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Updated 4.11.09
INTRODUCTION
The 500kHz band was historically
a maritime and emergency band but it has been little used in recent
years, at least in Europe. Several national radio societies have
been making overtures to their licensing authorities and now several
have allocated special frequencies near 500kHz for experimental
use by amateurs. There is a reasonable chance of a permanent allocation around 500kHz after 2012.
In the UK the band 501-504 kHz is available
by Notice of Variation (NoV) with an ERP limit of 10W (was 100mW). Despite
this, normal speed CW stations have been received at my location
at good strength with just a barebones FT817 (no up converters or
preamps) and an untuned 15m wire with a very basic earth (central
heating radiator). The band is ripe
for experimentation by many others.
INITIAL STEPS
My first efforts on TX were very crude - see left - and consisted of simply connecting up my LF signal generator to my wire antenna and keying the RF lead! Amazingly, this was received 3kms away by M0BXT, although the CW note was extremely chirpy. Also, in the early days I had a couple of crossband QSOs (me on 80m) with G3XIZ and GI4DPE. I also did a lot of listening at first and heard many stations on CW or slow CW.
WSPR BEACONING
My next stages have been to build a simple TX
down-converter taking the output of my FT817 on 28MHz and converting it
to 500kHz. I built a small PA stage using a 2N3906 and 2N3904 and this
produced around 700mW from the PA. A simple low pass filter cleaned up
the square wave into a nice sinusoidal output. This was matched using a
simple ATU based on a ferrite rod and coupled to the 5-6m long coax
leading up to the 28MHz halo which acted as a top capacity hat. The
ground connection is the copper piping in the home.
The original 700mW PA version
A picture of my ATU
To my amazement this weak signal with an ERP of well below 1mW was been received by 4 different stations with the best DX report being from M0BMU who is 69kms away. The next best was G3XVL some 61kms away. WSPR signals have been received from many stations in the UK as well as from SM6BHZ who is always a strong signal in the evenings.
This is a picture of my WSPR signal as received by G7NKS some 41kms away. My signal initially drifts some 40Hz HF as the transverter crystal oscillator warms and settles (it is just on the bench in the open). Some WSPR traces can be very strong (such as the signal from SM6BHZ or M0BMU at times) but WSPR can decode signals that definitely cannot be heard and are even hard to see on the WSPR display waterfall. WSPR allows VERY weak signals to be decoded and has been a superb mode for my 500kHz experiments so far.
This is the schematic of my first 500kHz transmit transverter which uses ubiquitous 2N3904/2N3906 transistors.
PA IMPROVEMENTS AND DX REPORTS!
The PA design has now been changed to an IRF510 FET and the power from the PA is now 5W. ERP is also up as a result. I now believe my ERP is around 1-2mW. Since increasing the power I've had reports on my WSPR signal from 29 different stations in 6 countries (G, GM, PA, ON, SM and F) with the best DX report being from Gus SM6BHZ in Sweden some 951kms to the east. The antenna and ground system have been only slightly changed and the antenna now has a better top capacity spiral hat (see picture)
The next stage is to add the RX part to the transverter so I can work full transceive using the FT817. This will allow me to upload WSPR spots in between TXing sessions. It will also allow me to try and have a few CW QSOs on 500kHz now my signal is a little stronger. When the transverter is completed I will put the full schematic on this page.
The TX down-converter with the 5W PA and LPFThis is a list of stations that have heard me on 500kHz WSPR so far (as of Nov 14th 2009).
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