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Re: VLF: getting on 8.970kHz

To: rsgb lf group <[email protected]>
Subject: Re: VLF: getting on 8.970kHz
From: Jacek Lipkowski <[email protected]>
Date: Fri, 8 Sep 2017 21:49:58 +0200 (CEST)
In-reply-to: <[email protected]>
References: <[email protected]> <[email protected]> <[email protected]> <[email protected]> <[email protected]>
Reply-to: [email protected]
Sender: [email protected]
User-agent: Alpine 2.11 (DEB 23 2013-08-11)
look for ublox neo-7m modules. they will go over 10MHz (neo-6m modules will generate <1kHz). they were avaliable on dx.com, ebay.com and other auction sites. these will work <10MHz (according to manufacturer specs, they will go higher). they can be used for generating a signal directly (it's an NCO with 48MHz reference, so try to use frequencies 48MHz/(integer value) for best spectrum purity), or as a reference for ebsynth
the neo-7m modules are very cheap (abt 10 euro). then only problem with
them is that they don't have a tcxo (blowing compressed air at them will
cause them to loose sync)
jacek


On Fri, 8 Sep 2017, JACK ASKEW wrote:

Date: Fri, 8 Sep 2017 11:17:05 -0600 (MDT)
From: JACK ASKEW <[email protected]>
Reply-To: [email protected]
To: rsgb lf group <[email protected]>
Subject: Re: VLF: getting on 8.970kHz

Hi Stefan

It appears that Amazon will not ship that XCSourse GPS Locating Module NEO-6M to 
Canada. 
I questioned XCSource why this is so and I'm waiting back for an alternate or 
answer from
them.  There might be another choice out there that does but have not come 
across it as
yet.

73, Jack - VA7JX

__________________________________________________________________________________________
From: "DK7FC" <[email protected]>
To: "rsgb lf group" <[email protected]>
Sent: Thursday, September 7, 2017 1:40:49 AM
Subject: Re: VLF: getting on 8.970kHz

Hi Jack,

Ok, so i'm continuing to write on the reflector. It is not at all a waste of 
time to read
the conversation. Most potential newcomers are in a similar situation like you 
and they
may be interested to see that there are more stations considering to get on the 
air down
there, world wide! For example, IK1HSS tried to receive my VLF carrier 
transmission, but
no one knows, except me. Sharing thoughts can never be a waste of time. Don't 
we all have
loads of time available anyway? As long as someone own a TV, there must be more 
time than
needed :-)...

Now, forget the loop for VLF transmissions. Your inv-L will give a very good 
radiator for
VLF! Important parameters are height and capacity, you know. In the first steps 
you don't
need QRO. 100 W from a normal audio PA is sufficient because the voltages will 
be very
high! At 250 W on 8270 Hz i'm getting about 30 kV across the wire. Your wire 
and the
isolators have to withstand that voltage. If the wire is to small, there will 
be partial
discharges. It makes no sense to run 1 kW then. It would rather make sense to 
use a bigger
wire or even more wire (capacity).... The first thing to concentrate on is a 
stable signal
generator using 1 PPS.
Buy that one for 
example:https://www.amazon.com/XCSOURCE-Locating-Aircraft-Controller-TE624/dp/B01N2GK1YK/ref=sr_1
_6?ie=UTF8&qid=1504772304&sr=8-6&keywords=neo-6m

You seem to have a high antenna capacity which is a big advantage. It is very 
promising
that you can radiate a very strong signal. There is no time to loose!
For the coil i suggest to use a single layer coil using 0.4 mm or even 0.6 mm 
diameter
wire on a tube with 0.3 m diameter or higher. It depends on the space you have 
for placing
the coil. It should stay dry all the time!
You need patience to wind it but it is very relaxing. :-)

I recommend to build an analog amperemeter covering 0...1 A antenna current. It 
is trivial
to build it. Just use a bridge rectifier out of fast switching diodes such as 
UF5404 and
connect the meter to the DC side. The AC side is connected between coil and 
ground.
The coil is for compensating the capacitive component of the wire. The residual 
resistive
component is transformed to the PA output impedance using a big ferrite 
transformer
(toroid) which also provides galvanic decoupling.

Now, just order the GPS module, the wire and search for a suitable coil body :-)

73, Stefan

PS: With that antenna, you can become the strongest amateur VLF station!


Am 06.09.2017 17:12, schrieb JACK ASKEW:
      Hi Stefan

Thanks for the reply.  Sorry to hear that my ERP will be so little with this 
setup. 
A few 10dBs is a lot, I had no idea it would be that much.  I just assumed I 
could
make up the difference by running a much larger audio amplifier.  It would no be
hard to put 1KW amplifier on with the availability of some cheap 12V car amps 
now
available.  But maybe this might not be enough power.

For MF I'm currently using a inverted L ~73m long, 24m of that has 3 wires as a 
top
hat, but hopefully will be increasing that soon.  The height of the antenna is 
~24m
at one end and >36m at the farthest end.  The Tx is a HB set up with 4 FETs 
running
class D, capable of 1KW but I have not pushed it that far as yet.   I have been
limiting it to ~300W for local contacts between here and stations South of the
Island.  I use an Icom R75 receiver for receiving, it seems to work very well 
on MF.
Best heard DX so far on WSPR is ZL2BCG and VK4YB.

I was hoping you would say that QRSS240 would work with this limited budget set 
up.
It doesn't sound like I need to proceed much further unless I can find a much 
larger
audio power amplifier, a lot of patience, a lot of luck and a good GPS 
receiver.  I
did look at a few of the NEO-6M GPS units, but not sure which one on Amazon you 
were
referring to.

I agree maybe I could go on the reflector with our conversations, however since
using even moderate size loop on this dreamer's band does not look realistic,
perhaps it would be a waste of everyone's time?
I'll play with it for a few more days if things don't improve I'll pack it all 
up.

Thanks for your help Stefan.
73, Jack - VA7JX


__________________________________________________________________________________________
From: "DK7FC" <[email protected]>
To: "Jack Askew" <[email protected]>
Sent: Tuesday, September 5, 2017 3:16:05 AM
Subject: Re: getting on 8.970kHz

Hi Jack,

Can we do the conversation on the reflector maybe? There is little activity and 
each
conversation may help to rise some inspiration to lead to an increased 
activity...
Your decision, just reply to the reflector in the next answer if you like.

Well, i understood the procedure you're describing and this is of course the 
way to
go for getting a resonance on the desired frequency.
But, the ERP will be so little with this setup, i guess you are a few 10 dB away
from leaving a trace on VE7SLs site.

Which antenna are you using for LF and MF? A typical top loaded vertical antenna
will give you the best results on VLF as well. What is the capacity of that 
antenna,
in pF?
But i understand, a loop is much easier to match on that frequency, easier than
winding a large coil :-) But if you want to cross 186 km, which is a serious
distance already, you will need to large coil and several kV across the antenna!
Furthermore you won't manage QRSS240 on that band. QRSS 240000 is more 
realistic!
That means, you need a receiver and transmitter that has the necessary 
stability.
The cheapest and best way to go is using a GPS module like NEO-6M, which is
available from Amazon. It provides a PPS pulse which must be fed into the mic 
input
of the soundcard. Together with SpecLab you can generate a perfectly stable tone
then, as well as DFCW, QRSS, EbNaut, etc.... The same must be used on the RX 
site.

It is also helpful to do local tests, maybe with a notebook, in
1...2...3...4...5...6 km distance, just to get an impression...

What do you think?

I would say you can build the system from junk box parts mostly, that the 
advantace
to the activity on the other end of the spectrum :-)

73, Stefan

Am 04.09.2017 22:42, schrieb JACK ASKEW:
      Hi Stefan

I'm having problems finding your right email, so if you get this twice I
apologize. 

I have been trying to get a signal on 8.970kHz but with little success.  Since
I'm on a limited budget, I have decide to try a large coaxial loop instead of
a large coil. I chose RG-59 coax (center and shield) since it has a low
resistance as appose to copper wire. The bottom of the loop is only ~10m off
the ground but the top side is ~21m up, circumference is ~76m. The mid point
goes down to a matching box consisting of a pc board with HV caps and a
FT-240-78 core with a sec and pri winding. The primary is 11T of of #14 ins
wire and a secondary of #18 awg enamel wire with 55T which connects to a
chassis mount SO239 for the coax which goes back to the Tx amp ~30m away.  The
HV caps totaled 2.86uF and is in series with one side of the coax loop. The
loop measured 100uH, so the combined capacitors plus the 100uH loop seemed to
be close to the calculated values, but I think it could have been higher. The
Tx is a simple 140W audio amp driven by a Windows free downloaded program
called Audio Measuring Systems.  I measured 2A of RF using a calibrated RF
ammeter. The same meter was used to select the capacitor values for maximum
O/P.  I tried using a scopematch designed for .475 MHz but I guess the toroid
across the internal coax line is too lossy as it gets warm and besides the
current reading was very low compared to the voltage. 
I don't know how far I can Tx yet.  Steve, VE7SL has tried to receive me, he
is ~186 km and used a Perseus receiver with ~24Hz BW and QRSS 240 but no luck
so far.
We think we might have too low of a EIRP for that distance.
Is there any other way of optimizing the RF O/P besides using a RF ammeter?
Your thoughts on this would be much appreciated.
Thanks in advance.
73,
Jack Askew - VA7JX




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