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To All from PA0SE
With Vaino, OH2LX, I have exchanged several
e-mail messages on the
subject of measuring field strength.
Vaino has
many years of experience in that field and I thought
subscribers to the
reflector might be interested in his
observations. So I asked Vaino
permission to distribute our
communications via the reflector and he kindly
agreed.
I compiled it into a single
message.
Vaino's remarks in red, mine in
blue.
We have been measuring a number of
LF/MF/HF stations
with calibrated measuring system using a R&S
ESH3
for more than 10 years.
Attached please find the monthly graphs
for stations
DCF77 and DCF39, with average hourly 50%
values.
The system noise threshold level (with Bw
= 200 Hz)
checked during DCF39 QRT hours seems to be
7 dBuV/m (equivalent
rx input level = -5dBuV).
There have been no breaks in DCF77
transmission.
In June the daytime values have been
stabilized to
show a rough summer time ground wave F-s.
The radiated power of DCF77 is about 25
kW, so the
radiated power of DCF39 probably is less than 25
kW.
Distances: to DCF77 = 1545 km, to DCF39 =
1224 km
Our attempts to calculate ERP even for
e.g. nearby
Decca station (d=12 km) have not been succesful
(after more
than 10 yrs of continuous measurements).
ERP's have been checked by
overflight measurements,
we use a Piper Arrow for such flight
measurements
and specially tailored sofware for
calculations.
Dear Vaino,
Thank you very much for your e-mails. I tried
to read the
attachments but the computer did not yet succeed
in opening them. But
that is entirely my fault. I only recently acquired Windows
98 after several
years operating under MS-DOS only. I still have to
learn a lot about doing
things under Windows. But I am lucky in having
several amateur
friends around that are willing and able to help me out.
So
don't worry.
I certainly am going to read the attachments after
enlisting
the help from one of those friends. Interesting to learn that
finding ERP
from field strength measurements even over short distances does
not
work. Does that imply the CCIR graphs are no good?
Allright Dick,
surely would appreciate your comments
about our experiences on the field of
measuring LF/MF
field strengths over various
distances.
Please let me know if you wish me to resend attachments.
I have
been using Win98 since February, Win95 before that.
Before I retired I was a member of CCIR
Study Group 6
(Ionospheric Propagation) but supposedly have been
spending
more time on monitoring and measuring VLF/LF/MF stations.
CCIR
Ground propagation curves are the best available and
they give good idea how
the different soils can behave.
Main problem is that they don't work in
everyday practice
while one tries to calculate EMRP from point
measurements.
DGPS advisor has been prof David Last
(G3???) at the
University of Wales. They have their own ground
conductivity
data bank for the whole world. We proved with our
measurements
that their data bank values are not directly applicable
for
our conditions. The situation elsewhere is not, of course the
same but
we were first to start using DGPS on our car ferries.
I understand the soil
in England is much more homogeneous, not
to talk about the Netherlands. We
have our archipelagos etc.
The seasonal GW variation was already documented
in 1940's
but some people on DGPS business have no knowledge of it.
The
variation on high seas is much less than on ground paths.
I have about 500 flight hours on that
specially equipped
Piper Arrow. In 1974-75 we produced a ground conductivity
map
of Finland by measuring available and some temporary stations.
It has
been a series of calculations, measurements,
comparisons.
First LF/MF
campaign for EBU started in 1948 at Hki/Laajasalo
with RCA 308 and other
rather difficult to use Fs equipment.
Latest assignment was to measure all
Finnish and Swedish
DGPS beacons and to produce reports for Maritime
Authorities.
So we still have 30 LF/MF/HF frequencies being measured 24h
a
day with R&S ESH3 and active CCIR type 1 m monopole.
I surely wish to
contribute for this 135 kHz business before
these ESH3 measurements will be
stopped at the end of 1999.
1989-1998 measurement data have been saved to a
CD Rom
and I have been hoping that some young student will help
me.
Contrary to most DGPS people we have no commercial interest.
We took
it as another interesting and rewarding hobby. Hi
I am grateful for your quick reply and
useful comments.
No, there is no need to send the attachments anew. I am
sure
that my good friend PA0GJH can help me out.
I think most LF-amateurs
will be most interested in your
comments. You must be one of the few having
real experience over many years with
respect to field strength
measurements.
I therefore ask whether you would mind me putting some
of
your e-mails to me on the reflecor of the
RSGB-LF-Group?
Sure Dick, use of any information would be
just fine.
I hate to sound 'professional' after all,
it's supposed to be
fun for most hams..?
I send monthly contribution to Martin
Harrison, G3USF
for 'The Six and Ten Report', for observed Au and Es.
This
contribution will continue in the present form
until the end of 1999, after
that Sodankyla VHF
measurements will be ended, which is
unfortunate.
Especially Band I observations have been
useful.
Jokela (60N34 25E00) VHF/UHF measurements
will continue
and we'll see what will happen to ESH3
measurements.
By the way, meanwhile I made graphics of
138.83 & 77.50
for the last half of 1998. They look amazingly alike
with
1999 graphs. So, hope we can put the graphics to some
Web site,
perhaps Steve, G0AEV can put them to PSC site.
PS I'll send you 1998 pictures
zipped for comparison
With the help of
PA0GJH as a test one of the graphs in your
attachment appeared on my
monitor in beautiful colours.
But this at the same time brings up a question:
what do the
different colours mean?
And what is the quantity along the
vertical axis? (db)microvolts I presume?
Thank you for your permission to put
some of the info in your
emals on the reflector!
Glad to hear you are
getting along with Win98.
Windows in general can be called a two-edged
sword.
My Windows generally collapses at least once every
day.
Also glad about your efforts to explain
people how to
construct a simple but useful instrument to measure Fs.
I
know we have had a luxury of using calibrated Fs
equipment ever since 1948,
first RCA then R&S HFH/ESH.
I have been producing most graphics with
Lotus Freelance
and the present version is Freelance 97 edition.
For some
special formats the earlier version is better.
Windows beats DOS in some
graphics work, but DOS is fb.
Freelance automatically produces different
colors for
every day of a month and legend shows the color vs day.
In
general this kind of picture shows a general daily
variation of hourly Fs
during a calendar month.
Of course, the fine structure, eg 'morning
effect'
don't clearly show like they are seen in a pen
recorder.
It has been an EBU practice to use dB(uV)
for eg input
voltage and dB(uV/m) for Fs, since the
1950's.
I zipped the available 1998 graphs for
138.83 & 77.50.
Some big Fs excursions must be due to change in
radiated
radiated power. In 1998 the noise threshold level for
138.83 with
200 Hz Bandwidth is 5 dB(uV/m)-> (-7 dB(uV).
There are some qrt periods on
138.83 but never with 77.50.
Your last message for the group was just
excellent!
Here is a special introductory version of January 1999
picture
for 138.83 kHz, all values in calibrated dB(uV/m).
There seem to be a limit
of 30 days per month in Freelance.
Anyway it sort of gives some idea of
day-to-day variation.
Instead of Excel form I can send numerical tables in
ASCII
form prepared by Windows Notepad (which I use almost daily).
So,
attached also PORKKALA 285 kHz results (invaluable!).
Vaino's last comment relates to my
e-mail via the reflector of 17-17-99 (ERP and all that jazz)
I did not include the attachments to
Vaino's e-mails because the reflector won't accept them.
They show among others graphs of the
field strength over 24 hrs for every day of months in 1998 and 1999 as
recorded on DCF39 and DCF77.
As an example the field strength of
DCF39 at 1200 hrs varied in June 1999 between 37 and 41 dB(microvolt)/m. But in
January of this year between 28 and 47 dB(microvolt)/m!
As stated earlier I will be happy to
forward Vaino's original e-mail messages, including the attachments, to anyone
interested by direct e-mail.
Vaino mentioned DGPS. This stands for Differential GPS. I have
heard that the corrections to be applied to the GPS data in order to become a
more accurate fix are transmitted via existing MF or LF beacons. Perhaps Vaino
can tell via a message on the reflector if what I have heard is correct or not.
73, Dick, PA0SE
JO22GD
D.W. Rollema
V.d. Marckstraat 5
2352 RA Leiderdorp
The Netherlands
Tel. +31 71 589 27 34
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