Re: ubitx schematic cleanup #ubitx

Jerry Gaffke
 

You can spend a week looking at thousands of posts debating how to get the uBitx PA to behave.
And wind up being more confused than when you started.
Most of the trouble in getting RF power out is due to issues other than the use of that IRF510 FET. 
(Looked down on by some, I guess because it was designed for use in automotive turn signals.)

Namely:  
    Gain stages from IF on through the power amp are all trying for about 16dB, and failing miserably on the upper bands
    Transformers are not optimal
    The 10W PA is on the same PC board as some very low level IF amps, feedback is inevitable
    Not enough drive into the IRF510 gates to overcome the capacitive load there on the upper bands
    
Going to RD15**/RD16** devices can help that last issue, but that won't help much.

A better bet might be to buy the excellent PA kit from QRP labs:  https://qrp-labs.com/linear.html
Can give a flat 26dB gain from 3 to 30 mhz, 10W out, roughly 200 ohms in and 50 ohms out.
    https://groups.io/g/QRPLabs/message/30760
Note that it uses the $0.50 IRF510's.

At any rate, I agree with Evan.
If whoever's maintaining documentation up on hfsignals could find the time to correct errors
and show some history and add some needed information as pointed out here in the forum,
it would make success for thousands of *Bitx* owners considerably more likely.

Jerry, KE7ER



On Sat, Feb 23, 2019 at 08:52 PM, MadRadioModder wrote:

Well I didn’t want to be so obvious to say you may consider reading through the history of the development of the alternate PA transistors in the forum.  This is a support group but it only works if you read what has happened previously so you are “up to speed”.  That will probably clear up 99%+ of your confusion.

 

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