A couple of amplifiers ready for 2022

[radiogareth]

I have been busy this week building and finalising a couple of amps for the coming 'season'. One is a 'kit' for 23cms that G4BAO offered around 2010 - that has been finally boxed and set up with a eBay DC-DC upconverter to deliver the required 28 Volts. Its mounted on an old Pentium 2 heatsink and fan assembly, the fan needed a bit more than 12 V to keep it all cool so a standard 7812 was hijacked with a red LED in the ground lead. The fan (and DC out to the pre-driver - another G4BAO product) now enjoy 13.8V. The 7812 needed some external heatsinking and to keep that under control a small portion of fan air is sent upwards through a small aluminium shield. In the pre-driver is another regulator, a 7805, which feeds out 5V for an eBay 50MHz-6GHz pre-amp. With the Pluto set to -5 I get 25W of DVBS2 with shoulders around the -30dB. More drive gives a few more watts but the shoulders creep up too.
The other amp was a chance eBay find - its a Toshiba unit for 3.4GHz, one of the later variants too so 40+ watts. I'd recently bought one from a German amateur (it wasn't cheap) and in searching for modification info I spotted the eBay listing. The vendor wasn't a specialist seller and it wasn't described as an RF amp so I was able to snag a bargain.
Other than needing a BIG heatsink and decent fans, its a very simple conversion mainly involving some re-wiring of the DC power and sorting out a PTT. I added a DC voltmeter, manual PTT switch and LED in parallel with a phono socket control to suit a closing contact for amp enable. The swept SMA output socket was rotated 180 degrees and the pots tweaked as described.
It uses 15amps of 12.6V DC so warms up fairly quickly. The fans are controlled by a small 12VDC fan speed controller, which can be variously programmed with speed and temperatures, but the default works fine even if the amp is on for long periods. The amp chain itself includes a circulator, so the PA is reasonably protected. It produces enough RF to warm up double braided PTFE coax cable, so I don't much doubt its output power. Looking forward to venturing out on both DATV and narrow band with them both this year.

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Gareth