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Stefan,
>> Is it possible to 'build' a cardioid
antenna by combing the signals of E and H within SpecLab? It is only a mixing of
these two signals with a different 'weight', right? This could be done in the
'left to right output amp', right?
Yes, this should be possible, although I never
actually tried it that way. The weight factor can be made positive or negative
for pointing the main lobe eg. west or east. Note that you will have to
adjust the analog hardware such that the phase difference between the whip
and the loop channel is either 0° or 180°, so that the signal from the
unwanted direction can cancel.
> I assume i will need a relay to select one of
the two loops to feed it to the RX, but what happens if i use the combined loop
signal to try that?
If you use the 90° combined signal, you still
get a null in the back side of the cardioid - this is what can be selected
as "single, sharp cardioid" in SpecLab's RDF menue. Despite of having only
two input channels, you can conveniently point the antenna in any direction
by software. The difference to the "classic" cardioid pattern is
that the "other" loop antenna also contributes signals from the sides,
effectively reducing the forward gain and making the null sharper ( |cos|
instead of cos^2 pattern).
Usually that sharper null is more of a
disadvantage, for example if you want to suppress QRN from a
range of angles around the back side (eg. statics from southeast
Europe). But occasionally sharpness can help to null
an undesired signal coming in from a direction near that of
the desired signal.
All the best,
Markus (DF6NM)
Sent: Monday, June 01, 2015 1:39
AM
Subject: Re: LF: Small MF ferrite
antenna games
Hi Markus,
Yes yes, great ideas. I will go
on step by step. First i need to configure the link in stereo mode and see if it
runs stable. The mono-stream needs about 220 kBit/s. It's availability is fine
now over 2.4 km even in slight rain. I assume it will work. If this runs stable
then i can build a stereo-RX.
Is it possible to 'build' a cardioid antenna by
combing the signals of E and H within SpecLab? It is only a mixing of these two
signals with a different 'weight', right? This could be done in the 'left to
right output amp', right? I assume i will need a relay to select one of the two
loops to feed it to the RX, but what happens if i use the combined loop signal
to try that?
73, Stefan
Am 27.05.2015 12:32, schrieb Markus
Vester:
Yes Stefan,
bring colour into your life ;-) Even after more than 10 years, I still
sometimes enjoy just sitting and watching things roll by on the colour-RDF
screen.
With crossed
loops and an E-field antenna you have a number of options.
1. The
colour-DF scheme takes the E-field on one channel and a 90°-combination from
two loops on the second, providing omnidirectional reception with 360° RDF
functionality. The combiner is simple to make, and you'll have to add a second
RX channel. A stereo soundcard can be used, and SpecLab has everything needed
onboard. Having a 475 kHz directional grabber available in Heidelberg would
surely be very useful to the community.
2. Then you can
hardware-combine whip and loop for a unidirectional cardioid pattern. This is
equivalent to K9AY or similar antennas, which on LF have provided outstanding
results for a few observers in quiet locations. The crossed loops can be used
with electronic steering or a small goniometer, which allow you to virtually
rotate the cardioid in the shack. Note that the phase-based colour-DF scheme
still works if the cardoid antenna instead of the whip is used as intensity
source. I have tried this on LF, but in my location SNR gain was not up to
expectations because my loops are too much affected by noise from underground
cables.
3. The next
step would be downconverting and digitizing all three channels separately,
allowing you to steer the cardioid by software and even monitor different beam
headings simultaneously. But a three channel digitizer is not so easily
available, and you'll need dedicated software for postprocessing. Paul
Nicholson can do this at VLF, using three stereo soundcards augmented by GPS
ticks, and a posteriori synchronisation in his own software.
All the
best,
Markus (DF6NM)
-----Ursprüngliche
Mitteilung-----
Von: DK7FC <[email protected]>
An: rsgb_lf_group <[email protected]>
Verschickt: Mi, 27 Mai 2015 2:13 am
Betreff: LF: Small MF
ferrite antenna games
MF,
Today i've played a bit with a small ferrite antenna for 630m.
It is 14 cm long and has 8 mm diameter.
Without any calculations i wound a winding of unknown number of turns
around the rod and quickly found C about 200 pF at resonance (475 kHz).
Then i added a few turns for a 50 Ohm output (measuring the voltage of
an induced signal at resonance. When applying 50 Ohm, the voltage has to
decrease to 50%) to the RX.
https://dl.dropboxusercontent.com/u/19882028/MF/small%20MF%20ferrite%20antenna.jpg
As expected the input signal is to low, it does not rise the noise of
the RX, so i'm missing about 20 dB. It can't be much more though because
i can receive IQ2MI/B clearly in QRSS-30 on 476.180 kHz with 25 dB SNR
in 122 mHz, see attachment.
The antenna is hanging in 6m AGL in a tree in my garden...
I'm playing with the idea of a rotary H-field RX antenna for MF, maybe
in combination with a stereo receiver and a E-field antenna. Oh and
maybe with a colour spectrogram as known from DF6NM. A lot of things to
do :-)
73, Stefan
PS: Yesterday, in a CW QSO with DK6SX/p on the loop he once completely
disappered into QSO which never happend before when receiving on a
omni-directional antenna. So i guess the colour changes in such a
spectrogram must be quite interesting and informative...
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