Experimenting with WSPR

Having used some of the WSJT suite during the Norfolk Island VK9NA expedition in January 2011, and following some postings to the VK1 mailing list in recent weeks, I was curious to know how to use WSPR.  The best reference is at the website of its author, Joe Taylor W1JT.

WSPR is part of a suite of software tools that use digital signal processing (DSP) to detect and decode very weak signals, much weaker than can be even detected by the human ear, let alone understood.  Possiblly the best known modes are the FSK441 mode used for meteor scatter contacts on vhf bands, and the JT65 series used for terrestrial dx contacts and Earth-Moon-Earth (EME) contacts on various vhf and uhf bands.  The JT65 modes were used at VK9NA.

Having downloaded and installed the software I then had to see what audio levels were suitable.  I first tried connecting a cable from the speaker/headphone socket of the radio to the mike input on the computer.  Levels were very sensitive and I had to cut everything down, but even then it didn’t work well.  I needed to cut down the audio level output from the radio, an FT817.  It was overdriving the mike input of the sound chip in the laptop.  If there had been a “line in” option I think that would have worked almost without any further change. The microphone input is more sensitive as it is designed for the much lower level of a microphone.  I wired up a potentiometer to enable the sound level going to the computer to be set as a fraction of the output from the radio and that worked very well.  I finished up setting that to about 10% of full scale.

The website http://wsprnet.org/drupal/ is the next resource I found very useful.  It lists the beacon frequencies commonly used world wide, for each band.  I have tried the 7, 10 and 14 MHz bands and found it worked very well.  A good read of the user manual is advisable.  Adjusting the input level on noise to be around 0 db was quite important.  After that it was just a matter of tuning the radio to the correct dial frequency, using USB mode.

Before long I found the screen was gradually building up a list of callsigns received and their signal levels, frequency offsets and the stated power level of their transmitters.  Most seem to be 5w but some are less than 1w and one notable station indicated 1000 watts, but was no stronger than others running 5w, so I think he specified his power incorrectly.

The WSPR screen looked like this at one stage today.

WSPR screen while monitoring 10.140 MHz
WSPR screen, 10.140 MHz

Thanks to Ian VK1HOW for sparking my curiousity about this mode. This must be providing a wealth of data for propagation students.

QRP Hours contest 2011

This is a short contest for QRP operators.  It runs for one hour on CW mode, then 1 hour on SSB.  A truly easy contest to participate in.  All licence classes can participate as QRP (low power) or their ordinary power.  The contest was sponsored by the CW operators QRP club.

I wasn’t sure I would have an opportunity to operate in this contest but at about 6:30pm on Saturday 2nd April I decided I should put up an 80m antenna and have a go.  At 6:40 I had identified a two section telomast and was measuring out some guy ropes for it.  Having found some stakes, guying ring and found the wire antenna cross-boom with the attached halyards and pulleys, I was able to assemble the mast, attach the cross-boom, lay out the guy ropes and do a trial setup to get the guys set to the right lengths.  Once that was done I hammered in three stakes and attached the guy ropes to two of them.  Walking the mast up to vertical showed I had set one guy at an impossibly long length so it all had to come down.  Next time was ok so I could walk the third guy out to the stake and tie it off.  One 20 ft feedpoint suspender ready for action. Time about 7:15.

I had a 80/40m dipole assembly last used two years ago at a rental property in Canberra.  I attached the centre conductor to one of the halyards and hauled it up to the dizzy 20ft height of the mast.  Then I attached some light cords to the antenna ends and tied it to the fence at one end, and to some ground stakes at the other end of both dipole wires.  This work was completed in the dark as the sun set at about 6pm local time.

The two dipoles are joined at the centre.  This works because the 80m antenna is a very high impedance on 40m, so is virtually “not there at all”. The 40m dipole detunes the 80m one slightly but I went through the adjustment process with this antenna about 20 years ago and have simply rolled it up when I finished using it each time.

Then I got out the FT817 and found a suitable keyer cable, microphone, power supply.  On 80m the dipole presented a 1:1 match on the CW end of the band so that was fine.  On 3690 it was about 1.3 but my Emtron tuner handled that mismatch with a fairly broad dip.  The time now was about 19:45 local and the contest started in 15 minutes, or so I thought.

At 20:00 local time I heard a station calling CQ TEST so I answered, received a number, gave a number, signed off.  Good start to the contest, I thought. Then I called CQ TEST myself.  No replies.  Tuning around showed nil activity.  Called CQ again.  This time I got a reply from an operator who kindly advised me that the contest was not due to start until 2100 local time.  I opened up the computer and checked the contest rules.  Start time 1000 UTC, which was 9pm local, but somehow I had reverted to non DST in my calculations due to daylight saving ending later that night.  1000 UTC was almost an hour away.  So I had time for some dinner!

About 45 minutes later I went back to the radio and started the contest again at the right time.  Signals were strong and most stations were in the vk2, 3 and 4 areas though there were some vk5, vk7 and ZL stations worked too at signal reports of 559 or so.  I made 10 cw contacts in this hour.  A slow contest compared with the DX contests but it was also quite relaxed and unrushed.

At 1100 UTC the SSB section commenced, operating between 3550 and 3590. Signals were very strong from some stations.  Again a few names were exchanged as well as the contest numbers.  15 contacts on SSB, and I got the impression the antenna was working well, as mostly my replies were answered after only one call.  Quite good for a 5 watt signal.

I have sent in my log and I don’t think this is the only QRP event I will operate in.  This was a very enjoyable process and quite rewarding for the minimal effort required to get on the air.  Next time: antenna up another 10 feet.  And the ends should be higher too!  Should be no problem.  I might even do most of the work in the daylight next time.

Mast and 80/40m dipoles
Mast and 80/40m dipoles
Feedpoint of 80/40m dipole
Feedpoint of 80/40m dipole