Hi, Mike
Yes, after I wrote that coment yesterday, I did realize that the lower
ground 1/4 wave element could, indeed, be shunt fed. I guess I'm more used
to collinear arrays at VHF and UHF where they are routinely used as
base-station antennas in the land-mobile radio services to provide some
omni-directional gain. At VHF/UHF the normal practice is to use shorted 1/4
wave phasing lines between the vertical; 1/2 wave collinear elements.
I have a similar experience to yours regarding 5/8 wave radiators. Some
years ago, I put up a full-size 1/4 wave ground p[l;ane with three elevated
resonant radials for 80m. It was an excellent 80m DX antenna, but in
addition, I found that I could load it well on 30m. On 30m, it was a really
outstanding worldwide DX antenna! Not exactly 5/8 wave, but it worked very
well!
Probably the ideal site for 160/80m antennas is a salt marsh on a
mountain-top or high plateau! :-)
This thread has surely generated an amazing amount of traffic!
73,
Charlie, K4OTV
-----Original Message-----
From: Topband [mailto:topband-bounces@contesting.com] On Behalf Of Mike
Armstrong
Sent: Saturday, September 07, 2013 8:28 AM
To: Charlie Cunningham
Cc: ZR; <topband@contesting.com>; Shoppa, Tim
Subject: Re: Topband: Are stacked verticals feasible?
Charlie, just to complete my thought..... Yes, I would use something along
the lines of a gamma feed to a grounded tower. There are probably better
matching techniques, but that would certainly be a start. I have to admit,
though, that I have never tried the whole idea with a tower because I never
owned one that was tall enough :) :)
This topic sure has generated some discussion, that's for sure. Also, Tom
answered back with some of what I was wondering about..... Extremely low
angles of radiation on 160 are not good, apparently. Forcing the main lobe
lower will definitely cause more ground loss and 160 seems to be more
sensitive to ground losses than the higher bands. That is certainly an
important thought and I have seen the concept on the higher bands.
Strangely enough, 20 meters seems to be one band where it doesn't matter if
you ground mount or elevate (ground plane). The lower angles of radiation
are very much desired on that band..... forcing the main lobe lower doesn't
seem to have any negative effect, but rather definitely appears to improve
the situation on that band...... at least from my own experience, which is
rather substantial on that particular band. The same cannot be said for
15/10. Those bands DEFINITELY prefer an elevated vertical radiator. Ground
mounting, even with an extens ive radial field, on those upper bands is a
loser..... unless you have sea water underneath the antenna, of course. So
it may well be that 20 just happened to be the band where those collinear
(Paul Lee's antenna in his book) and 5/8ths wave on the ground, with a
decent radial field, work well. Like I said in another email, my experience
with the 5/8 vertical here in AZ is almost what it was in Hawaii...... but I
do have more than the average amount of radials underneath it and it is
possible that my land just happens to contain a higher salt content. AZ is
famous for that in places...... I might just be lucky. Even 1/4 wave
verticals work well on my property, but the 5/8ths is a definite improvement
over them. Side by side comparisons are easier here than they were to set
up in Hawaii because my back yard was shared with other neighbors in
military housing. Kids around, too..... had to make sure they wouldn't make
contact with the radiators live :) :)
Anywho...... that is all I have on the subject. I wish I had, at the time,
the measuring equipment to truly test the antennas out there on Oahu
(Iroquois Point military housing). Instead, as I more than once mentioned,
I had to count on anecdotal/subjective evidence from my system "users." But
like I mentioned, when I first changed over to the 5/8 wave, I was getting
emails from my system users (sailboat guys mainly) out in WestPac that were
unsolicited and quite glowing. Of course, the sea water didn't hurt, but
you have to keep in mind that the 1/4 wave that I replaced was also over
that same sea water, so the improvement didn't have anything to do with the
seawater itself because that was the same for both antennas...... as was the
radial field. I have to say, it was gratifying to know that a small change
(and it really wasn't any harder to erect than any other vertical) made such
a large difference. I DID forget to mention that from that point forward I
didn't hav
e to turn on the full-gallon amplifier except when conditions were
particularly bad...... which was easy to detect with throughput reports.....
I could start it up remotely from my office at SUBPAC via a packet link (I
had a straight shot to my house from where my office was located) or via
telephone modem (MAN, that was a long time ago..... he he he). So I wouldn't
hurt the guys using my system if I didn't happen to be present when
conditions went south.
I sure did have fun with that setup...... Providing that service for Sailors
was a ton of fun and THEY certainly seemed to appreciate it. Whenever any
of them pulled into Alawai or the Iroquois Point marina that was directly
across the street from my house, they would immediately invite my family to
dinner or a luau or whatever they had going on. Made alot 'o friends with
that system. LOL.
Have a terrific weekend, my friend!
Mike AB7ZU
Kuhi no ka lima, hele no ka maka
On Sep 6, 2013, at 20:34, "Charlie Cunningham"
<charlie-cunningham@nc.rr.com> wrote:
> But, how would we feed it" Unless the tower has a base insulator??
>
> Maybe a shunt feed might be possible?
> Charlie, K4OTV
> -----Original Message-----
> From: Topband [mailto:topband-bounces@contesting.com] On Behalf Of Mike
> Armstrong
> Sent: Friday, September 06, 2013 11:25 PM
> To: Charlie Cunningham
> Cc: ZR; <topband@contesting.com>; Shoppa, Tim
> Subject: Re: Topband: Are stacked verticals feasible?
>
> Hey...... IF the tower is tall enough for that duty (3/4 wave tall), then
> you could put that "skirt" on the "middle" 1/4 wave, as it were, and you
got
> 'er...... Could he be that lucky? I have to admit, other than right this
> second, I hadn't ever considered that as a possibility. It "should" work
so
> long as the height is close to correct and whatever is mounted to the
top,of
> the tower doesn't make the structure look too,much larger than it should
> look for resonance.
>
> HMMMMMMMM
>
> Mike AB7ZU
>
> Kuhi no ka lima, hele no ka maka
>
> On Sep 6, 2013, at 19:58, "Charlie Cunningham"
> <charlie-cunningham@nc.rr.com> wrote:
>
>> Hi, Mike
>>
>> I remember the guy that you are referring to, but it's been so many
>> years that I don't remember his last name tither. He published a book
>> via either ARRL or CQ mag.
>>
>> A collinear 1/2 wave over a 1/4 wave GP has certainly been done and
>> used commercially at VHF. The "skirt" can also be replaced with a
>> shorted 1/4 wave phasing line.
>>
>> Well, Tom's tower is probably tall enough - but how in heck would we
>> get the verticals far enough away from the tower??
>>
>> Charlie, K4OTV
>>
>> -----Original Message-----
>> From: Mike Armstrong [mailto:armstrmj@aol.com]
>> Sent: Friday, September 06, 2013 10:42 PM
>> To: Charlie Cunningham
>> Cc: ZR; Shoppa, Tim; <topband@contesting.com>
>> Subject: Re: Topband: Are stacked verticals feasible?
>>
>> Carl and Charlie,
>> I am not sure it would even be close to practical or even doable, but
>> I remember seeing an old book on verticals written by a prior Navy
>> Captain, I believe. He had a very interesting design for what WE
>> would, today, call a collinear that was 3/4 wave length tall on 20
>> meters..... it was, in reality what looked like half of a double-zepp
>> antenna in a vertical orientation. It intrigued me that it was like a
>> half wave stacked on top of a 1/4 wave worked against ground (normal
>> radial field). The interesting part was how he used a "skirt" around
>> the "middle" quarter wavelength portion to produce the the in-phase
> relationship with the physically lower 1/4 wave.
>>
>> You guys may already know the design I am talking about. I saw that
>> book a long time ago, like back in the late 60's I think..... maybe
>> early 70's. I was considering trying to find the article or book whenI
>> was looking for a better vertical for my winlink node on 20
>> meters..... the one I have been talking about. However, I tried the
>> 5/8ths first because I knew how to build one without having to possess
>> any special instructions. It was so successful, that I completely
>> forgot about the "collinear." On the other hand, this discussion
>> reminded me of that book and how author "raved", a little anyway, over
>> its performance. I remember that the height of the finished antenna
>> for 20 meters was something very close to 50 feet...... and that is
>> not much taller than a 5/8ths..... maybe 7 or 8 feet taller. So on
>> 20 it is very doable and, supposedly, it has some reasonable gain for
>> the effort. I would like to find the book because it described a good
>> way to make that all-important skirt that got the phase correct
>> between the upper half-wave and the lower quarter-wave sections. Due
>> to its relatively tall structure, it probably wouldn't even be "possible"
> to build one for 160.....
>> at least not by most of us. It would be interesting to see if it has
>> the same "problem" that Tom was referring to for the 5/8ths..... "too
low"
>> radiation angle. I know it isn't supposed to have that secondary lobe
>> that a 5/8ths has...... So maybe it would be an improvement ..... IF
>> it was even possible to build one. That would be one tall structure on
> 160.... LOL LOL.
>> Still, for someone needing an omni antenna with some gain on the
>> higher HF bands, it might be a decent answer. Never built one, so I
>> really don't know if it really works or not. Although, as I said,
>> that author was a Navy Captain whose job was designing some of the
>> shipboard antenna systems, like the NORD and some other odd ducks....
>> Well, "odd" to those who don't have to build low loss, low band
>> antennas on a floating "postage stamp." I know, I know, you might
>> have trouble thinking of something the size of an Aircraft Carrier
>> being referred to as a floating postage stamp, but if you have spent
>> any time at sea on a "big deck," you know exactly what I mean by that
>> statement...... he he he he. I really should remember his name, darn
>> it..... with all the time I spent on ships at sea working with his
>> designs, it is really sad (bad?) that I don't remember his name......
>> Paul "something?" I'll find out..... lol
>>
>> Mike AB7ZU
>>
>> Kuhi no ka lima, hele no ka maka
>>
>> On Sep 6, 2013, at 19:03, "Charlie Cunningham"
>> <charlie-cunningham@nc.rr.com> wrote:
>>
>>> Well, Carl
>>>
>>> You just proposed a total height of 3/4 wavelength, it seems. Do you
>>> have that much height?
>>>
>>> Charlie, K4OTV
>>>
>>> -----Original Message-----
>>> From: Topband [mailto:topband-bounces@contesting.com] On Behalf Of ZR
>>> Sent: Friday, September 06, 2013 9:26 AM
>>> To: Shoppa, Tim; topband@contesting.com
>>> Subject: Re: Topband: Are stacked verticals feasible?
>>>
>>> Look at it as 2 ground planes with the lower feed point 1/4 wave
>>> above ground along with its elevated radials which should make it
>>> pretty much ground independent according to what has been published
>>> on here and elsewhere.
>>>
>>> The second ground plane would be identical with 1/4 wave spacing from
>>> the top of the lower antenna or a 1/2 wave between feed points.
>>>
>>> Then I would think that the ground conductivity at the reflection
>>> point would be the only concern as far as efficiency and gain??
>>>
>>> If installed as vertical dipoles then there would also have to be
>> additional
>>> spacing between them.
>>>
>>> I would think that at 6-12' spacing from the tower it would minimize
>>> interaction on 160 or 80?
>>>
>>> Does anyone on here have EZNEC and can plot this?
>>>
>>> Carl
>>> KM1H
>>>
>>>
>>>
>>> ----- Original Message -----
>>> From: "Shoppa, Tim" <tshoppa@wmata.com>
>>> To: "Carl" <km1h@jeremy.mv.com>; <topband@contesting.com>
>>> Sent: Thursday, September 05, 2013 10:30 PM
>>> Subject: Re: Topband: Are stacked verticals feasible?
>>>
>>>
>>>> Isn't this a "Vertical dipole"? Two quarter wave radiating elements?
>>>> And
>>> tower behind it will be some kind of reflector/director depending on
>> height.
>>> The radials seem unimportant if thought of this way.
>>>>
>>>> Tim N3QE
>>>> ________________________________________
>>>> From: Topband [topband-bounces@contesting.com] on behalf of Carl
>>> [km1h@jeremy.mv.com]
>>>> Sent: Thursday, September 05, 2013 9:17 AM
>>>> To: topband
>>>> Subject: Topband: Are stacked verticals feasible?
>>>>
>>>> Assuming that sufficient tower height was available, guy wires are
>>> insulated
>>>> or broken up into short non-resonant sections. Tower face is 12 or 18".
>>>>
>>>> Start at 1/4 wave up with a 1/4 wave ground plane with radials
>>>> sloping at about 45 degrees. The vertical wire is 6-12' away from the
> tower face.
>>>>
>>>> Then a 1/4 wave (or 1/8) up install a duplicate.
>>>>
>>>> What does EZNEC say about this?
>>>>
>>>> With the different spacings?
>>>>
>>>> Effect of starting lower and how low before there are ground related
>>>> problems?
>>>>
>>>> Phasing with coax or a LC network?
>>>>
>>>> Switching in a delay line to tilt the lobe up a bit?
>>>>
>>>> Curiosity got the cat!
>>>>
>>>> Carl
>>>> KM1H
>>>>
>>>>
>>>>
>>>>
>>>> _________________
>>>> Topband Reflector
>>>> _________________
>>>> Topband Reflector
>>>>
>>>>
>>>> -----
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>>>> 09/05/13
>>> _________________
>>> Topband Reflector
>>>
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>>> Topband Reflector
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