A Tour of VE7TIL's 2200m Station
The station has evolved over a number of years into its present configuration. On 2200m home brewing your equipment is the name of the game as you will see from this brief station tour.
On receive the venerable Kenwood TS-440S is used with the AM broadcast band attenuator that comes stock in the rig bypassed as it is switched in on the LF frequencies as well.
The MOALFA (Mother of All LF Amplifiers), named by J. VY1JA, is the primary DX transmitter. It is capable of 1.1KW (Stun Mode) and 2KW (Kill Mode) keydown. The unit is an array of four seperate class-D transmitter modules combined with a lumped four port Wilkinson combiner.
A smaller 500W transmitter is used for routine station maintenance tasks and testing new antennas. This rig has the flexibility of allowing the operator the choice of power from 25-500W. Handy when you are loading up an antenna for the first time. This transmitter design is the same as one of the transmitter modules in the MOALFA.
This transmitter is a surplus Canadian NDB unit pulled from Prince George, BC. It was modified for 2200m operation and is used primarily for experiments requiring linearity.
On 2200m it is handy to have a very stable frequency reference. As such I built a GPS disciplined 10MHz reference oscillator for the shack. The unit comprises of two DDS boards and home brew control firmware to control the DDS systems as two separate VFOs. Full station control is possible via one RS-232 link with this box.
QSK capability is provided by this custom sequencer and relay control rack. Full QSK is provided along with the needed delays to ensure the RX system is fully protected from QRO power levels.
The primary antenna now used is a 20m high by 30m long loop. A lot of capacitance is needed to tune the loop, about 8.4nF and the Q of it is very high so precision adjustment is needed and provided by a vacuum variable. Impedance matching is provided by three stacked ferrite cores (3C90) configured into a matching transformer.
This spreadsheet shows the design parameters of the loop tuner. Careful consideration was made to both the current and voltage levels through every part to ensure the delicate and expensive capacitors could reliably handle up to 2KW of power.
The wire used for the loop antenna was a #2 AWG Aluminum seven strand conductor commonly used for power distribution. Certified by CSA to 600V but the certification testing would have also confirmed the dielectric strength to well in excess of 3KV. A handy feature as the loop is fully tree supported and in contact with branches...
This antenna performs very well on both transmit and receive.
The loop is supported in a line of thick cedar trees on my property. The antenna is rather invisible and doesn't photograph very well.
The above shows you the orientation of the loop antenna and the calculated losses relative to the main lobes of the antenna for given directions of interest.
Arguably the most important part of the station is the operator. Here's me caught in the light of morning with my QRM (son) Felix after the QSO with JA7NI. Credit for this shot goes to my father-in-law, Copyright 2010, Arn Lund Inc. :-)