Topband: Fw: GAP VERTICAL QUESTION

[DAVID CUTHBERT]

Guy,

here is where I believe your mysterious extra "loss" in NEC is coming from.
You are reading the "average gain" loss. NEC calculates that by integrating
the power at infinity and dividing by the power into the antenna. This
accounts for the far-far field ground losses that vertically polarized
radiation encounters.

But, this is not how we report the radiation efficiency of a vertical. That
is defined as the radiated energy in the far field (but not too far)
divided by the power into the antenna.

    Dave WX7G

On Wed, Dec 12, 2012 at 4:34 PM, Guy Olinger K2AV <olinger at bellsouth.net>wrote:

> [I may have sent an incomplete version of something on this topic.
> Apologies]
>
> 6 dB would be someone's calculation based on currents.   The sometimes
> abysmal performance of a ground rod based vertical system cannot be
> explained by 6 dB.  Cutting my amp from 1500w to 375watts just doesn't get
> bad enough.  Not close.
>
>  Part of the problem is that we figure all the current in the vertical is
> free and clear to useful radiation and is not affected by the RF
> "appearance" of the ground.
>
> You can model a near perfect commercial grade radial field, with a radial
> system apparent series resistance of a few tenths of an ohm, and NEC4 will
> still come back with an overall loss of 3 to 4 dB.  There is no
> book-keeping of that loss in the 34 ohm vertical radiator in series with
> the near zero resistance of the radials, as people typically talk about it.
>
>
> If I run my EZNEC Pro NEC4 3D all points azimuth and elevation run for a
> gold standard commercial installation, 120 1/4 wave buried radials in
> "average" ground, at the bottom of the main window I will get a rather
> typical 3.9 dB overall loss.  IF we have to understand loss as only
> book-kept in the feed resistance numbers, one would have to APPORTION the
> 34 ohms resistance to account for the loss.  That would be 47 percent in
> the pattern and 53 percent lost somewhere, by some means, 16 ohms
> apportioned out to the pattern with 18 ohms of loss somewhere, but not in
> the radials and not in the vertical wire.
>
> Great radials.  Top of the line radials.  BUT there is still some
> mechanism draining off 53 percent of the power.   The math in NEC 4 is
> doing and sensing something that explains loss not book-kept in our
> all-loss-is-shown-in-the-feed Z mental picture.
>
> Where's the loss, loss that does not change the feed Z as it comes and
> goes.  How does it work?  Can this non-Z-changing loss increase without the
> commercial radials and a wire fed right at the ground?  One could picture
> my installing a really good antenna at a place looking at a fairly distant
> horizon.  However, I could  have trucks and bulldozers built a 1000 foot
> high dirt wall encircling my place a mile away, and my feed Z would not
> change.  The wall would just soak up RF that otherwise would be out doing
> wonderful things at low angles.
>
> How much additional does "unshielded" dirt underneath a naked vertical
> soak up in terms of dB that does not alter the feed Z?
>
> Persons unnamed in 1995 recommended two 1/4 wave radials on the ground.  I
> remember that K4CIA from the other side of town, running QRP on his well
> constructed 160 vertical could often beat me out running 100 watts.  What I
> had was like running QRP on a good antenna.
>
> We don't know everything.  And there are a lot of people that have awful
> results with hack job radials.  We need to quit recommending hack jobs
> until we know exactly why they do or do not work, and can explain a FAR
> greater percentage of the anecdotal material than we can now, and can
> explain how in some scenarios how we can get results that ARE plainly down
> 20.  If we're not careful, at some point we can be blowing off the
> essential majority story because we just don't want to listen.
>
> 73, Guy
>
> On Wed, Dec 12, 2012 at 3:17 PM, DAVID CUTHBERT <telegrapher9 at gmail.com>wrote:
>
>> Correction, 100X the loss.
>>
>> The deal difference between a single ground rod and a BC station ground
>> will be about 6 dB.
>>
>> Dave WX7G
>> On Dec 12, 2012 1:13 PM, "DAVID CUTHBERT" <telegrapher9 at gmail.com> wrote:
>>
>> > 20 dB implies that the ground system loss is 10X the inverted-L
>> radiation
>> > resistance.
>> >
>> > This would result in an input resistance of 250 ohms and a minimum VSWR
>> if
>> > 5:1.
>> >
>> > I don't think that is what the real deal will deliver, do you?
>> >
>> > Dave WX7G
>> > On Dec 12, 2012 12:54 PM, "Guy Olinger K2AV" <olinger at bellsouth.net>
>> > wrote:
>> >
>> >> With the following caveat:  The very sparse and short buried radial
>> >> systems
>> >> he is showing are FAR more lossy in practice than shown in his gain
>> >> tables.
>> >>  Four twenty foot buried radials beneath a 1/4 wave L on 160, could
>> place
>> >> you down 20 dB.  You really can't do that as your 160 meter counter
>> poise
>> >> and expect decent results.  You can end feed the same wire on 80/40/30
>> >> meters (full wave worth of wire in the L on 80m) with four buried 20
>> foot
>> >> radials and it will be an excellent antenna.  This is due to the high Z
>> >> feed at the ground with current max AWAY from the feed point.
>> >>
>> >> A quarter wave L on 160 MUST deal with the counterpoise loss issues,
>> one
>> >> way or another.
>> >>
>> >> 73, Guy
>> >>
>> >> On Wed, Dec 12, 2012 at 2:07 PM, Ashton Lee <Ashton.R.Lee at hotmail.com
>> >> >wrote:
>> >>
>> >> > This wonderful article written by L.B.Cebic W4RNL sure can make you a
>> >> > believer in a simple wire inverted L. It is the last antenna
>> discussed.
>> >> > http://www.users.on.net/~bcr/files/backyard%20wire%20antennaes.pdf
>> >> >
>> >> > A $3 wire pulled up into a tree will beat just about any commercial
>> >> > antenna… because it is longer. So on low bands it has increased band
>> >> width
>> >> > and efficiency, and on higher bands it has gain. Yes, I know , some
>> of
>> >> that
>> >> > high band gain is horizontally polarized, but that's not all bad.
>> Just
>> >> get
>> >> > the vertical portion 33 feet or so and you'll be happy as Larry. The
>> >> > article shows that an extensive radial field may not be necessary.
>> >> >
>> >> > And a wire is a lot less visible than a big hunk of aluminum. Without
>> >> > trees, just top load a 43 foot (or possibly even shorter) vertical.
>> The
>> >> top
>> >> > loading could be a T just as easily as an L. People can argue that
>> one
>> >> all
>> >> > day.
>> >> >
>> >> >
>> >> >
>> >> >
>> >> > On Dec 12, 2012, at 11:30 AM, k6xt <k6xt at arrl.net> wrote:
>> >> >
>> >> > > My first antenna, still in use, on moving to CO is a GAP Titan,
>> >> > advertised to load up 80 thru 10 including WARC bands. The Titan is a
>> >> bit
>> >> > shorter than Voyager, 28 feet or something like it. The advertising
>> is
>> >> > correct, it loads up 180 thru 10.
>> >> > >
>> >> > > But wait. Is it effective on all those bands? No.
>> >> > >
>> >> > > On 80 its a dummy load. On 40 it works extremely well after I
>> added a
>> >> > one foot extension to the bottom wire that encircles the antenna. In
>> >> some
>> >> > cases it is the equal of my shorty HyGain 40 at 70 ft - which
>> probably
>> >> says
>> >> > more about the HyGain than the GAP. For the rest its better on the
>> >> > traditional bands than the WARC bands. It worked a lot of DX for me
>> for
>> >> the
>> >> > couple years it was my only antenna.
>> >> > >
>> >> > > Carrying my experience to the few feet taller Voyager, and from
>> what
>> >> > I've been told by Voyager users, the ant will meet its spec which is
>> to
>> >> > load up on the low bands. Expectation wise I'd expect it to be like
>> the
>> >> > Titan. It loads up but is otherwise a dummy load. Maybe with a batch
>> of
>> >> > radials it could be made to work as well as any other extremely short
>> >> > vertical or GP.
>> >> > >
>> >> > > Not to say there's anything wrong with GAP. My brother had up an R7
>> >> > which he rated about like the GAP on bands both cover. Those
>> multiband
>> >> > halfwave short verticals work but you get what you pay for.
>> >> > >
>> >> > > 73 Art K6XT~~
>> >> > > Success is going from failure to failure without a loss of
>> enthusiasm.
>> >> > > ARRL, GMCC, CW OPS, NAQCC
>> >> > > ARRL TA
>> >> > >
>> >> > > On 12/12/2012 10:00 AM, topband-request at contesting.com wrote:
>> >> > >> With the prospect of downsizing and moving into senior housing in
>> the
>> >> > future
>> >> > >> I am starting to look at vertical antennas that will allow me to
>> >> > continue
>> >> > >> this wonderful hobby.? I have heard "some" good things about the
>> GAP
>> >> > series
>> >> > >> of antennas but the company says they do not need radials on most
>> of
>> >> > them
>> >> > >> and that worries me.? Over the years I have become very skeptical
>> >> about
>> >> > >> claims and the other BS put out by most companies ( maybe it is a
>> >> > function
>> >> > >> of age I dunno) so I wonder if these antennas really work.? The
>> two
>> >> > antennas
>> >> > >> that I am interested are the Voyager DX for 160/80/40? and the
>> Eagle
>> >> DX
>> >> > for
>> >> > >> the rest of the bands.
>> >> > >>
>> >> > >> So my question is.... does anyone have actual experience with
>> these
>> >> > antennas
>> >> > >> (especially the voyager) as compared to other antennas for a
>> specific
>> >> > >> frequency.? Now guys .. I know you cant really compare a 6 element
>> >> beam
>> >> > to a
>> >> > >> vertical of this kind but I am talking about a comparison that is
>> >> > >> realistic.. like how does it hear, tune, match & get out compared
>> to
>> >> > >> something like another vertical or a dipole up some reasonable
>> >> distance.
>> >> > >>
>> >> > >> I sure hope this has not opend another can of worms.. some how I
>> seem
>> >> > to do
>> >> > >> that .. private emails are ok..especially it the topic gets out of
>> >> hand
>> >> > and
>> >> > >> we get a large volume of comments (Tree please dont shoot me
>> before
>> >> > >> Christmas my wife will miss me.)
>> >> > >
>> >> > > _______________________________________________
>> >> > > Topband reflector - topband at contesting.com
>> >> > >
>> >> >
>> >> > _______________________________________________
>> >> > Topband reflector - topband at contesting.com
>> >> >
>> >> _______________________________________________
>> >> Topband reflector - topband at contesting.com
>> >>
>> >
>> _______________________________________________
>> Topband reflector - topband at contesting.com
>>
>
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