Author Topic: 1-930MHz,2.0W RF broadband power amplifier  (Read 1464 times)

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Offline mankan

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1-930MHz,2.0W RF broadband power amplifier
« on: May 03, 2020, 08:02:07 pm »
I recently got one of these from eBay. Did some quick tests and it seems to work as specified, see picture below.
Then I decided to put into a casing which also required removing the SMA connectors. I taped the board with some kapton tape and used hot air to remove the SMAs.

But now, no output  :(

First fault I traced back to the input DC blocking capacitor. Changed that and now I have signal to the final transistor input and none on its output. I say transistor since both input and output are biased, 1.67V and 11.7V respectively unless a fried more components which offsets the measurements.

It's a SOT-89 and it is marked KB 863 with a logo (a Z in a circle), see picture below. The pre-amplifier is a SBB2089z which has a P1dB at 18.5-21 dBm so the final gain ought to be around 12-14dB.

Anyone has a clue what transistor this is?

 

Offline radioactive

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Re: 1-930MHz,2.0W RF broadband power amplifier
« Reply #1 on: May 04, 2020, 04:41:16 pm »
I don't know the part#, but judging from the image, I  suspect a bad solder joint on the output pin of that SOT-89.  You might try hitting the output pin again with a soldering iron so that it looks more like the input side (good solder fillet).
 

Offline Grandchuck

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Re: 1-930MHz,2.0W RF broadband power amplifier
« Reply #2 on: May 04, 2020, 05:05:38 pm »
radioactive has a good eye ... it sure does look like a cold joint.
 

Offline Theboel

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Re: 1-930MHz,2.0W RF broadband power amplifier
« Reply #3 on: May 04, 2020, 05:43:49 pm »
Hi,

I think its AFT05MS003N
https://www.nxp.com/docs/en/data-sheet/AFT05MS003N.pdf
the builder use "brute force" to made it work all the way from 1,8 to 941MHz
I use this transistor for FM broadcast exciter.
 

Online bob91343

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Re: 1-930MHz,2.0W RF broadband power amplifier
« Reply #4 on: May 04, 2020, 06:57:03 pm »
I might be interested in one of these but nowhere in the specs do I see any info on distortion or linearity.  So I presume it's intended only for FM or such, not AM or SSB.  I thought it might be a nice adjunct to my signal generator to get higher level output.
 

Offline mankan

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Re: 1-930MHz,2.0W RF broadband power amplifier
« Reply #5 on: May 04, 2020, 07:02:05 pm »
Yeah, I also thought about AFT05MS003N (which I have a few in stock) but have they really upped the voltage that much from the recommended 7.5V to just shy of 12V when absolute max is 12.5V?
The marking (AFT503AWLYWZ) is not matching either.
If re-soldering of the output-pin does not work I might try to replace it with a AFT05MS003N .
 

Offline mankan

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Re: 1-930MHz,2.0W RF broadband power amplifier
« Reply #6 on: May 04, 2020, 07:13:19 pm »
Bob, if I get it to work again I could do some linearity tests as well by sending some AM thru it.
 

Offline Theboel

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Re: 1-930MHz,2.0W RF broadband power amplifier
« Reply #7 on: May 04, 2020, 07:22:05 pm »
Hi,

Thats why I said the builder use "brute force" in my application I use 8v
 

Online bob91343

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Re: 1-930MHz,2.0W RF broadband power amplifier
« Reply #8 on: May 05, 2020, 05:18:06 am »
Mankan I hope you can do the test.  My current generator has a problem with output above a few hundred millivolts.  I don't usually need more but for bridge measurements it would be nice to have a strong signal.  Distortion is important for a bridge, otherwise a null is broad if there are harmonics.
 

Offline KE5FX

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Re: 1-930MHz,2.0W RF broadband power amplifier
« Reply #9 on: May 05, 2020, 07:37:26 am »
That 100-ohm resistor has certainly seen better days...
 

Offline mankan

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Re: 1-930MHz,2.0W RF broadband power amplifier
« Reply #10 on: May 05, 2020, 09:03:30 pm »
Yep, radioactive was right from the start. It was a cold solder joint. 100 Ohm resistor sure looks bad but still measures 100Ohm and looks a bit better after cleaning.
Amplifier is now working again. :D Thanks all.

And here are some measurements pictures. dBM figure in file name is input power set on signal generator. Single 10MHz tone is with 0dBm input.
To me the amplifier does not look linear at all but I'm new to interpreting IP3 figures.
 
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Offline 1847123212

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Re: 1-930MHz,2.0W RF broadband power amplifier
« Reply #11 on: June 07, 2020, 06:37:08 am »
I know this high freq mosfet.
It is RD01MUS2B.
Here goes the datasheet
 
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Online bob91343

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Re: 1-930MHz,2.0W RF broadband power amplifier
« Reply #12 on: June 08, 2020, 12:18:00 am »
Those spectra look more like FM than AM.
 

Offline 1847123212

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Re: 1-930MHz,2.0W RF broadband power amplifier
« Reply #13 on: June 08, 2020, 04:52:47 am »
could you give me the ebay address, I am interested in this power amplifier😀
 

Offline mankan

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Re: 1-930MHz,2.0W RF broadband power amplifier
« Reply #14 on: June 09, 2020, 06:53:12 pm »
 
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Online bob91343

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Re: 1-930MHz,2.0W RF broadband power amplifier
« Reply #15 on: June 09, 2020, 11:24:32 pm »
I would like to find an inexpensive amplifier that covers up to maybe 1 GHz.  Say 3 V out into 50 Ohms with 100 mV input.  Good linearity.
 

Offline mankan

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Re: 1-930MHz,2.0W RF broadband power amplifier
« Reply #16 on: June 10, 2020, 07:25:43 pm »
Voltages in peak to peak? I.e. from -16dBm to 13-14dBm? So around 30dB gain. By searching for "LNA 30dB" on eBay I found this: eBay auction: #322906863480 which gets you to 10dBm, 2Vpp. No idea about its linearity.
 


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