Stefan
I've tried a number of receive antennas for 137 / 185 and 500 kHz and the K9AY, with it's ~20 dB F/B
has performed the best of the lot on 137 and 185 kHz. With the pattern directed toward the NE
listening for EU stations the null is SW ... which is handy here as thunderstorms are most likely to
be in that direction. A standard loop antenna's figure 8 pattern provides equal reception in the
direction of the thunderstorms - not a good plan. So the decision to use a standard figure 8 pattern
loop or a K9AY cardiod will depend on the direction of the desired signal and direction of the
interference.
The value of the terminating resistor is somewhat critical for optimum F/B response. Once the
optimum value is found one could probably replace the variable R with a fixed R if desired. I've
found it beneficial to install a small ground screen (about a dozen radials that extend slightly
beyond the loop) to stabilize the F/B under varying ground moisture conditions. BTW, the F/B holds
all the way down in frequency to where the ferrite cores run out of steam ... and up in frequency to
the point where the loop is about 1/8 wavelength in circumference (750 kHz).
A couple years back I installed 1000' BOG (Beverage on ground) for 500 kHz oriented the same
direction as the K9AY. The Beverage wins out over the K9AY due to the tighter pattern and lower
overhead response. Wish I had space for the equivalent 3600' BOG for 137 / 185 kHz! Until that day
comes I'll make do with the K9AY.
Jay W1VD WD2XNS WE2XGR/2
Typical front-to-back
----- Original Message -----
From: "Stefan Schäfer" <[email protected]>
To: <[email protected]>
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 a nearby forest. I quickly
came to the pages of W1VD and saw his 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 perform, i.e. how many dBs
can a noise source be attenuated by adjusting the potentiometer (that changes the dynamic
"resistor", i.e. the output of the optocoupler? What angle is covered by this 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 to be QRV on LF without the
need to carry my rather big and heavy RX 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 and the total power needed
is 12V*12 mA! So i got the idea to try a DC/DC converter to supply the RX out of the USB! This
would make a heavy battery obsolete. I took a 4.5 Euro 1W unregulated converter and added a 78L12
and 2* 100 nF. As far as i can see the converter (=SMPS) adds to moving or broadband noise to the
signal received! Good news for sceptics about SMPS ;-)
If all works well i just need the netbook and the RX which is in the format of 10cm x 3cm x 8cm
and a /p 70cm radio to become QRV soon :-)
73, Stefan/DK7FC
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