--- In ham_amplifiers@..., R L Measures <r@...> wrote:
On Nov 1, 2006, at 12:20 PM, zerobeat40 wrote:
--- In ham_amplifiers@..., R L Measures <r@...> wrote:
zerobeat40 <zerobeat40@> wrote:
Hey, I tried to put the NFB into a solid state amp once, being
used as
a driver for commercial HF SSB. It was not so easy.
Assuming a pair of NPN transistors delivering 100 watts at 30MHz,
running from 13.8VDC, producting -30dBc IMD that we want to
improve by
about 10dB. The correct value resistor is approx 0.2 ohms and it
must
dissipate 15 watts, if the amp is to survive clumsy tuning into an
antenna tuner at full power. You could get away with a 5 watt device
if you insisted on only SSB (no CW or FM) and only into a matched
load. Smallest resistor I was able to find to meet this was a chip
style component, about 1/2 inch X 1/2 inch. It measured 5nH of
inductance. At 30MHz, XL=nearly one ohm. The stage gain at 30MHz was
reduced to approx 2dB, and the phase shift of this inductance
reduced
the IMD benefits of the NFB to having no IMD reduction at all. At
1MHz, the solution worked very nicely - stage gain stabilized at
14dB,
and IMD measured about -42dBc (referenced to either of two incident
carriers)
If you could somehow create a 15 watt resistor that is 0.2 ohms and
under approx 0.2nH of inductance, then your proposed solution will
work.
!. I would use 50v transistors.
For 50V transistors operating at 100W per pair, the required resistor
is 0.8 ohms, wherein you'd need 0.8nH of inductance or less, still at
15 watts. Can you find that one? For MRF150s, it's 0.5 ohms, needing
less than 0.5nH of inductance, this time at 25 watts.
Let us know.
Z
Do you have a FCC callsign?
No, sir. Is that a requirement for inclusion in this group? I came
here to avoid the censorship of another group that looked down upon
those of us who were not licensed. If, however, this group is
similarly exclusionary, then please accept my apologies, and I shall
depart with what little grace I may have left.
Z
