Baofeng Cemetary

It’s my old website on IZ5CMC’s iPad!

As of the date of this post, you can get a Baofeng UV-5R for $28, or buy two for $50. Dirt cheap.

I bought my first Baofeng UV-5R back in 2012 when they were priced around $62 on Amazon. I thought this was a cracking deal. Upon testing the thing out, I found that the transmit audio was terrible, so I went digging around for a schematic and I actually found one! I made a crude modification which linked out some passive filter components and created a wider sound, albeit not that much louder. I quickly put up a page on my website (long gone now), with an accompanying YouTube video (also now long gone) detailing the tear-down of the UV-5R, the modification, and reassembly. It became quite popular, with plenty of discussion on the page. Colin, G5EML saw the page that I had published on my website, and got in touch. We put up a modification which used the VOX transistor as an additional gain stage for the microphone. This worked very well, and was widely adopted. See the image above, with IZ5CMC carrying out the modification.

So, the last time I took a UV-5R apart was in 2012. It seems that I have way less patience in 2018. Or, maybe it’s just the price that has made me look at this thing as a throwaway item.

When I joined SCARS in 2015 (I think), I was given a Baofeng UV-5RT as a welcome gift (how nice!). Unfortunately, this radio had obviously become tired of throwing 4 W towards the antenna, and decided that about 300 mW was a much more comfortable number. I wasn’t convinced.

So, I opened it up, and sure enough, the final output transistor was dead. Hardly surprising if you look at the amount of heatsinking the final has. Almost none. There is a thick blob of thermal pad on top of the final output transistor. Functionally more or less useless as a heat sink. I did consider (briefly) replacing the transistor, so I got out my UV-5R schematic:

OK, so the final is a BJT? A bit odd these days, since they usually go for FETs, but enough. Let’s Google the part number and check out the datasheet:

Oh it IS a FET. I then noticed that there are no FET symbols on the UV-5R schematic at all. So, ok. It’s a FET, and it’s a Renesas part. Great. A bit of history here…
Renesas took over RF components from NEC, which were exclusively distributed in the US by California Eastern Labs (CEL).
In 2009, NEC and Renesas Technology merged, and Renesas eventually discontinued the CEL line of RF/Microwave devices. This process happened between 2013 and 2016. So, it’s unlikely that I’ll find a replacement in the usual Mouser or Digikey channels….

Found something which looks like an equivalent:

Good old Freescale (or we should say NXP these days… it’s hard to keep up!)

The AFT05MS004NT1 is available at Mouser and Digikey. Great!

I’m curious – what is the ruggedness of this device?

Better than 65:1 VSWR, at all angles, powered by 9V and being driven hard, with twice the power it’s used to handling. That’s excellent! Let’s plug that into my spreadsheet…

65:1 VSWR? That’s less than 240 mW radiated from 4 W (given a 100% efficient antenna, single wave)

I wonder what the ruggedness was of the original Renesas part? Well, I continue to wonder, since there are no ruggedness metrics in the datasheet. Somewhat unusual – even RFPA IC’s have this data. However, S-parameters are in the datasheet so we can figure out how to match it for a particular frequency range. Not that it matters since they’re obsolete.

I do wonder though, especially since according to the UV-5R user’s manual:

A VSWR 1.5:1 to avoid damage? I am positive that the RF final sees way more than 1.5:1 during normal use. I’ve seen >3:1 from the stock antenna on a VNA depending on ground plane and proximity effects… I digress.

I have ordered some of the AFT05MS004NT1 parts, and I plan on using the PCB as a test-bed to see how rugged these replacement parts are, and what is required in tuning up these as final output devices.

For now though, the radio will remain in the following configuration:

Watch this space…

I figure that I can get SOME use out of the guts of this device, and gain some useful data in the process. Thanks SCARS! 🙂

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AD5GG

AD5GG works in the real world primarily as a board-level RF designer in the UHF (300 MHz - 6 GHz) range. Occasionally, he posts articles on this very site. Sometimes they're even worth reading.
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