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XM vs ADS-B

Bluelabel

Well Known Member
Is it worth it?
Is there anyone that has flown with both? Preferably with the G3X system since that's what I have.

I opted to not do XM when I built my panel since I didn't already have a SiriusXM account for anything. But now, with the new GDL 51R coming out this fall, I can add it my system. Mainly for the music. (I have an iPod doc built in too).
The ADS-B info seems pretty darn accurate albeit, somewhat low res. Just need to know if it's worth the $30-40/month for the XM info.

Thanks,
 
John

From my perspective, the answer is "no" it is not worth it. I agree that XM has better resolution. I used it for ten years. When I switched to ADS-B and its FIS- B weather, I immediately yearned for my old XM. But frankly the ADS-B is just fine. It shows where the serious/ heavy weather is and that's basically what you want to know so you can avoid it. If you are like me and only need weather a few times a year then the free stuff is sufficient. If you are flying frequently on cross-country then the smoother display of XM and associated cost might be worth it to you. My caveat is that in bad weather XM can have reception issues. At least it did for me. On more than one occasion when I really needed an update, it wasn't there.

Chris
 
I first flew with XM weather back in about 2006 or so - fell in love with it immediately. Doing lots of cross-country in the middle of the continent, I felt like the airplane was broken if the XM was down. I was very skeptical about ADS-B due to resolution and the fact that I was moving to the mountains, where you just don't get good sight-lines to a transmitter until you're airborne, so I was really comfortable having the weather come in by satellite.

Now I have been using ADS-B in all of airplanes for a year or two, and I have to say - its pretty good. Except for the fact that I don't have the audio to keep me entertained on the long legs, I really didn't notice any deficiencies this year on the way to or from Oshkosh. I probably use the METAR's and TAF's as much as I do the NEXRAD, and they work fine. And I have lots of Car Talk podcasts stored on my phone to keep my brain engaged (and laughing) while crossing Souith Dakota and Wyoming (and Utah, and......).

Because of my job, I was fortunate to be subsidized for the XM subscriptions much of the time I was using it, so the cost was not an issue. But its not cheap, and the ADS-B is really more than adequate, especially in the west, so I am not missing XM (much).
 
I've used both. Started with XM and loved it as it was the only thing available. When ADS came out gave it a try. While I'll agree with the better resolution the update rates are better with the ADS. I've seen long period of time between updates with the XM. I prefer the ADS. Canceled XM and haven't been disappointed.
 
I had xm. I had issues with needing to contact xm to "re-initialize" a few times. Once I lost it in the middle of nowhere. The resolution looks better, but that's misleading. XM has the same latency (delay) issues as ADSB-in wx. I dropped xm wx (I still have xm music in the car, and I move the receiver to the plane when I fly).
 
I went ADS-B and I'm happy with it. The added features of XM just weren't worth the subscription for me. For music I listen to iTunes on my iPhone over my headset. My wife and kids do the same so everyone is happy listening to their own music.
 
For the savings and less hassle factor, I've found ADSB to work fine for me so far in my Cirrus. I haven't had enough x-country time in the -8 yet to assess that, but I do not expect to go back to XM soon. If they lowered the cost, I'd certainly consider it.
 
I run both the XM and the ADSB in the RV-10. I've noticed that the ADSB does seem to update faster, but the XM seems to load faster, and it also loads while still on the ground. In the Southeast during Thunderstorm season, it is a nice feature to have.

I flew the RV-14 to OSH this year which only has ADSB. I was watching some weather at the half-way destination during the 3 hour leg. I had filed for KLAF, but the weather didn't seem to be moving as fast as I had hoped. I change the destination enroute to KDNV, a little to the west. The rain was showing red on the radar, as was the METAR at the ariport. I had also taken my IPAD with Foreflight and the Stratus, as I didn't want to be without any traffic capabilities when near OSH. As we got north of KHUF I asked for direct to one of the fixes on the apporach to runway 3 into KDNV, as it would take me a little farther West and hopefully let the weather move out of the way. It wasn't looking real hopeful on the G3X, but the Foreflight was updating much more quickly and presented a different weather picture. As it turned out, the Stratus and Foreflight provided very timely information. The rain moved out while about 10 miles away according to Foreflight (but not the G3X), and we landed at KDNV with barely a sprinkle, even though the ground was drenched.

I am going to try to run some more comparisons.. I never had reason to watch 2 different ADSB representations that closely before.

Vic
 
I run both the XM and the ADSB in the RV-10. I've noticed that the ADSB does seem to update faster, but the XM seems to load faster, and it also loads while still on the ground. In the Southeast during Thunderstorm season, it is a nice feature to have.

I flew the RV-14 to OSH this year which only has ADSB. I was watching some weather at the half-way destination during the 3 hour leg. I had filed for KLAF, but the weather didn't seem to be moving as fast as I had hoped. I change the destination enroute to KDNV, a little to the west. The rain was showing red on the radar, as was the METAR at the ariport. I had also taken my IPAD with Foreflight and the Stratus, as I didn't want to be without any traffic capabilities when near OSH. As we got north of KHUF I asked for direct to one of the fixes on the apporach to runway 3 into KDNV, as it would take me a little farther West and hopefully let the weather move out of the way. It wasn't looking real hopeful on the G3X, but the Foreflight was updating much more quickly and presented a different weather picture. As it turned out, the Stratus and Foreflight provided very timely information. The rain moved out while about 10 miles away according to Foreflight (but not the G3X), and we landed at KDNV with barely a sprinkle, even though the ground was drenched.

I am going to try to run some more comparisons.. I never had reason to watch 2 different ADSB representations that closely before.

Vic

That's very interesting. I'm assuming you are using a GDL-39 or GDL-39R for the FIS-B input to the G3X. I wonder why the refresh rate / presentation would be different between the systems since both the Stratus/Foreflight and Garmin solutions rely on the same datalink (although the antennas are presumably in different locations.)
 
I am going to try to run some more comparisons.. I never had reason to watch 2 different ADSB representations that closely before.
Is it possible your iPad's data connection was still on, and it was actually pulling weather live from the internet? That would explain the difference between what the Stratus was seeing and what your built-in system was seeing. Wouldn't explain why the weather wasn't the same on both, of course...
 
I have both in my plane. One screen displays XM the other ADSB.

XM has base reflectivity and composite radar while ADSB has composite only, and composite almost always looks worse.

XM also has lightning data, cloud tops, satellite images, ADSB doesn't.

XM works in mountains and on the ground ADSB doesn't.

They both take time to update, but when cutting it close (not that i would ever...) and watching the weather move you get updates more often than you would from a single source.

ADSB has a cool feature that I haven't seen implemented yet: Special Use Airspace status. Is any software displaying that data on their map?

Foreflight has a good comparison of XM and ADSB: https://www.foreflight.com/support/xmvfisb/

At low altitudes I also use RadarScope on my iPhone, it updates faster, it's more accurate (super-res radar), and you can select any radar tilt you want, it even has live precipitation and wind data.
 
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Good info, thanks,
Does anyone know if, say you had a G3X with XM or the GDL51R, can you use the music side of it without the weather?
 
Is it worth it?
Is there anyone that has flown with both? Preferably with the G3X system since that's what I have. SNIP

I was an early ADS-B in/out guy in the RV-10 (dual 10" SkyView setup with Dynon ADS-B receiver). I did not have faith in the ADS-B weather so I ran XM weather side by side with the SkyView system for the first long cross country to Key West. As is normal for Florida, we had massive thunderstorms to fly around. The SkyView ADS-B weather was identical to the XM, and in no case did the SkyView not update at least as often as the XM.

After returning home the XM receiver was removed from the plane and the overpriced XM subscription cancelled. I have several years flying with the SkyView ADS-B data and have always been ahead of the controllers on weather and contacts. Of late I've been flying an RV-8 that does not have ADS-B and have used an iPad running ForeFlight and a Bluetooth connected ADS-B in receiver. While this works, I hate it. With the SkyView the data is always displayed. With the iPad you have to think about looking and just when you really want data the iPad picks that point to overheat and shut off. While the iPad is a good backup, I recommend it not be used as a primary ADS-B display.

Carl
 
Yes

. . . . . Does anyone know if, say you had a G3X with XM or the GDL51R, can you use the music side of it without the weather?

I do this now on my GDU-375 G3X display - don't know about the GDL51R. Used to have the XM weather as well, but dropped it when I went to ADSB using the GDL-39R.
 
ADS-B

This year our little 8 went to KOSH and had to face a lot of weather, headed down to the south east on Thursday to get home. The refresh rate was about every five minutes and was very correct all the way home for some 575 Nm.
The square blocking look to it we found was not a hold back. You just got used to it and it did paint everything with the correct coloring for what we had to work around, through and in. If it were not for the G3X "GDU-460" we should have stopped in Frankford Ky. for the evening, but we could see that we would be able to go do south down to Knoxville and then get behind a long line that was across our path. We then worked around the south edge of that line watching the weather most of the way for another 150 miles or so. We found it to be fully useful and up to the task. Hope this helps, Yours, R.E.A. III #80888
 
I hope everyone remembers that the refresh rate, and the update time shown on the screen, are not the true total delay. Whether xm or ADSB, they have to wait for all the radars to sweep, and for the NWS computers to put it all together, and send it out. While usually just a few minutes the actual delay is unknown to the pilot. This data is great for strategic avoidance. It was never meant for close in maneuvering.
 
I hope everyone remembers that the refresh rate, and the update time shown on the screen, are not the true total delay. Whether xm or ADSB, they have to wait for all the radars to sweep, and for the NWS computers to put it all together, and send it out. While usually just a few minutes the actual delay is unknown to the pilot. This data is great for strategic avoidance. It was never meant for close in maneuvering.

Very well said. These tools are for strategic weather avoidance, and should never be used around fast-moving fronts for penetration. The delay is just too great. Using them in far enough ahead during the trip usually means heading changes of only 5-10 degrees along the route.

Except in the Southeast in the summer time with the thunderstorms. The T-storms tend to stay put as they are not associated with fronts. You really can use it to circumnavigate the big ones, giving them a wide margin. I fly trips from Atlanta to Florida now that I would never have done just a decade ago. However, I never file IFR when there are T-storms along the route. I always use flight following and its a lot easier to make heading and altitude changes without waiting to request it from ATC. Usually the frequency is the busiest right when you need to make a request. I've learned to tell ATC that I'll be up and down, sometimes 4K'-5K' with some heading changes. They can usually see what you are looking at as well, and it works out well. I also like to see that the view out the window is matching the picture depicted on the screen. If it's not matching close enough, I make the appropriate routing changes.

Back in the late 70's before we had all of this on-board weather equipment, I was inadvertently left to fly into a really big cell while IMC over the Gulf of Mexico. I don't ever care to see the inside of a cell again.

Vic
 
Be careful out there

I hope everyone remembers that the refresh rate, and the update time shown on the screen, are not the true total delay. Whether xm or ADSB, they have to wait for all the radars to sweep, and for the NWS computers to put it all together, and send it out. While usually just a few minutes the actual delay is unknown to the pilot. This data is great for strategic avoidance. It was never meant for close in maneuvering.

I want to echo and underscore what Bob said about both of these products -- they are designed for strategic planning, not tactical maneuvering.

There have been fatal accidents that resulted from folks using ADS-B or XM radar data as if it were weather radar to try and navigate through severe weather.

Both products are great and both have the same limitation - what you see is what has already happened - it is NOT a CURRENT or LIVE picture of the weather - merely a picture of where the weather was at a certain PAST point in time.

Generally speaking the information on "how old" the data is indicates how long ago it was transmit, not when the data was actually recorded.

There can sometimes be up to a 30 minute delay from data collection to actual transmission.
 
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