Re:Best 144/440 Antenna for Attic Installation
Rollie
They're small and very inexpensive. Mine works great. Rollie
Alan WA4SCA
J-pole so it is only the height of a basic 2 meter J-pole, very
sturdy, and does not require a ground plane. Mine is on the roof, but
I have a good friend who has his installed in the attic of a condo. He
hears and transmits very well.
--
Alan
WA4SCA
tom
> The Arrowantennas.com OSJ 146/440 J Pole antenna should work great for you.
> They're small and very inexpensive. Mine works great. Rollie
>
>
I built a replica, since he provides the dimensions, and it works very well.
Just make sure you decouple the feedline with a choke.
tom
K0TAR
HamR...@dontask.com
On 20-Jul-2009, "Rollie" <rol...@iowatelecom.net> wrote:
> The Arrowantennas.com OSJ 146/440 J Pole antenna should work great for you.
> They're small and very inexpensive. Mine works great. Rollie
I see that they have a 4.8/5 rating on eham.net. I will definitely look into them.
From the picture, it looks like one of the poles has a SO239 connector, but the others don't. Are
the two other poles passive?
What's the radiation pattern?
Another antenna I've been looking at is the Diamond X50A.
Dave Platt
>into them.
>
>From the picture, it looks like one of the poles has a SO239 connector,
>but the others don't. Are
>the two other poles passive?
The Arrow is an "open-sleeve" J-pole design. The other poles aren't
actively fed, but make up a critical part of the antenna design.
A standard (traditional) J-pole is an extended zepp. It consists of a
half-wave end-fed radiator, connected to a transmission-line matching
section (nominally a quarter-wavelength). The matching section is
usually made up of an extension to the radiator, and a second element
located an inch or two away.
The matching section is usually shorted at the bottom, and fed at a
tap point an inch or two above the short... a point at which the high
impedance of the end-fed half-wave radiator has been transformed down
by the transmission line to something close to 50 ohms.
An "open sleeve" J-pole (which Cebik calls a "nontraditional" J-pole
on his web site) is a bit different. It's somewhat shorter (the long
arm is less than 3/4 wavelength), the short arm is longer than 1/4
wavelength, and it's fed differently (at the bottom, with one arm
being grounded and the other being insulated from ground and fed
directly from the feedline). Cebik's website has a very nice
discussion of it.
The Arrow OSJ is actually two open-sleeve dipoles, in parallel. The
longest arm and the shortest arm are grounded, and the medium-length
arm is connected to the hot side of the feedline.
On 2 meters, the long and medium arms form an OSJ and are active...
the short arm is simply a grounded stub which carries very little
current and doesn't radiate much.
On 70 cm, the medium and short arms form an OSJ and carry most of the
current. The long arm probably carries a small amount of current, but
since it's a couple of wavelengths long its radiation resistance is
high and its current flow and radiation are only a small percentage of
the total.
>What's the radiation pattern?
Very similar to any other half-wavelength radiator... 0 dBd, plus or
minus a few fidgets.
The Arrow OSJ is not actively decoupled from the feedline (there's no
balun) and thus there may be a small amount of RF current flowing on
the outside of the feedline, and some amount of disturbance of the
pattern. The amount of current on the feedline will depend on the
details of the individual installation (e.g. the length of the
feedline). I don't think the effect will be significant in most
installations; reflections from the ground, building structures, etc.
are likely to alter the pattern just as much or even more.
You may, if you choose, mount the Arrow on an insulated mast, and
include some sort of choke in the feedline (e.g. a small loop of a few
turns in the coax, or some ferrites) in order to reduce the effect of
feedline radiation.
I think that the Arrow is a good performer and a good value. You can
even make 'em yourself if you wish - Arrow sells the parts
individually and (last time I looked) had complete construction
dimensions and plans somewhere on their web site.
--
Dave Platt <dpl...@radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!
HamR...@dontask.com
On 22-Jul-2009, dpl...@radagast.org (Dave Platt) wrote:
> The Arrow is an "open-sleeve" J-pole design. The other poles aren't
> actively fed, but make up a critical part of the antenna design.
What are the pros and cons of an Arrow J-pole versus a Diamond X50A pole?
Dave Platt
>> actively fed, but make up a critical part of the antenna design.
>
>What are the pros and cons of an Arrow J-pole versus a Diamond X50A pole?
The Diamond X50A has a somewhat higher gain than the Arrow on 2 meters
(about 2 dB higher, if I'm reading the stats correctly) and a
significantly higher gain than the Arrow on 70 cm (about 5 dB higher).
The Arrow is about 6" shorter than the Diamond (might fit into an
attic space where the Diamond will not), has been tested at power
levels of up to a kilowatt (the Diamond is rated for 200 watts), and
costs only 40% as much as the Diamond.
The Diamond has decoupling radials, and I infer that it's less likely
to have a feedline-RF situation than the Arrow - its actual pattern
may be more consistently like its theoretically-calculated pattern.
The Diamond looks more like a traditional antenna... the Arrow is more
likely to get "What the >bleep< is that thing?" questions, if mounted
outdoors.
The Arrow may be easier to field-repair, since it's mostly just
aluminum angle and rod stock.
Roy Lewallen
>>> The Arrow is an "open-sleeve" J-pole design. The other poles aren't
>>> actively fed, but make up a critical part of the antenna design.
>> What are the pros and cons of an Arrow J-pole versus a Diamond X50A pole?
>
> The Diamond X50A has a somewhat higher gain than the Arrow on 2 meters
> (about 2 dB higher, if I'm reading the stats correctly) and a
> significantly higher gain than the Arrow on 70 cm (about 5 dB higher).
>
> The Arrow is about 6" shorter than the Diamond (might fit into an
> attic space where the Diamond will not), has been tested at power
> levels of up to a kilowatt (the Diamond is rated for 200 watts), and
Wow, 5 dB extra gain for an extra quarter wavelength, and 2 dB for an
extra 7/100 wavelength of size. That's quite a trick!
Do you maybe mean to say that the Diamond has a somewhat higher
*claimed* gain than the Arrow? If we're looking for high claimed gains
(and claimed power handling capability for that matter), some of the CB
whips should take the prize.
Roy Lewallen, W7EL
Dave Platt
Roy Lewallen <w7...@eznec.com> wrote:
>Wow, 5 dB extra gain for an extra quarter wavelength, and 2 dB for an
>extra 7/100 wavelength of size. That's quite a trick!
>
>Do you maybe mean to say that the Diamond has a somewhat higher
>*claimed* gain than the Arrow? If we're looking for high claimed gains
>(and claimed power handling capability for that matter), some of the CB
>whips should take the prize.
You're quite correct. I'm going by "claimed" gain figures, and those
that Diamond cites do sound a trifle high to be believable.
HamR...@dontask.com
On 23-Jul-2009, Roy Lewallen <w7...@eznec.com> wrote:
> > The Diamond X50A has a somewhat higher gain than the Arrow on 2 meters
> > (about 2 dB higher, if I'm reading the stats correctly) and a
> > significantly higher gain than the Arrow on 70 cm (about 5 dB higher).
> >
> > The Arrow is about 6" shorter than the Diamond (might fit into an
> > attic space where the Diamond will not), has been tested at power
> > levels of up to a kilowatt (the Diamond is rated for 200 watts), and
> > costs only 40% as much as the Diamond. . .
>
> Wow, 5 dB extra gain for an extra quarter wavelength, and 2 dB for an
> extra 7/100 wavelength of size. That's quite a trick!
>
> Do you maybe mean to say that the Diamond has a somewhat higher
> *claimed* gain than the Arrow? If we're looking for high claimed gains
> (and claimed power handling capability for that matter), some of the CB
> whips should take the prize.
I don't know what the actual gain is, but Diamond has been in business a long time, and I've never
seen any reports of them misreporting gains.
Does the Arrow have any gain? I thought it was close to 0.0. If it does, how do you know it's
correct?
The overall rating for the X50A on eHam.net is 4.7/5. The average rating for the Arrow J-pole is
4.8/5. It sounds like both products are highly regarded.
Roy Lewallen
> . . .
> The overall rating for the X50A on eHam.net is 4.7/5. The average rating for the Arrow J-pole is
> 4.8/5. It sounds like both products are highly regarded.
So the Arrow is rated 0.09 dB higher than the Diamond. That's probably
realistic.
Roy Lewallen, W7EL
JB
news:6KidndO_ePbwtPTX...@giganews.com...
Rather than punching a hole in the roof to accommodate your attic co-linear,
how about the ELK 2m/440 log periodic or Cushcraft A270-6s. A small Yagi is
not so directional that you can't use it for the local stuff while pointing
it yonder for a few weak ones.
HamR...@dontask.com
On 24-Jul-2009, "JB" <nos...@goofball.net> wrote:
> Rather than punching a hole in the roof to accommodate your attic co-linear,
> how about the ELK 2m/440 log periodic or Cushcraft A270-6s. A small Yagi is
> not so directional that you can't use it for the local stuff while pointing
> it yonder for a few weak ones.
I want to be able to hit a dozen or so repeaters in different directions, so I don't want a
directional antenna.
I believe I have enough height in the attic for the X50A. If I measure and come up short, I will
get the X30A instead.