Message-ID: <4E349643.5080904@iup.uni-heidelberg.de>
Date: Sun, 31 Jul 2011 01:39:47 +0200
From: =?ISO-8859-15?Q?Stefan_Sch=E4fer?= <schaefer@iup.uni-heidelberg.de>
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References: <4E341070.60400@iup.uni-heidelberg.de> <000601cc4f0c$dfc5b620$8d01a8c0@JAYDELL>
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Subject: Re: LF: Re: K9AY loop for LF at W1VD
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Many thanks for that interesting Mail Jay. Oh dear, another new project=20
on LF ;-) It never comes to an end... So, it makes sense to have both=20
types of loop antenna present fro RXing, depending where the desired=20
signal and noise comes from. Fine.

Am 31.07.2011 01:03, schrieb jrusgrove@comcast.net:
> Stefan
>
> I've tried a number of receive antennas for 137 / 185 and 500 kHz and=20
> the K9AY, with it's ~20 dB F/B has performed the best of the lot on=20
> 137 and 185 kHz. With the pattern directed toward the NE listening for=20
> EU stations the null is SW ... which is handy here as thunderstorms=20
> are most likely to be in that direction. A standard loop antenna's=20
> figure 8 pattern provides equal reception in the direction of the=20
> thunderstorms - not a good plan. So the decision to use a standard=20
> figure 8 pattern loop or a K9AY cardiod will depend on the direction=20
> of the desired signal and direction of the interference.
>
> The value of the terminating resistor is somewhat critical for optimum=20
> F/B response. Once the optimum value is found one could probably=20
> replace the variable R with a fixed R if desired.  I've found it=20
> beneficial to install a small ground screen (about a dozen radials=20
> that extend slightly beyond the loop) to stabilize the F/B under=20
> varying ground moisture conditions. BTW, the F/B holds all the way=20
> down in frequency to where the ferrite cores run out of steam ... and=20
> up in frequency to the point where the loop is about 1/8 wavelength in=20
> circumference (750 kHz).
OK, so i will try a fixed value first.
>
> A couple years back I installed 1000' BOG (Beverage on ground) for 500=20
> kHz oriented the same direction as the K9AY. The Beverage wins out=20
> over the K9AY due to the tighter pattern and lower overhead response.=20
> Wish I had space for the equivalent 3600' BOG for 137 / 185 kHz! =20
> Until that day comes I'll make do with the K9AY.
This could be interesting for Alex/LU8YD who prepares a new improved LF=20
grabber. We plan to do some RX/TX tests. I will TX :-)

Tnx and 73, CU, Stefan/DK7FC

PS: When will you be active on LF again? :-)



>
> Jay W1VD  WD2XNS  WE2XGR/2
>
>
>
> Typical front-to-back
> ----- Original Message ----- From: "Stefan Sch=E4fer"=20
> <schaefer@iup.uni-heidelberg.de>
> To: <rsgb_lf_group@blacksheep.org>
> Sent: Saturday, July 30, 2011 10:08 AM
> Subject: LF: K9AY loop for LF at W1VD
>
>
>> LF,
>>
>> I just searched for a LF /p antenna that can be fixed in the trees of=20
>> a nearby forest. I quickly came to the pages of W1VD and saw his=20
>> design of a K9AY loop ( http://www.w1vd.com/k9ay11.pdf).
>>
>> Jay, if you are still QRV here (long time ago), how well does design=20
>> perform, i.e. how many dBs can a noise source be attenuated by=20
>> adjusting the potentiometer (that changes the dynamic "resistor",=20
>> i.e. the output of the optocoupler? What angle is covered by this=20
>> method?
>> It is an interesting idea to do it this way!
>>
>> Can you give us a short report about the performance of your antenna?
>>
>> I would like to arrange a fixed loop for LF receiving in the forest=20
>> to be QRV on LF without the need to carry my rather big and heavy RX=20
>> loop antenna in the car. So i could use my bike instead.
>>
>> BTW, my /p LF homemade receiver using the SBL3 has only one amp stage=20
>> and the total power needed is 12V*12 mA! So i got the idea to try a=20
>> DC/DC converter to supply the RX out of the USB! This would make a=20
>> heavy battery obsolete. I took a 4.5 Euro 1W unregulated converter=20
>> and added a 78L12 and 2* 100 nF. As far as i can see the converter=20
>> (=3DSMPS) adds to moving or broadband noise to the signal received!=20
>> Good news for sceptics about SMPS ;-)
>>
>> If all works well i just need the netbook and the RX which is in the=20
>> format of 10cm x 3cm x 8cm and a /p 70cm radio to become QRV soon :-)
>>
>> 73, Stefan/DK7FC
>>
>