Re: UBITX V3 TX GAIN VARIATIONS

MadRadioModder
 

Actually I’ve been doing a lot of experimentation on flattening/ linearizing the transmit chain.  The parts I’ve fallen on are the NE46134’s.  They have plenty of gain, Ft of 5 GHz, and with the proper inter stage transformer design… An almost flat (-0/+0.6 dB) frequency profile swept from 0.5-60 MHz is possible.  I suppose prototyped, it isn’t much of a uBITx though.

 

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Kees T
Sent: Thursday, August 30, 2018 10:46 AM
To: BITX20@groups.io
Subject: Re: [BITX20] UBITX V3 TX GAIN VARIATIONS

 

On Tue, Aug 28, 2018 at 04:25 PM, Rod Davis wrote:

WARNING: q911,q912,q92,q93,q96,q97 all dissipate at least 296 mW. That
means 250 mW transistors are not acceptable.

So, in searching for a better Ft device for the TX chain:
the BFR106 has the dissipation, but the 3.5 to 5GHz Ft invites instability
the MMBT10     lists dissipation at 225 mW, so it may not be a good candidate
the MMBT2369 lists dissipation at 225 mW, so it may not be a good candidate
the DTX2222A has the dissipation, but the Ft is not better than 2n3904, and
the footprint is not compatible with the board.

I was wondering about the reasoning behind using several parallel 2N3904 transistors in the uBITX circuit.....they are inexpensive, but why not just use a single 2N2222 ?

73 Kees K5BCQ


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