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From: <VE7SL@shaw.ca>
To: <rsgb_lf_group@blacksheep.org>
References: <4F935E6B.2020203@iup.uni-heidelberg.de>
In-Reply-To: <4F935E6B.2020203@iup.uni-heidelberg.de>
Date: Sat, 21 Apr 2012 19:04:55 -0700
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Subject: LF: Re: 137 kHz in South America !
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This is excellent news Stefan and Martin's grabber should make a great 
target for stations here in NA with so few permanent grabbers available. The 
propagation from VE7 rarely favors the E-W or polar path and is almost 
always best towards the S-E part of the continent, directly in line with YV. 
Hopefully he will stay around for some time and thanks for laying all the 
groundwork!

Steve / 73


> 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
>


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