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OH1XS > DRAKE 12.09.94 17:55l 30 Lines 990 Bytes #999 (999) @ WW
BID : 91770_OH1RBU
Read: GUEST
Subj: TR7 PA gain flattness
Path: DB0GOS<DB0END<DB0GE<DB0HOM<DB0AIS<DB0SIF<DB0NHM<DK0MNL<DB0DJ<DB0HRO<
OZ4BOX<OZ4BBS<OZ3PAC<OZ6BBS<SK7CY<SK7BK<SK7QJ<SM7RVR<SM7FEJ<SK6LK<
SK6SA<SK6YW<SM0ETV<SM5BKI<SK5DB<SK3SN<SK3JP<SM3ESS<SK3BG<SK3EK<SK3LH<
SK2AT<OH6RBG<OH6RBV<OH6RDC<OH6RBC<OH6RDP<OH6RBT<OH1RBF<OH1RBU
Sent: 940910/1732Z @:OH1RBU.FIN.EU #:191770 :91770_OH1RBU
Hi there!
I have DRAKE TR7 tranceiver and i found some "trouble" in
final amplifier section.
I found poor gain flattness in final amplifier, causing
ALC working hard in lower bands such as 3.5 and 7 MHz.
The gain is about 10dB higher in lower bands than upper
bands. Ref. schematic, there is L2307 and L2308. Their
value seems to be higher than many other PAīs and also
100 ohm resistors R2308 and R2310 seems to be high.
This overgain may cause spikes by "slow" ALC action
and may overdrive my MOSFET power amlifier input.
In normal operation this isnīt broblem,
but ALC needs to turn power down 10dB. Now i have a LC
trap in amplifier input to reduce the gain. I did try
some different coils and resistors, but they didnīt
work just right. My theory still is, that feedback
components arenīt in ballpark.
If somebody have experiments or theory about this,
please advice me by packet.
73! cuagn. tnx.
OH1XS @ OH1RBU.FIN.EU
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