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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