Build your own VOT for $5 - no, no joke

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NeverBlue
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Re: Build your own VOT for $5 - no, no joke

#51 Post by NeverBlue » Tue Feb 23, 2016 1:53 pm

Respectfully, I disagree. The engineering required to broadcast the signal is complex, but the signal itself is very straightforward: sufficiently simple to be decoded in a 1950s era radio set without any digital logic.
Respectfully???....well

You're confusing date of technology with complexity of...

the VOR signal is complex to transmit because IT IS complex.

Digital signals today are as about as simple as they could be to encode/decode.

The VOR signal is both an AM and FM signal in one carrier.... 30 Hz Variable, 9960 Hz FM'ing +/- 480 Hz at a 30 Hz rate and 1020 Hz all AM'ing a VHF RF signal.
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Re: Build your own VOT for $5 - no, no joke

#52 Post by photofly » Tue Feb 23, 2016 2:25 pm

NeverBlue wrote:
Respectfully, I disagree. The engineering required to broadcast the signal is complex, but the signal itself is very straightforward: sufficiently simple to be decoded in a 1950s era radio set without any digital logic.
Respectfully???....well

You're confusing date of technology with complexity of...

the VOR signal is complex to transmit because IT IS complex.

...

The VOR signal is both an AM and FM signal in one carrier.... 30 Hz Variable, 9960 Hz FM'ing +/- 480 Hz at a 30 Hz rate and 1020 Hz all AM'ing a VHF RF signal.
Whether you think it's complicated or not is a judgement call. One can describe it completely in a single line (you pretty much did that yourself) and produce it with three looped lines of computer code, using just some trig functions - two lines, if you don't want an ident. That's where this project started. The raspberry pi was just the quickest way I could find to modulate the signal onto a carrier. I have a synthesized signal generator that will generate the RF and modulate it, but it weighs 80lbs so it's not particularly easy to take it out on the ramp.

Most of the engineering complexity in the VOR transmitter is having to build the counterpoise, to alleviate terrain effects, and the complicated multi-antenna array with phasing arrangements to use the Doppler effect to avoid having an actual rotating antenna like the original stations did.
Digital signals today are as about as simple as they could be to encode/decode.
Now if you want a complex navigation signal, try synthesizing your own GPS data. Then encode it with BPSK using the correct CDMA codes. Bet you can't describe that in one line.
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Re: Build your own VOT for $5 - no, no joke

#53 Post by SuperchargedRS » Tue Feb 23, 2016 2:34 pm

plhought wrote:Don't know why everyone is s***ing on the OP for this - the knowledge and that little bit of motivated ingenuity is pretty f***in' impressive.

My head is chock-a-block full of flippin' enough BS airplane stuff - the fact the OP has enough left-over cells to learn a bit of Python is pretty neat.

'bout time we had that modern taste of motivation in this profession anyways ;)

Besides, what the heck do ya think your IFR4000 is doing anything different than this little unit anyways!
Very true, to the OP good stuff, the non knuckle dragging folks on this board love seeing someone posting cool tutorials like this
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Re: Build your own VOT for $5 - no, no joke

#54 Post by NeverBlue » Tue Feb 23, 2016 3:49 pm

Now if you want a complex navigation signal, try synthesizing your own GPS data. Then encode it with BPSK using the correct CDMA codes. Bet you can't describe that in one line
Uh...you just did...phase shift keying is not complex...it's FM...sort of...easy-peezy stuff to decode/encode...it's just a word...it's just software...that's why you can buy a GPS for your car for less than $100.
It comes in every smart phone now...complex????

VOR is not easy...your set-up is not common.
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Re: Build your own VOT for $5 - no, no joke

#55 Post by photofly » Tue Feb 23, 2016 4:54 pm

I'm sure the "aircraft are not science experiments" brigade will look up over their reading glasses at me in a disapproving manner because of the sheer pointlessness of it all, but I think this is cool:

http://www.rtl-sdr.com/decoding-aviatio ... h-rtl-sdr/
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Re: Build your own VOT for $5 - no, no joke

#56 Post by CID » Wed Feb 24, 2016 7:21 am

photofly wrote:I'm sure the "aircraft are not science experiments" brigade will look up over their reading glasses at me in a disapproving manner because of the sheer pointlessness of it all, but I think this is cool:

http://www.rtl-sdr.com/decoding-aviatio ... h-rtl-sdr/
Cute. Pointless. Harmless.
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Re: Build your own VOT for $5 - no, no joke

#57 Post by CpnCrunch » Wed Feb 24, 2016 9:39 am

NeverBlue wrote: It comes in every smart phone now...complex????
If you think a smartphone isn't complex, perhaps you should try designing and building your own from scratch.
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Re: Build your own VOT for $5 - no, no joke

#58 Post by NeverBlue » Wed Feb 24, 2016 10:50 am

I don't know what you're reading...

but I NEVER SAID THAT AT ALL!

what is the matter with you?

:rolleyes:
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Re: Build your own VOT for $5 - no, no joke

#59 Post by CpnCrunch » Wed Feb 24, 2016 11:05 am

NeverBlue wrote:I don't know what you're reading...

but I NEVER SAID THAT AT ALL!

what is the matter with you?

:rolleyes:
You said a GPS isn't complex because it comes in every smartphone. So you're saying GPS and/or smartphones aren't complex. You can buy a GPS chip for under $1, but that doesn't mean it isn't complex. Tell you what, try building your own GPS receiver from scratch and see how complex it is.
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Re: Build your own VOT for $5 - no, no joke

#60 Post by photofly » Wed Feb 24, 2016 11:28 am

It's a fair amount of work:
http://www.aholme.co.uk/GPS/Main.htm
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Re: Build your own VOT for $5 - no, no joke

#61 Post by photofly » Wed Feb 24, 2016 11:45 am

photofly wrote:It's a fair amount of work:
http://www.aholme.co.uk/GPS/Main.htm
It would be considerably easier to build your own VOR receiver.
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Re: Build your own VOT for $5 - no, no joke

#62 Post by NeverBlue » Thu Feb 25, 2016 6:10 am

What the?

A receiver is a receiver...they're pretty much all the same.

The decoding and processing of the signal is what can be complicated...but not in a simple GPS receiver!

It just receives a signal and calculates your position pretty much the same way LORAN did...through timing...

Yes the signals are different...but GPS is just a reciever...a decoder...not an encoder

All that mapping stuff is not part of the receiver at all.

What photofly is doing is generating a signal...way more complex to do.


And in no way shape or form is he using his airplane as a "scientific experiment"...he's not altering his airplane at all.

108.00 Mhz : ICAO, Honeywell, Rockwell, Garmin, Becker, IFR, TKM, HP, VOR test frequency
108.10 Mhz : ICAO, Honeywell, Rockwell, Garmin, Becker, IFR, TKM, HP, ILS test frequency
118.000 Mhz: ICAO, Honeywell, , Rockwell, Garmin, Becker, IFR, TKM, HP, Comm test frequency

It's no reckless experiment...it's "Standard Practice"
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Re: Build your own VOT for $5 - no, no joke

#63 Post by NeverBlue » Thu Feb 25, 2016 6:14 am

http://www.elecfreaks.com/store/fastrax ... p-236.html

There I just built one...by clicking a mouse...
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Re: Build your own VOT for $5 - no, no joke

#64 Post by NeverBlue » Thu Feb 25, 2016 6:43 am


You said a GPS isn't complex because it comes in every smartphone. So you're saying GPS and/or smartphones aren't complex.
What? You should re-read what you wrote.

You have a convoluted way of drawing conclusions. :rolleyes:
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Re: Build your own VOT for $5 - no, no joke

#65 Post by Posthumane » Thu Feb 25, 2016 8:14 am

NeverBlue wrote:http://www.elecfreaks.com/store/fastrax ... p-236.html

There I just built one...by clicking a mouse...
Right. And I built an airplane by going on barnstormers.com and calling some people. I also built a house by calling up a realtor. Wait, maybe "built" isn't the right word... Bought? Well, they both start with the same letter so they must mean the same thing.

The RF front end in a GPS receiver may not be anything spectacular, but processing the signals to determine a position definitely is. The principle is similar to loran, but the mechanics of it are quite a bit different.

Just transmitting a signal isn't all that complicated either - it can be done with a spark gap and an LC circuit made with some metal plates and a coil of wire.And receiving and demodulating an AM signal can be done with an LC circuit and a non-linear junction (such as a diode, or in a pinch an old razor blade and pencil).
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Re: Build your own VOT for $5 - no, no joke

#66 Post by photofly » Thu Feb 25, 2016 8:30 am

I was looking at the webpage of the guy that built his own GPS. The use of Gold codes means a 1-bit A to D converter can reliably pick out signals from individual satellites (all on the same frequency) that are all 20dB below the noise floor. Might not mean much to some, but as a system design, that's quite stunning.
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Re: Build your own VOT for $5 - no, no joke

#67 Post by NeverBlue » Thu Feb 25, 2016 1:14 pm

GPS signal contents are not complex at all.

Civil aircraft GPS receivers do not use the information contained in the signal as it was originally designed to be used.

They only use it to recognise the signal. It is all done by timing...that's it...nothing else.

Advacements in technology makes things easier to deal with...not more difficult.

It is much easier to send information digitally than with analogue technology...easier to encode and decode.

Why do you think mankind is slowly abandoning analogue technology?...because it's less complex?

Ok.....
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Re: Build your own VOT for $5 - no, no joke

#68 Post by Posthumane » Thu Feb 25, 2016 2:00 pm

You have a funny definition of complex NB. I suppose on the face of it any RF signal, either digital or analog, is "simple" in that it's just a time varying electromagnetic field. The way those signals are modulated and demodulated is what makes them interesting. Any RF engineer would consider modulating a VHF signal twice (once AM and once FM) a relatively straighforward process, but generating even the "simple" C/A code used to modulate the L1 GPS signal takes a bit more head scratching*. The L1 signal is also double modulated with both the C/A code and the encrypted P code.

Also, analog technology is very much alive and kicking. Digital transmissions allow you to do much more complex things than you could with analog though, such as having a lot of different transmitters operating simultaneously on the same frequency through things like CDMA.


*Btw, the C/A code is used exactly as it's intended on civil GPS receivers. Saying "it's just timing" is a lot like managers saying "it's just engineering" when asked about solving a problem. I suppose everything is simple when someone else is doing it. When you manage to design something (anything, really), then you'll have some basis on which to call it simple.
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Re: Build your own VOT for $5 - no, no joke

#69 Post by Aviatard » Thu Feb 25, 2016 2:15 pm

NeverBlue wrote: It comes in every smart phone now...complex????
NeverBlue wrote:I don't know what you're reading...

but I NEVER SAID THAT AT ALL!

what is the matter with you?
NeverBlue wrote:
You have a convoluted way of drawing conclusions.

You have a convoluted way of expressing yourself. What exactly did the complex???? mean? I interpreted it in exactly the same way: you were saying cell phones aren't complex. If that wasn't your intent, then what was the purpose of the 4 question marks?
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Re: Build your own VOT for $5 - no, no joke

#70 Post by NeverBlue » Thu Feb 25, 2016 2:44 pm

What about P code?

GPS receivers and Smartphones are 2 entirely different things.

I no very little about smartphones.

Complex?....they're computers...you decide

I never ever said smartphones weren't complex.

Please show me where I said that...
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Re: Build your own VOT for $5 - no, no joke

#71 Post by Aviatard » Fri Feb 26, 2016 6:23 am

NeverBlue wrote: I never ever said smartphones weren't complex.

Please show me where I said that...
NeverBlue wrote: It comes in every smart phone now...complex????
Right there ^

And if that doesn't mean you think smart phones aren't complex, then what does it mean?
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Re: Build your own VOT for $5 - no, no joke

#72 Post by CID » Fri Feb 26, 2016 7:22 am

And in no way shape or form is he using his airplane as a "scientific experiment"...he's not altering his airplane at all.
If you consider it a maintenance action, he's "testing" a system with a device that can't be traced to any standard. If it's an operational check, how exactly can he verify the VOR is within the acceptable error for instrument flight?

It's no more than a science fair experiment or a cheap magic trick if you can't take any meaningful credit for the test.
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Re: Build your own VOT for $5 - no, no joke

#73 Post by NeverBlue » Fri Feb 26, 2016 8:36 am

There is No Standard for this type of radiated test.

That's why they're called "Go-No Go"

There is no test required for your VOR receiver.

It's completely up to the PIC to decide whether it's working or not. How would he do that?...by using a VORTAC, VOR station, VOT, and/or a generated VOR test signal...just like the Manufactures Operating Instructions for the Nav receiver says...

There is no standard for the ERP of the signal.

There is no requirement to have your VOR annually checked or calibrated like there is for mechanical TACH!
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Re: Build your own VOT for $5 - no, no joke

#74 Post by photofly » Fri Feb 26, 2016 8:46 am

a device that can't be traced to any standard.
Of course it can be traced. I can put a 'scope on it and compare all the parameters to the VOR standard. I can even have my 'scope calibrated first, if that makes you feel warm inside.
CID wrote: It's no more than a science fair experiment or a cheap magic trick if you can't take any meaningful credit for the test.
I can take meaningful credit for the test. I actually put in my journey log today "VOR alignment verified within tolerance using VOT signal." Then I signed it. In ink. With my name. Goodness me, that must rip you up inside.
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Re: Build your own VOT for $5 - no, no joke

#75 Post by NeverBlue » Fri Feb 26, 2016 9:01 am

Ok now that's completely wrong.

You can not "align" your VOR in the aircraft with a VOT signal.

You in no way did that...
You did nothing that required a log book entry....why did you?

Now you would have to prove that your Test Set is calibrated to a known standard...which you can't because there is none....you can't prove it's in tolerance because you have not calibrated your test signal.


Your entry is false...why would you do that?
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