FlightAware Discussions

New filter or LNA

With two female sma, you‘d still need an adapter, as the sdr also have a female sma connector. Or even two, depending on the cable you are going to use.

The only problem with the other bias-t was that it is very tempting to plug it the wrong way round or maybe buy a wrong antenna cable, or forget to buy adaptors.

This biast has one side sma-male, other side sma-female. However it has disadvantage that it does not have any terminal marking, and a user may easily connect the biast the other-way round.



I have 2 bias tees:

  1. https://www.ebay.com/itm/132678347178.
    It has both sides sma-female.
    It has the SMA terminals marked RF and DC+RF, and hence has less chance of wrong connection.



  1. https://www.ebay.com/itm/183768806247 ( sold out)

    It has one sides sma-female, other side sma-male.
    It has the SMA terminals marked RF and RF&DC, and hence has less chance of wrong connection.


That picture shows the capacity on the SMA female side, which is generally not what you want.

Isn’t that to block DC going into the dongle?

The capacitor (C1) is going to block DC at the output it’s closer to than the inductor/coil (L1).

Most SDRs have a female SMA connector, so if you connect that part to the SDR, the SDR will get DC and the LNA will get nothing.
That’s the reason why this bias-t is problematic in our typical use case.

Use sma-male to sma-male adapter supplied with tripple-filtered LNA


Now I’m really starting to get confused. If I would get this one I can see which end goes to what (RF to dongle, DC+RF to LNA/antenna) and as long as I have the proper adapters, I can connect everything together.

I have to get some adapters anyway; including one that goes from F-female to SMA-male (coax to LNA) and SMA-male to N-male (LNA to FA antenna)
I can connect the bias tee to the FA filter or FA dongle with the SMA-Male to SMA-male adapter that’s included with the LNA.
If have move the LNA underneath the rooftiles; that’s another section between the LNA and antenna that’s going to require some connectors and adapters.

bias-t sma-female both ends

Absolutely correct. With that bias-t, you will need following:

  • Dongle should be connected to the terminal marked RF. To connect bias-t to dongle, you will need either an adapter “sma-male to sma-male”, or a pigtail with sma-male at both ends.

  • LNA should be connected to the terminal marked DC+RF. To connect bias-t to LNA, you will need either an adapter “sma-male to sma-male”, or a pigtail with sma-male at both ends.

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Doesn’t anyone own a soldering iron?

I purchased one bias-t similar to the photos I have posted, but instead of DC screw terminals, it had copper pads to solder the DC wires. After soldering the DC wires, a little pull on wire, and the copper pad got detached and torn off from the PCB. :angry:

Your soldering iron was too hot

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Actually my 40W soldering iron had burnt out, and I made a mistake to use my 200W soldering gun.

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That’s my point as well. I can see problems with boards that do not have any marking, but to argue about male or female put me at a total loss.

The problem is which end of the soldering iron to handle. :rofl:

Those are the best, everything is ‘bonded’ together now. :sweat_smile:

Like this isn’t it?


You got it!

The only thing worse is handling SMDs with this:


That shop must be closed for failing to provide proper PPE (gloves) to employees. :wink:

Soldering: If it smells like chicken, you’re doing it wrong.

Power has nothing to do with it, it’s the temperature that was wrong.

So it’s been a while, but shipping the various adapters and connectors from China took some time.
(Though the LNA was delivered fast!)
But everything is in so when the weather permits and I’m OK with going up the roof; the LNA can be installed. My plan was to install the LNA directly to the antenna with a SMA-male -> N-male adapter.
But since the LNA is not waterproof; I’m think of ways to make it waterproof.
A box around it would mess with the LNA-antenna connection, taping it with whatever may cause overheating.

Anyone have any ideas?

EDIT: oh, and one other thing; probably a stupid question; but how can you tell the LNA is actually working; if it gets the power from the bias-t correctly and so on?