500 kHz - 600 m

The 600 m band is now allocated to amateurs in some countries. It is not yet allocated to Australian Amateurs, but some special scientific licenses have been issued by ACMA to WIA.

The following table shows the callsign allocation, frequencies and operators. Activity is mainly on the weekend evenings and operation is usually announced on the 600m yahoo mailing list (see links below).

All six WIA licensed are now (24/01/2011) allocated.

AX2VKY

My transmitter is now complete. It is based on a single IRF540 and it produces 25 W output with an efficiency of 80% or better. I will be using the callsign AX2VKY, which is part of the 6 scientific licenses allocated to WIA for the study of the propagation in the 600 m band. The oscillator is based on a 8.200 MHz computer TTL oscillator, divided by 16 to produce a 512.5 kHz which is within the band (505 kHz to 515 kHz). A low pass filter attached at the output of the transmitter, ensures MW listeners in the vicinity will continue to enjoy listening to their broadcasts!

The variometer used is VK1DSH Dale's old inductor which he used on LF. Since his new antenna requires much less inductance, he kindly let me have it. It's dimentions and inductance make it excellent for tuning my antenna on 600 m, but I needed to convert it to a variometer instead of a fixed coil before I could use it:

There are taps every 10 turns, which make it ideal for tuning a wide range of antennas.

The antenna is a wire that exits through my radio room window to a 4 m pole, then travels to an 11 m pole about 13 m away. This is the same antenna I am using on LF. The ground consists of three ground rods in a line, about 1.5 m apart.

An alternative variometer I am using is this one which I bought from a local trash and treasure.

All reception reports received will be placed in a log file for future reference.

New transverter

I have now completed a modular 500 kHz transverter. It consists of a 10 MHz LO with a home made "oven", a 17 dB attenuator, a Mini-Circuits SBL-1 mixer in the same box as the attenuator, a 5 pole Chebyshev mixer LPF, a 5 W power amplifier and an output 5 pole Chebyshev filter. IF is provided by the FT-817 set up at 1/2 W power output. The 17 dB addenuator brings this down to about 10 dBm which is what the mixer likes. The T/R control is done by a separate box with power and coaxial relays. I can use a separate antenna (PA0RDT mini-whip) for receive which is automatically powered down on transmit. There is a current indication which shows the overall current of the PA. The PTT signal is taken from the 817's "ACC Jack", pins "+13.5 V" and "TX GND". The PA is based on the this G3XBM design. There are plenty of interesting QRP designs for LF and MF in Roger's web site, I recommend a visit if you are in simple and functional projects.

My motivation for making such a modular transverter is that I want to reuse it on LF with a different LPF/power module. I also want to easily be able to test the performance of each component and easily replace modules as I produce equivalent ones with better performance.

Hint: if you don't like soldering mini-DIN connectors like me, you can sometimes get lucky by having a computer cable that has the same connector in your junk box. In the FT-817's case, the "ACC Jack" has the same connector as a Macintosh serial port or a Sun microsystems Type 4 and Type 5 keyboard. I had a cable from a Type 5 keyboard which I cut in half and now have one in my T/R box and one spare! The "Data Jack" of the FT-817 uses a different connector to the "ACC Jack". It is the same as the PS/2 port of older PCs. Unfortunately, most PS/2 keyboards and mice don't have all pins connected. I used a KVM cable which had all pins connected. You can also use an extension PS/2 cable which should have all pins connected too.

This transverter, together with the FT-817, my TX antenna and my PA0RDT mini whip are used for collecting propagation data through WSPR.

Links

• AX2VKY log file: many interesting spectrograms and plots
• AX2VKY impedance matching transformer
• A cheap and cheery MF TX from GW3UEP.
• The 600m yahoo group.