Chinese Pre amp v2. My first question is whether i this is a different design or an improvement over some previous design

[Sunil Thomas Thonikuzhyil]

Hello all,

    I am rather new here. Got a radioberry from Ali express and it is working fine . I purchased a preamp from  aursinc last week.

  

https://www.aursinc.com/products/aursinc-radioberry-preamp-board-v2-a-addition-to-turn-the-radioberry-into-a-small-qrp-radio-output-1-5w-3w-for-hf-power-ampfier-10w-100w-pa-for-raspberry-pi-4-4b.  

Unfortunately the documentation they provided is useless. 

The board I i have is shown in the picture below

I have a few questions

1) Is it  different form the circuit  shown on the github page

2). What tis the purpose of the white  jumper?

3) Can I directly plug in to radioberry and work in phHPsdr or some adjustments  have to  be done in software

4) Is there a pdf of the schematic of this board anywhere ?

5) i am confused about wiring a ptt  to the micro phone jack .

6  What is the purpose of PA current holes ?Do i have to connect something here.

7 How to adjust the potentiometers shown?

Regards

Sunil vu2swx

 .

[Michael Bales]

Ok, first, these are not well designed pa boards. I've been through 5 in as many months.
The bias should already be set.
It needs to be setup using Spark SDR. The current pads are where you can check to make sure that you have proper bias to the gates, about 2.8vdc.
You need 8-8.4vdc power. Keep the whole stack cool!!! Lastly, no, there is no proper documentation on this thing, as it is a modified Chinese knock off of an open source project.

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[Michael Bales]

I was eventually able to get Aursinc to send me this attached schematic.

---

From: Michael Bales <kb8...@gmail.com>
Sent: Friday, May 23, 2025 10:13 AM
To: Sunil Thomas Thonikuzhyil <vu2...@gmail.com>
Cc: Radioberry <radio...@googlegroups.com>
Subject: Re: Chinese Pre amp v2. My first question is whether i this is a different design or an improvement over some previous design

 

[Sunil Thomas Thonikuzhiyil]

This is great, thank you!

[SNAIL]

According to schematic diagram posted by Michael Bales the bias need to be set by pot adjustment to 2.2 volts. DAC circuit to set bias by I2C as it was in original design is stripped out and substituted by simple on/off IC switch U8 on diagram providing 5 volts to pots.

On Wednesday, May 28, 2025 at 11:48:26 PM UTC-6 Mario Kerst wrote:

1) Is it  different form the circuit  shown on the github page

Yes but not sooo much.

2). What tis the purpose of the white  jumper?

Connecting SMA Antenna plug to the Board. I think it is made to to plug a antenna cable there, if you dont want to use the SMA.

3) Can I directly plug in to radioberry and work in phHPsdr or some adjustments  have to  be done in software

Try QUISK. For me the best alternative to Sparksdr or piHPSDR. Quisk looks more professional. You can use the hermes lite settings. Somewhere is a youtube video about these settings.

4) Is there a pdf of the schematic of this board anywhere ?

If you find it, please provide :)

5) i am confused about wiring a ptt  to the micro phone jack .

never used, works only in piHPSDR i think.

6  What is the purpose of PA current holes ?Do i have to connect something here.

same as you can see on github.

7 How to adjust the potentiometers shown?

Never do something on these potis.

Additional: Cool down the preamp. The small ldmos heating up to 155 degres celsius on full load.

cheers

[Frank Thomsen]

Hi All,

We are all experimenters in this space I believe, however, I, for one, think I have wasted my money buying this Aursinc product - but hopefully I can learn something from it so it won't be a complete loss.

The documentation from Aursinc does not reference anything so I went looking:

Data sheet for AFT05MS004NT1 states MAX 2.5V bias.

The referred "typical" 2.2V in the data sheet is too low for any kind of linearity.

Even 2.7V does not really produce good enough linearity for SSB.

I got reasonable linearity at about 3V forward bias - for about 5 seconds, then the transistors popped one by one - part of it was my own fault, I had too much input!

When run at that voltage they are at a very high level of conduction and produce a LOT of heat just idling.

I have ordered a whole bunch of them to test - but I have little hope they will perform well enough for anything but FM and other constant amplitude modes (FT8 for instance) at 2.2-2.5V bias, however, cooling is still going to be an issue. My best guess is 1-2W FT8.

FETs, like the RD series might have been a better choice - they are pricier for sure, but could be worth it.

I believe the current crop of Hermes Lite 2 uses the AFTM05M's too. Cooling is somewhat better but I doubt it is good enough to run the AFT05M's at 3V bias.

The puresignal feature in piHPSDR may be a solution, I have no experience with that, but I have watched a couple of YouTube videos ;-)

OZ5ACI - Frank