Sawtooth+ H1 LNA with Nooelec NESDR SMArt V5 SDR.

[Arjun Shenoy]

Hi

I am Arjun. 

I had bought Sawtooth+ H1 LNA from fab to lab. I recieved the pacakage ON 26 may 2023.

The connection is completed for receiving signal from milky way galaxy.

Signal from antenna is fed into LNA, then this LNA is connected to SDR via proper channel. Power supply for LNA is supplied using a powerbank. Finally SDR is connected to my laptop.

The power LED on LNA is ON when i haven't connected the SDR( Only the power supply from power bank is fed into it ). But when the wire from LNA is connected to SDR, the LED automatically turns off. I am not getting signal which i am supposed to get. ( antenna is set on correct direction of milky way galaxy from the data obtained from stellarium app)

Is this supposed to happen?

Why does my LED turns off?

I enquired this at fab to lab and got to know that i need to install a DC block for proper working. But they had mentioned that this model didnt need DC block. The SDR that i use is Nooelec NESDR SMArt v5 SDR. What should i do to make this SDR work with my new LNA. If DC block is only way for it, please mention some method via which i can introduce DC block.

[tedcl...@gmail.com]

Hi Arjun,

Yes, that is puzzling.

That LED is convenient.

Same problem when touching just outside of coax connector ?

Is the coax shield grounding the LNA power supply ?

(A surprise electrical path through LNA power supply ?)

If not, then yes, perhaps the LNA power is coming down the inner coax conductor and fighting the SDR.

A "DC Block" would be a simple test ?

A "DC Block" would place a capacitor in the path of only the inner coax conductor, for SMA connectors,

https://www.nooelec.com/store/sdr/sdr-addons/dc-block.html

But I use cheaper 75-ohm coax, with F connectors,

https://www.amazon.com/Ancable-F-Type-Voltage-Blocking-Capacitor/dp/B074K51D7X

More expensive, but maybe you can find faster, a Bias Tee as a "DC Block" ?

https://www.minicircuits.com/WebStore/dashboard.html?model=ZFBT-4R2G-FT%2B

https://www.amazon.com/10MHz-6GHz-Broadband-Frequency-Microwave-Amplifier/dp/B07Q7HKWZZ

Shop around.

---
Ted Cline   N0RQV

On Friday, June 16, 2023 at 6:27:52 AM UTC-6 Arjun Shenoy wrote:

Hi

I am Arjun. 

...

 

[Alex P]

Arjun,

You can use Only One Power Source ..

 Either an External 5V through the small USB connector on the SAWBird  or

via the BiasTee capability of the Nooelec NESDR SMArtee  over the coax But Not Both

If you want to use External ( USB ) power for the SAWBird, then you need a DC_Block

between the SDR and SAWBird

Alex KK4VB

 

[b alex pettit jr]

SMA SMA  DC_Block

https://www.amazon.com/RF-Block-Watt-SMA-Connector/dp/B0BFCWBGJ4/ref=sr_1_5?crid=ODVOPI6S6B31&keywords=sma+dc+block+in-line+50+ohm&qid=1687522274&sprefix=sma+dc%2Caps%2C217&sr=8-5

[mike....@gmail.com]

Arjun,

Why not just disconnect the power bank on the SawBird and feed the LNA with the power through the coax from the SDR?  That would be simpler.

[b alex pettit jr]

That is obviously the best solution.

There is an option in the SDR# setup to [ Enable]  Bias T 

Then, powering up the SDR should turn On the white power indicator on the SAWBird.

[mike....@gmail.com]

As I understand from this thread was that there was contention between the SDR and the power pack on the LNA.  So that would mean that the SDR was already putting out power.

The sdr (not NooElec) on the " scope in the box" project I worked on this spring was already putting out power to the LNA without any software manipulation.

And the  two NooElec Smartee 's that I am using on the interferometer , were also putting out power with out software manipulation. 

On Friday, June 16, 2023 at 7:27:52 AM UTC-5 Arjun Shenoy wrote:

[Marcus D. Leech]

On 23/06/2023 14:03, mike....@gmail.com wrote:

As I understand from this thread was that there was contention between the SDR and the power pack on the LNA.  So that would mean that the SDR was already putting out power.

The sdr (not NooElec) on the " scope in the box" project I worked on this spring was already putting out power to the LNA without any software manipulation.

And the  two NooElec Smartee 's that I am using on the interferometer , were also putting out power with out software manipulation.

Indeed, the NooElec SmartTee radios have always-on 5V bias on the output connector.  I think only the "SDR Blog" devices have
  a software-controllable bias-T, and you have to have the right drivers to turn it on.

On Friday, June 16, 2023 at 7:27:52 AM UTC-5 Arjun Shenoy wrote:

Hi

I am Arjun. 

I had bought Sawtooth+ H1 LNA from fab to lab. I recieved the pacakage ON 26 may 2023.

The connection is completed for receiving signal from milky way galaxy.

Signal from antenna is fed into LNA, then this LNA is connected to SDR via proper channel. Power supply for LNA is supplied using a powerbank. Finally SDR is connected to my laptop.

The power LED on LNA is ON when i haven't connected the SDR( Only the power supply from power bank is fed into it ). But when the wire from LNA is connected to SDR, the LED automatically turns off. I am not getting signal which i am supposed to get. ( antenna is set on correct direction of milky way galaxy from the data obtained from stellarium app)

Is this supposed to happen?

Why does my LED turns off?

I enquired this at fab to lab and got to know that i need to install a DC block for proper working. But they had mentioned that this model didnt need DC block. The SDR that i use is Nooelec NESDR SMArt v5 SDR. What should i do to make this SDR work with my new LNA. If DC block is only way for it, please mention some method via which i can introduce DC block.

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