Re: RF power chain mods and improvements..

ajparent1/KB1GMX <kb1gmx@...>
 

Tim,

It could have maybe.  But even it if were saturated the down stream can't follow so....
no significant power.

The other and likely is the MMIC took off at UHF  and the poor transistor following that
stage was simply driven off the rails bias and inability to produce gain there wise.

Each stage has to do three things. 
Produce enough power without compression.
Operate at the selected frequency with the defined gain. 
Any failure of one of the three results in a loss of output power or distortion.

Between Q90 and the predriver is better as with the pot out and 
some landscape there you have room. 

Gain and power line up (some wishful...):

Mixer output at full tilt about -10 dbm.

Q90 no mods at 80m about 16db at 10M about 10-11db  and not more than 3mW power.

Pre-driver  take that 1mw and boost it to about 40mw, We hope.
What I saw was about 45mW at 80m and barely 8mW. 
note gain at 80m is about 16db and at 10m maybe 9db..

Driver  take that 40mw and make about .4W at 80 and sinks to barely .08W at 10M
Gain for that stage is supposed to be about 16db and likely is at 80mbut at 10M
I measured for different 3904s 8 to 11db. 

Finals IRF510 at 80M approaches 15-20W with a gain over 17db,  at 10M
its about 13db and but the drive is so low that yields maybe 2W.

Maybe its me but there is a pattern and its 3904s.  Some maybe "hotter"
and some just really fall short.  Solution, make sure each stage retains
enough gain at 10M to produce at least 13db of gain and will produce
the required power.


Allison



Allison

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