LNA power fed through bias tee and coaxial cable or through independant DC line

[Henri NICOT]

Good day to all,

I would like for you to help me choose the best option to feed DC power to my LNA, located at the source of the parabolic antenna. Currently, it is the only active component located there, so I chose the bias tee and the coaxial cable which is also downloading the signal: classical case where only one cable goes to the source.

Now I am adding new equipment at the source, in order to regulate the temperature of the LNA aluminium case. This new equipment includes Peltier module and PID controller. They must be fed by an independent 12 V. line (carrying 3 to 4 amps) and a USB cable (to monitor the LNA temperature). These two additional cables will have to run along the coaxial cable. I guess there are no other options. My question is the following. I will now have a choice to feed the LNA: still through the bias tee and the coaxial cable or through a separate DC feed plug, also existing on the side of the LNA case.

What is the best option?

Henri Nicot

+33 665 433 623

[Alex P]

Henri,

What LNA are you using and What type of Radio Astronomy are you performing ?

For typical H Line work and using a nooelec SAWBird H1 LNA,  temp stabilization may not be useful..

The nooelec SAWBird H1 LNA has a thermal gain drift coefficient of only    -0.1 dB / 10 dgC

Due to the PID switching, I'd suggest separate power for the LNA and temp control system  .... 5V Bias T for LNA, & 12V wires for Other hardware

[Henri NICOT]

Alex,

Thank you for answering me.

These are a picture and a quick presentation of the LNA I am using.

For the time being I am only doing full power recording (centered on 1420 MHz with 4 MHz of bandwidth), either transit or tracking. I have not yet studied spectral analysis but I will soon.

Constantly striving for a stable flat background signal that would allow me to detect objects, I have learned that SDR components are sensitive to even  0.1 °C. I have equipped the receiver with a temperature regulation based on a Peltier module and PID controller. This has greatly improved the stability but also allowed me to discover that the LNA, which I first disregarded as being able to cause gain drifts, was also sensitive to very small temperature changes. So I am implementing a similar process for the LNA.

I understand there may still be other factors which create gain drifts... I will see what happens after that change is implemented and I will let you know the result.
In the meantime, I will continue to feed the LNA through the coaxial cable and the other components through an additional 12 V. DC line.

Henri Nicot

+33 665 433 623

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[b alex pettit jr]

Hello Henri,

What is the size Antenna are you using ?  Feed ?

==================================================

FYI, here is info on software & hardware for 21cm

https://github.com/AP-HLine-3D/HLine3D

Alex

Project HLine3D

On Tuesday, April 22, 2025 at 02:13:45 PM EDT, Henri NICOT <henri.je...@gmail.com> wrote:

Alex,

Thank you for answering me.

These are a picture and a quick presentation of the LNA I am using.

For the time being I am only doing full power recording (centered on 1420 MHz with 4 MHz of bandwidth), either transit or tracking. I have not yet studied spectral analysis but I will soon.

Constantly striving for a stable flat background signal that would allow me to detect objects, I have learned that SDR components are sensitive to even  0.1 °C. I have equipped the receiver with a temperature regulation based on a Peltier module and PID controller. This has greatly improved the stability but also allowed me to discover that the LNA, which I first disregarded as being able to cause gain drifts, was also sensitive to very small temperature changes. So I am implementing a similar process for the LNA.

I understand there may still be other factors which create gain drifts... I will see what happens after that change is implemented and I will let you know the result.
In the meantime, I will continue to feed the LNA through the coaxial cable and the other components through an additional 12 V. DC line.

.

[Henri NICOT]

Alex,

Please find below a copy of an email of presentation I sent to SARA last November, with more details on my installation.

Greetings to all of you,

I subscribed to SARA's group a few years ago and I have been following the conversations and the videoconferences quite regularly. I am a retired French mechanical-electrical engineer, always fascinated by antennas but with no specific background in astronomy, electronics, computer science or radio communications. The beginning in amateur radio astronomy was a bit frustrating with many new matters to learn. Now, I will feel more comfortable about sticking my neck out and joining some conversations.

I am residing in Paris and in the countryside of the Czech Republic where I conduct my observations.

As a first token of entry, I am happy to share with you my concept of geodesic parabolic antenna. I find it to be as light and sharp as the Oled system is for TV screens! After choosing the reflector diameter, focus length and grid pattern, I determine the 3D coordinates of the cross points of the grid. These coordinates give the drilling pattern along the rods. I check that the proposed rod profile (flat bar 2 x 25 mm in these particular cases) will generate acceptable gravitational deformation (under 1 mm in these cases), depending on the back support hanging points.

The "First parabola" photo shows a 1.9 m. diameter prototype, with a f/D of 0.5, a round perimeter and an aluminum mesh, both of them a bit challenging to implement. The "Second parabola" photo shows a 2.0 m. diameter version, with a 0.25 f/D, a square perimeter and a plain surface, both of them much easier to implement. The surface is simply made of adhesive aluminum roll, taped on each side of the rods, in perpendicular directions. Since it was built two years ago, it has remained outside all the time under wind, rain and hail without any significant change or required maintenance.

If you would like to know more, I would be glad to describe in detail the concept and construction, on the forum, in the journal, in private one-to-one or during videoconferences.

      

The equipment that I currently use includes:

• the homemade 2 m. diameter parabolic reflector, on the right,
• mounted on a Spid rotator Big RAS HR Az/El,
• a homemade dipole backed with cavity and VNA tuned up,
• an LNA centered on 1420 MHz, behind the antenna,
• an Adalm-Pluto SDR,
• a laptop computer hosting:
• a homemade Matlab program which reads, processes and plots samples of absolute power signals in a transit curve,
• the PstRotator application that drives the Spid rotator,
• a Skychart astronomical software.

Henri Nicot

+33 665 433 623

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[b alex pettit jr]

Hello Henri,

I also have some skills in mechanical and electrical engineering .. and why I have found radio astronomy so enjoyable and challenging.

I prefer taking the time to analyze and construct Well Made Systems as You have Done.

Each of Your systems is relatively the same size, but the depth of the dishes dramatically different . 

It would be useful to compare their performance using the simple test shown below.

I have found good correlation between measuring a non HLine signal level between Earth and Cold Sky and actual H Line performance

( the correlation being : the Earth<>ColdSky dB difference is about 3.5 - 4 X higher than ColdSky<>max HLine )

Measure the dB difference between Earth & Sky for each system ..

Have you verified the calibration of your software using SMA attenuators to ensure the scaling ?

I also wrote software in Matlab ~ 5 years ago ,but it required changing many lines of code for processing each data set.

It uses SDR# & IFavg to acquire ,average, and save spectra sets

I recently had some major assistance converting some of it to Java to allow it to be easily used by others. ( as shown in the prior email )

Best Regards,

Alex Pettit

On Wednesday, April 23, 2025 at 01:54:08 AM EDT, Henri NICOT <henri.je...@gmail.com> wrote:

Alex,

Please find below a copy of an email of presentation I sent to SARA last November, with more details on my installation.

Greetings to all of you,

I subscribed to SARA's group a few years ago and I have been following the conversations and the videoconferences quite regularly. I am a retired French mechanical-electrical engineer, always fascinated by antennas but with no specific background in astronomy, electronics, computer science or radio communications. The beginning in amateur radio astronomy was a bit frustrating with many new matters to learn. Now, I will feel more comfortable about sticking my neck out and joining some conversations.

I am residing in Paris and in the countryside of the Czech Republic where I conduct my observations.

As a first token of entry, I am happy to share with you my concept of geodesic parabolic antenna. I find it to be as light and sharp as the Oled system is for TV screens! After choosing the reflector diameter, focus length and grid pattern, I determine the 3D coordinates of the cross points of the grid. These coordinates give the drilling pattern along the rods. I check that the proposed rod profile (flat bar 2 x 25 mm in these particular cases) will generate acceptable gravitational deformation (under 1 mm in these cases), depending on the back support hanging points.

The "First parabola" photo shows a 1.9 m. diameter prototype, with a f/D of 0.5, a round perimeter and an aluminum mesh, both of them a bit challenging to implement. The "Second parabola" photo shows a 2.0 m. diameter version, with a 0.25 f/D, a square perimeter and a plain surface, both of them much easier to implement. The surface is simply made of adhesive aluminum roll, taped on each side of the rods, in perpendicular directions. Since it was built two years ago, it has remained outside all the time under wind, rain and hail without any significant change or required maintenance.

If you would like to know more, I would be glad to describe in detail the concept and construction, on the forum, in the journal, in private one-to-one or during videoconferences.

      

The equipment that I currently use includes:

• the homemade 2 m. diameter parabolic reflector, on the right,
• mounted on a Spid rotator Big RAS HR Az/El,
• a homemade dipole backed with cavity and VNA tuned up,
• an LNA centered on 1420 MHz, behind the antenna,
• an Adalm-Pluto SDR,
• a laptop computer hosting:
• a homemade Matlab program which reads, processes and plots samples of absolute power signals in a transit curve,
• the PstRotator application that drives the Spid rotator,
• a Skychart astronomical software.

Henri Nicot

+33 665 433 623