Re: boosting the power on 28 MHz #ubitx

Ashhar Farhan

I forgot the picture of the experiment.
- f

On Sun, 6 May 2018, 09:58 Ashhar Farhan, <farhanbox@...> wrote:
So, here are the final mods, 
Replace C81 from 0.1uf to 470pf
Replace R83 from 10 ohms to 2.2 ohm
(you can short R83 as well) 
Replace 97, R98 from 47 ohms to 220 ohms
Remove C261, C262. 

So, what happens is that removing the C261 and C262 increases the gain of the finals. They are run open. Hence greater gain at 28 mhz. 
However, the gain is very high at lower frequencies. So, in order to reduce the gain at the lower frequencies, the 0.1 uf cap is replaced by the 470 pf. As the frequency of the signal drops, less and less RF flows through the 470 pf, decreasing the gain of the predriver. 470 pf is not a magical value, 220 pf works almost as well. 
Here are the pictures at 14 mhz. The two tone test reveals 20 db IMDR, which is alright. If you want to see better, buy yourself two RD16HHF1s. 

- f

On Sat, 5 May 2018, 22:02 Kees T, <windy10605@...> wrote:
Are you able to measure compression for linear operation (SSB) ? Harmonic content and levels ?

73 Kees K5BCQ

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