GPS backup

dtuuri said:
Yeah! That was MY post! But you might agree that with 592 AM radio stations in Florida it would be nice to have a simple device that keeps a running estimate of your position by utilizing them as a backup to GPS. https://radiostation.info/am/florida/
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While there are 592 radio stations in Florida, most of them are FM which legacy ADF cannot use. According to Radio-Locator.com Florida has 209 AM stations, more than enough to dial up a station within 40 miles of your location in a pinch. I live in Virginia which has 131, and the GPS interruption occurred in Ohio which has 111. I'd say my flight that day had the potential to use maybe 10 or more different AM stations along my route, including one less than 8 miles from my home airport. That's more than the VORs that were available, including Cassonova which was out of service at the time.

What I am trying to say is if you use GPS and expect RNAV VOR to be available as a secondary source, you may find it is not as readily available as you think. 5 years ago I pulled the ADF out of my bird in favor of a better GPS unit. I am rethinking that decision now. Maybe you should too.
 
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Another thing just occurred to me. I spend a lot of time on top the clouds. If I lost gps above the clouds, pilotage isn’t gonna be of much help.
 
dtuuri, in an early post pointed out that a completely new ADF concept that was microprocessor based, did all the thinking inside, had a data base of all the USA broadcast stations, and a fixed but directional antenna, could solve the problem.

Operationally, when you turned on the radio power, and the display came up, input the airport you are on, and it has a fix for a stating point. As you fly, the fix should remain very good. With a database of airports, it would also be capable oe 'direct to' guidance to any airport, or search and display 'Nearest airport'. My old database RNAV LORAN, had this capability, but it is now in the College Park Aviation Museum,

This could pass the resolved position to whatever nav display you have in the same format as GPS, or to a dedicated display for continuous normal navigation.

This might not be limited to either AM, or FM, as identifying with audio would not be required, and the basic frequency would be the only signal needed to pinpoint the direction. Errors of as much as 10 degrees in areas with many stations would be smoothed out by normal surveying algorithms, to provide a position with a precision of a fraction of a mile, and high degree of certainty.

In areas with fewer transmitters, the motion of your aircraft would move the direction of the signal, and processing would gradually pin down an accurate position, and that accuracy would generally continue as long as the unit continued calculating.

Strikefinder technology achieves directional information with fixed antenna, so that technology is readably available. Standard AM has longer range, useful in less populated areas, but there are a lot more FM stations, and at our altitudes, they can be received well outside their normal service circle.

I have lived in the ADF world of home brew approaches, and have flown them in VFR conditions, to make sure that I was aware of the limitations and risks they had. Anybody here heard of he WTOP, or KXEO approaches? Both were popular, in widely different parts of the USA. WTOP morphed into a GPS approach.


Edited to add, the location of the transmit towers is already in a Federal database, Lat/Long/height MSL and AGL. Frequencies are there too.
 
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Lon Stratton said:
Seems like they could just "turn it back on"
Probably not though......
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that was regarding LORAN....

Just a few weeks ago I was back home in NC visiting family and took a scenic drive past the old Loran station near Carolina Beach (34.06259460717931, -77.91309685852718). I noticed the old Loran towers have been torn down and I was wondering what the Coast Guard is doing with that land these days....
 
Skip Miller said:
I’ll offer a one word solution: Omega.

I used it while in the Navy. But it has its quirks, too.

-Skip
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We had VLF/Omega in a few Army Helicopters for a short while. It was decent RNAV, but not as robust as LORAN-C.

One of the local airports here had its VOR/DME decommissioned and is now just a civil DME with no associated ATC function. Part of the Minimum Operating Network.
 
RussR said:
Those coordinates seem preposterously precise. 0.00000000000001 degrees is a resolution of 0.00000004 inches, or approximately 1 nanometer. Or about 1/3 the width of a DNA molecule. If I did my math right.
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straight from a click on google maps
 
RussR said:
Oh, I believe you, I just see any reason for any navigation software to provide coordinates at the molecular level!
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yeah, I think 7 digits gives you to less than an inch and 6 to less than a foot.
 
Brad W said:
that was regarding LORAN....

Just a few weeks ago I was back home in NC visiting family and took a scenic drive past the old Loran station near Carolina Beach (34.06259460717931, -77.91309685852718). I noticed the old Loran towers have been torn down and I was wondering what the Coast Guard is doing with that land these days....
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Good Question. Actually, both questions. The first being, @Lon Stratton's: why don't we just turn it back on? Almost all of the equipment has been disposed of and the towers torn down as indicated in Brad's post. This was done under the Obama administration (not making a judgement on his time as President, just giving context as to the timeline) and we had been moving toward disestablishing LORAN for several years up to that point. The decision was made during his tenure to finally flip the switch. At that time, there were a couple sites in very remote locations (Alaska, for example) that remained operational for a while. To my knowledge those have been disestablished as well. So no, we can't just turn them back on unfortunately. As for the question about the land, the answer varies widely. In some places, land was given back to local land management whether that be federal, local, tribal, state, whatever. In a few others, the federal government found other uses for the land. More often than not, it was repurposed for conservation of some sort. If I remember correctly, the LORAN site on the northern tip of Galveston Island, for example is a bird sanctuary today.
 
But loran had distance limitations, whereas the vlf/omega was good world wide. Not sure about the poles.
 
geezer said:
Operationally, when you turned on the radio power, and the display came up, input the airport you are on, and it has a fix for a stating point. As you fly, the fix should remain very good. With a database of airports, it would also be capable oe 'direct to' guidance to any airport, or search and display 'Nearest airport'. My old database RNAV LORAN, had this capability, but it is now in the College Park Aviation Museum,
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With an integrated system, it could find initial position from a connection to your GPS. Like some ELTs do.
 
WSJ has an article on gps spoofing linked on drudge today. Not sure if anything is new, just more general alarm and happening more here than before
 
The entire Google Earth data on an iOS or Android device and a special onboard camera to match what is under the plane. You'll know Lat Lon, heading/track, groundspeed, AGL and MSL, and since Earth knows airports, the destination's fix. Minimal cost and 100% onboard like an INS, dependent on nothing but a clear view of the ground. For above the clouds, same thing, but look at the stars, like an old Astro tracker in a B-52.
 
William Pete Hodges said:
The GPS network is a remarkable system allowing navigation flexibility and ease of use, but it is only as good as the signals available. My recent flight proved to me it's vulnerability to be interrupted. My situation occurred mid flight so it was easy for me to maintain my flight but what if it had happened during IMC conditions or during an IFR approach?

I have been doing some research into this and I think the FAA needs to rethink this policy and add back some ground based radio navigation systems especially NDBs. Why NDBs? NDBs are the least expensive ground based navigation system available. They are easy to maintain as they require minimal maintenance. In the cockpit they are less precise and harder to use than VORs but they have the advantage of using not only dedicated NDBs but also AM radio station signals that require zero maintenance costs incurred by the FAA.

In short I think the FAA should reevaluate their position on NDBs and reinstate many of them for use as navigation aids as a backup to GPS. I realize I am likely in the minority in this line of thinking, but I am intending to reinstall an ADF in my airplane for this reason.

I am interested on your thoughts on this subject. What do you think?
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Given that the standard service volume of an NDB was only 25 miles IIRC, you're gonna need a lot of 'em. There are better options.
SoonerAviator said:
Bring back LORAN, lol.
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Well... There was talk briefly of the new eLORAN system being the ground-based backup. It requires far fewer stations than either VOR or NDB.
WDD said:
Interesting topic
1) Like stated above, why not have a device that can pick up multiple frequencies and triangulate your position? Make the FAA talk to the FCC, find out where ground based towers are and what frequencies, keep the map updated, and let your nav computer figure it out.
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That works for a lot of types of transmitters. A single VORTAC can be used to get a position, but you'll need more than that for non-directional signals. It can be done though.
WDD said:
3) Even at 10,000 feet my adult kids track me when I fly up to see them. On "Find my I Phone". Actually easier to use than flight tracking software. So let's incorporate that tech.
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Ummm... That's just using GPS.
Half Fast said:
Yes, but I believe they're focusing on decommissioning the low altitude VORs and that the MON will be primarily high altitude stations. Since piston GA flies at lower altitudes, I think the impact on little gasoline burners will be more significant than the overall hit.
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High altitude VORs have the same service volumes at lower altitudes that the low-altitude VORs do, so they're effectively exactly the same to those of us down in the normally aspirated piston altitudes.
 
William Pete Hodges said:
Not too long ago I flew through an area where GPS coverage was interrupted or possibly jammed for about ½ hour. I continued navigating by dead reckoning and dialed up the nearest VOR to use as a reference. Fortunately there was an active VOR along my route, but VORs are being decommissioned every day and the number remaining is dwindling fast along with their NDB counterparts.

The GPS network is a remarkable system allowing navigation flexibility and ease of use, but it is only as good as the signals available. My recent flight proved to me it's vulnerability to be interrupted. My situation occurred mid flight so it was easy for me to maintain my flight but what if it had happened during IMC conditions or during an IFR approach?

I have been doing some research into this and I think the FAA needs to rethink this policy and add back some ground based radio navigation systems especially NDBs. Why NDBs? NDBs are the least expensive ground based navigation system available. They are easy to maintain as they require minimal maintenance. In the cockpit they are less precise and harder to use than VORs but they have the advantage of using not only dedicated NDBs but also AM radio station signals that require zero maintenance costs incurred by the FAA.

In short I think the FAA should reevaluate their position on NDBs and reinstate many of them for use as navigation aids as a backup to GPS. I realize I am likely in the minority in this line of thinking, but I am intending to reinstall an ADF in my airplane for this reason.

I am interested on your thoughts on this subject. What do you think?
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Boating years ago I had a handheld am radio direction finder that you waved around until you received a station with known heading to plot. Had a compass built in and earplug speaker. Cheap backup
 
A lot of jets use DME/DME or DME/DME/DME for position. DME stations are small, don't require the real estate of a VOR.
 
My paper map, watch and ruler, and a compass.
Being able to do basic math and some trig doesn't hurt, either.
I wish planes still had ADF.
Not without it's issues, but I flew a lot of miles, AM radio station to AM radio station, back in the day.
 
VHF/UHF Direction Finders are getting smaller and smaller. Using one to home on FM stations would be nice.
Or airport AWOS/ATIS transmitters.
 
Shepherd said:
I wish planes still had ADF.
Not without it's issues, but I flew a lot of miles, AM radio station to AM radio station, back in the day.
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Some do. And used ones are VERY cheap
 
WDD said:
Interesting topic...

3) Even at 10,000 feet my adult kids track me when I fly up to see them. On "Find my I Phone". Actually easier to use than flight tracking software. So let's incorporate that tech.
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It's "poor man's" ADS-B. The iPhone is sending GPS coordinates when pinged. GPS goes down so will "find my iPhone" unless it's in the same proximity of bluetooth range.
 
NordicDave said:
It's "poor man's" ADS-B. The iPhone is sending GPS coordinates when pinged. GPS goes down so will "find my iPhone" unless it's in the same proximity of bluetooth range.
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Ah. I had thought it was cell tower generated. I was way off track on that. (Pun intended :) )
 
NordicDave said:
It's "poor man's" ADS-B. The iPhone is sending GPS coordinates when pinged. GPS goes down so will "find my iPhone" unless it's in the same proximity of bluetooth range.
WDD said:
Ah. I had thought it was cell tower generated. I was way off track on that. (Pun intended :) )
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You're actually also right. If GPS unavailable, Apple uses relative strength of cells towers to triangulate an approximate location. Easy to tell which, GPS is a pinpoint while relative tower strength is large circle sometimes small and sometimes several blocks large in depiction.
 
WDD said:
Ah. I had thought it was cell tower generated. I was way off track on that. (Pun intended :) )
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To conserve battery life, phones don't leave their GPS powered on all the time. When Location Services requires an accurate position, they first query the nearest tower to get the time and approximate position (really, the position of the tower) and that is how it knows which GPS satellites should be "visible" in the sky so it can specifically tune those and get a position as quickly as possible.
 
flyingcheesehead said:
To conserve battery life, phones don't leave their GPS powered on all the time. When Location Services requires an accurate position, they first query the nearest tower to get the time and approximate position (really, the position of the tower) and that is how it knows which GPS satellites should be "visible" in the sky so it can specifically tune those and get a position as quickly as possible.
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Both iOS and Android are also using WiFi and Bluetooth as inputs to the AGPS solution these days also.

WiFi receiver and Bluetooth receiver both listen for known fixed location things in range like fast food chains and stadium systems and such.

Ever notice how near certain fast food chains you always seem to switch into the highest “5G” mode your carrier markets?

They combine the gear and work with each other to do cross-service things. Fast food place gets “free wifi”, cellular carrier adds more site density to short haul super high speed cell network.

Seeing it out here in the boonies even. On a lonely stretch of County Line Road (since you know where that is) someone built a very nice little wedding and party venue on top of a hill.

Verizon didn’t waste any time in offering them free event WiFi for patrons of the venue, on their fiber backhaul, in return for placing microcell panel antennas in the roofline of the building. (I think net/net Verizon even ends up paying the venue owner a bit of money every month, similar to hotel chain microcell deals.)

Drive the road now, it’s one bar of low band LTE that’s not really working for miles on either side of that hill in the rolling hills of no man’s land with no cell towers in sight — then a mile-ish of 5G ultra-wideband. Ha.

I pulled into their parking lot with no event going on and was getting about 800Mb/s to Speedtest.net. Hahaha. Must be gig fiber backhaul.

Anyway. Back to the aviation discussion.

One downside to the DME idea. DME is nothing more than a ground based transponder. What the AIRCRAFT transmits is simply bent pipe’d back up on the transponder up frequency. Aircraft box times the transmit to reception to calculate distance.

What this means in this implementation is both the aircraft and the ground station have to transmit.

A better system would simply mimic GPS but coming up from the ground and on different frequencies. A synchronized clock, and let the receiver and math be done in the aircraft. (It’s not a clock per se, it’s just counting zero crossings of a known clock reference — usually a Temperature controlled crystal — internally in older units.)

I forget what it is, but there’s an upper limit to the number of users on a traditional DME. You run out of transponder airtime. It’s a high number but it’s there.

It wouldn’t be a smart system to add more transponders on the ground to. Not today anyway.

Honestly the cell network is also sending out a clock plenty accurate for such things all the time also, but it would never be allowed to be certified for IFR. That said, a $15 SDR stick can receive that timestamp, I believe.

(Can’t remember if the carriers have gotten antsy about needing those portions of their signal encrypted but I don’t think so.)

Using a cellular transmitter aloft on certain frequencies is still banned by FCC, but receivers are fine.

One could likely implement a fairly good location system as long as the database of cell site locations was truly provided (public records have some purposeful errors in them for security reasons, don’t trust the FCC data either — they know), from the carriers — and a receiver could throw away any clearly oddball sites — since there’s no guarantee a site is truly operational/not whacked out.

There’s boatloads of open source code to already sniff various types of cell tower signals with cheap SDRs. I’d have to go read the code and see what timestamps are embedded and whether they’re accurate enough for measurements of time delta at reception to generate a time relative to a small on board undisciplined clock to start to mathematically measure distance from the transmitter.

Like I said, never in a million years certified for IFR. But as a backup to just know damn near exactly where you are, likely buildable from the existing code base already out there on cheap SDR receivers.

Maybe something to compile and play with sometime when I’m bored. I still suck at SDR coding but can read through a bit of it and generally follow what the author is doing…. Kinda. Ha.

Anyone who codes SDR stuff, especially someone already in the cell biz, could likely slap a receive only location hack together, pretty fast.

Device would be cheap and quite “if it breaks, you get to keep both pieces”, but similar to the early ADS-B receiver made from two RTL-SDR USB sticks, folks turned into a viable little uncertified thing you could self-assemble.
 
denverpilot said:
I forget what it is, but there’s an upper limit to the number of users on a traditional DME. You run out of transponder airtime. It’s a high number but it’s there.
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It's not that high of a number - low 100s range IIRC. There used to be a note in the A/FD remarks for ORD that aircraft on the ground should turn off their DME so as to avoid flooding their DME frequencies.
denverpilot said:
One could likely implement a fairly good location system as long as the database of cell site locations was truly provided (public records have some purposeful errors in them for security reasons, don’t trust the FCC data either — they know), from the carriers — and a receiver could throw away any clearly oddball sites — since there’s no guarantee a site is truly operational/not whacked out.
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An interesting idea.
 
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