Richard Harrison wrote:

Phil found a simple dipole only a few feet above ground would
outperform a mobile whip on 40 or 75 meters.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Without more information, this comparison is flawed. A mobile whip has
a lower angle of radiation than a horizontal dipole. On 40 or 75, the
vertical component of radiation can be quite significant for close-in
stations (100 miles or so). At night, working long distances, the whip
may outperform the dipole. During the day, the dipole will probably
outperform the whip.

It all depends.

73, Bill W6WRT

Bill Turner wrote:
"Without more information, this comparison is flawed."

I agree the information was incomplete. I dfid not reproduce the whole
article. The fault was mine, not Phil`s. A low dipole has a high
radiation angle. For comparison, Phil was working Airstream net stations
in New York, New Jersey, Maryland, Pennsylvania, Ohio, and New England.
Phil was located in Ontario near Buffalo, New York when he collected his
data. His in-laws lived there. Phil`s home QTH at the time was the
highest spot in Western Connecticut, with a line-of-sight path to New
York City. Phil had surrounded his mountain top with rhombic antennas
pointed toward his likely targets. Amateurs answered when he called.

In the Airstream net, most of the contacts were made Sundays on 3963 kHz
at 8 am local time. Sky wave was mostly near vertical incidence. The low
dipole was good for the job. Not too directional and a lot of radiation
nearly straight up. Phil noted that several times when he switched to
to the mobile whip, he could not be heard through the QRM.

The numbers Phil put in Table 3 are only true under the conditions
prevailing when he made the checks.

Best regards, Richard Harrison, KB5WZI

On 13 Sep 2005 16:15:08 GMT, "Bill Turner" wrote:

Richard Harrison wrote:

Phil found a simple dipole only a few feet above ground would
outperform a mobile whip on 40 or 75 meters.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~

Without more information, this comparison is flawed. A mobile whip has
a lower angle of radiation than a horizontal dipole. On 40 or 75, the
vertical component of radiation can be quite significant for close-in
stations (100 miles or so). At night, working long distances, the whip
may outperform the dipole. During the day, the dipole will probably
outperform the whip.

It all depends.
73, Bill W6WRT


Correct on radiation angle, however the average mobile whip at 3.8mhz
is around 10% efficient. Even at 7Mhz it doesn't improve much
efficientcy wise. The low dipole (low being less than .25WL) is
close or better than 95% efficient but has a rotten radiation angle
for DX however close in it will be very good.

Myself in that situation.. I'd put a poles at either end of the
trailer (thats 50ft length) and if possible get it up 30ft or better
and hang a dipole. If the antenna is 66' (40m) the excess length
can hang. The support poles can be anything that will stay up. At
20m 30ft is 1/2WL up and will be decent. Even if you can't do two
support poles and only one make that one high as possible and mount
a dipole as a sloper. It will be somewhat directional but performace
will be far better than any ground mounted vertical that has no ground
plane.

If money wasn't a limiting factor. put down a base and put up a
freestanding tower.

The rules remain. More metal, higher the better.


Allison
KB1GMX

An antenna doesn't have a single "radiation angle". It radiates at all
angles. The relevant question is how much does it radiate at the
particular angle of interest, not at which angle does it radiate the
most. An antenna which radiates its maximum at a high angle might well
radiate more at a low angle than an antenna with a lower angle of
maximum radiation.

Roy Lewallen, W7EL

wrote:
On 13 Sep 2005 16:15:08 GMT, "Bill Turner" wrote:

Without more information, this comparison is flawed. A mobile whip has
a lower angle of radiation than a horizontal dipole. . .

Correct on radiation angle . . .

On Tue, 13 Sep 2005 20:43:23 -0700, Roy Lewallen
wrote:

An antenna doesn't have a single "radiation angle". It radiates at all
angles. The relevant question is how much does it radiate at the
particular angle of interest, not at which angle does it radiate the
most. An antenna which radiates its maximum at a high angle might well
radiate more at a low angle than an antenna with a lower angle of
maximum radiation.

Roy Lewallen, W7EL

Hello Roy,

I do understand that. I also understand when you say radiation angle
your talking about the primary or dominent lobe(s). There may be
many other lobes at useful or less than useful angles present as well.

However, how does that relate to using a shortend antenna with maybe
10% radiation efficientcy to a dipole at a reasonably attainable
height?

Allison
KB1GMX


wrote:
On 13 Sep 2005 16:15:08 GMT, "Bill Turner" wrote:

Without more information, this comparison is flawed. A mobile whip has
a lower angle of radiation than a horizontal dipole. . .

Correct on radiation angle . . .

However, how does that relate to using a shortend antenna with maybe
10% radiation efficientcy to a dipole at a reasonably attainable
height?

Well....Exactly as he described.
An antenna which radiates its maximum at a high angle might well
radiate more at a low angle than an antenna with a lower angle of
maximum radiation.

The thing is "might".... My mobile antenna on 40m is *much* less
efficient than my dipole at 40 ft. But...It still is the best to longer
hauls over about 800 miles, and to dx. In it's case, it does radiate
more at the lower angles I'm using at that time, vs the dipole.
With some lesser mobiles, "mine is fairly stout", this might not be
the case. The best antenna should always be decided to fit the
usual paths to be used. In the case of my mobile vs the dipole, it's
possible that if the dipole were raised another 1/4 wave higher, it
could match the mobile at those lower angles.
At home, I often ran a dipole at 40 ft vs a full size ground plane at
the same height. Both were pretty efficient. Efficiency comparisons
were fairly useless as to actual performance. What really decides
which is best at a given time, is the path, and angles to be used.
Now, if you compare two same length low dipoles, both to NVIS, both
shooting straight up, and one is less lossy than the other as far as
feeding method, etc, then yes, efficiency will decide which one is
best.
MK

wrote:
On Tue, 13 Sep 2005 20:43:23 -0700, Roy Lewallen
wrote:


An antenna doesn't have a single "radiation angle". It radiates at all
angles. The relevant question is how much does it radiate at the
particular angle of interest, not at which angle does it radiate the
most. An antenna which radiates its maximum at a high angle might well
radiate more at a low angle than an antenna with a lower angle of
maximum radiation.

Roy Lewallen, W7EL


Hello Roy,

I do understand that. I also understand when you say radiation angle
your talking about the primary or dominent lobe(s). There may be
many other lobes at useful or less than useful angles present as well.

However, how does that relate to using a shortend antenna with maybe
10% radiation efficientcy to a dipole at a reasonably attainable
height?

Allison
KB1GMX

The context was that one antenna was better for DX than the other
because it had a "lower radiation angle". An antenna with a "low
radiation angle" which is 10% efficient probably radiates less at low
angles than a more efficient antenna with a "high radiation angle".
Therefore it's not a better DX antenna. My point is simply that the
angle of maximum radiation is not a valid criterion for comparing antennas.

Roy Lewallen, W7EL

Roy Lewallen wrote:


An antenna doesn't have a single "radiation angle". It radiates at
all angles. The relevant question is how much does it radiate at the
particular angle of interest, not at which angle does it radiate the
most.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

That's true, except few if any hams have a specific "angle of
interest", since different angles are used at different times. For
most of us, the angle of maximum radiation gives a general indication
of how the antenna will perform. A better indication would be a
graphical representation. It's always a problem when one tries to
reduce a complex situation like this down to a single number.

73, Bill W6WRT

A better indication would be a
graphical representation.

The EZNEC demo does that well. There is a little green ball
that you can grab with your mouse, and place it at any angle
you wanna check. Makes it quite easy to see, or compare
various angles. MK

wrote:
A better indication would be a
graphical representation.

The EZNEC demo does that well. There is a little green ball
that you can grab with your mouse, and place it at any angle
you wanna check. Makes it quite easy to see, or compare
various angles. MK


Better yet, you can superimpose the plots from two antennas for direct
comparison. In v. 4.0, you can even get a numerical readout of the
difference between the two in dB at the angle of the cursor (the little
green ball).

Roy Lewallen, W7EL