An UN-UN transformer for my end-fed wire antenna

Prior to installation; coax cable ( left ), insulated wire ( right )

Construction detail - eye bolt is for installation purposes

Raised into position above house roof ridge

Method of installation and connection

For many years, my general purpose antenna for short wave has been a horizontal 46m long end-fed wire; see post dated 12 August 2011. However it had always been difficult to match it's feed-point impedance to my transceiver's 50 Ohm antenna connector on some bands using my station antenna tuning unit, ( ATU ); the impedance being too high. For those particular bands I would sometimes temporarily change the length of the wire; but that wasn't very convenient. So instead I have now made an UNbalanced to UNbalanced ( UN-UN ) impedance step-down transformer, placed it in a small plastic food storage box, connected it to the feed-point of the antenna and to the ATU with coax cable.
The transformer windings consist of 9 turns, trifilar wound, on a T200-2 iron powder toroid core, using insulated wire. The core is held in place with a nylon bolt and a small piece of acrylic. The slots shown in the picture are not required; it had been used for something else. The coax cable is secured inside the box with a 'P' clip. The windings were interconnected to produce a turns ratio secondary:primary of 3:1; hence impedance ratio 9:1. This had the desired effect of transforming the impedance to lower values within the tuning range of the ATU on all bands.
With this modification I converted my simple end-fed wire antenna from a multi-band antenna to an all-band antenna !

New mosfets for the dual band amplifier

Four IRFP360 mosfets mounted on heatsinks inside the dual band amplifier

In March I bought new mosfets for the dual band amplifier ( see post 6 December 2015), but only recently had the time to fit them. I always knew that the original IRF640 types were underrated when I started running the amplifier from a 54V power supply, and there were reliability issues with several of them failing with a loud bang. The new type I've now fitted is the IRFP360 which is a 400V mosfet. During the last couple of evenings I've been transmitting with the amplifier for long periods without any further mishaps occurring. I had to fit these mosfets with a different orientation from the IRF640 ( see previous amplifier images ) as the mounting hole is insulated ( no insulating collar required for the bolt ) and the drain connection was made to the centre pin, not the case. A mica insulator, however, was still necessary under each mosfet between it and the heatsink. The insulator required is slightly larger than the standard TO-220 size. To begin with I didn't have any suitable until I found that Farnell stock them, ( item code 520-214 ). The mosfet and data sheet can also be found at Farnell, ( item code 864-9359 ).