Like Tom said earlier, it's all about ground loss. Near the sea, a 1/2 or
5/8 wave vertical may perform very differently than a duplicate antenna a
long way from the sea. The near-field and far-field losses at the lower
angles would be much lower.
73, Mike
www.w0btu.com
On Fri, Sep 6, 2013 at 7:04 PM, Bob K6UJ <k6uj@pacbell.net> wrote:
> Mike,
>
> Tom, W8JI has a comparison between 1/4 wave and 5/8 wave vertical mobile
> antennas here: http://www.w8ji.com/VHF%20mobile%20vertical.htm
> He is comparing mobile antennas but it looks like the 5/8 wave can be 2 db
> better than the 1/4 wave.
> Looking at the radiation angle graphs it shows the 5/8 has more gain at
> lower radiation angles in particular.
> If you were doing your comparison on long haul contacts it makes sense
> that the 5/8 would do better.
>
> Bob
> K6UJ
>
>
>
> On Sep 6, 2013, at 4:35 PM, Mike Armstrong wrote:
>
> > Guy, you aren't reading my emails...... because that question is not
> appropriate to the conversation. I am NOT, I repeat NOT talking the
> difference between LOCATIONS, but the difference between ANTENNAS AT THE
> SAME LOCATION! I am NOT talking about RURAL ANYTHING. That location being
> on Gannet Avenue across from the Marina that was LITERALLY across the
> street from my house.
> >
> > I say again, READ MY EMAIL as your question has absolutely NOTHING to do
> with the conversation. The fact that you sent the same email to me after I
> answered you tells me that you are not reading what I wrote. I am not
> being insulting, but if you don't read ALL of what I wrote, you cannot
> possibly ask a valid question or make any statements about its content. If
> you read it, you would know that I am not saying ANYTHING about location
> changes or differences. OF COURSE a sea water location is better than a
> rural location. THAT fact has nothing to do with the comparisons I am
> making or asking Tom to discuss. Sorry for the repetition, but I want to
> make sure that you will see that, even if you don't read this email
> entirely. Again, no insult intended, but it is tiring trying to respond to
> someone who isn't reading ALL of what I wrote and jumping to incorrect
> conclusions as a result. I WILL tell you the address, if you still want to
> know, after you have read and responded
> to
> > the content of this email specifically.
> >
> > Mike AB7ZU
> >
> > Kuhi no ka lima, hele no ka maka
> >
> > On Sep 6, 2013, at 13:38, Guy Olinger K2AV <olinger@bellsouth.net>
> wrote:
> >
> >> Mike, could you kindly supply the address on Iroquois Point? If it's in
> >> the area I'm looking at with Google Earth, the answer why the
> difference is
> >> pretty plain, and points to why such a difference vs. a 160m vertical on
> >> rural terra firma.
> >>
> >> 73, Guy.
> >>
> >>
> >> On Fri, Sep 6, 2013 at 1:30 PM, Mike Armstrong <armstrmj@aol.com>
> wrote:
> >>
> >>> Oh, I didn't address one comment you made, Tom...... 5/8ths are dogs on
> >>> 160? Really? That is odd in the extreme to me. I had incredible
> success
> >>> with a ground mounted 5/8 on 20 meters while I was stationed in
> Hawaii. I
> >>> was rather space limited, so I could only go up and a tower mounted
> beam
> >>> was a "no fly zone" in that particular situation. So, I decided to
> try the
> >>> 5/8ths wave vertical and its performance was nothing short of
> spectacular
> >>> when compared to a 1/4 under the same circumstances. Not to malign the
> >>> simple 1/4 wave, but the 5/8ths performance improvement went way beyond
> >>> what I would have expected...... and my expectations were certainly
> >>> reasonable. My thinking was that lifting the major current node a bit
> >>> above ground would probably be an improvement and, to my surprise,
> that was
> >>> an understatement in the extreme.
> >>>
> >>> I wouldn't want to overblow the results, but I simply couldn't believe
> how
> >>> well the antenna performed on 20. To be sure, I was on Oahu out in
> >>> Iroquois Point housing, which is well situated with regard to the sea
> (you
> >>> are basically ON the water in almost all directions). Additionally, I
> had
> >>> 60 radials underneath the thing, spread evenly around the base (in
> straight
> >>> lines, no bending). So it was definitely an ideal vertical location.
> But
> >>> the difference between it and the quarter wave was what truly
> surprised me
> >>> (with all else being the same.... sea water location, number and
> length of
> >>> radials, etc). To hear that it doesn't translate to 160 is really a
> >>> surprise to me...... Tell me more, assuming you did any kind of study
> into
> >>> why it didn't seem to work well. I am as interested in why something
> >>> DIDN'T work as I am in why it does..... If for no other reason than to
> save
> >>> a few bucks and alot of time.... LOL
> >>>
> >>> Mike AB7ZU
> >>>
> >>> Kuhi no ka lima, hele no ka maka
> >>>
> >>> On Sep 6, 2013, at 9:25, "Tom W8JI" <w8ji@w8ji.com> wrote:
> >>>
> >>>>> Fully understood. I wasn't referring to the usual collinear antennas
> >>> sold by "comet" or anything of that nature. I am referring to the
> stacking
> >>> arrangements used for ops like moonbounce, etc. As far as the design
> >>> theory (and practical application) goes, I have a reasonable amount of
> >>> schooling and experience (been active since 1966..... he he he). Just
> so
> >>> you realize I am not referring to the often (always?) false gain claims
> >>> made by manufacturers for their antenna designs.
> >>>>
> >>>> ........but this is verticals, and not a narrow BW like a long Yagi.
> The
> >>> narrower the pattern of a cell in the stack, the wider minimum useful
> >>> stacking distance becomes.
> >>>>
> >>>> Also, for 160, antennas are near earth. Earth spoils everything. A 160
> >>> antenna at 260 feet is like a two meter antenna at 3.25 feet above
> ground.
> >>>>
> >>>>
> >>>>> All I was saying was, "yes, it is possible and is done" when speaking
> >>> to vertical stacking. As far as stacking what we would call "ground
> plane"
> >>> antennas (quarter wave vertical element against elevated radials), the
> only
> >>> example I have seen with any regularity is done aboard some Naval
> vessels
> >>> (stacked/phased, if you will, horizontally on a yard arm). I "think" I
> have
> >>> seen the same thing at airports, but I cannot tell for certain that
> they
> >>> are phased arrays or just happen to "look" like they are related.
> >>> Understand that in all cases to which I refer, including my own, I am
> >>> speaking of phased arrays, which I believe is what we are talking
> about as
> >>> well. I may have misinterpreted the question to some degree.
> >>>>
> >>>> This is 160. The distance ratio for the same behavior on two meters is
> >>> 80:1. If we look at:
> http://www.w8ji.com/stacking_broadside_collinear.htm
> >>>>
> >>>> we see **freespace** short dipole stacking distances, between current
> >>> maximums, is 0.35 WL for 1 dB stacking gain. This is for freespace.
> That
> >>> means the current maximums have to be .35*160 = 56 meters apart **if**
> the
> >>> elements are in freespace. They have to be even further apart if near
> >>> earth, because the earth reflection already compresses the vertical
> >>> pattern. I'd guess, for 1 dB stacking gain over a ground mounted
> vertical
> >>> (ignoring ground losses), we could move the lower current maximum to
> about
> >>> 50 meters above earth and eliminate the upper element. That would
> pretty
> >>> much be a vertical dipole. If we wanted to get 2-3 dB gain, we'd
> probably
> >>> need 300 feet of height and an inverted groundplane at the top.
> >>>>
> >>>> For 160, is it is a useless endeavor at normal heights.
> >>>>
> >>>> Making matters worse, 5/8th wave verticals are dogs on 160. Been
> there,
> >>> done that, used them. A 1/4 wave vertical, or something up to maybe 200
> >>> feet, is actually better. They have never worked well here, they never
> >>> worked when I used broadcast towers, and when W8LT used them in 160
> >>> contests they were also pretty weak.
> >>>>
> >>>> The whole thing is a waste of time on 160. Even if someone could run a
> >>> vertical collinear with useful gain, it would just kill their signal by
> >>> focusing it at too low an angle for 160, while nulling more useful
> angles.
> >>>>
> >>>> 73 Tom
> >>> _________________
> >>> Topband Reflector
> >> _________________
> >> Topband Reflector
> > _________________
> > Topband Reflector
>
> _________________
> Topband Reflector
>
_________________
Topband Reflector
|