Nice design on the UI.
Interesting specs.
What did it cost?
Thanks
The signal source I mentioned is
ERASynth Micro
ESM-1206
I purchased it on a Croud sourced deal about 2021. May not be available now.
I sent ERA asking about availability and will pass along if they respond.
<https://www.crowdsupply.com/era-instruments/erasynth-micro> ERASynth Micro
<https://www.crowdsupply.com/era-instruments/erasynth-micro> crowdsupply.com
This is open source so in theory you could make your own.
Bob
On Mar 7, 2025, at 7:59 AM, Corey Minyard via pacsat-dev <pacsat-dev(a)amsat.org <mailto:[email protected]> > wrote:
On Fri, Mar 7, 2025 at 7:34 AM Corey Minyard via pacsat-dev
<pacsat-dev(a)amsat.org <mailto:[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
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The signal source I mentioned is
ERASynth Micro
ESM-1206
I purchased it on a Croud sourced deal about 2021. May not be available now.
I sent ERA asking about availability and will pass along if they respond.
<https://www.crowdsupply.com/era-instruments/erasynth-micro>
[erasynth-micro-main-clipped_jpg_open-graph.jpg]
ERASynth Micro<https://www.crowdsupply.com/era-instruments/erasynth-micro>
crowdsupply.com<https://www.crowdsupply.com/era-instruments/erasynth-micro>
This is open source so in theory you could make your own.
Bob
On Mar 7, 2025, at 7:59 AM, Corey Minyard via pacsat-dev <pacsat-dev(a)amsat.org> wrote:
On Fri, Mar 7, 2025 at 7:34 AM Corey Minyard via pacsat-dev
<pacsat-dev(a)amsat.org> 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
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On Fri, Mar 7, 2025 at 7:34 AM Corey Minyard via pacsat-dev
<pacsat-dev(a)amsat.org> 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 -- pacsat-dev(a)amsat.org
> View archives of this mailing list at https://mailman.amsat.org/hyperkitty/list/[email protected]
> To unsubscribe send an email to pacsat-dev-leave(a)amsat.org
> Manage all of your AMSAT-NA mailing list preferences at https://mailman.amsat.org
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.
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
I won't make it today. Sorry for the late notice. I thought I would
be able to make it.
Let me know if I have actions.
73
Chris
On Thu, Mar 6, 2025, 09:42 Bill via pacsat-dev <pacsat-dev(a)amsat.org> wrote:
> *Pacsat-dev mtg 3/6/2025*
> Mar 6, 2025, 7:00 – 8:00 PM (America/Chicago)
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Corey,
You can likely improve the performance of this system.
Jim’s comments are all good to keep in mind.
The first filter element is the antenna. We have to get the signal from the antenna to the gate of the device. Everything required to do this has impact on performance.
The antenna can accumulate static charge in initial handling and in space. A DC path at the antenna will help protect the sensitive gate of the FET.
Limiting the bandwidth of the input will reduce noise if your approach is not adding noise or attenuation at the frequency of interest. The goal is to improve the impedance matching between the antenna feed point and the FET gate.
The FET is the first stage of gain and most important part of the receiver. After the FET you have more control of the circuit and impedance.
There can be an issue with temperature performance so the coupling circuit needs to be studied over temperature. The satellite will be moving in and out of the sun and can be spinning which can cause significant changes in temperature.
Getting the FET gate bias voltage correct over temp can be a issue also.
I say you can improve because I have recently seen preamps designed for radio astronomy which have such a low noise level the noise cannot be measured. It makes a smaller antenna compete with larger higher gain antennas.
While the FET selection is important part of this the coupling between the antenna and the gate are just as important. The Blinky prototype is using a short piece of 50 ohm cable and connectors so the performance of this is ok for
testing and prototype but not so good for actual operation in space.
Bob
> On Feb 21, 2025, at 9:13 PM, Jim McCullers via pacsat-dev <pacsat-dev(a)amsat.org> wrote:
>
> Bob did that design and I assume it may have to do with the LNA. I've never
> read the datasheet on the transistor so am not aware of the recommendations.
>
> I'm doing the redo for the new LaunchPad board to try another configuration
> on the AX5043 input.
> There is a great argument in the pre-amp world of where the selectivity
> should be.
> One opinion (and the common in products) is to amplify first then do the
> selectivity, the though being the LNA should pull in and amplify weak
> signals before selectivity.
> The other opinion is to filter first, then amplify to reduce intermodulation
> products.
> I'm of the second opinion and believe filters on both ends of the LNA are in
> order. I'm not certain if a low loss but less tight in bandwidth and slope
> should be on the first or if full filtering should be first with a small
> filter on the output to clean up any generated products.
>
> Remember, preamps in general are to overcome system losses and not pull
> magic out of the air. Noise is amplified as well as any signals reducing
> the noise to signal ratio.
> Preamps are like SWR, subject to many misunderstandings.
>
> You are correct that a shunt filter on the input would bleed off any charges
> that may (will) build up on the antenna.
>
> Jim
>
>
> I was looking at the blinky board receive section and I had a question. It
> has a shunt resistor for bleeding charge off the antenna and a series
> capacitor on the antenna input with a note that the shunt resistor will add
> some noise. I was wondering why it didn't have a small 2nd order shunt
> first filter there instead. Since it's shunt first, the inductor will bleed
> off any charge from the antenna. And it would provide a little filtration
> on the input, which would seem good to me.
>
> Just more curious than anything.
>
> -corey
>
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Can’t make the meeting tonight.
Work is progressing on LaunchPad V2 and receiver test circuit board.
Jim
pacsat dev mtg 2/27/2025
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Bob did that design and I assume it may have to do with the LNA. I've never
read the datasheet on the transistor so am not aware of the recommendations.
I'm doing the redo for the new LaunchPad board to try another configuration
on the AX5043 input.
There is a great argument in the pre-amp world of where the selectivity
should be.
One opinion (and the common in products) is to amplify first then do the
selectivity, the though being the LNA should pull in and amplify weak
signals before selectivity.
The other opinion is to filter first, then amplify to reduce intermodulation
products.
I'm of the second opinion and believe filters on both ends of the LNA are in
order. I'm not certain if a low loss but less tight in bandwidth and slope
should be on the first or if full filtering should be first with a small
filter on the output to clean up any generated products.
Remember, preamps in general are to overcome system losses and not pull
magic out of the air. Noise is amplified as well as any signals reducing
the noise to signal ratio.
Preamps are like SWR, subject to many misunderstandings.
You are correct that a shunt filter on the input would bleed off any charges
that may (will) build up on the antenna.
Jim
I was looking at the blinky board receive section and I had a question. It
has a shunt resistor for bleeding charge off the antenna and a series
capacitor on the antenna input with a note that the shunt resistor will add
some noise. I was wondering why it didn't have a small 2nd order shunt
first filter there instead. Since it's shunt first, the inductor will bleed
off any charge from the antenna. And it would provide a little filtration
on the input, which would seem good to me.
Just more curious than anything.
-corey
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