Cable length between LNA and RTL-SDR

How much cable loss can be tolerated between the LNA and the RTL-SDR stick?
I see in the docs that the LNA has a gain of 34dB, how much of that is excess?
(i.e. more than the difference between sensitivity at the LNA input and the RTL-SDR input?)

I would like to mount the antenna outside and given the issues w.r.t. power-on of the CHIP and
reflashing it, it is probably best to mount only the antenna and LNA outside and feed the signal
inside over coax (vs. putting everything in a box outside and feed it only with DC power).
But that means I need about 5m of coax, and I would like to know what loss is tolerable to know
what kind of coax to use. (preferably of course the thin teflon coax like on the antenna)


Yo tengo 5 metros de cable LMR200 entre el LNA y el E4000, un adaptador de SMA-RPSMA y un latiguillo N-SMA de 15 CM, y con todo esto el SNR es de 7.5 dB de media, 5 metros de cable detrás del LNA no debería perjudicarte mucho.

También dependerá del cable que uses.



I have 5 meters of LMR200 cable between the LNA and the E4000, a SMA-RPSMA adapter and a 15 CM N-SMA hose, and with all this the SNR is 7.5 dB on average, 5 meters of cable behind the LNA It should not hurt you much.

It will also depend on the cable you use.

Ok thanks. I can consider LMR200, I have some SMA-N adapters or I could put SMA on LMR200.
I was thinking more of using RG316 or similar.
5m of LMR200 would have about 2.2dB loss plus the connectors, 5m of RG316 is more like 5.5dB loss.
But according to your experience, it will probably not matter as there is enough excess gain in the LNA.

Anyone from the development team? Did you calculate the gain distribution and allowed loss between

I have 5mtrs of CFD-200 cable between them with no issues

7.62m of LMR-240 lost about 1dB SNR and about 1 dB RSSI in my test. LMR-240 is readily available with SMA connectors installed. Be sure you are getting SMA male and female, not SMA-RP.

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Ok here is a fun one for you…

Sitting inside I had -118 to -119 rsl. I move the antenna to a plastic box, hang it outside with the LNA and a SMA to N connector, run it inside 4ft, add another N to SMA connector and still have -118 to -119.

That is not so interesting, the fun part was the SNR level. Inside I was clipping 2-3 on the SNR, but with the same RSL outside I was getting 5-6 SNR.

Don’t you just love radio? Never know what you will get until you try it.

[edit] Oh it is a LMR-400 Jumper.


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Ok I am just going to try it… I need 5m of cable preferably of a thinner type so I ordered a 5m RG-316
cable (looking carefully that it is not RP-SMA, I know that) and will see how much influence it has when
just inserting it between my current indoor setup. I now have around 4-5dB of SNR and only 3 bad
packets in 200000. The reason to move it outside is that the installation on the window sill is kind of
prone to getting misaligned.

my indoor window installation setup :slight_smile: works since almost half year, only once fallen down :slight_smile:

some modern thermal insulator windows might have thin metallic foil which can have significant effect on RF propagation…

For me the window direction is such that the antenna has to look out in a very shallow angle
and the luxaflex blinds cannot be easily closed because there is not enough distance between
them and the glass (12cm required). So I plan to put the antenna on the roof in a Tupperware box
and bring the cable in through the gap at the bottom of the hinged window.
(that is why I opt for RG-316 instead of LMR-200)

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I have 10meters and it works just perfect with SNR of 5.


Does a POE option would be useful for distant rooftop users, what do you guys think?
I’m just thinking out loud as most of the mid / pro wifi devices also use POE infrastructure for practical reasons.

It might be useful powering the SDR/LNA with POE, but I would be reluctant to send power outside the house - - up a wire to the roof to the SDR (then to the LNA). Of course with the SDR outside cooling it wouldn’t be a problem.

Seems as thou cable lengths between the PATCH and LNA/SDR are relatively large without appreciable loss and degradation which should allow outside PATCH antenna installation. Then you wouldn’t have to climb up to the roof to fiddle with the SNR/LNA as we all seem to like doing. Ken

Hmmm okay, so like a classic “satellite tuner box -> coax -> LNB” chain is making more sense?

That’s my sense. Ken

Just as a point of reference on Power Over Ethernet (POE).

We use POE systems on microwave back haul for cell towers on top of mountains that are inaccessible during the winter months at ATT sites. There is no issue with POE outdoors if you have the correctly rated cable and waterproof connectors.


I’ve been using POE outdoor receiver systems for ADS-B with virtually identical components to Outernet (RPi, RTL-SDR, LNA) for over a year with no issues. It’s quite reliable. We have to keep in mind that this hobby gear is in no way anywhere near the sort of build or durability of a commercial outdoor access point or bridge, IP camera, etc.

With Outernet, the signal integrity is somewhat more fragile than ADS-B, and there is the added issue of heat sensitivity. A ventilated ADS-B system runs fine at 50-60C all day long. A loss of sensitivity there means a few less planes spotted, while for Outernet it can mean total lack of decoding, rendering the system useless

For a “permanent” home installation, a suitable NEMA IP66 enclosure for the Antenna/LNA combo can be achieved for relatively low cost, around $15. Then the RTL/CHIP can be kept indoors in a controlled environment. A ventilated project box would suffice, with a good fan or heatsink/fan for the RTL. The total cost for “remoting” the Antenna/LNA is probably around $40-$50 after you include the coaxial cable and connectors, unless you have these items in the junk box.

A complete system in an outdoor enclosure could be accomplished with some creative airflow engineering. Making it POE adds another significant heat source to the mix unless there is a CHIP POE “shield” that can handle the RTL load and run cooler than a typical POE splitter.

The LNA should always be as close to the antenna as possible for best performance.


The exception might be if the coax run is very short. Otherwise, by placing the LNA at the receiver instead of at the antenna, you are also amplifying all the noise that is picked up by the coax along the way, rather than boosting the desired signal to overcome the line noise, starting at the antenna.

Well, the chip does not even have an ethernet connector, and I don’t remember seeing applications of
It appears there exists an ethernet interface as a “shield”, but I don’t know if the Outernet software
would support that.
W.r.t. PoE there are two different standards in use: the official 802.3AF/AT standard which has an
elaborate protocol for negiotiating the delivery of power. It is the protocol supported by most PoE
switches. It requires quite some circuitry at the receiving end, however it appears that there are
standard modules/chips for this now.
Then there is the “passive” PoE “standard” that is used by many (older) WiFi APs etc. It just puts
a voltage (12-24V) between the two ethernet pairs in “phantom supply” mode. It only requires center
taps on the ethernet pulse transformer and a bridge rectifier to get the power off the center taps.
(some equipment omits the bridge rectifier and requires a certain polarity, however both polarities
are in use by different manufacturers)
This is easy to add to a device, but it requires a special PoE switch (Ubiquiti, MikroTik etc) or
the use of “power inserters” that insert in the ethernet line indoors to apply the power.
I agree it is a solution, however for here I will stick to putting the antenna+LNA in an outdoor box,
use a coax to get inside, and put the RTL stick and CHIP indoors where it can be easily supplied,
maintained, and be within WiFi range.

Debéis tener en cuenta que la red ethernet cableada produce ciertas interferencias.

Alejar la antena y el LNA de los cables ethernet.

Adivina, ¿Quién es quién?


Keep in mind that the wired Ethernet network produces some interference.

Move the antenna and the LNA away from the ethernet cables.

Guess who’s who?

I agree with Rob @pe1chl. All said, yes you can do a POE, but it opens up other issues I don’t think are worth pursuing in the Lantern development process.

We know the SDR can be connected to the LNA by a specific length of 50 ohm cable from other discussions, and maybe extended if you put an in-line amplifier in the cable as we do with free-to-air (FTA) satellite feeds. In other words - - the classic approach. Ken