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Author Topic: Making a cheap eBay RF Power Amp Sorta Work  (Read 5019 times)

Offline ChrisSmolinski

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Making a cheap eBay RF Power Amp Sorta Work
« on: October 06, 2019, 1627 UTC »
You've probably seen those "2MHZ-700MHZ 3W HF VHF UHF FM Transmitter RF Power Amplifier" listings on eBay. Here's what they look like:



I bought one to see how they work, and whether I could use it as the basis for a QRP beacon on 40m or perhaps even 10m if the band ever opens again.  Well, the answer is they don't work very well.

They are biased in such a way that they draw a substantial current in idle mode. I didn't measure it, but the heatsink quickly gets hot, in a few minutes it got up to 130F. I aborted the test before it got any hotter.

They use a RD01MUS1 for the amp, here's the datasheet: https://www.modelithics.com/models/Vendor/Mitsubishi/RD01MUS1.pdf

There's also another, low power, RF amp on the front end, as well as a 7805.

The heatsink is just clamped to the back of the PCB. There is a tinned area, but I didn't see evidence of any heatsink compound.

I rigged up a fan aimed right at the heatsink, this keeps the temperature down to 90F which seems reasonable. I can get about 1-2 watts out on HF onto a dummy load, less on lower frequencies, more on higher frequencies. I suspect it may do better on VHF, I need to find my 2m power meter and see. Not sure if you'll ever get 3 watts, and if so for how long  ;D

« Last Edit: October 06, 2019, 1632 UTC by ChrisSmolinski »
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Chris Smolinski
Westminster, MD
eQSLs appreciated! csmolinski@blackcatsystems.com
netSDR / AFE822x / AirSpy HF+ / KiwiSDR / 900 ft Horz skyloop / 500 ft NE beverage / 250 ft V Beam / 58 ft T2FD / 120 ft T2FD / 400 ft south beverage / 43m, 20m, 10m  dipoles / Crossed Parallel Loop / Discone in a tree

Offline OgreVorbis

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Re: Making a cheap eBay RF Power Amp Sorta Work
« Reply #1 on: October 06, 2019, 1831 UTC »
I'd recommend to always go with Greek gear for MW and HF. There's something about Greece that they seem to be obesesed with these frequencies. There is so much stuff available that's better than the Chinese. They even make custom Class D and E.

Here is a good amp from a vendor I've used for a while:
https://www.ebay.com/itm/RF-POWER-LINEAR-AMPLIFIER-AM-MW-HF-HAM-RADIO/323931112378

It might need a pre-amp because I don't know what you're driving with.

Even if you don't need it, I think others might find this guys wares interesting :)
https://www.ebay.com/sch/kleop313/m.html?_nkw=&_armrs=1&_ipg=&_from=
« Last Edit: October 06, 2019, 1850 UTC by OgreVorbis »
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Offline Stretchyman

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Re: Making a cheap eBay RF Power Amp Sorta Work
« Reply #2 on: October 06, 2019, 1852 UTC »
You could, "Go English"!

Str.
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'It's better to give than receive' so why Rx when you can Tx!

                                              ;)

Offline OgreVorbis

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Re: Making a cheap eBay RF Power Amp Sorta Work
« Reply #3 on: October 06, 2019, 2037 UTC »
That too :)

I am really curious about Greece though. Do they not have any radio laws there? There are so many pirates.
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Offline Teotwaki

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Re: Making a cheap eBay RF Power Amp Sorta Work
« Reply #4 on: December 17, 2019, 1704 UTC »
« Last Edit: December 17, 2019, 1721 UTC by Teotwaki »
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Jim
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Offline syfr

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Re: Making a cheap eBay RF Power Amp Sorta Work
« Reply #5 on: June 05, 2020, 1343 UTC »
How did it work? Any better than Chris's mini space heater?
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Kiwsdr x 2. TenTec Paragon/NRD535
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