Clemens you need to be careful about extrpolating this information!! dont
forget that skywave at HF comes generally from the F layer which can be
600km up. LF signals come from the lower E-region or upper D-regoin at
around an apparent altitude of about 90km. There will be little difference
in arrival angle between stations over 700km away, and at about 2000km (or
1000km in daytime) they arrive at zero degrees.
Alan,
thanks for that.
My last email was focused on *how* the special 'reverse mode' operation
of G3LNP's K9AY variant works, but I didn't think further about the usability
of the reverse mode beam steering for LF.
My own K9AY which uses only a vactrol, no reactance tuning,
has two loops with 25m circumference each.
It gives excellent F/B ratio,~25dB, on MW and LW,e.g. I can separate DLF
on 153kHz (500kW) completely from Brasov/Romania (300kW).
I think both should arrive at zero degrees?
In winter 2010/11 I could decode WSPR transmissions from across the pond with 1W
ERP
and most active UK WSPR stations, one with 1mW ERP.
Recently also a few but not all active CW stations from the UK could be heard.
73
Clemens
DL4RAJ
----- Original Message -----
From: "Alan Melia" <[email protected]>
To: <[email protected]>
Sent: Tuesday, May 15, 2012 12:16 AM
Subject: Re: LF: Cardioid RX antenna for LF...
Clemens you need to be careful about extrpolating this information!! dont
forget that skywave at HF comes generally from the F layer which can be
600km up. LF signals come from the lower E-region or upper D-regoin at
around an apparent altitude of about 90km. There will be little difference
in arrival angle between stations over 700km away, and at about 2000km (or
1000km in daytime) they arrive at zero degrees.
Thus they may be useful for nulling relatively close QRM, but dont let that
stop you trying it out. Looking at the gain ......that will be very low at
136, hence my suggestion of tuning to cancel the reactive component on the
K9AY. You will need to scale the reactance tuning for 136 but also hope that
the performance is not dependent on ground reflection. I make these comments
because I dont remember Finbar reporting this effect on his NDB K9AY, though
it had a very useful back to front ratio.
Some observers very close (<100km) to VLF transmitters used for Solar flare
detection have reported advantages by nulling the groundwave and tilting the
loop "backwards" slightly. This seems to increase the ratio of skywave to
ground wave, but this is not useful at 136kHz.
Alan
G3NYK
Alan
G3NYK
----- Original Message -----
From: "Clemens Paul" <[email protected]>
To: <[email protected]>
Sent: Monday, May 14, 2012 10:07 PM
Subject: Re: LF: Cardioid RX antenna for LF...
Warren,
I've buried out the article which was pubished in QST Oct 2010
and carefully studied again.
Below you see a short excerpt from the text:
-----------------------------------------------
"Results:
Forward gain with 180 feet of feeder,
assuming a 2:1 VSWR, was predicted to vary
from -28.6 dBi at 1.8 MHz to -6.4 dBi at
10.1 MHz and this appears to have been
achieved. On all bands noise from the OS
antenna exceeded that due to the receiver.
Additional amplification above that from the
preamplifier in the radio may not have been
necessary if the antenna was only used in the
forward direction. In this application, while
receiving off the back, an additional ampli-
fication stage may be needed, especially on
the lower bands."
--------------------------------------------------------
One point of G3LNP's approach is in fact -as I said - to use the
orthogonally steerable null
to suppress an interfering station which arrives on the same bearing (and
frequency),
but at a different vertical angle than the desired station.E.g. he could
separate Polish
stations
from German stations on 160m because their signals arrived at different
vertical angles yet
on the same bearing.This special feature is only usable when the antenna
is receiving off the
back.
The second point is that in the normal forward mode the *range* of the
steerable vertical angle
of the backward null can be extended..
While the standard variable resistance can change the angle between 85°
and ~40°
the variable rectance can extend this range to zero degrees.
73
Clemens
DL4RAJ
----- Original Message -----
From: "Warren Ziegler" <[email protected]>
To: <[email protected]>
Sent: Monday, May 14, 2012 1:26 AM
Subject: Re: LF: Cardioid RX antenna for LF...
Clemens,
The G3LNP reactance tuned loop receives off the front so it has
the same output level as a similar sized K9AY etc, the vertical angle
of the rear facing null is steerable by varying the reactance.
73 Warren K2ORS
On Sun, May 13, 2012 at 6:26 PM, Clemens Paul <[email protected]> wrote:
>> BTW, Tony Preedy G3LNP published an article last year in QST which
>> had a loop with variable reactance and resistance termination, by
>> varying the reactance one could adjust the vertical angle of the main
>> lobe.
>
>
> If_I_recall_it_correctly this design uses the *backside* lobe of the
K9AY
> for vertical beam steering which is as we know a lot, 20dB-30dB,even
weaker
> than the low gain frontside lobe.
> 73
> Clemens
> DL4RAJ..
> ----- Original Message ----- From: "Warren Ziegler" <[email protected]>
> To: <[email protected]>
> Sent: Sunday, May 13, 2012 11:37 PM
>
> Subject: Re: LF: Cardioid RX antenna for LF...
>
>
>
--
73 Warren K2ORS
WD2XGJ
WD2XSH/23
WE2XEB/2
WE2XGR/1
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