ADS-B IN Antenna

JohnAJohnson

JohnAJohnson

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JohnAJohnson
Can two ADS-B IN receivers share the same antenna? I would use something like this at the antenna:

bnc.jpg
 
I have never tried it, but can’t see any good reason why it wouldn’t work.
 
Just make sure you have two 1090Mhz receivers connected to the 1090Mhz antenna or two 978Mhz receivers connected to the 978Mhz antenna rather than mixing and matching 978Mhz and 1090Mhz receivers/antennas.
 
Truly receive only and not transceivers it’s doable with resultant receive losses if using a passive device. Active amplification is usually used to alleviate that unless you can take the performance hit.

If it’s not experimental and either radio has an approved installation manual, it’ll have to be followed or you’ll need appropriate FAA approval to deviate from the approved installation guide. The manufacturers sometimes have approved antenna sharing configurations and specific components required if your installer doesn’t want to mess with field approvals.

As asked, doable. But maybe not legal, or... whatever. Too vague.
 
asicer said:
Just make sure you have two 1090Mhz receivers connected to the 1090Mhz antenna or two 978Mhz receivers connected to the 978Mhz antenna rather than mixing and matching 978Mhz and 1090Mhz receivers/antennas.
Click to expand...
I really don’t think this matters. Many receivers are dual-band, and have a single antenna for both bands.
 
NO, NO, NO. Almost all ADSB GPS antennas are "active" which means that they need power (generally +5 volts dc) to operate. THerefore, connecting the +5 lines from two separate receivers together is almost sure to destroy the one that is only millivolts below the other one. THe odds of them both being PRECISELY 5 volts is about the same odds as winning an argument with an umpire, the FAA, or your wife. Not necessarily in that order. Splitters like that are prohibitively expensive. I've got one due out in a few months that should go for $50 or so, but it is not yet been proven in service.

Jim
 
Jim, to clarify, I am pondering using a CI 105 antenna to receive 1090 and 978 mhz signals into two separate, independent ADS-B IN receivers. Shouldn't be anything on the coax except RF from the Comant. No?

weirdjim said:
NO, NO, NO. Almost all ADSB GPS antennas are "active" which means that they need power (generally +5 volts dc) to operate. THerefore, connecting the +5 lines from two separate receivers together is almost sure to destroy the one that is only millivolts below the other one. THe odds of them both being PRECISELY 5 volts is about the same odds as winning an argument with an umpire, the FAA, or your wife. Not necessarily in that order. Splitters like that are prohibitively expensive. I've got one due out in a few months that should go for $50 or so, but it is not yet been proven in service.

Jim
Click to expand...
 
Wow. Y'all don't get it, do you? The INPUT to an ADSB unit is the GPS antenna that needs 5 volts to run the antenna. Connect two GPS receivers together with an adder that connects their inputs together is going to blow one of them up. The coax contains BOTH the RF GPS signal AND the DC voltage to run the antenna. Will somebody that knows what the hell I'm talking about PLEASE come on here and verify what I'm trying to tell the OP?

Jim
 
weirdjim said:
Wow. Y'all don't get it, do you? The INPUT to an ADSB unit is the GPS antenna that needs 5 volts to run the antenna. Connect two GPS receivers together with an adder that connects their inputs together is going to blow one of them up. The coax contains BOTH the RF GPS signal AND the DC voltage to run the antenna. Will somebody that knows what the hell I'm talking about PLEASE come on here and verify what I'm trying to tell the OP?
Click to expand...

I can't claim to know what I'm talking about. But I can say from experience that I have to agree with Jim. You aren't necessarily going to blow up one of your receivers immediately, but you likely will over time. There is a reason there are a number of "DC blocking" GPS splitters out there, that may be what you really want. What ADS-B in receiver(s) are we talking about here?
 
Does ADSB IN even need a dedicated, powered GPS antenna? My iPad running WingXPro runs fine without one, just utilizing the GPS receiver in my iPhone or iPad. I thought the OP was referring to just splitting the signals from the 1090/978 mhz antennas, as asicer also assumed.
 
I am pretty sure Jim knows what the hell he's talking about, but I'm thinking the OP was talking about the antennas that recieve ADS-B traffic and weather information (stick and ball and the like) since the OP had a picture of a BNC splitter, and the GPS antennas I know of for these systems use a TNC connector.

Eggnog for all my friends.
 
The Stratux I built has two antennae... one for 1090 and one for 978.. and they feed the two SDR USB dongles. Nothing about any of that has anything to do with GPS. The GPS, and AHRS, that I added as options during the build, were their own dongles, and the GPS antenna was built into the GPS dongle. Works fine. I guess my question is why would you want/need TWO adsb-in receivers? For most of them, you can read the data via wifi coming from the receiver on as many devices as you wish...?
 
weirdjim said:
Wow. Y'all don't get it, do you? The INPUT to an ADSB unit is the GPS antenna that needs 5 volts to run the antenna. Connect two GPS receivers together with an adder that connects their inputs together is going to blow one of them up. The coax contains BOTH the RF GPS signal AND the DC voltage to run the antenna. Will somebody that knows what the hell I'm talking about PLEASE come on here and verify what I'm trying to tell the OP?

Jim
Click to expand...

My portable ADS-B receiver has 2 antennas. An internal GPS receiver antenna and a removable RF antenna for reception of 978 and 1090 MHz signals (see image below). It sounds like the OP is asking if the RF in connections of 2 ADS-B receivers can be supplied by a single 978/1090 MHz antenna. I don't think he is asking anything about the GPS antenna.

Does that change anything about what you are saying (writing)?

ATBHBRXOCM3CRFJCHWRV2T4X34.jpg
 
bkspero said:
My portable ADS-B receiver has 2 antennas. An internal GPS receiver antenna and a removable RF antenna for reception of 978 and 1090 MHz signals (see image below). It sounds like the OP is asking if the RF in connections of 2 ADS-B receivers can be supplied by a single 978/1090 MHz antenna. I don't think he is asking anything about the GPS antenna.

Does that change anything about what you are saying (writing)?
Click to expand...

I don't want to speak for Jim, but what he is saying doesn't ONLY apply to GPS antennas, it applies to all ACTIVE antennas. Although I'm unsure if the CI 105 the OP is using is active or not not.
 
weirdjim said:
NO, NO, NO. Almost all ADSB GPS antennas are "active" which means that they need power (generally +5 volts dc) to operate. THerefore, connecting the +5 lines from two separate receivers together is almost sure to destroy the one that is only millivolts below the other one. THe odds of them both being PRECISELY 5 volts is about the same odds as winning an argument with an umpire, the FAA, or your wife. Not necessarily in that order. Splitters like that are prohibitively expensive. I've got one due out in a few months that should go for $50 or so, but it is not yet been proven in service.

Jim
Click to expand...

weirdjim said:
Wow. Y'all don't get it, do you? The INPUT to an ADSB unit is the GPS antenna that needs 5 volts to run the antenna. Connect two GPS receivers together with an adder that connects their inputs together is going to blow one of them up. The coax contains BOTH the RF GPS signal AND the DC voltage to run the antenna. Will somebody that knows what the hell I'm talking about PLEASE come on here and verify what I'm trying to tell the OP?

Jim
Click to expand...

Jim- I agree with you about the GPS antenna that you wrote above. I also have a Stratux with no GPS, just the ADSB receiver antennae as mentioned below.
Are we talking about the same inputs (GPSr vs. ADSB in)? Or are the ADSB receiving antenna active devices too?

Thanks for any clarifications!

bkspero said:
My portable ADS-B receiver has 2 antennas. An internal GPS receiver antenna and a removable RF antenna for reception of 978 and 1090 MHz signals (see image below). It sounds like the OP is asking if the RF in connections of 2 ADS-B receivers can be supplied by a single 978/1090 MHz antenna. I don't think he is asking anything about the GPS antenna.

Does that change anything about what you are saying (writing)?

ATBHBRXOCM3CRFJCHWRV2T4X34.jpg
Click to expand...

MuseChaser said:
The Stratux I built has two antennae... one for 1090 and one for 978.. and they feed the two SDR USB dongles. Nothing about any of that has anything to do with GPS. The GPS, and AHRS, that I added as options during the build, were their own dongles, and the GPS antenna was built into the GPS dongle. Works fine. I guess my question is why would you want/need TWO adsb-in receivers? For most of them, you can read the data via wifi coming from the receiver on as many devices as you wish...?
Click to expand...
 
weirdjim said:
Wow. Y'all don't get it, do you? The INPUT to an ADSB unit is the GPS antenna that needs 5 volts to run the antenna. Connect two GPS receivers together with an adder that connects their inputs together is going to blow one of them up. The coax contains BOTH the RF GPS signal AND the DC voltage to run the antenna. Will somebody that knows what the hell I'm talking about PLEASE come on here and verify what I'm trying to tell the OP?
Click to expand...
That is the input to an ADS-B OUT transmitter. The OP is talking about an ADS-B IN receiver. No GPS antenna should be involved.
 
To clarify to Weird Jim and a few others, if the OP is using a Stratux ADS-B receiver, it has separate sdr’s for 1090 and 978 and normally requires 2 separate antennas. You can use a y cable and connect both receivers to a single antenna...like a stick and ball antenna on the aircraft belly. The active WAAS GPS antenna plugs directly into the usb bus of the Radpberry Pi used as the heart of the Stratux system. Most other portable ADS-B receivers use a single antenna instead of two for 1099 and 978 reception.
 
MuseChaser said:
...why would you want/need TWO adsb-in receivers?
Click to expand...

I wish I didn't, but more and more, we're seeing closed, proprietary ADS-B IN systems that'll only feed its own manufacturing line. So for instance, if I want to have traffic and weather displayed on a G3X, I'd need a Garmin brand receiver. And if I wanted to have traffic and weather displayed on non Garmin Pilot tablet software, I'd need something else like a Stratux, and if I wanted it displayed on a Dynon HDX, I'd need their receiver, ad nauseam.

I don't want to muddy up the waters with the "Why" though. I know there are workarounds to the above, but my point is valid. As tax payers who funded capstone and the GDL90 protocol, we shouldn't be accepting of this walled garden method of forced brand loyalty.
 
Thanks Brit. I'll try it without, and if there is too much of a loss, I'll try this. By the way, from the spec sheets, I can't figure out how this device is powered. Do you know?

flyingbrit said:
The device in the first post looks more like a tee (or y) connector than a true power splitter. This may work, but a power splitter will maintain correct 50 ohm impedances and also provide about 20dB isolation between the two receivers. An example of a suitable power splitter is here:

https://www.minicircuits.com/WebStore/dashboard.html?model=ZFSC-2-5+
Click to expand...
 
JohnAJohnson said:
I wish I didn't, but more and more, we're seeing closed, proprietary ADS-B IN systems that'll only feed its own manufacturing line. So for instance, if I want to have traffic and weather displayed on a G3X, I'd need a Garmin brand receiver. And if I wanted to have traffic and weather displayed on non Garmin Pilot tablet software, I'd need something else like a Stratux, and if I wanted it displayed on a Dynon HDX, I'd need their receiver, ad nauseam.

I don't want to muddy up the waters with the "Why" though. I know there are workarounds to the above, but my point is valid. As tax payers who funded capstone and the GDL90 protocol, we shouldn't be accepting of this walled garden method of forced brand loyalty.
Click to expand...

I agree... one of the reasons, as good as their products are, I've avoided Garmin in my plane... at least so far. The Stratux is compatible with virtually every other EFB out there, including ForeFlight, FlyQ, iFlyGPS, FltplanGo, and Avare. The only one that doesn't recognize Stratux data is... you guessed it... Garmin Pilot.

http://stratux.me/#efb-compatibility
 
JohnAJohnson said:
I can't figure out how this device is powered. Do you know?
Click to expand...

The Mini-Circuits power dividers are passive, i.e. they don't need external power. There will be a 3+dB loss because the power is split two ways. However, dual VORs are typically connected like this and the loss of range (30% in theory) is tolerated.
 
I repeat...a “Y” cable is all that is necessary to connect both sdr’s to a single antenna on a Stratux....no need for a SAW filter or power splitter. Isolation is incorporated already in the front end of the sdr’s. Adding filters or splitters will cause loss of signal due to insertion loss. Over and out....
 
weirdjim said:
Wow. Y'all don't get it, do you? The INPUT to an ADSB unit is the GPS antenna that needs 5 volts to run the antenna. Connect two GPS receivers together with an adder that connects their inputs together is going to blow one of them up. The coax contains BOTH the RF GPS signal AND the DC voltage to run the antenna. Will somebody that knows what the hell I'm talking about PLEASE come on here and verify what I'm trying to tell the OP?

Jim
Click to expand...

No because he’s not talking about the GPS input at all. :) You misread his post directly above yours.

He just wants to know if he can split a single antenna and receive 978 and 1090. He can with associated losses.

This assumes he is truly using receivers ONLY and neither of his ADS-B receivers are also transmitters.

Others have speculated he’s talking about a portable device like a Stratux that truly has two receivers and no transmit capability but he hasn’t said.

If he’d simply spit out the exact gear he’s trying to use, the question becomes super easy to answer accurately, without having to type up all the caveats and miscommunications.

The usual “Why do we have to play twenty questions?” problem. ;)
 
Nate, I didn't think I was being vague, but I'll be specific. I actually had everything I needed way up in the thread when I thanked everyone for their input. But here's what I plan to do:

I'll install a Comant CI 105 Antenna:
comant.jpg

I will connect this to the Comant:
bnc-jpg.80934

I will connect a Dynon ADSB-472 (ADS-B IN RECEIVE ONLY 1090/978) device to one side of the splitter above.

SV-ADSB-472Dual-01.png
I will connect a Stratux (ADS-B IN RECEIVE ONLY 1090/978) device to the other side of the splitter above.

stratux.jpg

And I'll do it with one of these:

y cable.jpg
 
If I misunderstood his post, then I stand corrected. If there is NO GPS and NO transponder involved and you are willing to have the antenna input circuit on #1 affect the signal strength at #2, then gopher it. I have never had any decent luck connecting the inputs of two receivers together without SOME sort of isolation between the two, but if you want to try it I can not see any reason why. THe caveat is that there is NO dc voltage on the input connectors of EITHER receiver.

JIm
 
weirdjim said:
If I misunderstood his post, then I stand corrected. If there is NO GPS and NO transponder involved and you are willing to have the antenna input circuit on #1 affect the signal strength at #2, then gopher it. I have never had any decent luck connecting the inputs of two receivers together without SOME sort of isolation between the two, but if you want to try it I can not see any reason why. THe caveat is that there is NO dc voltage on the input connectors of EITHER receiver.

JIm
Click to expand...

You got it now, Jim. :)

I also don’t like and haven’t had much luck with splitting receivers across one antenna other than very expensive perfectly engineered pre-amp and filter systems typically seen on the ground, and nowhere near an aircraft.

It’s all good. I just happened to notice nobody was understanding the question. :)
 
denverpilot said:
I also don’t like and haven’t had much luck with splitting receivers across one antenna other than very expensive perfectly engineered pre-amp and filter systems typically seen on the ground, and nowhere near an aircraft.
Click to expand...

Ernest Wilkinson taught us (Nov 1960 IEEE Transactions on RF and Microwave) how to make splitters that are "lossless" (over a 3 dB split) and isolated between outputs at least 30 dB. It involves S, the number of splits and N = Sqrt (S) where N *Zo is the impedance of the quarter wave sections and Zo is the characteristic impedance of the source (in this case the antenna). It can be realized in coax, stripline, and microstrip. In the simple case of a two-way split, N*50 is 72 ohms, 2 sections, quarter wave each. There is still some stuff floating up a few hundred miles overhead that i did in the early 70s that is still working. Microstrip, silver on sapphire.

There are also several hundred of them out there in our GA airplanes that I designed in 72 ohm coax and built in Bud miniboxes that are happily splitting the VOR/LOC signals for NAV radios from a single horizontal dipole (catswhisker).

They are not quite octave wide, but certainly +/- 20% is trivial. Happy to design one for this application if anybody is interested.



Jim
 

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JohnAJohnson said:
I wish I didn't, but more and more, we're seeing closed, proprietary ADS-B IN systems that'll only feed its own manufacturing line.
Click to expand...

It's a nuisance even within the same manufacturing line. I wish Garmin made an ADS-B IN only receiver, to feed a Flightstream 210. My ADS-B Out needs are already handled with the 330ES transponder.

My only choice seems to be use the "cheap" half of the expensive GDL88 and not use the Out functionality ($4K to do the job of a $200 Stratux or GDL50). Or keep the little portable Stratux or GDL50 in parallel with the FS210 and suffer the digital tumbleweed of cables everywhere and I suppose the need for two wireless connections to the iPad.
 
schmookeeg said:
It's a nuisance even within the same manufacturing line. I wish Garmin made an ADS-B IN only receiver, to feed a Flightstream 210. My ADS-B Out needs are already handled with the 330ES transponder.

My only choice seems to be use the "cheap" half of the expensive GDL88 and not use the Out functionality ($4K to do the job of a $200 Stratux or GDL50). Or keep the little portable Stratux or GDL50 in parallel with the FS210 and suffer the digital tumbleweed of cables everywhere and I suppose the need for two wireless connections to the iPad.
Click to expand...

They put that into the 345 after they got everyone to buy the 330ES. :)
 
weirdjim said:
Ernest Wilkinson taught us (Nov 1960 IEEE Transactions on RF and Microwave) how to make splitters that are "lossless" (over a 3 dB split) and isolated between outputs at least 30 dB.
Click to expand...

Good old Wilkinson. ;-)

His nice divider enabled GE to get more power out of their PA at the cost of lovely arcing and board charring between the PA board and the LPF board of certain radios that didn’t have enough distance between the traces at the junction between them and the stupid metal strip they silver soldered across the gap.

Repaired enough of those that the first check is always to look for black between the boards and smell... haha.
 
And enabled me to get a divide by 6 (Zl = 122) and a subsequent 6 divide by 6 to get a 6x6 square array of transmitters & receivers to phase array a beam out and receive a beam in with a whole BUNCH of gain at 3 gigs. State of the art in '68, poor design in '19. Better ways to do it today.

Jim
 
Coming in a little late and little different.
Just purchased a 2007 Highlander that has ADS-B out already installed and I am adding a box similar to Statux , Flight Box from openflight solutions.
From what I have read here, it look like I will not be able to share the currenly installed antenna for ADS-B out with the new Flight Box, Correct?
Thanks for patience with a newbe :D
 
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