Bob

On Mar 7, 2025, at 7:59 AM, Corey Minyard via pacsat-dev <[email protected]> wrote:

On Fri, Mar 7, 2025 at 7:34 AM Corey Minyard via pacsat-dev
<[email protected]> wrote:

I realized a problem with the AGC design I talked about: The output

impedance will vary a lot with gain. I'm not sure how much of a

problem that is, I guess it depends on what it's driving, but it's

definitely an issue. I'll have to simulate that.

One other thing I forgot to mention was that the transistors I was
using are switching transistors, not RF amplifiers. So they aren't
going to perform very well as amplifiers, but I can't find any
suitable RF amplifier MOSFETs or JFETs with simulations available.
They have poor amplification characteristics. I didn't show the
curves, but the ones I used start to lose gain at about around 10MHz;
they were 6dB down at 40MHz. Unless it's something about the circuit
design, but that's pretty straightforward.

And apparently you have to know device geometry to create simulation models.

Another question on that: the input to that MOSFET is obviously going

to be high impedance, but it's coming from a filter that's going to be

low impedance. (high impedance LC filters don't seem to be feasible).

Normally you would put a resistor to ground to terminate the

connection, but then you are introducing noise. Is that an issue?

Since the frequency is fixed, could you put an inductor of the right

value there?

Also, Bob, you mentioned building boards for testing. How do you do

that? Do you put a zero-ohm resistor between sections and an SMA

connector on each side of it? You probably want some way to enable

power per section. Anything else I need to worry about?

As far as building boards, getting the board itself isn't that

expensive, but how much does it cost to populate the board? The

processor is a BGA; I'm not sure I can solder that, and having someone

else handle all the soldering would be nice.

Also, there's the signal generator you mentioned. I found a couple,

like https://www.amazon.com/Seeku-WB-SG1-Signal-Generator-1hz-8ghz/dp/B082WBZ9S3

but I'm not sure which you are talking about.

Thanks,

-corey

-----------------------------------------------------------

pacsat-dev mailing list -- [email protected]

View archives of this mailing list at https://mailman.amsat.org/hyperkitty/list/[email protected]

To unsubscribe send an email to [email protected]

Manage all of your AMSAT-NA mailing list preferences at https://mailman.amsat.org

-----------------------------------------------------------

pacsat-dev mailing list -- [email protected]
View archives of this mailing list at https://mailman.amsat.org/hyperkitty/list/[email protected]
To unsubscribe send an email to [email protected]
Manage all of your AMSAT-NA mailing list preferences at https://mailman.amsat.org