Wide Band LNA RTL-SDR Inmarsat without signal

[Angelo2021]

Hi

I am having some problems with the Inmarsat signal when I connect a RTL-SDR wide band LNA between the patch antenna (RTL-SDR) and the V3 dongle. No signal is displayed on the sdrsharp screen.

I have the bias tee activated with a 4.7 volts in the LNA output and the green light active.

When I remove the LNA, signals are displayed in the screen.

Can someone help me?

Thanks in advance

Angelo

 

[prcguy]

Your noise floor is lower with the LNA connected, is it hooked up backwards?

 

[Angelo2021]

No, the connection is Ok. In another forum someone told me that the problem is that any power is passing to the antenna on this lna.

It's necesarry another bias tee to activate the lna.

Thanks for your help.

Angelo

 

[prcguy]

If you have an active antenna and the bias tee doesn't pass power through then that's your problem. In my opinion you don't want to use an LNA after an active antenna unless your using splitters to feed multiple receivers and the LNA is only making up for splitter loss. The active antenna sets the noise figure of your "receive system" which includes the antenna, feedline and receiver. Adding an LNA at the radio end will not improve reception and in many cases it makes things worse.

No, the connection is Ok. In another forum someone told me that the problem is that any power is passing to the antenna on this lna.

It's necesarry another bias tee to activate the lna.

Thanks for your help.

Angelo

 

[Ubbe]

I am having some problems with the Inmarsat signal when I connect a RTL-SDR wide band LNA between the patch antenna (RTL-SDR) and the V3 dongle. No signal is displayed on the sdrsharp screen.

It doesn't look like a RTL-SDR brand of LNA. What are its exact model name? What are the patch antennas model name?

If the antenna isn't narrow banded it could pick up a lot of unwanted frequencies that overloads the SDR receiver. If you have set it to auto AGC it will reduce its sensitivity. You'll have to set the receiver to a fixed gain at a setting where you get the best signal noise relation, not the highest signal level, when you get a signal.

/Ubbe

 

[dlwtrunked]

It doesn't look like a RTL-SDR brand of LNA. What are its exact model name? What are the patch antennas model name?

If the antenna isn't narrow banded it could pick up a lot of unwanted frequencies that overloads the SDR receiver. If you have set it to auto AGC it will reduce its sensitivity. You'll have to set the receiver to a fixed gain at a setting where you get the best signal noise relation, not the highest signal level, when you get a signal.

/Ubbe

I think you are on the right track. One has to make certain that the LNA will cover the 1.5 GHz INMARSAT frequencies. In some cases, nearby cell phone/PCS/etc. signals will de-sense the receiver unless filtered out with a SAW filter. Additionally, one does need to adjust the gain as you note. Additionally, some SDRs do not pass enough power for some LNAs. Personally, I use an externally powered LNA as I want to use better LNAs and avoid such hassles. While we are at it, attached is my most recent frequency list.

 

[K5MPH]

What antenna are you using......

 

[Angelo2021]

The antenna is patch path RLT-SDR: https://www.aliexpress.com/item/4000311955837.html
The LNA is also RTL-SDR: https://www.aliexpress.com/item/33011424874.html

 

[prcguy]

A friend of mine just bought a bunch of similar LNAs and they were all defective. They use the SPF5189 chip and it seems all the amplifier chips were Chinese counterfeits and they drew a lot more current than spec and they all burned up within minutes. You might try the LNA by itself fed by just a piece of wire, turn the LNA on and off and see if your noise floor goes up or if signals are their with power applied and they go away when power is removed. That will at least prove the LNA is good or bad.

The antenna is patch path RLT-SDR: https://www.aliexpress.com/item/4000311955837.html
The LNA is also RTL-SDR: https://www.aliexpress.com/item/33011424874.html

 

[Ubbe]

The antenna are already amplified. You can't improve on that, you'll only add noise.
The LNA doesn't have any power pass choke on it so it won't pass any power to the antenna.

/Ubbe

 

[K5MPH]

Yes I have that same antenna and if I remember it already has a amp built inside the antenna.......