Re: Transmitter Mods


Howard Fidel
 

The theory is very simple. The closed loop gain of Q911 and Q912 is set by the ratio of R86/R85, or a gain of 10. Adding an inductor into the path in the feedback loop increases the effective impedance at higher frequencies, adding "peaking" to the circuit, thus making the closed loop gain higher. I think the poor frequency response is in the transformer as well as the transistors hfe falling to under 25 typically at 30 MHz. Also, the open loop gain is also increased by bypassing the emitter resistors for higher frequencies.

The transformer is a 2 to 1 step down, (it looks like a trifilar winding) so the theoretical gain of the stage is 5.

Howard

On 4/19/2018 12:36 AM, ohwenzelph via Groups.Io wrote:
How and why does this mod work? What was the calculation that came up with 220pF and 27 uH? 
For the inductor does it matter how many ma it can handle or what it’s self resonant frequency is?
(doubt I will be able to follow the answer but still curious)
thanks!


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