Allison,
Jerry,
I have my little mmic board built. Would it be ok to add it before Q90
by removing C80 and inserting the input and output on those pads. Doing
that would allow me to stick the board on top of the relay that is right
beside Q90. It would facilitate testing, experimentation, and
parts changeout if needed. It would also be right beside my 7812
voltage regulator so I would have short power leads.
Will another 10-12db of gain into Q90 be a problem?
tim ab0wr
On Wed, 06 Jun 2018 15:42:13 -0700
"ajparent1/KB1GMX" <kb1gmx@...> wrote:
One of the factors not reported was the consistency of the gain vs
spur. Simple put the gain and the spur interacted even when I held
the level to the mixer constant. I'd lower the gain and the spur
would get worse as an example.???It varied greatly with supply
voltage as well.
Reason sluggish 3904s (low FT, Maybe Low? HFE).? Remember we are
using a 300mhz device and that is a typical value and can be as low
as 250 (batch and vendor) or much higher.? I changed them out for
BFR106 (Q20, Q21, Q22), Seems the 3904s were not up to the task of
keeping the amp load independent.?
The net result was what others had reported as lower spur production,
in mine it dropped the 10M spur nearly 12db.? So it was either
distortion in the? 45Mhz amp or its ability to be a low output
impedance which should be with emitter follower with the 47ohm making
it look near 50 ohms.? I didn't? try 2n2963A as I didn't have any
left in SMT but I suspect they would have been better.
For now I'm taking a break on output power and addressing other
things.? The power thing stands at 10W at 80m, 7W at 10M with the
spur 46db down.??
I'll list all the changes as my unit stands while I do pop/click and
mod then agc.
For now mods I have in place, I'm not 100% happy but that is what
us experimenters enjoy.? Likely others to come. ;)
?
Replace and reset bias OF Q90 with 2n2369A or better (BFR106),
Set bias for 18ma (r86 2.2K).? Make C81 470pf, and r83 8.2ohms.
Change C82 to 470pf (peaking for 10M).??
T9 is now 9 turns #28 bifilar (one winding was never used).
All the 2n3904s in the predriver and driver replaced with 2n2222A or
better. Hint I mounted them on the underside with very short leads as
it makes the top less crowded.??
Driver amp has 2.7uh SMT choke in series with R86 and that is now
1.6Kohms R87, r88 Both have a 270PF cap in parallel with them.
R911,r96, R941, R942 emitter resistors for driver reduced to 11ohms
(add parallel 22ohm). R92, R95 replaced with 1.5K ohm in series with
2.7uh choke.? (resets bias and adds peaking.)
T10 has one less turn.
T11 reduced by 1 turn.
45mhz IF replace (Q20, Q21, Q22) with BFR106.? Change R23 to 18ohms.
Change R27 to 39 ohms. !2mhz IF amp change R43 to 18 ohma and put
a .1uf in series with 680 ohms across R41.
Replaced Q10 with BFR106 for better receive gain at 20mhz and up.? (I
may change out the two 3409s).
Add LM7806 regulator in handy location to limit voltage to ta2822 to
6V on pin 2. Add 1K resistor from negative side of C77 to ground
(prevents pop when pluging in headphone or speaker)
Add 16K resistor from base o ground of Q70 for better overload
performance.
The one change that really helped the transmitter was going to the
2n2222A (TO18) part. Before that it was 13W on 80 and barely 7 on 40
and less on 20.? After that change alone 40 was near 10W and 20 was
about 8.5W.? This has been tried on another unit that was weak on 40M
and it really helped with no other tricks.
Enough for now.? I plan to spend a few days re-rolling the software
off the V4.3 release for my user interface which will not include
CAT, CW or a rotary encoder.? Without CW mode the sidetone CW-Tone
and CW-KEY pins are usable for general IO by removing R256 and R105.
Allison
