Hi Stefan, VLF
>Don't expect better results from a larger antenna at the same location
Not the same location. I'm using my Tx antenna in Benidorm (IM98wn). My grabber runs in Albir, another location at 7km at IM98xn
Finally used a simple audio transformer to connect the vertical LF resonant antenna to the PC audio card
And results are quite interesting. This is the 24KHz VLF band in a 20 minutes spectrogram
https://www.dropbox.com/s/fsmk8lbti8ap90d/Benidorm%2090m%20vertical%20LF%20tuned%20VLF%2024KHz%20spectrogram%2020%20minutes.JPG?dl=0
Comparing with Paul's VLF receiver I can see also the same stations here. The lower JXN and the S/N are
The most important is that QRM from lift motors variators is produced just in a few frequencies, not wipping
all the band. You can see the elevators activity as signals around 16KHz, 15KHz, 10.5KHz and strong at 8 and
around 5.5KHz
During the 20min there was a sudden reduction in background noise. This is not due to modifications in my
settings, but real QRM stopped. Has to investigate why it happens
I made a detailed spectrogram around 8KHz
https://www.dropbox.com/s/cjnsc0mpqdec5ho/Benidorm%2090m%20vertical%20LF%20tuned%20VLF%208270Hz%20spectrogram.JPG?dl=0
Fortunately the offending signals are concentrated on 7700, 8000 and 8300Hz. So 8270 with high integration will be out of the
elevators interference, which is a very good news :-)
I need a signal. And connect the audio to 1pps
Tonight I will be tuning the 11.904 Alpha. Seems that there is a fainth trace in my grabber
73 de Luis
EA5DOM
Hi Luis,
Moving the grabber to a quiter place is an “old” plan. There are some options but all of them requiere dedication
and negotiation. in other words …. time!
I know :-) Everything needs dedication.
Using the transmitting antenna for Rx in VLF may be the quick option
Don't expect better results from a larger antenna at the same location.
It may be an option to build an active symmetrical antenna, as recently described by DF9RB, and lift this as high as possible out of the 'cloud' of QRM which surrounds the building. But this is a new experimental project which, again, needs time and dedication
:-) And it will never give the same good results as you can get from a quiet location.
I would suggest to use your existing VLF RX antenna and try it out on the alternative location, using a notebook running SpecLab. Just for a few minutes. Use a fast running spectrogram, 500 ms/pixel covering 0...24 kHz. And then take a screen capture...
I’m looking for 11.907Hz Alpha using the 90m vertical tuned for LF. I can get fainth traces with the MiniWhip
from 06 to 10 UTC which can be seen in my grabber. Let’s see if there is something detected with the vertical
despite the elevators QRM
The Alphas are OFF since some months, except some temporary periods taking a few hours, sometimes with reduced power or not all transmitters active.
ZEVS is back with good availability since some time again but it is more challenging to receive it at all.
I’m using the Perseur for that. The PC soundcard would be better at that frequency. Must make an interface
T-O-D-A-Y ;-)
That was yesterday. And did you? :-)
73, Stefan
