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Stefan,
just tried some more WSPR between 12:44 and 13 UT,
but with the current intense QRN there's just no chance. In the morning, there
were only sparse flashes (maybe 1 to 5 per WSPR sequence), which would have been
easily cured by noise blanking. I was actually wondering why the
decodes were so much affected by a small number of spikes.
73, Markus
Sent: Saturday, June 27, 2015 2:26 PM
Subject: Re: LF: Heidelberg remote MF receiver
Hello Markus,
Most interesting, thanks! Let us use the
strong QRN to check if SL does perform better if the SpecLab NB is used in front
of WSPR. Ah i could use a 2nd instance for a 2nd instance of WSPR(2), feeding
VAC1 to VAC3 including the NB, while the current instance feeds VAC1 to VAC2
without a NB to WSPR(1).
Just continue to run your WSPR in 100% mode, if
you like :-)
73, Stefan
Am 27.06.2015 14:12, schrieb Markus
Vester:
Hi Stefan,
since last night your two receivers have been
operating without interruption, allowing to compare results from your two
grabbers.
- WSPR: Last night, 21 of my low-power
WSPR transmissions were decoded simultaneously by DK7FC/p and DK7FC. On
average, the /p receiver had a 5.67 dB SNR advantage. For my
direction, the receive loop and the T antenna seem to have performed
similarly.
Today between
11.08 and 11:24 I sent some more SNR sequences with higher
power (0.1 W EMRP), expecting a higher SNR difference in the lower daytime
background noise. However half of the transmissions were not decoded on
either grabber, and those that were picked up by both showed only a small
advantage. This is probably due to the strong QRN from flashes from a nearby
thunderstorm, which for some reason are heavily affecting WSPR decodes.
It might help to use effective noise blanking in the SpecLab instance
which is feeding WSPR. Anyway if the
statics happen to ease off I will attempt another daytime comparison
later today.
- DFCW: Between the thunderstorms this
morning, my 2 mW DFCW-60 transmission was definitely picked up more
clearly on the /p receiver. However this one suffers from a large
frequency drift (10 Hz upwards), which appears to be strongly correlated with
RasPi core temperature and solar chargerate plots - so presumably just
crystal temperature. In addition, some of the dashes appeared
slightly disrupted, either by audio glitches or by fast and small LO
frequency jitter. During the storms, my impression was that noise
blanking in the narrow spectrograms could also be optimized a
bit.
There are a couple of QRM lines which are always
commonly visible on both receivers (472.36 and 477.74 kHz). I am
wondering whether you could perhaps use them as references for a SpecLab
frequency drift correction?
BTW. I have taken a number of
screenshots from your grabbers which I have copied to our private
dropbox folder.
All the best,
Markus (DF6NM)
Sent: Saturday, June 27, 2015 12:39 AM
Subject: LF: Heidelberg remote MF receiver
Hi Stefan,
it looks like signals are consistently
better on your remote receiver, perhaps around 6 dB or something in that
ballpark. So it seems that all your work is finally paying off! I'm
looking forward to see a daytime comparison tomorrow.
My guess is that the main contributor to
frequency variation would be the 461 kHz LO crystal rather than the soundcard
samplerate. Anyway exchanging the 12 MHz crystal may possibly have no effect
at all, because the samplerate of USB soundcards is usually derived
from the bus master clock (ie the RasPi) and not from the internal
crystal on the dongle.
Best 73,
Markus (DF6NM)
Sent: Friday, June 26, 2015 11:22 PM
Subject: Re: LF: 476.181 kHz from indoor loop
Hi Markus,
Really? Wonderful! :-) And the stream is
still running. I'll watch it some days now to see if all Raspi problems are
gone, then the next part-project is the RX.
Meanwhilethe sky wave is
present and i can see you quite strong in DFCW-30 with your 3 mW ERP from the
loop. I missed watching you on the remote grabber in daytime. What was the SNR
ralative to the city location? Same or better? I switched back to the T
antenna in the afternoon. It would be interesting so see you on my loop. On
21:19 i switched to the loop!
Ah and now you can see the drift of my RX
which is quite visible, but still uncritical for QRSS-30 or WSPR.
I
thought about changing the 12 MHz xtal of the soundcard. It is the cheap SMD
xtal which has 100 ppm/K but there are other versions with 30 ppm/K. Maybe an
idea, they are no expensive and still compact...
73, Stefan
Am
26.06.2015 21:04, schrieb Markus Vester:
Hi Stefan,
good to see the remote
station working nicely now.
>> but don't see you
...yes you do ;-) There is a slight
frequency offset in the remote grabber which had put me out of your
QRSS-30 band. I now switched to my "heritage" QRG 136172.5
ahem 476172.5 Hz, and voila there it is, loud and clear.
Currently still on the low Marconi, also
about 2 mW EMRP. The relatively strong coupling to the LF
grabber E-field antenna produced some aliases and noise there, which
have been mitigated by a 475 kHz Saugkreis (trap) - same as in old AM
radios ;-)
73, Markus
Sent: Friday, June 26, 2015 7:46 PM
Subject: Re: LF: 476.181 kHz from indoor loop
Hi Markus,
Thanks for your DFCW-30 transmission. I
can see you clearly in daytime on my RX in the city! However i can't see you
on my RX is the garden! The remote system seems to run stable now, at least
for a longer time then in the last 3 days :-)
http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_remote_Grabber.html
I
switched between a T antenna and a loop beaming 300/120 deg but don't see
you. It appears that the hill between us is (my garden is on the hill side,
the city antenna is more distant to the hill) actually reducing the SNR. So
it also reduces QRN from the east and favours the west. But i would prefer
an omnidirectional pattern :-/
73, Stefan
Am 24.06.2015 12:11,
schrieb Markus Vester:
I am currently running a DFCW-60 beacon on 476.181 kHz, using
the same 10m^2 indoor transmit loop as previously on LF. With 35
Watts of RF input, estimated radiated power is around 2
mW, with lobes pointing west and east.
The daytime groundwave signal is visible in the bottom panel of the
DK7FC MF grabber. Going by the CCIR plots for 3 mS/m conductivity,
the groundwave attenuation for this distance would be about 23 dB in
excess off lossless 1/r propagation, resulting in approximately 0.2 uV/m
in Heidelberg.
Best 73,
Markus (DF6NM)
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