Message-ID: <007001cd32c2$b3398d30$1502a8c0@Clemens04>
From: "Clemens  Paul" <cpaul@gmx.net>
To: <rsgb_lf_group@blacksheep.org>
References: <4FAFEA71.8030700@iup.uni-heidelberg.de><4FB01B8C.8050004@gmx.de><CAMFjj70BFLwZTGS_+WCcs_mmhTB=sfPYY7_U-4bw9k1YVqzuCA@mail.gmail.com><3f9e01cd3157$72c9dc80$1502a8c0@Clemens04> <CAMFjj71ogEu-6BJUOLDa-EotC1tDuM3jO+9AEo7DtyZiCi2D+A@mail.gmail.com> <009b01cd3215$b135d690$1502a8c0@Clemens04> <00d901cd321f$4a386fc0$4001a8c0@lark>
Date: Tue, 15 May 2012 19:46:44 +0200
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Subject: Re: LF: Cardioid RX antenna for LF...
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> 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" <alan.melia@btinternet.com>
To: <rsgb_lf_group@blacksheep.org>
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" <cpaul@gmx.net>
> To: <rsgb_lf_group@blacksheep.org>
> 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" <wd2xgj@gmail.com>
>> To: <rsgb_lf_group@blacksheep.org>
>> 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 <cpaul@gmx.net> 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" <wd2xgj@gmail.com>
>> > To: <rsgb_lf_group@blacksheep.org>
>> > 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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> 13.05.2012
>>
>>
>
>
>
>
> -----
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