VHF Station (50MHz and 144MHz)

The 50MHz station is simple. It’s a Dual (brand) 6-element Yagi at about 13 metres connected to the IC-7300 via Westflex 103 semi-rigid coax. The coax loss is about as good as possible considering the need to drop the mast from time to time and hence flex the cable. A flexible RG213 tail is used from antenna to masthead to allow rotation.

The VHF station is shown below.

GM8JBJ VHF Station

The 144MHz is similar. The rig is the Icom IC-9700. As shown on the previous page, I’ve used a low noise pre-amp at the mast head and a 100W power amplifier in the shack. The amp is in circuit pending replacement with something more powerful in the future. I therefore needed a simple sequencer a) on TX-key to delay the transmit RF until the pre-amp is powered down and put in by-pass mode and b) to delay powering the pre-amp and coming out of by-pass until there is no RF power from the transmitter and power amplifier.

The sequencer and the various wiring to power the pre-amp and power amp are shown below.

PA and LNA Sequencing

The electrolytic capacitors a) in the collector of the second transistor and b) in the base of the third transistor were selected by observing the timing. The final values were less than shown.

The 144MHz antenna is a Dual (brand) 11-element Yagi at about 14 metres. A flexible tail of RG213 is used from antenna to pre-amp to allow rotation.

GM8JBJ VHF Antennas

At present I only use 144MHz. The plan is to install skywards antennas for 144MHz, 432MHz, and 1296MHz in due course.