3.750 MHz
One WaveLength 80M = 268 Feet
Half WaveLength = 134 Feet = Dipole's Total Length
Quarter WaveLength = 67 feet = Each Arm of the Dipole
NOTE: If you are looking for a single Band Antenna
for Amateur-HAM use with a specific direction in mind;
then the Dipole may be a very good choice. Provided you
can mount it as high as required for the best results.
The Inverted "L" Antennas is the most common and practical SWL Antenna.
For the 80 Metre Band and above. A Quarter Wave Length
Inverted "L" Antenna that is 66 Feet Long and has a
Vertical-Up-Leg of 22 Feet from Ground Level with a
Horizontal-Out-Arm of 44 Feet should work very well.
Consider the LONGWIRE [Random Wire] Antenna for SWLs:
* The commonly called 'LongWire' Antenna is actually a
"Random Wire" Antenna that is used by Shortwave Listener's.
* The most 'common' form of the Random Wire Antenna used by
SWLs is the Inverted "L" Antenna.
* This Inverted "L" Antenna Configuration lends itself to
the Low Noise Antenna design that was popularized by John Doty.
Inverted "L' Antenna Reading List
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/message/374
"LOW NOISE SWL ANTENNA" - by Mark Connelly [WA1ION]
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/message/119
"Another Look at Noise-Reducing Antenna Systems"
Inverted "L" Antenna as an 'available space' SWL Antenna
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/message/54
"LOW NOISE SWL ANTENNA" - popularized by John Doty.
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/message/2
Balun Reading List ( Long )
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/message/337
Also the Shortwave SWL Antenna's Photo Section has a Photo Album
of BALUN Images and Diagrams to Take-A-Look-At:
http://photos.groups.yahoo.com/group/Shortwave-SWL-Antenna/lst
.
.
REMEMBER: "The Shortwave Antenna is 55.5% of the . . .
Radio/Receiver and Antenna/Ground Reception Equation"
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/message/288
A Shortwave Antenna is "Equally" Important for Good Reception [.]
.
.
iane ~ RHF
.
Some Say: On A Clear Day You Can See Forever.
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/message/502
I BELIEVE: On A Clear Night...
You Can Hear Forever and beyond, The Beyond !
.
.
= = = "JEFF UK" <Birdn...@btopenworld.com> wrote in message
= = = news:<c31gks$m9k$1...@titan.btinternet.com>...
.
DxAce
RHF wrote:
> JEFF-UK,
>
> Thinking of a Dipole - Consider the Inverted "L" Antenna for SWLing
>
> The Dipole is not the greatest SWL Antenna.
> 80 Meter Band 3.5-4.0 MHz
> BMP = 3.750 MHz
> One WaveLength 80M = 268 Feet
> Half WaveLength = 134 Feet = Dipole's Total Length
> Quarter WaveLength = 67 feet = Each Arm of the Dipole
> NOTE: If you are looking for a single Band Antenna
> for Amateur-HAM use with a specific direction in mind;
> then the Dipole may be a very good choice. Provided you
> can mount it as high as required for the best results.
Absolutely correct. If one wants good single band performance then the dipole,
or inverted vee configuration if just fine.
But if you want a good 'all 'round' antenna then go the random wire, matching
transformer route.
I'm currently using the random wire(s), but I plan to put up an inverted Vee
for 60 meters this summer.
Steve
Holland, MI
Drake R7, R8 and R8B
http://www.iserv.net/~n8kdv/dxpage.htm
DxAce
-=jd=- wrote:
> On Sun 14 Mar 2004 11:26:10a, DxAce <n8...@nospam.iserv.net> wrote in
> message news:405487A2...@nospam.iserv.net:
>
> > [brevity snip]
> >
> > Absolutely correct. If one wants good single band performance then the
> > dipole, or inverted vee configuration if just fine.
> >
> > But if you want a good 'all 'round' antenna then go the random wire,
> > matching transformer route.
> >
> > I'm currently using the random wire(s), but I plan to put up an inverted
> > Vee for 60 meters this summer.
> >
> > [brevity snip]
>
> I've seen the pic of a wire antenna on your web page and I was wondering
> if that's a current or outdated pic and is it your main antenna. It looks
> like it's strung on 4x4 posts - can't get a feel for the total length from
> the pic. The height from that pic seems like it's 10 feet (more or less)
> off the ground.
4x4x12's sunk 3 feet into the ground. That pic shows the antenna at 100' in
length. It is now 200'.
In the back, running at a 90 degree angle to the 100' wire pictured is a 70'
wire.
>
>
> In comparison, my wire is strung (for the most part) 30 to 40 feet up
> following a more or less "Z" figure along the edge of the tree line on my
> property for about 300 feet. It's fed with coax through a matching
> transformer (grounded to the shield). The ground is about 20 feet from the
> transformer (the earliest point where I could ground it).
Both my 70' and 200' wires are grounded at the base below the co-axial
feedpoint.
If you have additional questions which I've failed to answer (i'm sure I
have), feel free to ask.
Jim Douglas
http://braincambre500.freeservers.com/Balun%20for%20dipole.htm
"JEFF UK" <Birdn...@btopenworld.com> wrote in message
news:c31gks$m9k$1...@titan.btinternet.com...
JEFF UK
"DxAce" <n8...@nospam.iserv.net> wrote in message
news:4054A17B...@nospam.iserv.net...
Wizard@hiz.biz Chief Suspect
"JEFF UK" <Birdn...@btopenworld.com> wrote.
> I am now planning to put up my first dipole for SWL.
............. let me ask first, why you especially want a dipole? Dipoles
are great for directional
broadcasting. Shortwaves come in from random reflection points only in the
general direction
of ..... there-to-there. :>) Different frequencies will resonate best at
certain angles from the
antenna. 90-degree broadside is only for transmitted frequencies specific to
the cut dipole
lengths.
> 1) A sensible length for general SWL.?
.............. for the range you specified, you might be well satisfied with
50-100 feet of wire.
The idea is to get it as high as possible off the ground, and not threaded
through trees.
>
> 2) I would like a diagram of a 1:1 balun construction.
............. Construction of a Balun for impedence matching is a matter of
some patient
engineering. Better to purchase one already made. A good one for use with
52 ohm coax
will best be mounted at the top where the legs of the dipole meet, before
signal travels down
the coax to your RX.
> 3) I will be using 75 ohm tv coax to its feed point which is 90 feet from
the house.
> Will this be ok ?
>
................ 75 ohm coax will be fine. Too much emphasis is placed on
use of 52 ohm coax.
Both are considered low-impedance. But, get 100% insulated shield. Braid,
not aluminum
sheath TV cable. Better, however, would be 600-ohm TV track wire for that
distance.
Cheap stuff. 600 Ohm is considered hi-impedence, and should enter the RX
using that
connection instead of the PL-259 Lo-Z input.... or feed it thru a passive
tuner. See below.
> 4) I will need to bend the legs of the antenna to fit them in the garden.
................. Uh Oh! Yes, this will indeed affect impedence, freq
response, as well as
Mu factor and shape of Q. Consider, frequency response may be enhanced one
way
or the other by passing the signal through chokes or coils. Bending your
antenna around
corners "to make it fit" is essentially starting such a "coil" and the
frequency response will
be affected according to how much wire length you are using.
Bottom line: Keep it straight, high, well insulated with propers hardware
mountings. Feed
your downlead end through a passive tuner such as a TUN-3 or TUN-4 then to
the RX.
GROUND the receiver chassis with THICK cabling, perhaps several strands of
THICK
twisted TV aluminum grounding wires. Go the shortest, most direct route to a
real earth
grounding rod, or bury a piece of concrete reinforcement grid underground to
hook onto.