LF!
I'm glad to tell you about a most interesting and pleasant story and
good news for the LF DX interested OMs, especially in the U.S., the UK
and EU.
Some weeks ago the VK guys and me decided that the EU-VK 137 kHz spring
season is over now. The DCF39 S/N became lower and lower and QSB rised.
An overview of my worked DX (one-way) showed that i have EU, AS, AF, NA
and OC but SA, the South American continent is missed.
Compared to the VK path, where a significant part goes above land, even
desert, SA should be much easier, at least the northern part.
From the recent history i know that it is possible _for all of us_ to
motivate and recruit radio amateurs to the LF and VLF band, even if they
didn't even know that an amateur allocation arround 137 kHz exists for
many countries. I can tell you it is an exciting work to tell others
about the LF hobby and we could do much more to make the band more alive.
Well, so my idea was to find someone in SA to arrange a LF system (at
least for receive) and a grabber page that makes it available to all.
First i wanted to concentrate on the northern part of the continent.
That's how it goes: :-)
A very suitable website to find potential LF newcomers is
http://pskreporter.info/pskmap.html. You can simply zoom the country
where you like to have a new station and see if you can find a callsign
:-) You can be sure that everyone who apperas on this website is an
active amateur radio station that has a RX, antenna, PC and internet
connection. Most often they have an account at www.qrz.com too. Here you
will find their email adress.
It doesn't matter if they are still concentrated to HF and digimodes.
You know, LF is a very interesting part of amateur radio work and if you
can fascinate them, it is a small step!
Quickly i actually found a station in Venezuela, Martin/YV7MAE. He is in
the very north east, in FK81BD. He has never done anything on 137 kHz
but is very interested... The receive setup is a IC706 and a IC703. The
703 is used for LF now. In that country it is not so easy just to build
a PA0RDT antenna or a resonated loop since the electronic parts are
simply not available. Parts are rare and expensive. Even ordering parts
from ebay or so isn't easy since it's not so easy to change the money in
USD or EUR. So we had to improvise and were limited to some few antenna
systems. There is not even a chance for him to get an oscilloscope or a
signal generator. So we tried to get out a signal from the 703 or 706
but nothing seems to come out.. It would be possible to down divide a
signal at 1.8 MHz to the LF band, using a CD4060 or so. But it is not
available!!...
So, we decided to use a normal wire antenna and took an old ferrite
transformer from an old damaged PC supply. A isolating transformer was
wound with 60 turns on the antenna side, grounded at the lower end with
an exclusive LF earth. The RX winding has 20 turns and is connected by a
short 75 Ohm coax cable to the RX (all improvised). Martin still plays
arround to find the best ratio and number of turns for an optimal S/N,
i.e. matching, because the magnetic parameters of the transformer are
unknown. BTW the wire is a 38m long iron wire (improvised :-) ) at about
7m above ground.
First nothing at all was received. There was a misunderstanding how to
connect the antenna to the transformer but later it was all fine. In the
web i found a NDB which is very close to his QTH:
http://www.ourairports.com/navaids/MTA/Margarita_NDB_VE/
After spending some disappointing receive nights, now Martin actually
received another NDB, TAB at 323 kHz! This was his first received signal
with this receive setup, yesterday! Now he acutually has a reference
signal which comes from the far field. Quickly he found that 60 turns
primary were better than 40 and that 80 turns resulted in the same
signal strength than 60.... So far so good...
We tried then to receive the carrier of the 153 khz AM broadcast
staions, which worked very well in the first attempt. Slowly it became
dark in YV and so we actually successfully received traces of DCF39!!!
:-) The mile stone! After preparing the grabber page i prepared a
SpecLab file to display DCF39 in 45 mHz over the night. The images were
uploaded to the webpage and saved to a local folder. Now looking to the
archive, best S/N was arround 20 dB (so far without any noise
reduction!), seen here on Martin's dropbox:
http://dl.dropbox.com/u/74746618/Pictures%20for%20exchange/DCF39_09.jpg
This is a very clear trace but still it looks like lack of sensitivity,
so we have to improve the system further. Also the typical QRN morning
dip is not visible! But anyway a very good result after some days. It
shows that the frequency drift and offset of the 703 is reasonable, also
suitable for QRSS-60 detections later. We also checked in a wideband
window, covering 0...3 kHz, i.e. the SSB filter width, that there seems
to be no drifting mains harminics or SMPS sidebands, hopefully not due
to lack of sensitivity ;-)
Probably we need an air coil and a well resonated receive system to
generate a higher signal level for the deaf IC703. He also has some
variable capacitors that look like arround 200 pF or so. So it should be
possible to match the system if it has some Q. This first success with
the SMPS transformer was very important though! Also the absence of
strong QRM makes the project even more promising now.
Luckily Martin has a internet flatrate, so we worked together on his PC
using a Teamviewer remote connection to install a dropbox, a grabber
page and SpecLab, with automatic jpg upload. It was quite difficult for
me since the PC is in Spanish :-)
Who knows, maybe some day he will appear here in the LF reflector. He is
also in a nice local radio club where they have a high tower for a VHF
repeater. Maybe they will add a transmit antenna soon? ;-) Does someone
know about a LF allocation in Venezuela?
Not only for US, UK, and EU but of course for the southern stations in
South america this could be an interesting new challenge. Soon we will
make first tests in the 137 kHz band but it looks like we have to find
another 10 dB S/N from somewhere. Any good ideas? No, a preamp cannot be
built, due to lack of electronic parts! Somehow i find that all very
exciting, i mean not having all the parts available but have to
improvise, maybe like in the very early days! :-)
So let's hope for continued progress, improvements and interest!
Ah, of course, the link tho the new Venezuela LF Grabber (still in test
mode): http://dl.dropbox.com/u/74746618/LF/YV7MAE_LF_Grabber.html
It becomes more interesting at night of course. Local time is UTC-4. So
far a test window of DCF39 is shown but soon we will run a EU60 and/or
TA60 window.
73, Stefan/DK7FC
