radioberry preamp

[pa3gsb]

Hi Group,

Hereby the scheme of the preamp. 

The amp is based on all the hard work done by Steve.

I like the design.

Hope you also.

73 Johan

PA3GSB

[Bob A. Booey]

Hi Johan,

Have you considered using the QSK TR switch design I shared on the forum?  I have tested it with a more powerful amp (the QRP-Labs QSX Amp) and it works well.  Being a CW operator myself, a QSK TR switch is very desirable to me.

In any case, thank you for another nice addition to the Radioberry!

73 and Happy Holidays,

Robert, WA2T

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[Mike Richards]

Hi Johan,

That amplifier looks like an excellent addition to the project and is just what we need to make it into a complete QRP transceiver.

Regards,

Mike - G4WNC

[Martin Škutek]

Hi Johan, nice job.

How or where do you implement I2C bias driving?

Martin OK2MTW

Dne pá 18. 12. 2020 22:19 uživatel pa3gsb <pa3...@gmail.com> napsal:

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[softerh...@gmail.com]

Hi Johan,

The main contributor and developer of the Hermes-Lite 2.0 RF power amplifier was Claudio, IN3OTD. He has a website with details on various RF amplifier experiments and measurements.

Are you using the low power TxDAC output or the higher power IAMP on the AD9866? With the Hermes-Lite 1, we found that the IAMP generated nonharmonic spurs which would violate US and EU regulations for spurious emissions when amplified. Because they were nonharmonic, they could not be filtered by traditional filters. This is why we use the cleaner TxDAC output with an additional OPA2677 RF preamp. There are details in the HL2 group as well as on this old wiki page.

73,

Steve

kf7o

[pa3gsb]

Hi Robert

I did not consider it... the amp will be used in combination with mine 100W amp which also uses relais...

but for QRP use it could be a nice option.

I will take a look... if i can make it  an option would be fine. and if it fits on the 2 layer board 

73 Johan

PA3GSB

Op vrijdag 18 december 2020 om 23:53:42 UTC+1 schreef rent...@comcast.net:

[pa3gsb]

Martin

Do you have an idea? 

I have no idea yet; i did not think how to set the bias and where to keep the configuration of the bias setting!

73 Johan

PA3GSB

Op zaterdag 19 december 2020 om 00:35:48 UTC+1 schreef martin...@gmail.com:

[pa3gsb]

Mike

Tnx for your feedback!  

73 Johan

PA3GSB

Op zaterdag 19 december 2020 om 00:16:25 UTC+1 schreef mi...@photobyte.org:

[pa3gsb]

Steve

 I will mentioned that also in the drawings. Tnx. 

The IAMP is used for now and i am accepting it for now!  It is already on the list for some time to adapt to the TxDAC output....

I have limited time to do it all.... in winter season i do have some more time for the hobby and i like to make a start with adding a preamp and hope to get a good overview and implementation of the amplifier.

Tnx for all your work and sharing of it.... i am really standing on your shoulders!

Have fun,

73 Johan

PA3GSB

  

Op zaterdag 19 december 2020 om 08:03:20 UTC+1 schreef softerh...@gmail.com:

[Radioberry]

Hi All,

I have done some measurements about the spurs in band.

Especially the one 24.895 MHz.

2Fs - 5Ftx

The Fs is changed from 73.728 into 76.8 MHz

The spur should now occur in 153.6 -(5 * 24.895) = 29.125 MHz (the calculation matches the actual spectrum)

By changing the sampling freq this spur is moved out of the band.

The additional filtering bringing this spur down with 20 db is still on the wish list.

73 Johan

PA3GSB

Op zaterdag 19 december 2020 om 14:30:56 UTC+1 schreef pa3gsb:

[softerh...@gmail.com]

Hi Johan,

This spur is very hard to filter out as it is very close to frequencies of interest. Imagine trying to transmit on 10 meters and filter out a spur at 29.125MHz. The spur will be amplified by the PA. Most filters are designed to suppress the second, third and higher harmonics. The second harmonic for 15 meters up to 10 meters is in the 40 to 50 MHz range, quite far from 29.125MHz.

There were some early experiments where the IAMP output was reduced from 20dBm to ~10dBm by adding a filter to the TxDAC output. This seemed to eliminate the spur. The details are buried in the Hermes-Lite Google Group. For the Hermes-Lite, we ended up just using the TxDAC output and adding an external preamp.

73,

Steve

kf7o