All

Can anyone point me to some simple designs for a home made 17 metre
antenna. I am looking for some simple half wave dipole type designs. I
have a short back yard and have struggled to put up a half wave G5RV
(managed in the end with a pole on side of the house) so it cant be
too long.

I have had a quick google search and did not come up with much.

Thanks for support

Andy

Can anyone point me to some simple designs for a home made 17 metre
antenna. I am looking for some simple half wave dipole type designs. I
have a short back yard and have struggled to put up a half wave G5RV
(managed in the end with a pole on side of the house) so it cant be
too long.
================================
Suggest you consider installing the above antenna as an inverted Vee,
using that pole with the 2 legs sloping to suitable points .


Frank GM0CSZ / KN6WH

On Sep 3, 3:56 am, Andiroo wrote:
All

Can anyone point me to some simple designs for a home made 17 metre
antenna. I am looking for some simple half wave dipole type designs.

468/18.1mhz=25.85 total feet for a half wave dipole. Divide by two for
each leg.
Feed with 50 ohm coax. Can't get much simpler than that. Can't get
much more
efficient either unless maybe you have to run 500 ft of coax. .
MK

wrote:
On Sep 3, 3:56 am, Andiroo wrote:
All

Can anyone point me to some simple designs for a home made 17 metre
antenna. I am looking for some simple half wave dipole type designs.

468/18.1mhz=25.85 total feet for a half wave dipole. Divide by two for
each leg.
Feed with 50 ohm coax. Can't get much simpler than that. Can't get
much more
efficient either unless maybe you have to run 500 ft of coax. .
MK
===================================
A current balun near dipole in the shape of ferrite cylinders or ,when
using RG58 type of coax, 7 - 9 windings of the coax on a larger toroid ,
will ensure no RF interference in the shack /house (eg no RF current
flowing along coax braid)
It is even better to use a balanced feeder instead of coax.
You then either need a matching unit for a balance feeder or use a balun
as described above near the transmitter ,connecting coax to feeder
through a dual plastic connecting block .

Personally I would always use a balanced feeder for any wire antenna.


Frank

"Highland Ham" wrote in message
...
wrote:
On Sep 3, 3:56 am, Andiroo wrote:
All

Can anyone point me to some simple designs for a home made 17 metre
antenna. I am looking for some simple half wave dipole type designs.

468/18.1mhz=25.85 total feet for a half wave dipole. Divide by two for
each leg.
Feed with 50 ohm coax. Can't get much simpler than that. Can't get
much more
efficient either unless maybe you have to run 500 ft of coax. .
MK
===================================
A current balun near dipole in the shape of ferrite cylinders or ,when
using RG58 type of coax, 7 - 9 windings of the coax on a larger toroid ,
will ensure no RF interference in the shack /house (eg no RF current
flowing along coax braid)
It is even better to use a balanced feeder instead of coax.
You then either need a matching unit for a balance feeder or use a balun
as described above near the transmitter ,connecting coax to feeder
through a dual plastic connecting block .

Personally I would always use a balanced feeder for any wire antenna.


Frank

Use 50 Ohm coax (RG8X, or better) unless you are in love with your antenna
tuner. I have tried it with and without a balun, and can't really tell any
difference. However, right now there is a 1:1 current balun at the feed
point. Trim the length for best SWR, 25.85 might be a bit long. I am using
#14 stranded/insulated wire.

Tam/WB2TT

On Sep 4, 7:04 pm, Highland Ham
wrote:


===================================
A current balun near dipole in the shape of ferrite cylinders or ,when
using RG58 type of coax, 7 - 9 windings of the coax on a larger toroid ,
will ensure no RF interference in the shack /house (eg no RF current
flowing along coax braid)


True. I usually just roll a choke from the coax. You don't need a
toroid for single band use. Or even 20-10 triband use for that
matter.. May have problems trying to do 80-10 well with a single
choke though.

It is even better to use a balanced feeder instead of coax.

Only if one intended to use it for other bands.
For single band use it would probably have a higher system efficiency
using coax, being most that run ladder line use tuners, etc
which add some loss to the system.

You then either need a matching unit for a balance feeder or use a balun
as described above near the transmitter ,connecting coax to feeder
through a dual plastic connecting block .

Dunno, I prefer to keep things simple. I would usually prefer a 50 ohm
radio, feeding a 50 ohm feedline, to a 50 ohm antenna.
Using a 50 ohm radio to a balun or tuner feeding a 450 ohm feedline to
a
50 ohm antenna seems kind of silly to me in comparison, if for a
single
band. But to each his own I guess..
BTW, I have compared the two, and the coax fed always slightly beat
the
ladder line/tuner fed system as far as efficiency on any HF band.
Of course, my coax runs are never over a 100 ft.. Often half that.
But when using a 989c tuner and ladder line, I could never get quite
the
system efficiency vs using coax, even using the most careful tuning
methods.
IE: using the minimum inductance needed to get a match.


Personally I would always use a balanced feeder for any wire antenna.

I'm usually about the opposite. The only time I use ladder line is
if
I intend to use a single wire for multiple bands. In that case, I can
see it.
Or if maybe I had to run a line several hundred feet, but I've
never had to do that yet..
But for single band use, it's going to be very hard to beat the
efficiency of a coax fed system with any type of ladder line system,
unless maybe you use the "Cecil" no tuner method.
And then.. it's more work, and the feedlines have to be off the
ground,
coiled just so, etc..... :/ The coax can be running anywhere. Even
in standing water.. On the lower/mid HF bands where I'm usually at,
the losses using coax are so low as to be a non issue. Trying to
beat the loss by using ladder line is not going to make any noticable
difference as far as the line itself. But.. Adding a matching device
almost always will. I can actually see it on receive just A/B
comparing using the S meter readings as an indicator.
I have no problems with ladder line, but the usual claims of
better performance isn't really true in the majority of cases on HF.
Often, quite the opposite, because of the matching devices usually
used with ladder line systems. Their loss usually overshadows the
slightly lower feedline loss.

Now, on UHF feeding say a TV corner reflector-yagi thing I use for
ATV, I prefer the twin lead.
Unless it gets wet, it's gonna beat most runs of coax as far as the
system loss. In that case, the matching devices don't overshadow
the higher more noticable coax losses at those higher frequencies.
MK

On Sep 5, 3:02 am, wrote:
On Sep 4, 7:04 pm, Highland Ham
wrote:



===================================
A current balun near dipole in the shape of ferrite cylinders or ,when
using RG58 type of coax, 7 - 9 windings of the coax on a larger toroid ,
will ensure no RF interference in the shack /house (eg no RF current
flowing along coax braid)

True. I usually just roll a choke from the coax. You don't need a
toroid for single band use. Or even 20-10 triband use for that
matter.. May have problems trying to do 80-10 well with a single
choke though.

It is even better to use a balanced feeder instead of coax.

Only if one intended to use it for other bands.
For single band use it would probably have a higher system efficiency
using coax, being most that run ladder line use tuners, etc
which add some loss to the system.

You then either need a matching unit for a balance feeder or use a balun
as described above near the transmitter ,connecting coax to feeder
through a dual plastic connecting block .

Dunno, I prefer to keep things simple. I would usually prefer a 50 ohm
radio, feeding a 50 ohm feedline, to a 50 ohm antenna.
Using a 50 ohm radio to a balun or tuner feeding a 450 ohm feedline to
a
50 ohm antenna seems kind of silly to me in comparison, if for a
single
band. But to each his own I guess..
BTW, I have compared the two, and the coax fed always slightly beat
the
ladder line/tuner fed system as far as efficiency on any HF band.
Of course, my coax runs are never over a 100 ft.. Often half that.
But when using a 989c tuner and ladder line, I could never get quite
the
system efficiency vs using coax, even using the most careful tuning
methods.
IE: using the minimum inductance needed to get a match.



Personally I would always use a balanced feeder for any wire antenna.

I'm usually about the opposite. The only time I use ladder line is
if
I intend to use a single wire for multiple bands. In that case, I can
see it.
Or if maybe I had to run a line several hundred feet, but I've
never had to do that yet..
But for single band use, it's going to be very hard to beat the
efficiency of a coax fed system with any type of ladder line system,
unless maybe you use the "Cecil" no tuner method.
And then.. it's more work, and the feedlines have to be off the
ground,
coiled just so, etc..... :/ The coax can be running anywhere. Even
in standing water.. On the lower/mid HF bands where I'm usually at,
the losses using coax are so low as to be a non issue. Trying to
beat the loss by using ladder line is not going to make any noticable
difference as far as the line itself. But.. Adding a matching device
almost always will. I can actually see it on receive just A/B
comparing using the S meter readings as an indicator.
I have no problems with ladder line, but the usual claims of
better performance isn't really true in the majority of cases on HF.
Often, quite the opposite, because of the matching devices usually
used with ladder line systems. Their loss usually overshadows the
slightly lower feedline loss.

Now, on UHF feeding say a TV corner reflector-yagi thing I use for
ATV, I prefer the twin lead.
Unless it gets wet, it's gonna beat most runs of coax as far as the
system loss. In that case, the matching devices don't overshadow
the higher more noticable coax losses at those higher frequencies.
MK

All

Welll once again this proves the theory - two amateurs = three opions.
However, this is a very useful discussion and the 25ft (ish) simple
dipole seems to be the easiest thing to work with and the length is
very achieveable in the space. I therefore have to get to a decision
on what i use in the centre. I estimate from the centre of the antenna
to the shack would be approx 50-75ft max even if i run it neatly
around the walls. I am happy to use an ATU to achieve a perfect match.
So what do i go for?

Secondly, is there an optimal height. My half size G5RV is at the top
of the 30 ft pole so this would need to be below that? Also does it
matter if it is on a slight incline with the lowest part closest to
the house?

Many thanks for all the great advice

Andy

Highland Ham wrote:
wrote:
On Sep 3, 3:56 am, Andiroo wrote:
All

Can anyone point me to some simple designs for a home made 17 metre
antenna. I am looking for some simple half wave dipole type designs.
468/18.1mhz=25.85 total feet for a half wave dipole. Divide by two
for
each leg.
Feed with 50 ohm coax. Can't get much simpler than that. Can't get
much more
efficient either unless maybe you have to run 500 ft of coax. .
MK
===================================
A current balun near dipole in the shape of ferrite cylinders or ,when
using RG58 type of coax, 7 - 9 windings of the coax on a larger toroid ,
will ensure no RF interference in the shack /house (eg no RF current
flowing along coax braid)
It is even better to use a balanced feeder instead of coax.
You then either need a matching unit for a balance feeder or use a balun
as described above near the transmitter ,connecting coax to feeder
through a dual plastic connecting block .

Personally I would always use a balanced feeder for any wire antenna.

That reel of cable marked "balanced feeder" is a myth!

Twin feeder is not self-balancing. It never will be "balanced" unless
your installation has MADE it balanced.

As it comes off the reel, twin feeder is capable of carrying unwanted
common-mode currents just as easily as the intended differential mode.
All practical antenna installations are unsymmetrical (either the
antenna, its environment or both) so there will always be some unwanted
common-mode current. Common-mode current will cause the feedline to
radiate and will conduct unwanted RF back into the shack, where it often
flows through into your house wiring... all of which is regarded as a
Bad Thing.

Twin feeder will only become more "balanced" if you - the user - have
taken some positive action to suppress the common-mode current. When you
install a typical link-coupled ATU designed for "balanced" feedline, the
low capacitance across the link coupling creates a high impedance to
block the entry of common-mode current into the shack. A suitable balun
would also create a high impedance to block the common-mode current, so
in this case you would need a choke balun (aka feedline choke or line
isolator).

When you insert this high impedance in the path of the common-mode
current, the current distribution over the whole antenna-feedline system
readjusts itself to take account of this new factor. The new current
distribution will be forced towards better symmetry on the antenna
itself, with a smaller common-mode current on the feedline... so the
feedline has now become more "balanced".

What should take the credit for this good result? It was the ATU or
balun that you installed - so all the credit goes to you. The so-called
"balanced" feeder deserves no credit at all, for it did nothing more
than react to the change that you made.

Many people confuse the cause and effect here. If they believe that the
feedline is in some sense "ready balanced", they will install a suitable
ATU or balun "because that's what balanced feedline needs". Very often,
it all works out OK because they have done exactly the right things,
even though they misunderstand the reasons. But if it doesn't quite
work, and something more is needed to suppress the common-mode currents,
this wrong thinking comes completely unstuck.

Coaxial feedline has the major advantage that you can insert a choke
balun right at the feedpoint, which substantially prevents common-mode
current from being launched onto the outer surface of the cable[ 1]. The
entire current distribution will then change, to take account of the
fact that you have forced a minimum in the common-mode current at the
feedpoint. Because the feedline is in the near field of the antenna,
radiative coupling may cause common-mode current to reappear on the
surface of the coax, starting with a new maximum a quarter-wavelength
down the line from the feedpoint. But the size of this maximum is
generally much smaller, and so too will be the residual current arriving
at the shack - where, if needed, you can insert a second feedline choke.
In really desperate situations, you can have as many common-mode chokes
along the coax as you like.

With twin feeder, you don't have those options. Your only practical
options are at the ATU, or where the twin feeder makes a transition into
coax. That restriction makes it even less likely that twin feeder will
ever be truly "balanced".

Bottom line: twin feeder has many advantages, especially for multiband
operation... but automatic balance certainly isn't one of them.




[1] In coaxial cable, the inside and outside of the shield behave as
two independent conductors for RF current, giving a total of three
current pathways. The centre conductor and the inside of the shield have
very tight coupling between their electric and magnetic fields, which
ensures that their RF currents are exactly equal and opposite (the
differential mode) and their net field on those two conductors remains
completely inside the cable. The third conductor is the outside of the
shield, and behaves a a single fat wire carrying an RF current that is
totally independent of what's happening inside. Although strictly
speaking this is not a common-mode current, that's what it is generally
called by analogy with twin feeder.



--

73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Ian White GM3SEK wrote:

Personally I would always use a balanced feeder for any wire antenna.
===========
That reel of cable marked "balanced feeder" is a myth!

Twin feeder is not self-balancing. It never will be "balanced" unless
your installation has MADE it balanced.

As it comes off the reel, twin feeder is capable of carrying unwanted
common-mode currents just as easily as the intended differential mode.
All practical antenna installations are unsymmetrical (either the
antenna, its environment or both) so there will always be some unwanted
common-mode current. Common-mode current will cause the feedline to
radiate and will conduct unwanted RF back into the shack, where it often
flows through into your house wiring... all of which is regarded as a
Bad Thing.

Twin feeder will only become more "balanced" if you - the user - have
taken some positive action to suppress the common-mode current. When you
install a typical link-coupled ATU designed for "balanced" feedline, the
low capacitance across the link coupling creates a high impedance to
block the entry of common-mode current into the shack. A suitable balun
would also create a high impedance to block the common-mode current, so
in this case you would need a choke balun (aka feedline choke or line
isolator).

When you insert this high impedance in the path of the common-mode
current, the current distribution over the whole antenna-feedline system
readjusts itself to take account of this new factor. The new current
distribution will be forced towards better symmetry on the antenna
itself, with a smaller common-mode current on the feedline... so the
feedline has now become more "balanced".
etc
========================
Ian , You are right ,I should have used the term 'twin feeder' instead
of 'balanced feeder'. Tnx for the correction.

In my situation the twin feeder from the dipole comes through a double
concrete block wall ,runs over the loft ,through the plaster board
ceiling (meeting very few metal parts) into the shack . No RF
interference anywhere in the house ,operating with approx 100 W PEP on
any of the HF bands between 3.5 - 29.7 MHz
I intend to make an RF current probe ( 2 half ring ferrite parts -diode
-connected to a DVM) to see whether there is any unbalance current .
This is more sensitive than taking the difference between measuring
individual currents in the feeder lines.

My next activity will be to extend the feeder to a suitable length
(Cecil style) such that I 'll be able also to operate on Top Band (1.8
-2.0 MHz) ,the dipole being 2 times 21.35 metres (2 x 70 feet)
With a twin feeder the actual length of the dipole is not critical ,
however in order to get a reasonably high current (low impedance) at the
matching unit (of the E-Zee Match variety and the like) it is important
that the total length of half the dipole plus the feeder is about an odd
number of quarter wave lengths at the operating frequency .
The velocity factor of the 450 Ohms twin feeder I use is published to be
0.99 ,so for the above purpose it can be taken as 1.
This total length is more critical at the lower frequency HF bands
because of the higher wavelength.

Frank GM0CSZ / KN6WH

wrote:
On Sep 3, 3:56 am, Andiroo wrote:
All

Can anyone point me to some simple designs for a home made 17 metre
antenna. I am looking for some simple half wave dipole type designs.

468/18.1mhz=25.85 total feet for a half wave dipole. Divide by two for
each leg.
Feed with 50 ohm coax. Can't get much simpler than that. Can't get
much more
efficient either unless maybe you have to run 500 ft of coax. .
MK



------------------


MK has given the proper way to do it - but then there is "MY" way. G

I have one of those cheap ($200) metal sheds that I bought from Home
Depot a while back. The kind that takes you and someone else nearly an
entire weekend to assemble because of all of the screws.

Well, mine leaks water, but it is still better than having nothing at
all...I think.

Anyway, if you happen to have one of these all metal sheds, plop a
magmount, or a through the metal mount, with a 17 meter Hamstick on it
and call it a done deal. Will it work as well as a dipole? In some
directions yes and in some directions no. You won't equal the dipole's
broadside radiation, but you can stomp the grape juice out of its end
point radiation. G

If the band is open, you don't need a fancy antenna or a lot of power.
If the band isn't open, no one is going to hear you even if you are
running full legal limit power output. I run my little Yaesu FT-817ND
QRP rig on this set up and it talks around the world - when the bands
are open.

The good thing about this set up, if you're a digital and CW man, in
addition to phone, is that you can replace the 17 meter Hamstick with
any other band Hamstick and still have some fun. PSK-31, Amtor and
Pactor with 5 thundering watts and a Hamstick will yield amazing
results. The key is patience and knowing which Hamstick to put in place.

Gonna have a terrible storm and you're worried about your Hamstick?
Well, you can always remove it - OR, you can buy ten quick disconnects
off'n a fellow on eBay for a ridiculously low price and fold over and
lash down your precious Hamstick.

Anyone can talk all over the world with the best antenna, highest power
output, etc. QRP can bring back the excitement of operating once again,
assuming you're not a 75 meter rag chewer. For the latter, they truly
need the best antenna and amp in order to be heard. Just the nature of
the band. However, scoot down to 80 meters and once again, QRP and
minimal antennas gain a great measure of equal footing.

Ed, NM2K