During the measurements in October 2018 I experienced several times a day
that the peak marker was not on top off the received beacon signal
We started to suspect the beacon reference (Rubidium) as possible problem.
After a few days we concluded that the signal received is shifting in frequency
due to ionospheric Doppler
For this effect take a look at this page: Doppler in ionosphere
For example the picture is off a very unstable ionosphere causing lots of
Doppler on the received signal,
several jumps of about 0,8 Hz are visible in this plot
On the left side you can see the local reference 10 Hz below the received
This measurement was done on 25 October starting 15.10 (top) until 17.45 UTC
In September 2018 I added (for short time, just as experiment) a second
receiver at my remote QTH
to see how the beacon is received at another site
The receive antenna is at my remote QTH in Netherlands;
Antenna is the same active loop as used in Germany, also the receiver is the
At this moment differences are in the distribution of the antenna signal, for
this I have a few dB
difference in gain which is clearly visible in the results.
Also I have to set the resolution bandwidth of the receiver larger, it's now set
at 2 Hz.
The RBW at my receiver in DL is set at 0,5 Hz.
After almost 3 days measurement I am quite amazed by the results.
In the plot below the results are shown
The red line is the beacon signal received at DL
The blue line is the beacon signal received at NL
The black line is the noise received at NL
The white line is the noise received at DL
What I did not expect but what clearly becomes visible in the results is that
the noise at both locations behave almost exactly the same.
The beacon signal also is quite comparable but showing differences what we tend
to call QSB
In March 2018 I started an experiment to measure the
QRP NVIS beacon on
80 meter band from PA0RYL
Some data of the beacon
frequency 3555.555 kHz
10 mWatt output
Antenna Full size 80 mtr loop
I wanted to measure the signal to noise ratio and tried to
search for ways to get this done.
I found some software from G4JNT for this but after a while I
found that with the very low S/N ratio
from the beacon this was not good enough for my purpose.
I was using a Perseus receiver for receiving the beacon and I
found the function Mkrlog which generates a logfile of the selected markers.
first I tried to see how this would work but at that time I never could find the log
file created by Perseus.
I tried it several times and the way Perseus software responded seemed normal to
me as if all was working fine.
I decided to let my computer do a file search for the marker.log file and after some
time it found the file in a hidden directory,
so that was the reason why I could
not find it before.
With the marker.log file I have the measurements from the
I have put a marker on the beacon, and a few markers around
the signal to measure the noise level.
The data is then used in Excel to create a graphic picture of
It took me a few days to find the best way to use Excel and
create a clear picture of the measured results.
I measure each 5 seconds the power level received at 3
first is the beacon frequency and then two ore more close by the beacon to
measure the noise level.
During a 24 hour period I make 17.280 measurements.
The beacon on my Perseus screen
If you want to see how I receive the beacon real time take a look at my
video stream showing the spectrum display and the audio from the RX.
Mind that the beacon signal (at marker 1) needs to be about 20 dB above noise
before it is audible.
This is caused by the very small Resolution Bandwidth used for the spectrum
The audio is decoded using an bandwidth of 47 Hz
I started the measurements using a Resolution Bandwidth of 1
Hz, later I increased this to 1,9 Hz because the beacon fell of the marker,
probably my receiver frequency drifted due to temperature drift. Some days after
I decreased it to 0,5 Hz, the lowest RBW that can be selected in the Perseus
software I use.
Since then the measurements went well. The lower the RBW the lower the noise
floor will be giving a better performance.
I found that many amateurs use the frequency of the beacon or close by and a
smaller RBW improves the interference rejection also.
If you read this, please do not
transmit on the
frequency of the beacon because it will influence the measurements.
Frequency drift of the Perseus As I wrote above, I am using a resolution bandwidth of 0.5 Hz which most
of the time works out fine.
Sometimes I have some frequency drift in my RX due to change of temperature in
I have been looking for ways to lock the Perseus RX frequency on to a reference
I found a modification published by W7MLG which seems quite possible and
probably worth while if needed:
I tried to get to a quote for the 80 MHz reference
oscillator from Wenzel but found this impossible to get.
I then considered a modification of the
existing LO by putting a small temperature heater on top of the existing
By using a small design from Kuhne microwave, I modified my Perseus in a way that the LO
is temperature stabilised.
This is a small quartz heater regulating temperature within 0.1 degrees.
I mounted this one on top of the 80 MHz oscillator with a little temperature
paste between this board and the oscillator,
in the Perseus and now have to experience if this modification is enough
improvement for this application
The first impression of this modification is
that it works out fine.
My receive and logging system
The receiver is a modified Perseus with improved frequency
The computer is a small, low power mini PC, running Windows 10
With my big computer running 24/7 power consumption was just a bit too much to
Each day I copy the logfile from the mini PC to my network
hard disk, then the data can be used in Excel to make the graphs
The first result looked like this, it is a measurement from
27-3-2018 from 18 UTC until 21.36 UTC
The same measurement but then with small dot's
Here I added a trendline, giving an average of 100
This will be the format how I want to publish my measuring results
For the results of my measurements take a look at the pages below