LNA/PreAmp+Bias Tee for long (50ft) cable)

[mish130]

G’day,

Can someone please recommend a solution for an LNA/Pre-Amp+Bias Tee (i.e. products) that would largely be “Plug 'n Play” for me. I have a 50ft coax cable between my antenna and dongle (which includes a filter + amplified but no Bias tee).

I’ve seen there is a long thread about it but couldn’t really see a firm “Buy X + Y” recommendation.

Thanks in advance.

[geckoVN]

Before you commit yourself, it’s important to realise most LNA’s are not water resistant.

Presumably you want to mount the LNA at the antenna?

[rugomol]

Ideas

What does your setup look like?

I’ve been feeding for one month now (started Nov 6/2019). My setup: Raspberry Pi 3 B+ 1 GB RAM Added hardware clock 3D printed case Running raspbian with PiAware add-on $10 eBay DVB-T SDR for 433 mhz weather sensors feeding WeeWx (and others) FlightAware Pro Stick Plus (Blue), plugged directly into the RPi 25’ RG58 cable (N to SMA) ADSBExchange dual 1090/978 mhz antenna Mounting hardware from Lowes The antenna is mounted almost at the apex of the 2nd story. My rang…

[eepete]

I recently tested a Bias Tee that seems to be available from a lot of places. Bottom line is the feed through loss was perfectly acceptable, about .1 dB-ish.

Enclosed is picture of the Tee and a screen shot from the spectrum analyzer. The waviness is due to the 20" cable at one end. Need to make/find some 3" cables for this sort of testing… but look closely at the Y scale at the left. It’s .2 dB per division. And note that when I went from a 20" cable to a 36" cable (same cable type), you can see the cable loss.
Now the yellow and green used the same 20" cable, so the loss induced by the cable is the same. Cable was a RG58 type that has the foam insulation.
And then, just for grins, I tried a 40" higher loss (RG-174-ish but Teflon for all the insulation).
I did not test the power input to output to see if power supply noise would leak through, will do that when I have the LNA I’m home brewing done. I will be adding more filtering at the Tee and also add an 18 TVS (Transient Voltage Suppressor) diode as a safety measure (for ESD - Electro Static Discharges AKA “door knob sparks”). this will also protect the internal capacitor that has a 50V maximum rating.

If the tech talk is too much…
Bottom Line: I think this injector is fine, and compared to the cable losses you will have, the losses due to the Bias Tee are negligible. Of course the Tee would most likely be near your PI and Dongle, and as such either not exposed to or protected from the weather elements.

[SoNic67]

My cable is 150 ft long RG6, with transition from 50ohm/75ohm vis cheap adapters.
Any double filtered LNA will do (that means two stages) for your case.

[mish130]

G’day everyone.

Thanks for the responses. How do I power the bias tee?

Can someone provide some links to products? (I’m a retired pilot, not an engineer. Good at breaking stuff, not good at building stuff )

This is the cable I have: Amazon.com: Proxicast 50 ft Low-Loss Coax Extension Cable (50 Ohm) - SMA Male to N Male - for 3G/4G/LTE/Ham/ADS-B/GPS/RF Radio to Antenna or Lightning Arrester Use (Not for TV or WiFi) : Electronics

Current Coverage:

Thanks so much for the advice.

[SoNic67]

That is not a good cable, too long, because you can’t connect the LNA close to the antenna. You need one like 5 ft long, then connection to the LNA.
Then a long cable to indoors.
Antenna needs to be higher than surrounding houses.
LNA: https://www.amazon.com/Performance-Triple-Amplifier-RTL-SDR-Blog/dp/B078TBG4H8

[mish130]

Thanks. Yes, I was planning on putting the LNA of a very short cable, then the outside to the long cable.
What cable size does that Triple Amplifier LNA take?? Just trying to work out what connectors/cable I need between the antenna and LNA, and then LNA to the coax I posted above.

[jaymot]

I use these:

My USB pigtail has a type A plug so I can just plug it into my Pi. I took an old plastic sauce bottle, cut off the neck with a hacksaw, painted it inside and out with acrylic spray paint (black on the inside for shade, white outside to reflect heat) and attached it to the mast upside-down with the LNA inside, connected via a couple of short RG316 jumpers leading to the antenna and my LMR240 coax. That keeps the rain off of the LNA. Or you could get a small waterproof electrical junction box, but being square or rectangular those are a bit harder to attach to a mast. The bias-T supply board has screw terminals for the DC power supply and two SMA connectors. You can get these things on Amazon or eBay. I put my bias-T board inside my old plastic Pi case as I had replaced it with a ventilated aluminum one with a fan. That keeps it from shorting out or anything. I’m using two more short RG316 jumpers to connect the board to the dongle and LMR240. This is just a temporary arrangement until I can get a dongle with its own bias-T supply but it works very well in the meantime. (FYI my LNA is an RTL-SDR Blog triple-filtered one for 1090MHz.)

[SoNic67]

@mish130

What cable size does that Triple Amplifier LNA take??

SMA. Same like your cable (smaller end). On the output of the LNA, I used an RG6 cable (cheaper), pre-connected, with adapters from F female to SMA male. I have 150 ft of that.
Amazon.com: F Type Female to SMA Male Adapter 3-Pack RF Coaxial Coax Antenna Cable F Female to SMA Male Connector : Electronics