Jerry,
One of the reasons I want to put it before Q90 is to make it easy to
access and test.
If you'll remember I was the first person on here to show spectrum
analyzer screen shots showing how the 3rd order IMD and carrier
suppression is marginal. I don't plan on doing anything less with this
amp in the chain. If Q90 distorts it should show up in 3rd order IMD
results.
I'm not much on LTSpice and that genre of software. I tried using it
once but just too many demands on my time to learn how to use it.
Easier to just measure actual results!
tim ab0wr
On Wed, 06 Jun 2018 21:14:50 -0700
"Jerry Gaffke via Groups.Io" <jgaffke@...> wrote:
Tim,
The reason to add a stage of amplification like that is so we can
reduce the amplification of pretty much all the other stages.
With reduced gain, they have a much better chance of giving the same
gain at 30mhz as they do at 3.5mhz.
You could try patching this amp in when operating at 30mhz.
Turn RV1 down all the way, then slowly bring it up to get the power
you want. But you had best be ready to measure distortion in your
signal before getting on the air with it.
It could well be that Q90 will not work properly with the 10dB
increased input signal and will distort.? Having the amp after Q90
allows you to adjust RV1 down until any stage after the new amp does
not have too strong a signal, strong enough to distort.
I don't think you want this new amp in there at all when operating on
the lower frequencies with an otherwise stock rig.? Too much gain.?
I'm just kibitzing here, have not analyzed the Q90 stage.
You could take the LT-Spice model for the uBitx power amp from the
KE7ER directory in the files section, see what the simulation does
when Q90 is driven harder.
Jerry
On Wed, Jun 6, 2018 at 07:36 pm, Tim Gorman wrote:
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
