On 2/8/2011 12:23 AM, Richards wrote:
On 2/7/2011 5:03 PM, NL7VL wrote:
O.T. for just a bit ...
<SNIP>
because of the nature of the tube's ability to clip
harmonically, whereas a solid state amp will just distort everything
evenly to the point where it sounds like mud.
Hmm... I suppose that would apply to tube-based
linear amps and tube transceiver finals ? Seems like
our radios would benefit that. Maybe that is why so
many radio guys love the older, tube-based rigs.
Collins set a standard of 3rd order intermod 30 dB down. Those linear
tubes did better 5th order with 7th and 9th order not usually detected.
Swan did the opposite using nonlinear TV sweep tubes as linear
amplifiers settling for 3rd order intermod less than 25 dB down and
nearly all solid state amps since have settled for even poorer intermod
performance with stronger 3rd order, 5th, 7th and 9th order easily
detected. It should be possible with modern techniques to get an HF
linear as cleans as a 32S from Collins, its done every day at cell phone
towers where one amp shares many independent carriers. One technique
besides RF feed back is predistortion. Where the drive envelope is
distorted in the opposite direction of the PA effects (gain goes down as
the drive approaches saturation). Another technique is to modulate the
output of the PA to preserve linearity, or to run an error amp that adds
to the RF output power when the main PA is loosing gain from approaching
saturation. But these techniques aren't trivial to make work and keep
working.
<SNIP>
Thanks for allowing a brief OT slip, guys.
And now back to our regularly scheduled discussion...
=================== JHR =================================
73, Jerry, K0CQ
|