Many thanks for that interesting Mail Jay. Oh dear, another new project
on LF ;-) It never comes to an end... So, it makes sense to have both
types of loop antenna present fro RXing, depending where the desired
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
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).
OK, so i will try a fixed value first.
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.
This could be interesting for Alex/LU8YD who prepares a new improved LF
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 Schäfer"
<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
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
|
