Dick
You are saying that my 4 x inv L antennas each at 120 ft
vertical and 400 ft horizontal are only burning up the field under the
array.
My signal is reported throughout EU and beyond to Russia and the
USA as the strongest on the air only surpassed by MM0ALM when he was
active. As far as I can remember he was using 2 x inv L antennas at over 140
ft high using two masts.
I have never used a T antenna, my logic is that the more
independent wire in the air the better, you have the benefit in my case
of 4 top loaded verticals in parallel. All the bottom ends of the
verticals are connected to the top of the loading coil of about 0.3 mh.
The top of each L is about 10 feet out from the mast and the drop wires
taper to the bottom reducing capacitance to ground.
An inv L antenna is really a top loaded
vertical.
I hope you understand what I mean.
Calculations and theoretical assumptions are often way of the
mark when it comes to small antenna systems like radio amateurs use on LF.
The only solution is the practical approach, common sense
gained with experience and put up the best antenna you can then
judge the results. As a matter of interest I have never burnt out any
insulators, antenna wires, ground radials or any vegetation underneath the
antenna array.
If you are working worldwide on normal CW then you have got it
right !!!!!!!
73 de Mal/G3KEV
I
Another point is that for DX the take-off
angle should be as low as possible and that is certainly not achieved this
way.
As a ground wave (surface wave) a horizontally polarised
cannot exist over a perfect ground and over real earth is so weak that it is
of no practical use.
The question has come up before on the reflector
and as far as I can remember the conclusion has always been that this is not a
viable solution for producing a useful sky wave.
73, Dick,
PA0SE
At 10:39 4-1-04, you wrote:
How much horizontally polarised
skywave is there and how well does it
propagate?
Would it be worth
constructing an aerial that favoured skywave?
73
John Rabson
G3PAI
----- Original Message -----
From: "Dick Rollema"
<[email protected]>
To:
<[email protected]>
Sent: Saturday, January 03, 2004
11:30 AM
Subject: RE: LF: Re: "T" versus "L"aerial
> To All
from PA0SE,
>
> Mike, PC4M, wrote:
>
> At
02:50 1-1-04, you wrote:
> >Dear Dick / Bob and Lofers,
>
>
> >Does the computer calculate the earth losses in the return
path from the
> >aerial system to the transmitter? If it would then
the earth losses in a
T
> >should have been significantly less
then the L alternative. There are two
> >separate return
currents
> >(parallel resistance) and each with a smaler physical
length (lower
> >R-earth) in a T system resulting in more ERP
if compared to an L system.
>
> In the computer simulation no
resistances were included. That means that
> the 1 kW fed to the
aerial is completely radiated. Even an extremelly
short
> vertical
with no top load would do so and produce the calculated 29.9mV/m
> at
10km
>
> Bu the point raised by Bob, ZL2CA, was that the current
in the single wire
> topload of the "L" would generate a
horizontally polarised field. In the
> "T" the currents in the
two topload wires flow in opposite directions so
> the horizontally
polarised fields caused by these currents would at least
> partially
cancel each other.
> The horizontally polarised field is radiated as a
sky wave and the power
in
> it detracts from that in the vertically
polarised field of the ground
wave.
> If the above reasoning were
correct it could be expected that the "T"
would
> produce a
stronger ground wave than the "L" because less power disappears
> in
the horizontally polarised sky wave.
> The simulation has shown that
this is not the case.
>
> The subject of losses in the
earth and surrounding objects has been
> treated very well by
Jim, M0BMU, in his e-mail.
>
> 73, Dick,
PA0SE
>
>
> >-----Oorspronkelijk bericht-----
>
>Van: [email protected]
> >[mailto:[email protected]] Namens Dick
Rollema
> >Verzonden: maandag 29 december 2003 16:37
>
>Aan: [email protected]
> >Onderwerp: Re: LF: Re: "T"
versus "L"aerial
> >
> >To All from PA0SE
>
>
> >Bob, ZL2AC wrote:
> >
> >
>
>
> >Dick PA0SE,
> >
> >Fine on the test
result. As you stated, the tested T has twice the
amount
>
>of top loading wire (2x 20 metres) than the L (1x 20 metres).
>
>
> >It would be interesting to know if a T is better than an L
for constant
> >length top loading i.e. what the difference is if
the upwire joins at the
> >end or the middle of the horizontal top
wire (theory suggests the T is
> >better as there is minimal
horizontally polarised component).
> >
> >Bob, I
cannot answer your question by a practical experiment but used
>
>computer simulation instead by means of K6STI's program
Antenna
Optimizer.
> >
> >I modeled two antennas with a
vertical element of 20m. One an Inverted
> >L-antenna with a
horizontal top load wire of 40m. The other a T-antenna
> >with a
top load of 2 x 20m.
> >Both antennas without losses, over
perfect ground and fed with 1kW.
> >
> >At a distance of
10km (so well outside the near field region) and over
> >perfect
ground both antennas produced a vertically polarised field of
>
>29.9mV/m. The horizontally polarised field was zero; but this is to
be
> >expected because over a perfect conducting ground a
horizontal field
> >component cannot exist.
> >
>
>73, Dick, PA0SE
> >
> >Original message:
>
>
> >
> >To: <mailto:[email protected]>LF-Group
>
>Sent: Sunday, December 28, 2003 3:09 AM
> >Subject: LF: "T"
versus "L"aerial
> >To All from PA0SE
> >Further to my
e-mail of 26 December I measured the field strength as
> >radiated
by the aerial in
> >Inverted L-configuration. From this I found
EMRP = 57 milliwatt.
> >This confirms the benificial effect of top
loading. The T-aerial radiated
> >140 milliwatt.
> >So
going from a single 20m top load wire for the "L" to 2 x 20m for the
>
>"T" resulted in an improvement by a factor 2.46 (3.9dB) in
radiated
power.
> >The vertical part of the "T" consisted of an
open wire feedline of 11m
> >with the two wires connected in
parallel in the attic shack. For the "L"
> >one of the feedline
wires was removed. I assume this did not appreciably
> >affect the
EMRP.
> >73, Dick,
PA0SE
>
