Me too. 
Our hobby is RX (Receive only), with power levels in milli and micro Watts, so 75 ohm instead of 50 ohm does not make any substantial difference.
I have been criticized many times before, including on this forum, for saying that I use RG-6 as a transmission line, up to 100 Watts, with no noticeable downsides, for many years now.
Quality is the differential. Dollar Store special won’t do.
Yes, you are 100% right.
RG6 is available everywhere, but in a wide range of quality.
- Core may be either copper or copper-coated steel
- Shield may be aluminum foil or copper foil
- Braid may be made of aluminum or copper
- Degree of shielding may vary from 60% to 90%
To get good performance, purchase the RG6 coax manufactured by a reputable manufacturer who has made his cable’s data sheet available.
The quad-shield coax is ideal, but is very costly.
The commonly available ones have double-shield (Foil & Braid)
The cheap ones have poor shielding say around 60%.
Most commonly available models have a core of copper-coated steel wire. For small power like in case of Receive only, copper-coated steel is OK, but in TX (Transmitting) where larger power is involved a coax with copper core is required. Some good quality RG6 do have copper core, copper foil and dense copper braid.
Not sure if this is still current as the whole thing is a long read …
Flat passthrough is not suitable for 1090 MHz, they are just terrible.
You could run the pi outside if it’s a balcony or something else that is somewhat protected.
Running power to the outside (12 V with a further drop to 5 V directly at the pi for example) is much simpler.
Be aware not all RG6 is created equal. Some is just a single layer of 60% braid and only good for VHF (maybe not even that). The quad shielded cable made for CTV or satellite feed is fine.
For me, the lack of wired ethernet is a show stopper, so I have no use for a Zero.
In Oz, a Pi3b+ is 80% the price of a 2G Pi5, so I can’t see myself buying anything less than a Pi5 in the future.
Yeah, I don’t know. I might just try to assemble a waterproof box and throw a RPi Zero2 W in there to do the decoding. I would prefer to have it inside, running on my PX install, but I’m sure I can live with the loss of Z2. Also, if I do that, I might just directly daisy chain them off the mast, with maybe a short pigtail to the SDR. In addition, do you think it would be advisable to buy this LNA and this SAW filter for my BlogV4 or would it be more worthwhile to just buy the seemingly recommended Chinese SDR (from here)?
I am a big fan of this idea. Zero 2 W is cheap. The expensive part is the housing.
Edit: You can probably stream from the zero 2 w the input directly into your other system. Not going to advertise here, but with stream1090 inbetween that is possible with some socat stunts.
Buy all 3, if you can. Always good to thinker. If not an option, buy the Chinese SDR only.
I didn’t know you can stream. I mean, I figure that the RPi Z2W is probably good enough for most decoding, and I have like 5 of them, so that should be fine. As per waterproofing, I’m planning on using 1 or 1 1/2 inch conduit/pvc pipe as my mast; it should probably be possible to mount my equipment inside the mast and waterproof the mast itself.
This one is also a candidate.
I have purchased 2 of these from 2 different vendors on Aliexpress (many vendors are available for this item on Aliexpress).
One of these was running very hot and failed after a month or so. Other one is also running hot, but not as hot as the one which has failed.
1090MHz 1.09GHz ADS-B Active SAW Filter & LNA 5V Power Supply
Size: 56 x 13 x 7 mm / 2.2 x 0.5 x 0.3 inch
Specifications:
TA1090EC (SAW Filter) +TQP3M9009 (LNA)
Nominal Gain: 21dB
Best Frequency: 1090MHz
Working Voltage: 5V
Working Current: 0.1A
Power Supply: USB-C
Connector: Double SMA (female connector)
Size: 56 x 13 x 7mm / 2.2 x 0.5 x 0.3"
Note that the RPi Z2 and the RPi Z2W are different boards.
As for your plan to place everything inside the PVC pipe, serving as a mast, it’s a great way to do it.
The downside is that it needs external power. For an outdoor installation, it’s another ‘complication’.
To be fair, the orange LNA also needs external power for continous use, but I have it indoors, not at the antenna. Actually my whole setup is indoors, so a ‘special’ case.
You have two options for streaming:
- rtl_sdr based 2.4 MHz samples into stream1090 (locally) and send it where ever you want. I have a Zero 2 W and last time i checked that was working fine (with rtl_sdr, not with airspy)
- Send the raw output of rtl_sdr to where ever your decoding/demodulator is. You may even compress it.
I havent tried option number 2.
The AirSpy is a great receiver, but overkill for ADS-B. Best to stick with the RTL-SDR style sticks.
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Yeah, I guess that’s a pretty major benefit for the SDR with built in filter and LNA; it seems to be one of the few low-price (or fairly low price) things with LNA that doesn’t require external power. The benefit of the inline one though is that I can reuse my current SDR (though is that a plus?) and it’s a third of the price that buying a new SDR would be; I’d probably be fine with the external power because I’m guessing that a solar panel and some sort of UPS hat will be thrown in.
That is not true. Source: a guy named Nyquist. Mode-S messages are coming in at 2 MHz. By the aforementioned guy you will need a sample rate of > 4MHz
Who am I to try to discredit Nyquist? I’ll let others here do it, and it will happen.
My point is: the RTL-SDR stick is good enough for most users, cheap and easy to setup. I’m always guided by the “Law of Diminishing Returns”.
And with only a 15 feet cable run, I’ll venture to say that you are better off keeping everything indoors, minus the antenna, of course.
If you still want/need to have the LNA at the antenna, use an LNA that can be fed by the RTL-SDR bias-T. Not all RTL-SDR based sticks have a bias-T option, keep this in mind as well when shopping for one.
NooElec has an RTL-SDR based stick that has a bias-T always on, the SmarTee. It may not be good for all applications, but something to consider.
Unfortunately the RTL-SDR Blog Triple filtered LNA is no longer available but they still offer the generic. Add a filter and you are good to go.
https://www.rtl-sdr.com/new-products-in-our-store-wideband-lna-spare-metal-v3-enclosures/
The power requirement of this Filter+LNA is only 0.1 A, so I feed power to it from a spare USB port of RPi as all my receivers, including their antennas, are totally indoor
Click on Screenshot to See Larger Size
Indeed…and I note that you still use a generic RTL-SDR stick, good man!
That’s the lowest cost entry point. I still have 3 or 4 of them.
Things may get more complicated if using an RPi Z2W, my default board now, but I have not looked into that.