propagation measurements

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In March 2018 I started an experiment to measure the QRP NVIS beacon on 80 meter band from PA0RYL

Some data of the beacon

PA0RYL
Location JO22PC
frequency 3555.555 kHz
 10 mWatt output
Antenna Full size 80 mtr loop

 

Measuring

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.
At 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 beacon available.

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 my measurements.
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 different frequencies,
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

Antenna

The receive antenna is at my home QTH in Haselunne, Germany; locator JO32sq

For receive I use an partial home made active loop antenna,
the loop with 1 meter diameter is made from a Wico copper tube with a weather proof coating

The amplifier is designed and build by LZ1AQ : http://active-antenna.eu/

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 my shack.
I have been looking for ways to lock the Perseus RX frequency on to a reference oscillator.
I found a modification published by W7MLG which seems quite possible and probably worth while if needed: https://sites.google.com/site/perseusmods/home  

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 oscillator.
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 stability
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 use.

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 measurements

 

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

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