Category: Amateur Radio

Canberra trip – APRS / GPS logger

I had occasion to make a trip to Canberra for a few days this week.

OpenLog07

It presented as a good opportunity to explore APRS by VHF radio and the stand alone GPS logger above attached to the case of the TinyTrak 3+. The transmitter is 65W output to a quarter wave in the middle of the wagon roof.

Over the three days, the extract from findu was 6240 APRS records (the vehicle was in a covered car park by night), and 389693 NMEA records (~20MB) logged to the logger, from which 6150 track records were extracted using GPSBABEL for track simplification. Both track sources were converted to kml files.

googleearth 14/01/16 , 07:57:54 Google Earth

Above is a screen shot comparing the track around Majura park for GPS logger in red and APRS in cyan. There are several instances of false double backs on the APRS track (a problem inherent to APRS and quite common), and very coarse track despite being less than 8km from the prominent digi on Black Mountain, and very good view of the digi on Mt Ginini.
Continue reading Canberra trip – APRS / GPS logger

Last update: 26th January, 2016, 5:10 AM

Update for FSM software (v1.11.0)

FSM has been updated to v1.11.0.

The update adds an export to Gnuplot file of the wave file to allow visual examination of the recording on which the measurements is based.

This replicates the utility of the existing Dplot export, but with the freely available Gnuplot package.

164

Above is an example of the receiver noise recording, and whilst it might not seem very interesting, it is interesting that it is of the character of white noise.

Of more interest are cases where there is a distant cyclic pattern at twice the AC power frequency which hints insulator failures on each half cycle. Some other types of periodic modulation are helpful in identifying possible sources of emissions.

References

  • Duffy, O. 2005. Field Strength Meter software (NFM). https://owenduffy.net/software/fsm/index.htm (accessed 11/01/2016).
Last update: 11th January, 2016, 8:44 AM

Quiet solar radio flux interpolations calculator

Further to the posting Quiet solar radio flux interpolations calculator…

With a change in hosting and the changes to adapt to supported and unsupported features, one of the positives is that the ‘short term’ fetching of data on which Quiet solar radio flux interpolations calculator is based is now happening two hourly at 5 minutes past the even hours. Continue reading Quiet solar radio flux interpolations calculator

Last update: 6th January, 2016, 11:23 AM

NEC model of the quarter size G5RV

Fractional G5RV antennas seem very popular in the US market, and they appeal to hams wanting multi band performance in small space.

One of the offerings is the quarter size G5RV, commonly marketed as the G5RV Mini.

The original concept set out by G5RV was a combination of a centre fed dipole and open wire transformation section to successfully deliver a lowish VSWR(50) on several of the pre-WARC bands. This enabled arbitrary length low Z feed extension to the transmitter, and allowed direct attachment to transmitters of the common design of the day (1950s). Continue reading NEC model of the quarter size G5RV

Last update: 2nd January, 2016, 5:29 PM

WSPR version confusion

Investigation whilst developing Evolution of WSPR revealed some potential issues relating to certain WSPR versions.

The WSPR 2.0 manual states:

Please note that messages with compound callsigns or 6-digit locators will not be properly decoded by WSPR versions earlier than 2.0. Further details on message formats can be found in Appendix B, and in the WSPR source code.

So, lets mine some data. Continue reading WSPR version confusion

Last update: 2nd January, 2016, 10:57 AM

Evolution of WSPR

WSPR (weak signal propagation reporter) is a system for recording on a central database, ‘spots’ of transmitting stations by receiving stations.

It is interesting to examine the contribution by transmitting and receiving stations, for without both, the system cannot work.

I downloaded the archive for December 2015 and did some basic analysis to explore the pattern of use on the 40m band, my main band of interest. Importantly, 40m provides opportunity for local, intermediate and long distance propagation though long distance paths might be restricted to just several hours on most days.

Screenshot - 1_01_2016 , 9_16_26 AM

The chart above shows that the T-index was near normal on most days, and 6 days it was quite poor, so propagation conditions during the month will be a little depressed. The effect on 40m is mainly on short ionospheric paths, say 50-500km. Continue reading Evolution of WSPR

Last update: 7th March, 2017, 9:42 AM

Is maximum power transfer and conjugate matching simultaneously possible

A reader has asked the question in a transmission line context after reading Walter Maxwell’s teachings on system wide conjugate matching.

In the real world, transmission lines have loss and almost always, the nature of that loss will mean that Zo is not purely real.

The answer to the question depends on whether or not there are standing waves on the transmission line.

Nothing in this article is to imply that a transmitter is well represented by a Thevenin equivalent source. Continue reading Is maximum power transfer and conjugate matching simultaneously possible

Last update: 1st January, 2016, 7:32 AM

Exploiting your antenna analyser #10

Measuring an RF inductor

This article walks through practical measurement of a ferrite toroidal inductor using an antenna analyser.

To be relevant practically, lets use an example from N4SPP’s end fed wire antenna on 3.6MHz. His coupling transformer uses a two turn winding on an FT240-43 core for the nominal 50Ω connection to the antenna system.

We could calculate the impedance of this winding using one of the plethora of online and desktop inductance calculators, but lets first fetch the data from the manufacturer.

Screenshot - 29_12_2015 , 11_05_50 AM

A simple statistic that is widely used is Al, and above, Fair-rite gives Al=1075nH +/-20%. Note that although they give a tolerance of +/-20%, it is not uncommon that manufactured product has greater error, they may have optimistically quoted the standard deviation and it is easy to fall outside that (37% chance). Continue reading Exploiting your antenna analyser #10

Last update: 30th December, 2015, 6:47 AM

Exploiting your antenna analyser #9

Disturbing the thing you are measuring

In all measurements, we need to be careful that the measurement does not disturb the thing being measured.

This article explores an example where the instrument measurements appear wrong.

The story starts with a mobile antenna that the transceiver indicates has very high VSWR over the 40m band, though starts to decrease towards 7.350MHz.

To assist in problem identification / tuning, the antenna connector is disconnected from the radio and connected to the AA-600 analyser and a sweep taken.

Screenshot - 16_12_2015 , 5_03_16 PM

Above is the sweep, but it is quite inconsistent with the transceiver’s VSWR meter readings. The plot above looks good, a little adjustment of the tip would get it down to 7.060… but the transceiver does not see it that way. Continue reading Exploiting your antenna analyser #9

Last update: 26th December, 2015, 8:45 AM