Bert Modderman PE1RKI

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EA7KIR
Posts: 86
Joined: Tue Feb 09, 2021 3:38 pm

Bert Modderman PE1RKI

Post by EA7KIR » Sun Sep 26, 2021 8:06 am

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.

mrf21030.gif
mrf21030.gif (20.71 KiB) Viewed 2561 times

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

Probably too many question for one post.
Michael EA7KIR

g0mjw
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Joined: Sat Sep 20, 2014 9:15 am

Re: Bert Modderman PE1RKI

Post by g0mjw » Sun Sep 26, 2021 8:38 am

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

EA7KIR
Posts: 86
Joined: Tue Feb 09, 2021 3:38 pm

Re: Bert Modderman PE1RKI

Post by EA7KIR » Sun Sep 26, 2021 9:19 am

Thank you so much Mike and for responding so quickly. I've sent you a PM. I hope you don't mind.
Michael EA7KIR

mccla5214
Posts: 61
Joined: Sun Sep 05, 2021 1:45 am

Re: Bert Modderman PE1RKI

Post by mccla5214 » Sun Sep 26, 2021 7:53 pm

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.

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