Saturday, 30 August 2014

630m Trans-Pacific WSPR

It looks like the new 630m band may hold some surprising opportunities once the winter DX season is upon us. A recent posting to the down-under 600m Yahoo Group by David (VK2DDI) in New South Wales, Australia, set off a flurry of excitement when he announced his August 25th (0950Z) reception of the 475kHz beacon signal from WG2XIQ, operated by John (KB5NJD) near Dallas, Texas.

This is particularly noteworthy in view of the relatively low power used for John's beacon....around 200W. With the typical backyard antennas being used at these frequencies, efficiencies are very low and John's actual ERP is less than 5W. The transpacific reception of John's signal by VK2DDI confirms what most LF'ers already know....that small suburban lot amateur installations can have positive results on 630m without the need for huge antenna systems.

The WG2XIQ beacon was operating in the WSPR mode, which has become very popular amongst 630m experimenters as well as those just interested in listening-in. WSPR is not a QSO mode but strictly a one-way 'beacon' mode. Although two stations may each spot each other, it is not considered to be a valid two-way QSO. A check of evening  WSPR activity will often reveal dozens of stations actively spotting what they are hearing.

Like most LF stations, John's is mostly homebrew.


I'll let him describe the details:

"I have a few ways of making RF in the shack. I can do CW with a very nice waveform using the GW3UEP VFO/Driver coupled with a GW3UEP 100w amp with waveform shaping. The other way is via the MF Solutions transmit downconverter, developed by John Molnar, WA3ETD/WG2XKA. I have two of those boards, one is a backup. I use a GPSDO for the LO and use that signal to drive two parallel GW3UEP amps with max power at 125 watts each. The W1VD Ø degree hybrid combiner brings them together in phase for close to somewhere between 200 and 250 watts TPO depending on how hard I drive and how close I match the TX levels entering the combiner. I filter the output with the W1VD KW LPF that was built by Dave Robinson G4FRE (ex WW2R). I power the amps with a pair of BK Precision 30V 6Amp variable power supplies (variable current limit threshold also). Scope match is used to resonate and match the the impedance. IF Rig on 630m is typically a Yaesu FT920. These days RX antennas are the VE7SL multiturn loop or the TX vertical, both of which have their own merits depending on the conditions at the time."

John's 630m Vertical

"Antenna is an 80 foot asymmetric T-top marconi with 100 foot and 200 foot legs....radial system is almost 3 miles of radials connected via various busses. 26 ground rods around the property. I monitor current in the shack and sample via a Bauer current transformer from an AM BC ATU."

630m Radial System

630m Antenna Loading Coil & Variometer
"As far as my system is concerned, I am the poster child for "If I can make it work, anyone can!" 

John's system does indeed work well...just last year at this time, his 630m signals were copied by KL7L near Anchorage, Alaska.

Of course, equal credit must be given to VK2DDI for having a system good enough to hear John's signal all the way down on Berry Mountain, New South Wales, Australia! It is there that David has set up a fine LF station, 500m above and overlooking the Tasman ideal location for weak-signal LF work.

VK2DDI - Berry Mountain, NSW

David's receive antenna at the time, feeding and SDR-IQ receiver, was a simple non-resonant 90' vertical wire, with no ground radials and no tuning. It seems that the old real-estate adage, "location, location, location", can also be applied to LF reception!

WG2XIQ Signal As Heard in VK
David's screen capture of John's WSPR signal, although very weak, is clearly visible at 09:50 and apparently, strong enough for a solid decode.
David also runs the Berry Mountain Grabber, providing other VK and ZL experimenters a handy way of checking their system progress or propagation conditions.

If you have been doing any WSPR work on HF, you might be surprised at what you can hear down on 630m, even without a dedicated antenna for that band. Surprisingly good results can often be had with a non-resonant antenna as the signal to noise ratio can often be better even though signals may sound weaker. Give it a try and spot what you hear!

If you are interested in learning how to receive WSPR, here is a nice tutorial by ZS6SGM. 

Should you be interested in knowing more about obtaining a Part 5 licence to transmit on 630m, John will happily guide you through the process. He can be contacted via email or you can find him hanging-out most nights on the ON4KST kHz (2000-630m) chat page.

To keep on top of what is happening or who is on-the-air, most LF'ers rely on three sources:

Radio amateurs in Canada have had 630m as an amateur band since May of this year but unfortunately are not allowed to contact any of the experimental stations. Hopefully the U.S. will also obtain 630m as a ham band some time soon. In the meantime, a Part 5 licence for any U.S. amateurs would be a good way to be  all set when that day eventually comes!

No comments: