BATC Forum

I'm exchanging emails with Bert Modderman PE1RKI http://www.pe1rki.com/index.html and more confused than ever. He's offering me a 100w PA for Oscar-100 DATV that takes an 80 milliwatt input. The website doesn't reveal much at all, with no specification or even a photograph. He sent this circuit diagram when I asked about PTT. I thought I understood enough about electronics, but this example has me baffled.

Please can someone explain what's going on here and perhaps answer a few more things I should to know about. Like needing a low power amplifier to go between an ADALM Pluto and his 100w Power Amp, needing a low pass (or bandpass filter?) and where it should go, ordering his 100w PA with or without his built in circulator, and anything else I need to buy.


1) PTT
2) BIAS
3) LPF or HPF
4) CIRCULATOR
5) Pluto to PA pre-amp

Probably too many question for one post.

Bert does really good stuff. Exceptional in fact. There is a long queue. Amplifiers are individually developed. The circuit implies an MRF21030 is being used, this is a 30W device and I think this is just an example showing you the internal biasing arrangement. It is showing you that a 28V supply is used for the PA and can be on all the time and you should apply bias to TX. The bias circuit is shown to be a 78L05 regulator and probably anything over 7V would do. The 78L05 will handle 28V but that's near its limit and it would be better to use 12V.

A warning. It is debatable if hams unfamiliar with microwaves should be let loose with a 100W 2.4 GHz amplifier. This isn't like HF. High power microwave can be dangerous in ways unexpected by those only familiar with HF/VHF. There are many potential risks from lose or inappropriate connectors, cabling, proximity to antennas. Imagine you are working inside a microwave oven, you don't want it be operating, even accidentally, while you are inside.

You will not get 100W out of a 100W PA with acceptable shoulders, but you know this already. As a consequence you will not need the full drive power. More likely only 20mW or so. Therefore a simple intermediate SPF5189 amplifier from China or the G0MRF 200mW design will be fine to drive it. I would go for a circulator because it might save the PA in the event of failure. Obviously the low pass filter goes on the output to remove harmonics. You would do well to use a bandpass SAW filter, as used in the G0MRF design after the Pluto to clean up the output.

Mike

Thank you so much Mike and for responding so quickly. I've sent you a PM. I hope you don't mind.

Don't know if the notes in the lower left are original or added by you but note 5 says Pluto to PA preamp so this will be 1 MW in to around 10W out. Similar to what I use on 1296 for my Pluto to drive my W6PQL 600 watt amp.