Month: January 2018

Testing the Red Pitaya on 70 MHz (4m)

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The Red Pitaya should not be able to receive signals on the 70 MHz band. The user manual states a range of DC-62.5 MHz. That being said, I decided to ignore the manual and perform some tests using WSPR to see if any results could be obtained.

Firstly, the write-c2-files.cfg file in Pavel Demin’s WSPR transceiver software was modified to add a line which included a centre frequency of 70.0925 MHz (70.091 + 1500 Hz).

Modified write-c2-files.cfg file

WSPR transmissions were started from the home location (IO83LS) which is 29 km from the receive site (IO83QV). In the absence of a 4m receive antenna, the 6m antenna was used. Despite this, multiple decodes were achieved.

70 MHz WSPR transmission successfully decoded

To get additional confirmation, further tests were conducted with Bri, G0MJI, near Liverpool.

G0LUJ received by the Red Pitaya of G0MJI

The ability of the Red Pitaya to receive on 70 MHz will be useful in the forthcoming tropo and sporadic-E season as CW Skimmer Server will be able to continually scan the band for beacon and other CW activity and provide early indication of elevated conditions.

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Searching historical WSPR data using a Python script

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The historical records held by WSPRnet are a valuable resource for analysis and data-mining, however the file sizes and number of records make data manipulation difficult and time-consuming.

Last year, I noticed a post by I2GPG – WSPR Log file creator – which used a small python script to search for and extract records from the gzipped monthly files that matched a particular callsign, producing more manageable file sizes ready for importation into spreadsheet applications. KI7MT has been developing something similar: KI7MT/wspr-ana, and there are probably many other approaches.
If you wish to try a search using I2GPG’s script (Windows):
1) Download and install Python 2.7 if required – link.
2) Create a ‘C:wspr’ directory.
3) Download as many .gz monthly files as required from WSPRnet into ‘C:wspr’.
4) Download I2GPG’s python script to ‘C:wspr’ – (save as) link.
5) Run the python script according to the instructions from I2GPG.
Alternatively, I have modified the script to allow separate receive and transmit callsigns to be entered, allowing more targeted search – (save as) link.
Search in progress
Completed .csv file viewed in LibreOffice
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Researching Aircraft Scatter opportunities on 4m

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Using Airscout, it is possible to evaluate the possibility of Aircraft Scatter (AS) assisting with several hypothetical contacts. If there are aircraft in the pink area of the lower graph, then an AS assisted contact could be possible.

Three active 4m WSPR stations were selected for evaluation. As the year progresses, wsprnet will be monitored and AS assisted contacts with these, and other stations, will be documented if they occur.

G3SPJ, 329 km

G3ZJO, 216 km

G6HSM, 406 km

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VHF Aircraft Scatter

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After the brief excitement of a small winter Sporadic-E opening last week, all has been predictably quiet on the newly installed 6m antenna. When trying to dial in the correct frequency offset for receiving WSPR I noticed Aircraft Scatter on my transmitted signal from home (IO83LS) to the remote site (IO83QV).

Numerous decodes were noticed from reflections. After further investigation, it is clear that I am fortunate (?) to live in an area of extensive aerial activity.

Trans-Atlantic traffic originating from Western European hubs such as Schipol and Munich passes over in an upper airway at high altitudes. More exploitable traffic regularly originates from Scottish airports travelling South at lower altitudes. A number of tests were performed, making use of the excellent Airscout Software by DL2ALF and Flightradar24.com.

1) FR24 was monitored until an aircraft appeared with an anticipated course that would pass through the area of interest at a useful height. EZY 1806 from Reykjavik to Manchester at approximately 19,300 feet on a track of 155 degrees looked a good candidate.

2) As hoped, the aircraft descended as it became closer to its destination. As the aircraft passed over the receive site (IO83QV) its altitude had dropped to approximately 12,150 feet on a track of 146 degrees.

3) The aircraft is now visible in Airscout, and it’s time to start transmitting. The transmit antenna is a 4 element Yagi with a beam heading of 130 degrees.

After transmitting three sequential WSPR transmissions, the results were available for review in WSPR-X (n.b. I’m only using WSPR-X for the purposes of this test – the most up to date and recommended software incorporating WSPR is WSJT-X).

No other stations decoded the primary or reflected signals – which was unsurprising due to the current flat conditions and lack of activity. Still, there remains optimism that from Spring the use of this technique could bring success, perhaps coupled with FT8.

For further background reading, I recommend reading the blogs entries of G3ZJO, G0ISW and G3XBM which contain much more detail of successful tests and to which I give credit for starting my interest.

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Adding a 50 MHz (6m) antenna to the remote site

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The Red Pitaya can function on the 50 MHz (6m) band. As the remote site is at relatively high elevation of approximately 200 metres ASL the decision was made to install a 6m antenna.

After some research, and reading the blog of GM4FVM, I purchased the Diamond A502HBR. This 2 element Yagi of the HB9CV type promised moderate gain, light weight and a reasonably wide F/B ratio which made it a good candidate for a receive antenna intended for activity detection and monitoring.

A502HBR on the workshop floor

Construction was rapid with so few parts and the use of colour coding on the elements. An initial continuity check of the coax after fitting a PL259 plug showed a connection between centre and braid, which was accepted after acknowledging that the Gamma match will produce this phenomenon with a multimeter – thanks to G0MJI for confirmation.

To mount the antenna, I purchased another L.G. Harris 731 5m pole which, for around £16, offered adequate strength and height for a temporary installation.

The A502HBR on the 5m mast

Not having an antenna analyzer to hand which covered 6m, the initial plan was to start receiving in a variety of modes using the Red Pitayas and see what could be heard. The antenna was fixed on an azimuth of 134 degrees, with the main lobe towards pointing towards Italy.

After a number of hours of silence, I was extremely fortunate to experience a winter Sporadic-E opening that afternoon to test the antenna. First impressions are that it is working satisfactorily.

Signal processing flow
Red Pitaya for WSPR & Red Pitaya for CW and FT8
Stations received on 18 Jan 2018, CW (including beacons) and FT8

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Optimising audio bandwidth on the KiwiSDR

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After comparing the KiwiSDR’s audio with an SDR from a different platform, I decided to look into the filter settings of the KiwiSDR.

The default settings on USB (and LSB) are a receive bandwidth of 2400 Hz, with a low of 300 Hz and high of 2700 Hz. While this is a good setting for weak signal intelligibility, on strong local signals a wider filter will produce more pleasing audio – particularly through headphones.

To change the filter, tune in then zoom on the waterfall to your signal of interest. The ends of the yellow filter bar above the signal on the waterfall are draggable by the mouse when clicked and held, enabling the high and low setting of the filter response to be changed to suit the signal of interest, resulting in more rounded audio.

80m LSB, audio response changed to 0 – 2900 Hz

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NO3M decoded in JT9 mode on 630m using the KiwiSDR

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Propagation on the low bands has been good in recent weeks. While it is now not unusual for WSPR to be heard from across the Atlantic most nights in the winter season, the digital conversational modes such as JT9 or FT8 are more challenging as they require a greater signal strength for a successful decode.

That some decodes were achieved indicates that the continual optimisation of antenna and processing paths, coupled with efforts at noise reduction, are producing results.

Setup: KiwiSDR – Firefox – Virtual Audio Cable –  3 x WSJT-X (WSPR, FT8, JT9)

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Reducing Ethernet interference

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Ethernet switches, routers and cables are a known potential source of interference to reception. The effect was visible using the KiwiSDR on the 20 metre band with spikes every 60 kHz.

To mitigate this interference source, the switch was changed from a TP-Link unit to a Netgear GS305. It was hoped that having a switch in a metal case would be better than one in plastic. In addition, all LAN cables were changed to shielded CAT6 and the switch placed 20 metres away from the receivers.

A subsequent check displayed significantly reduced interference.

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