QRP Holiday transmatch
For the use on holiday, I constructed a light weight, unbalanced transmatch, which I use with a single-wire antenna, without a ground system, with my FT-817 QRP transceiver of Yaesu.
The transmatch is based on a transmatch from the excellent book ”Solid state design” of the ARRL (page 165) and a transmatch of Charlos PA3CKR, which I used on an earlier holiday .
The transmatch is build around two variable capacitors, a toroïde inductor with 32 turns of 0.3 mm wire on a Amidon T68-2 core (red) and a single-pole rotary switch. The variable capacitors are foil capacitors from old medium wave receivers. The switch is used to select the frequency band and the capacitors for the precise adjustment.
Because of the positions of the taps, the number of turns is doubled in the next position of the switch, when turned from min to max. So also the frequency is doubled with each step.
The input of the transmatch is a thin coax-cable. The output consists of two single wire connectors.
An End fed that needs no ground system
I use a 300 ohm twin lead with a length of 4.8 meters to connect the antenna to the transmatch. The wire of the twin lead connected to the antenna is connected with the connection ”Single wire antenna” The second wire of the twin lead is only connected to the ground of the transmatch.
The twin lead is transforming the (high) impedance of the antenna to a lower value. The second wire in the twin lead acts as a counterpose, so the end fed needs no ground system.
While on holiday in Portugal in 2007, I used wire antenna’s of 20 meters, 10 meters or 6 meters. Adjusting the transmatch is easy, also with different lengths of the wire of the antenna. But the longer antenna gives the best signals. With a wire of 20 meters, from the balcony of the hotel room, to the top of a pine tree, I made about 30 QSO’s in the RDA contest. Because of the wind, the constant movement of the branch of the tree, broke my thin rope.
So in the next weekend I used the same antenna, but now running to the fence of the hotel, on a height of only 5 meters. I participated in the YO DX contest and made 80 QSO’s.
With 40 DXCC countries in the log, I convinced myself that the transmatch is working very well.
But that is not all. Later I received a beautiful award from Romania for the YO DX contest for the first place in Portugal SOSB on 20 meters.