Using WSPR to measure local paths

-this page is stub
GLMrasp.JPG

Summary:

-This page introduces use of WSPR to measure local signal paths

- Order is to predict and compare usability of certain frequency/antenna/path combinations on local communications.

- By using WSPR it is (I think) possible to use really low power for many kind of field testing.


Picture: GLM with back panel opened. On field I use Raspberry Pi headless throw wifi-dongle, with android phone or tablet. This also gives needed time synchronization for WsprryPi.



I often leave some software receiving signals on my shack when I leave home, and transmit test signals from somewhere. For example I have used Fldigi, Pskmail, or SpectrumLab.

Idea here is to use WSPR software for local fieldtesting. Why?
Well, it just makes some thinks very easy.
-WSPR transmit and receive automatically.
- WSPR can deal with small driftning.
- WSPR makes signal quality measurement automatically. It makes comparing easy.
-It works with very low tx-power. Less trouble.
-You can use Raspberry Pi as transmitter.

Thanks to PE1NNZ for WsprryPi. It makes Raspberry Pi to act like low-power WSPR transmitter, which have really wide frequency coverage. Link: https://github.com/threeme3/WsprryPi

On first test I used only raspberry and general filter. Filter was tuned with simple rf-probe power-meter hack to right frequency (I may put some better explanation on another page later when I have finished that meter).
Raspberry itself can produce something around 10mw of transmit power.

There is one place where I frequently visit, and take contact to home. I know that this contact can usually be done on 10 meter with 1 watt power on AM. So I estimated WSPR should get through with same antennas on 10mw.
It worked as expected. Signal quality WSPR showed was around -20dB.

Preliminary conclusion: If I can get 10mw WSPR signal through at -20dB, path should be easy for voice communication.
Theoretical limit for decoding WSPR signal is around -28dB. So If I can get 10mw WSPR-signal through at all, path should be about possible for ssb-communication.
It also seems that 10mw is enough for this kind of testing purposes! Very nice. Low power = less troubles.

Sorry, I have only bmp image here at the moment. It is screenshot taken from SpectrumLab. It is handy to leave SpectrumLab receiving along with WSPR-software, because it gives some information of what have actually happened while receiving, amount of interference etc.
On this capture WSPR-transmission is started at place mentioned before. Transmitter (GLM) is connected to car antenna. Then car have moved home.
You can see how I use little frequency "hopping" to avoid local interference. (solid lines on waterwall are local interference).

UPDATE: SORRY, picture seems not to be working, not even if you download it.