[AMPS] Advice about what linear to buy

[J. Bradshaw]

| Hi Jim,  (FM W8JI)
| 
| > overhauls. A small amp pushing the limits of its linearity will cause more
| > TVI and side splatter than a larger one putting out the same power, again
| > assuming similar operating modes. 
| 
| TVI has absolutely nothing to do with "headroom" in the PA. It is 
| entirely a function of the layout and shielding integrity.

Well, certainly there are many things to do with TVI.  Often many things act 
in concert, not the least of which could be the TV, or even materials not 
considered active that just happen to be within the RF field including 
shielding or other antennas and structures.

I'd go along with the rest though I don't really know the difference between 
side splatter and up and down splatter except as different visual 
representations of the same thing.  

The 706 in particular may have a spur on one or more bands that is NOT 
reduced when the power output is reduced, because the power is reduced 
by attenuating the IF, and there is a mixer following that stage.  I do recall 
seeing it on one unit at almost exactly 50 db down from the carrier at full 
ouput although I don't recall the exact frequency.  

| "Side splatter" (as opposed to "up and down splatter") is not 
| necessarily related to headroom either. An amplifier capable of 
| 3000 watts being operated at 500 watts can easily have more IMD 
| than an amplifier capable of 550 watts operated at 500 watts.
| 
| By far the most common cause of IMD is improper tuning, or 
| improper screen and bias systems in tetrodes when the IMD is 
| predominantly from the PA.
| 
| In the real world, most IMD is from the exciter with any reasonable 
| amplifier design.      
| 
| It's amazing how bad most rigs have gotten, and this especially 
| aggravated because some people think that a just because a radio 
| can put out 200 watts they can turn the internal power limiting 
| controls up to 130 watts or more without ill effect.
| 
| 
| 73, Tom W8JI
| w8ji@contesting.com
| 


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