--- In topband-helical@..., John Bastin <bastinj@...> wrote:
>
> For comparison, my vertical is using a 20-foot (slightly over 6 meter)
> piece of 2.5-inch (6.35 centimeter) PVC tubing, wound with about 260
> feet (about 80 meters) of number 12 insulated wire with three 18-foot
> (5.5-meter) wires extending out from the top for a capacitance hat,
> ground-mounted over 54 radials reaching to the property lines, lengths
> ranging from 45 feet (13 meters) to 130 feet (40 meters).
>
> I'm running 500 watts; so far I've worked 46 US states (missing
> Wyoming and North Dakota; Alaska and Hawaii are "countries" in this
> contest) and 36 countries. best distances from here seem to be OM, HA
> and 9A contacts, all around 4600 miles (about 7400 kilometers). The
> Hawaiian contact is about the same distance in the other direction.
>
> I've been very happy with the performance of the helical vertical this
> 160-meter season; it's done a very good job on my relatively small
> city lot.
>
> 73,
>
>
> John Bastin K8AJS
> bastinj@...

I'm sure I'm not the only one to ask this - how do you fit a 130 foot
radial on a "small city lot"?  The UBC standards in the US now define
  "standard city lot" as 4,000 square feet, which often is 40 X 100
feet, the goal being to fit maximal number of houses on a
street...short frontage.

On the other hand, I know about over-sized radials.  When I had my
last city lot (50 X 70 feet), I was able to string a few radials along
the lower support boards of neighbors' fences, and had one radial that
was over 200 feet long - went across four lots.  Naturally, things
always go better if you're on good terms with the neighbors.

I was only able to get into the contest briefly at the very start, and
I had not time this year to put together anything specific for 160.  I
was using a standard 80 meter dipole (I'm no longer on a city lot, so
I have room for such), at about 30 feet.  My tuner was not up to the
task, so my rig was operating into a 6:1 SWR and cutting back to about
15 watts, and obviously a good bit of that was reflected back to the
rig.  I am pleased to say that one of my QSOs was a full
coast-to-coast, from Oregon to Maine.  A real success for CW and the
good ears of those Northeast contest teams.

Dave W8NF

On Jan 27, 2008, at 13:08 , nu7t wrote:

> Fellow Radiators:
>
> The CQ 160m contest is over.

Gee, it's only about 2000Z here. Still about four hours to go in the
contest. I figure to get another 2 and a half hours of operation or so
as it gets closer to sunset. You're about three hours west of me (I'm
in Ohio), so you're right, you're probably out of darkness for the
rest of the contest period...:-)

>  I used the 160m helical.  About 70' (21
> meters) of house wire wound around a 10' tall and 1 1/2 " (3.8cm)
> diameter plastic pipe.  From the top of the pipe 70' more of wire was
> strung across the yard and garden never more than 3 meters high.
>     Under the plastic pipe were 4 radials ( a couple at 10m and a
> couple at 20m long) winding around the yard and garden.  The radials
> were buried under snow.

For comparison, my vertical is using a 20-foot (slightly over 6 meter)
piece of 2.5-inch (6.35 centimeter) PVC tubing, wound with about 260
feet (about 80 meters) of number 12 insulated wire with three 18-foot
(5.5-meter) wires extending out from the top for a capacitance hat,
ground-mounted over 54 radials reaching to the property lines, lengths
ranging from 45 feet (13 meters) to 130 feet (40 meters).

>
>     Running at 5 watts, the antenna covered a radius of 800km with
> several contacts out to 1000km.  Please remember, these contacts were
> with real contest stations.  I tried increasing power to make contacts
> further away, but to no avail.
>     I heard stations as distant as 3200km.
> This is fun

I'm running 500 watts; so far I've worked 46 US states (missing
Wyoming and North Dakota; Alaska and Hawaii are "countries" in this
contest) and 36 countries. best distances from here seem to be OM, HA
and 9A contacts, all around 4600 miles (about 7400 kilometers). The
Hawaiian contact is about the same distance in the other direction.

I've been very happy with the performance of the helical vertical this
160-meter season; it's done a very good job on my relatively small
city lot.

73,


John Bastin K8AJS
bastinj@...

Fellow Radiators:

The CQ 160m contest is over.  I used the 160m helical.  About 70' (21
meters) of house wire wound around a 10' tall and 1 1/2 " (3.8cm)
diameter plastic pipe.  From the top of the pipe 70' more of wire was
strung across the yard and garden never more than 3 meters high.
      Under the plastic pipe were 4 radials ( a couple at 10m and a
couple at 20m long) winding around the yard and garden.  The radials
were buried under snow.
      Running at 5 watts, the antenna covered a radius of 800km with
several contacts out to 1000km.  Please remember, these contacts were
with real contest stations.  I tried increasing power to make contacts
further away, but to no avail.
      I heard stations as distant as 3200km.
This is fun
      Now my 40m helical will replace the 160m helical for some everyday
use.  My HB 40m helical has 21 meters of house wire on a 2m piece of
plastic pipe with a pie tin top hat.
Good Luck everyone !
Steve, NU7T

DR OM Steve ,NU7T ,please send to me scheme ,draft for
antenna helical 160m from G3YCC ,that i try build one.
73 de 9a4zz ,Mladen





--- nu7t <nu7t@...> wrote:

> Fellow Radiators:
>
> My name is Steve, NU7T.
> I built a 160m helical from a description Frank,
> G3YCC,
> had posted, somewhere.  I used this antenna for a
> 160m contest last
> month working out to 1600 km with 5 watts.
> Some other local Hams are considering building this
> antenna.
>      While searching for another group, I stumbled
> into you folks.
> Over the next few days I will try to absorb previous
> postings.
>
> Steve, NU7T
> Sparks,  Nevada,  U.S.A.
>
>



      
________________________________________________________________________________\
____
Never miss a thing.  Make Yahoo your home page.
http://www.yahoo.com/r/hs

Fellow Radiators:

My name is Steve, NU7T.
I built a 160m helical from a description Frank, G3YCC,
had posted, somewhere.  I used this antenna for a 160m contest last
month working out to 1600 km with 5 watts.
Some other local Hams are considering building this antenna.
      While searching for another group, I stumbled into you folks.
Over the next few days I will try to absorb previous postings.

Steve, NU7T
Sparks,  Nevada,  U.S.A.

I can hardly believe it is a year since I posted my first message on
this site. I have just updated the description so hopefully people
wanting to Homebrew a Topband Helical find things easier to understand.
          I have posted quite a few photos & hope I have helped a few
people to get on Topband.
                          I am still enjoying using my own Helical. if
anyone has any photos or other info to put on the site, please do so. I
have also had some good success lately with a Homebrew, Topband Mobile
Antenna.
          73,
             Phil.   M0VEY

You can see some pictures of my helical windom here
http://tom.nc4tc.googlepages.com/helicalwindom

----- Original Message -----

From: Phil

To: topband-helical@...

Sent: Monday, November 12, 2007 12:15 AM

Subject: [topband-helical] Re: HELICAL

--- In topband-helical@yahoogroups.co.uk, "stefan allum G1NRL"
<stef@...> wrote:
>
> Forgive me for being for dumb,,, does G4SEF or M0VEY biuld these
> helicals to order? i'd like one. !
>
> stefan
>

This is a site for HOME-BREWING antennas. I.E. looking at some of
the pics, designs & info on here & building one yourself. The few
antennas that I have built were experimental antennas that were GIVEN
away to close friends. There is nothing commercial available on this
site.
Regards,
Phil. M0VEY

--- In topband-helical@..., "stefan allum G1NRL"
<stef@...> wrote:
>
> Forgive me for being for dumb,,, does G4SEF or M0VEY biuld these
> helicals to order?  i'd like one. !
>
> stefan
>

   This is a site for HOME-BREWING  antennas. I.E. looking at some of
the pics, designs & info on here & building one yourself. The few
antennas that I have built were experimental antennas that were GIVEN
away to close friends. There is nothing commercial available on this
site.
       Regards,
               Phil.   M0VEY

Forgive me for being for dumb,,, does G4SEF or M0VEY biuld these
helicals to order?  i'd like one. !

stefan

----- Original Message -----

From: Tom Conally

To: topband-helical@...

Sent: Sunday, November 11, 2007 9:49 PM

Subject: [topband-helical] new antenna operational

I finished my helically wound windom antenna and worked Cuba(5x8
report) today on 20 meters ssb with 100 watts. The antenna is an 80-20
off center feed with a 9-1 ferrite toroid balun (a kit) into 50 ohm
coax and an air core 1-1 choke balun. It is wound on 1.5 inch pvc
conduit which is laying on a privacy fence support about 5 feet off
the ground. The length of the conduit is 20 feet total with a total
wire length of 137 feet. There is very little local interference. My
IC 738 tuner tunes it to 1-1 swr on everything up through 160. I am
very pleased for it is a stealth antenna in my small private courtyard
(townhouse). I used a MFJ 204b antenna bridge to determine the
impedance--- about 450 ohms therefore the 9-1 balun.
I am going to write construction article with pics.

This antenna was completely experimental as I could find no info on it
except to combine windom info with slinky antenna info. Thank goodness
it worked out!

73
NC4TC

----- Original Message -----

From: Tom Conally

To: topband-helical@...

Sent: Sunday, November 11, 2007 9:49 PM

Subject: [topband-helical] new antenna operational

I finished my helically wound windom antenna and worked Cuba(5x8
report) today on 20 meters ssb with 100 watts. The antenna is an 80-20
off center feed with a 9-1 ferrite toroid balun (a kit) into 50 ohm
coax and an air core 1-1 choke balun. It is wound on 1.5 inch pvc
conduit which is laying on a privacy fence support about 5 feet off
the ground. The length of the conduit is 20 feet total with a total
wire length of 137 feet. There is very little local interference. My
IC 738 tuner tunes it to 1-1 swr on everything up through 160. I am
very pleased for it is a stealth antenna in my small private courtyard
(townhouse). I used a MFJ 204b antenna bridge to determine the
impedance--- about 450 ohms therefore the 9-1 balun.
I am going to write construction article with pics.

This antenna was completely experimental as I could find no info on it
except to combine windom info with slinky antenna info. Thank goodness
it worked out!

73
NC4TC

--- In topband-helical@..., "Tom Conally" <nc4tc-
tom@...> wrote:
>
>
>
> I finished my helically wound windom antenna and worked Cuba(5x8
> report) today on 20 meters ssb with 100 watts. The antenna is an 80-
20
> off center feed  with a 9-1 ferrite toroid balun (a kit) into 50 ohm
> coax and an air core 1-1 choke balun. It is wound on 1.5 inch pvc
> conduit  which is laying on a privacy fence support about 5 feet off
> the ground.  The length of the conduit is 20 feet total with a total
> wire length of 137 feet. There is very little local interference. My
> IC 738 tuner tunes it to 1-1 swr on everything up through 160. I am
> very pleased for it is a stealth antenna in my small private
courtyard
> (townhouse). I used a MFJ 204b antenna bridge to determine the
> impedance--- about 450 ohms therefore the 9-1 balun.
> I am going to write construction article with pics.
>
> This antenna was completely experimental as I could find no info on
it
> except to combine windom info with slinky antenna info. Thank
goodness
> it worked out!
>
> 73
> NC4TC
>

Hi Tom,
        this sounds very interesting. I certainly look forward to the
construction article & the pictures.
    I  have an 80m - 10m Radioworks carolina Windom as my main
multiband antenna . It is the cw160s but not very good tx on 160m.
   Fortunately I have my Helical for that.

     Thanks for writing Tom.
                             Regards,
                                     Phil.    M0VEY

I finished my helically wound windom antenna and worked Cuba(5x8
report) today on 20 meters ssb with 100 watts. The antenna is an 80-20
off center feed  with a 9-1 ferrite toroid balun (a kit) into 50 ohm
coax and an air core 1-1 choke balun. It is wound on 1.5 inch pvc
conduit  which is laying on a privacy fence support about 5 feet off
the ground.  The length of the conduit is 20 feet total with a total
wire length of 137 feet. There is very little local interference. My
IC 738 tuner tunes it to 1-1 swr on everything up through 160. I am
very pleased for it is a stealth antenna in my small private courtyard
(townhouse). I used a MFJ 204b antenna bridge to determine the
impedance--- about 450 ohms therefore the 9-1 balun.
I am going to write construction article with pics.

This antenna was completely experimental as I could find no info on it
except to combine windom info with slinky antenna info. Thank goodness
it worked out!

73
NC4TC

--- In topband-helical@..., "Jeff Kinzli N6GQ"
<jeff@...> wrote:
>
> Hey gents,
>
> I've been thinking of building some helical dipoles, and using them
as
> vertical dipoles, and if that works out, then taking a few of them
and
> phasing them into a 4-square arrangement.
>
> I wonder, my guess is that the tighter the helix, the less gain I'd
> see under a full-size dipole. I also understand that I'd need more
> wire than the traditional dipole formula calls for (468/f).
>
> Sorry if this seems like a stupid question, I'm just now looking for
> materials and simulations of this but haven't found anything on the
> web yet.
>
> Anyone try this? I've used vertical dipoles on 40M and they work
quite
> well, even without any radials.
>
> 73,
>
> Jeff N6GQ
>
    Hi Jeff,
            thanks for your interest in the group. Sorry I can't
answer your question as I never tried anything like this before. Also
I don't have that sort of room for antennas. My garden is 50 foot
wide & 65 foot long. I also have 20 foot to the front of my house.
Biggest antenna here is an 80m Windom which just fits in.
     If you do try the arrangement you mention, please call back in
this group & let us know the results.
      Regards,
              Phil.
                   M0VEY    East Yorkshire  England.

Hey gents,

I've been thinking of building some helical dipoles, and using them as
vertical dipoles, and if that works out, then taking a few of them and
phasing them into a 4-square arrangement.

I wonder, my guess is that the tighter the helix, the less gain I'd
see under a full-size dipole. I also understand that I'd need more
wire than the traditional dipole formula calls for (468/f).

Sorry if this seems like a stupid question, I'm just now looking for
materials and simulations of this but haven't found anything on the
web yet.

Anyone try this? I've used vertical dipoles on 40M and they work quite
well, even without any radials.

73,

Jeff N6GQ

My helical is coax fed. The base of the helical is 37' in the air.  If
you look at the picture in the photos section called "Feeding The
Helical", this shows the feed to the helical. The centre of the coax
feeds the helical. The braid side of the coax needs to be returned to
the earth ground system. This is done by connecting a piece of wire to
the crimp terminal on the lightning arrestor & in my case running 38'
of wire back down to one of the ground spikes.
                                   This then lets the helical see the
earth system, the copper tank & the 120' counterpoise.
Regards,
        Phil.   m0vey

My ground system consists of four 4' earth spikes which are each
connected to the 3' copper tank that is buried 4' in the ground.  I
also use a 120' length of wire connected to one of the earth spikes &
running underneath the top loading wire. This wire runs 60 foot down
the garden, before coming back on itself & still staying underneath the
top loading wire.
                                                     I also have a wire
from one of the ground spikes croc clipped onto the bottom strengthning
wire on my garden fence. This wire runs a few hundred feet along the
fence that seperates my garden & others from a field. If I had more
room to run radials I guess that might help. However I don't have room
for any more & I'm happy with the fact that installing the copper tank
dropped my background noise level from S9 to S7. It also improved the
TX.

Regards,
               Phil.     m0vey

Not for topband, but I'm working on a 3 element helical vertical
dipole yagi array for 40M. I wonder if anyone else has tried this?
That's a mouthfull, isn't it? :)

Jeff N6GQ

On 6/28/07, Phil <m0vey@...> wrote:
>
>
>
>
>
>
>   Not a great deal of activity during the summer. Although, I am still
>  on 1.972 every evening except Saturday 6.30pm onwards, for an hour or
>  so. (1730hrs GMT)
>                   I wonder if anyone has homebrewed a Helical ready for
>  the Topband winter season? I am still having good results with my
>  latest Helical & the background noise level is still relatively low.
>     Not heard much activity from the Hebridean Net on 1.957    so will
>  look forward to being able to operate in darkness during the winter
>  months.
>           Good luck to all who are experimenting with antennas for
>  160m.  I would be interested to hear from anyone with any success of
>  making a Helical or other antenna for 160m
>     Regards,
>              Phil.     m0vey
>
>

On Jun 28, 2007, at 4:11 PM, Phil wrote:

>   Not a great deal of activity during the summer. Although, I am still
> on 1.972 every evening except Saturday 6.30pm onwards, for an hour or
> so. (1730hrs GMT)

Doesn't help me much, it's early afternoon here (1:30 PM) and I'm at
the office...:-)

>
>                  I wonder if anyone has homebrewed a Helical ready for
> the Topband winter season? I am still having good results with my
> latest Helical & the background noise level is still relatively low.

My helical is lying in the back yard right now, I'll be getting to
work on it to get it ready for the season as soon as I get my quad
back to the top of the tower, and that project's over.

>    Not heard much activity from the Hebridean Net on 1.957    so will
> look forward to being able to operate in darkness during the winter
> months.

I *did* manaage to work VY2ZM from here in Ohio last evening on
topband, using my G5RV. The band isn't dead yet.

>          Good luck to all who are experimenting with antennas for
> 160m.  I would be interested to hear from anyone with any success of
> making a Helical or other antenna for 160m
>    Regards,
>             Phil.     m0vey

Hope to see you on topband this coming season...:-)

73,


John Bastin, K8AJS
bastinj@...

Not a great deal of activity during the summer. Although, I am still
on 1.972 every evening except Saturday 6.30pm onwards, for an hour or
so. (1730hrs GMT)
                  I wonder if anyone has homebrewed a Helical ready for
the Topband winter season? I am still having good results with my
latest Helical & the background noise level is still relatively low.
    Not heard much activity from the Hebridean Net on 1.957    so will
look forward to being able to operate in darkness during the winter
months.
          Good luck to all who are experimenting with antennas for
160m.  I would be interested to hear from anyone with any success of
making a Helical or other antenna for 160m
    Regards,
             Phil.     m0vey

--- In topband-helical@..., "Phil" <m0vey@...> wrote:
>
>    The latest antenna is 2.5mm diameter, as opposed to 1.5mm on the
mk1.
> This means the antenna is just over 3' in length now as opposed to
more
> than 5' in length on the mk1.  I used 65' of wire, which equated to
100
> turns on the MK2 as opposed to 142 turns on the mk1.
>    Regards,
>            Phil.    m0vey
>
  Correction to above.

THE LATEST ANTENNA IS 2.5" diameter as opposed to 1.5" on the mk1.

Hi All,
        I have just posted some new pics on the site. I made a new
Helical at the weekend. The previous one snapped the hard drawn top
loading wire at the top of the Helical. I have used stranded 1.5mm
covered wire which is more flexible on the latest antenna.
    The latest antenna is 2.5mm diameter, as opposed to 1.5mm on the mk1.
This means the antenna is just over 3' in length now as opposed to more
than 5' in length on the mk1.  I used 65' of wire, which equated to 100
turns on the MK2 as opposed to 142 turns on the mk1.
    Regards,
            Phil.    m0vey

On Nov 29, 2006, at 2:55 PM, g7lrr001 wrote:

> In one of their older books, ARRL featured a helical which
> had approximately 1/2 wavelength of wire on the form. This
> article said the antenna had a low impedance so the project
> featured an L-network tuner to step 50 ohms down to the
> lower Z of the antenna. Why the matching network was needed
> I don't know... many mobile helical and homemade helical
> antenna don't seem to need the impedance stepdown, and if
> they do, why not make a simple broadband ferrite RF
> transformer with taps?

This was probably the article I worked from on the original
80-meter version, back in the early 70s.

>
> The 1/2 wavelength of wire in some helical designs does not
> give you the performance of a 1/2 wave vertical, it's just
> that 1/2 wavelength and other lengths give an impedance
> close to 50 ohms. The antenna will perform like what it is,
> a short 1/4 wave vertical. The tradeoffs for short physical
> length are a little less efficiency and a narrower SWR
> bandwidth.... you're probably talking 15 Khz on 160 meters,
> 30 khz on 80 meters.

I can attest to the narrow bandwidth; my 160-meter antenna
resonates at about 1828 kHz, I'm using a tuner to get coverage
from the bottom of the band up through the DX window. As I
move across the band, I have to readjust the tuner about
every 10 kHz.

>
> In a basic experiment, I've tried winding a helical for a
> low band (40 or 80) and then feeding it with a simple
> L-network tuner (impedance stepup type) to get it to work on
> all higher bands. I don't think this worked too well,
> perhaps the helical winding was acting as an RF choke on
> some higher frequencies? Has anyone tried this?

I can get a match on my vertical on 80 meters; judging by
performance, though, it apparently radiates about as well
as a wet noodle in that frequency range.

>
> I've noticed that some helicals may have two resonant
> points, the fundamental and approximately a third harmonic.

I haven't tried that; maybe I should play with my 160-meter
antenna on 40?

> I've only briefly tried tapping a helical. This idea is very
> similar to the "Outbacker" antenna, a helical mobile whip
> with taps for Ham and (optional) marine bands. The user
> shorts the unused winding with a jumper and banana plug,
> fine tuning is done by a steel rod on the top of the
> antenna.
>
> For those building an 80 or 160 meter helical, it might be
> worthwhile to experiment with taps on the windings for low,
> mid and high portions of the lower bands. You probably won't
> need multiple taps for the higher bands.

That might be an interesting experiment to play with next
summer; I would have to use different wire, or find some
pins or something that would go through the insulation on
my wire.

>
> I've found that helicals, like all short verticals need a
> good RF ground. If you build a helical over one RF ground
> system and then move it to a different RF ground you may
> have to change the taps on the winding.

I've got 32 ground radials of various lengths lying on the
ground around the antenna, running from the antenna, roughly
in the center of the yard to the property lines in all
directions. If it stops raining sometime this weekend, I'll
try to take some pictures to post.

73,


John Bastin K8AJS
bastinj@...

On Nov 29, 2006, at 2:51 PM, g7lrr001 wrote:

> Hi All
>
> I found a good write up on PVC and Coils which i will post
> here for all to see.
>
> Generally PVC is quite adequate for antenna work, but a few
> precautions are necessary.
>
> First of all, contrary to common knowledge, it actually does
> have reasonable RF properties. Most samples I have have
> looked at have dielectric constants of between 3.3 and 3.7
> at normal temperatures and dielectric voltage breakdowns of
> 350 volts/millimeter are common.
>
> Since I am involved in manufacturing a line of antennas that
> use this material, I did a fair amount of investigating. One
> of the important factors to consider when using PVC for
> antennas is whether it can take the Ultraviolet radiation
> from the sun. There are chemicals that can be added to the
> compound to protect it and many manufacturers do this
> routinely, since one never knows where the stuff will end
> up. This is particularly true of present day white PVC. Not
> all are protected, but one brand name that comes to mind
> that is: Bristol Pipe PVC, schedule 40.

I'm using white PVC, don't know what brand it is. My contractor
got me a piece while he was working on the addition to our
house.

>
> Where one can get into trouble with PVC with RF is in the
> helical antenna arena. Here we have an antenna that can
> resemble a Tesla coil, if there is sufficient power and
> inductance. With very tight windings and not much radiating
> surface considerable voltages can be developed. The highest
> voltage point will be at the end of the antenna. With even
> moderate powers; 50 to 100 watts, several thousand volts can
> be developed.

I'm running 500 watts into it from my small amplifier. I've been
thinking about putting a little garden-edge type fence around
it just for safety's sake; don't want to fry one of the
neighbors if they happen to be trespassing in my yard...:-)

>
> Take for example the case where a helical antenna developed
> 1000 volts at the end. The formula for power is P= E^2/R (
> Power is E squared over R). 1000 Volts squared over perhaps
> 100,000 ohms can be 10 watts! If this power is concentrated
> in a rather small area it will start to heat the plastic.

Frankly, I think that a helical antenna mounted outside in the
winter, using number 14 wire on a 2-inch form should be able
to dissipate 10 watts of power with little difficulty.

> This heat will further reduce the voltage resistance of the
> plastic, increasing the heat and further deteriorating its
> ability to resist voltage breakdown.
>
> The estimate of 100,000 ohms was pulled out of the air.
> Actually, it is usually higher, but contaminants in the
> plastic and gas molecules in the material can drastically
> affect the outcome. Regional heating can become severe.
>
> DC voltages do not have quite the same effect on these
> materials because of the reaction the plastic has to AC.
> This is in great part due to the inherent "dipolar"
> characteristic of the plastic. AC tends to force the
> molecular dipole characteristic of the material to react to
> the direction change of the current, this is not resistance,
> but can have a similar end result.
>
> The bottom line here is that these problems only occur at
> very high voltages and particularly at elevated temperature.
> When used for a coil in a bottom loaded, or even
> center-loaded, the voltages remain low enough that there
> should be little reason for concern.

The helical antenna has what, linear loading over the length of
the form?

>
> Varnished wood works well because it has very little dipolar
> effect, although it does have some. The problem with the
> wood is that as the varnish deteriorates over time, moisture
> will find its way in and dramatically upset the apple cart.

I'm really hoping the PVC version of this antenna only has to last
for one winter season; I really want to go back to wood next
year. I typically apply three coats of spar varnish on wood that
is going to be living outside.

>
> When I wrote the article for QST in July, the staff at the
> League had me submit some test data because they had the
> same concerns. We also submitted a 144 MHz JadePole antenna
> for testing. They were pleased with the results and found no
> problems. At reasonable power levels there is little need
> for concern, especially at QRP levels. Once again QRP can
> have an advantage.

Life's too short for QRP.

>
> Many of the PVC materials can be used out beyond 1 GHz
> without concern.
>
> Dennis, K1YPP
>
> Jade Products, Inc.
>
> Engineer
>
> Well i have made and know many now with the Helicals wound
> on PVC pipe and Running 400 Watts for hours at time with NO
> melting or Burning.
>
> 73's Andy G7LRR

I've been running 500 watts into my antenna since it went up in
early October and have seen no problems so far.

73,


John Bastin K8AJS
bastinj@...

In one of their older books, ARRL featured a helical which had
approximately
1/2 wavelength of wire on the form.  This article said the antenna
had a low
impedance so the project featured an L-network tuner to step 50 ohms
down to
the lower Z of the antenna.  Why the matching network was needed I
don't
know... many mobile helical and homemade helical antenna don't seem
to need
the impedance stepdown, and if they do, why not make a simple
broadband
ferrite RF transformer with taps?

The 1/2 wavelength of wire  in some helical designs does not give
you the
performance of a 1/2 wave vertical, it's just that 1/2 wavelength
and other
lengths give an impedance close to 50 ohms.  The antenna will
perform like
what it is, a short 1/4 wave vertical.  The tradeoffs for short
physical
length are a little less efficiency and a narrower SWR bandwidth....
you're
probably talking 15 Khz on 160 meters, 30 khz on 80 meters.

In a basic experiment, I've tried winding a helical for a low band
(40 or 80)
and then feeding it with a simple L-network tuner (impedance stepup
type) to
get it to work on all higher bands.  I don't think this worked too
well,
perhaps the helical winding was acting as an RF choke on some higher
frequencies?  Has anyone tried this?

I've noticed that some helicals may have two resonant points, the
fundamental
and approximately a third harmonic.

I've only briefly tried tapping a helical.  This idea is very
similar to the
"Outbacker" antenna, a helical mobile whip with taps for Ham and
(optional)
marine bands.  The user shorts the unused winding with a jumper and
banana
plug, fine tuning is done by a steel rod on the top of the antenna.

For those building an 80 or 160 meter helical, it might be
worthwhile to
experiment with taps on the windings for low, mid and high portions
of the
lower bands.  You probably won't need multiple taps for the higher
bands.

I've found that helicals, like all short verticals need a good RF
ground.  If
you build a helical over one RF ground system and then move it to a
different
RF ground you may have to change the taps on the winding.

Hi All

         I found a good write up on PVC and Coils which i will post
here for all to see.


Generally PVC is quite adequate for antenna work, but a few
precautions are
necessary.

First of all, contrary to common knowledge, it actually does have
reasonable RF
properties.  Most samples I have have looked at have dielectric
constants of
between 3.3 and 3.7 at normal temperatures and dielectric voltage
breakdowns of
350 volts/millimeter are common.

Since I am involved in manufacturing a line of antennas that use
this material,
I did a fair amount of investigating.  One of the important factors
to consider
when using PVC for antennas is whether it can take the Ultraviolet
radiation
from the sun.  There are chemicals that can be added to the compound
to protect
it and many manufacturers do this routinely, since one never knows
where the
stuff will end up.  This is particularly true of present day white
PVC.  Not
all are protected, but one brand name that comes to mind that is:
Bristol Pipe
PVC, schedule 40.

Where one can get into trouble with PVC with RF is in the helical
antenna
arena.  Here we have an antenna that can resemble a Tesla coil, if
there is
sufficient power and inductance.  With very tight windings and not
much
radiating surface considerable voltages can be developed.  The
highest voltage
point will be at the end of the antenna.  With even moderate powers;
50 to 100
watts, several thousand volts can be developed.

Take for example the case where a helical antenna developed 1000
volts at the
end.  The formula for power is P= E^2/R ( Power is E squared over
R).  1000
Volts squared over perhaps 100,000 ohms can be 10 watts!  If this
power is
concentrated in a rather small area it will start to heat the
plastic.  This
heat will further reduce the voltage resistance of the plastic,
increasing the
heat and further deteriorating its ability to resist voltage
breakdown.

The estimate of 100,000 ohms was pulled out of the air.  Actually,
it is
usually higher, but contaminants in the plastic and gas molecules in
the
material can drastically affect the outcome.  Regional heating can
become
severe.

DC voltages do not have quite the same effect on these materials
because of the
reaction the plastic has to AC.  This is in great part due to the
inherent
"dipolar" characteristic of the plastic.  AC tends to force the
molecular
dipole characteristic of the material to react to the direction
change of the
current, this is not resistance, but can have a similar end result.

The bottom line here is that these problems only occur at very high
voltages
and particularly at elevated temperature.  When used for a coil in a
bottom
loaded, or even center-loaded, the voltages remain low enough that
there should
be little reason for concern.

Varnished wood works well because it has very little dipolar effect,
although
it does have some.  The problem with the wood is that as the varnish
deteriorates over time, moisture will find its way in and
dramatically upset
the apple cart.

When I wrote the article for QST in July, the staff at the League
had me submit
some test data because they had the same concerns.  We also
submitted a 144
MHz JadePole antenna for testing.  They were pleased with the
results and found
no problems.  At reasonable power levels there is little need for
concern,
especially at QRP levels.  Once again QRP can have an advantage.

Many of the PVC materials can be used out beyond 1 GHz without
concern.

Dennis, K1YPP

Jade Products, Inc.

Engineer


Well i have made and know many now with the Helicals wound on PVC
pipe and Running 400 Watts for hours at time with NO melting or
Burning.



73's Andy G7LRR

Hi Guys,
          Hmm you got a good sized antenna there 60 feet or so !!.
Iv'e been trying to get active with a max of 40 feet garden from the
back apex of my bungalow, which itself limits ant height.. to about
20
feet. Currently it's like a long wire (i use that term loosly) with a
loading "coil" which is similar to your helix, inso far as it's
approx
100 foot of wire coiled on a 1.5 inch former loading the ant at the
far end...You also seem to have discovered the rule that these ant's
MUST have a good earth to work at all, like you i was going to put
my
old leaky copper tank into he ground oustide my shack but, some Bar-
stewart waited until i had removed the foam insulation from it and
nipped over my back fence which is 6 foot tall and Nicked it !! when
i
wasnt looking..

Anyhoo, it does work this ant-config but it's not to efficent on 160
really. You may wish to look up the old VFA ant from the 60's and
70's
this was a small helical design, which covered most bands BUT again
the old timers i know recon it wasn't to great but did get you
active
where normal antennas (wire's & Dipoles Etc) were not possible..

regards for now Paul G4HDS

P.S. I am at present playing with a crossed field loop for 160m..

Phil,

I've found your words about your helical antenna for 160 to be very interesting.
I've just
started seriously operating on 160 and chasing DX, after many years of operation
on the
other bands and only a passing touch at Topband from time to time.

In 1970, when I was just getting started in ham radio again after a lapse of a
few years, I
constructed a helically-wound vertical antenna for 80 meters; little or no
ground system
but it did a passable job. I decided to try the same method this year for my
first real foray
into Topband. I have limited space available (although more than you have, by
the sound
of it), and it was late in the fall when I started on this project, so I thought
this antenna
construction would give me a chance to get a start.

My helically-wound vertical consists of approximately a half-wave of number 14
insulated
wire wound on a 2-inch (50-mm) piece of PVC tubing that is 20 feet (6+-meters)
long. I
was immediately interested in your use of the hot glue solution for attaching
the wire to
the tube; I had a real fight with that, finally just wrapping the coil of wire
with electrical
tape every few feet to hold it on the form (my first vertical 35 years ago was
on a wooden
form, and the wires were held in place with staples into the wood every two or
three
turns).

My antenna is completely contained on the form, with just a short whip coming
out the
top. There is a loading coil at the bottom; I jumpered it at the top to get
resonant
frequency, and at the bottom for an impedance match. The coil is only about 5
inches
long, the impedance at the feed point is about 24 ohms resistive. Next year I
think I will
try to go with a 10-inch coil; I may be able to achieve a better match to the
50-ohm coax.
At the bottom of the antenna, I have 32 radials laid on the ground, ranging in
length from
about 45 feet (13.5 meters) to 100 feet (30 meters), working to the limits of my
property.

The antenna works; I've been into Europe and the Pacific, as well as some Middle
East and
Africa. Right now I'm at 58 countries worked (24 confirmed). I'll try to post
some pictures
of my cobbled-up construction later.

73,

John Bastin, K8AJS
bastinj@...



--- In topband-helical@..., m0vey@... wrote:
>
> In early 2005 I spoke with Andy, G7LRR about homebrewing an antenna for
> Topband that I could fit in my garden.Andy suggested using a design by Alan,
> G4ERZ that I could fit in the 60' space I had. I had a head start, because
Paul,
> G6AXW had already made one which just needed altering so it could be coax fed
> instead of being fed with a length of wire.
>     This antenna is space wound on a 6' length of 1  1/2" plastic pipe. It is
> fixed to the pipe using a hot glue gun. Total length of  wire is approx 130'
> with half the wire helically wound on the pipe & the  other half of the wire
> left as a top loading wire. For this mk1 antenna a hole  was drilled in the
> side of the antenna, 2" from the bottom. I fed the coax in  here & joined the
> centre part of the coax to the Helical wire, using a  choc-block. The braid
side
> of the coax was also connected to a choc-block  so a wire could be attached &
> returned to the ground system once the antenna  was in the air. I will
> describe in my next posting how to use an   S0-239 connector as on the mk2.
>                                                 I  made a mounting loop at
> the top of the antenna so that I could pull the antenna  to the top of my 40'
> flagpole I use as a mast. I will describe how to base mount  this antenna in
> another posting.  I use 2 counterpoises connected to  my ground system. One is
> 125' long & runs under the top loading wire. The  other is a very long wire
> running thru the bottom of a wooden fence alongside my  garden.
>
>               I  also buried a 3' copper hot water tank, 4' in the ground.
> This took 2 s points  off my background noise level & improved my TX signal.
> After trimming the  antenna wire the overall length of my Helical is approx
125'
> My antenna is 40' in the air with the top loading wire sloping to 20' above
> ground. I have had some good dx results & inter G contacts with the Helical.
> Please post any messages to this group if you have any questions to be
> answered.
>                                                                     Details
> of any of your homebrew Topband, base or mobile antennas would be 
appreciated.
>                                                                     Regards,
>
>    Phil.    m0vey
>