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

[NeverBlue]

Please...show me a VOR ground station on 108.00 Mhz!...don't just say it.

Every VOR test set I've ever seen has it as it's test frequency....RADIATED!...in free air...

[NeverBlue]

....and somebody please explain these "square waves".....

[photofly]

Go ahead, argue this is the worst way to do it. It's about one thousand dollars cheaper than any other wheel I've seen, and I get a kick out of wheels I've designed and built myself vs. ones I bought from someone else. I'll fight for your continued right to feel "anything I bought is better than anything I made myself", though.

So....you can't build a simple oscillator and AM modulate it for under a thousand? Maybe I gave you too much credit.

When did I say that? But this uses a single $5 off the shelf part, a length of wire, and a phone. It requires no test gear to tune an oscillator or adjust the depth of modulation.

Here's your challenge then: You find another way to do it that other people who are interested can try for themselves without lifting a soldering iron. don't forget you need to be able instantly to change the frequency to 329.15MHz to test your glideslope receiver, too.

Come back when you finally have something intelligent to say; I can wait as long as it takes.

[all_ramped_up]

Ingenuity? Any electronics tech can figure out a multitude of ways to broadcast a VOR test signal but why reinvent the wheel or choose what is arguably the worst way to do it and with risk to damaging your computer?

Square waves are composed of a fundamental frequency with an infinite number of odd harmonics in decreasing amplitudes. Operating this gizmo is wreckless at best. Thinking it's a valid test is inadvisable.

It's not hard to solder up a simple bandpass filter if one was motivated enough.

Two caps and a resistor... that's what? $5 and 15 mins of effort? The filter would also take a little off the radiated power even if slightly.

[NeverBlue]

...it's not reckless

http://www.ic.gc.ca/eic/site/smt-gst.ns ... 10208.html

[CID]

But this uses a single $5 off the shelf part, a length of wire, and a phone.

So...your phone is free? Please let me know where I can get a free phone. Also let me know where to get a free replacement when it breaks from using the way you suggest here.

As for 108.00, it looks like my information is outdated. There weren't many but the last ones (I think the last one was in Germany) changed when Europe adopted VHF FM Immunity. 108.00 was just too close to some commercial FM radio stations. There are still however some airports that use 108.10 for LOC/ILS. You can check them out here:

http://www.icao.int/apac/documents/edoc ... list02.pdf

photofly, airplanes are not highschool science fair experiments. I'm not going to invent or suggest a shitty way to do anything to an airplane because it's cheap. That's not to say that I think the most expensive way is always the best way but this idea is half baked. That's my opinion. Go ahead and use this to your heart's content but at least people won't just blindly do this. Maybe my opinion will have them think twice.

Now let's go on to how to test a DME with paper clip and free DME test set set.....

[CID]

When did I say that?

Go ahead, argue this is the worst way to do it. It's about one thousand dollars cheaper than any other wheel I've seen

[Posthumane]

Photofly - I, for one, am interested in a little more detail about how you synthesize the wav files. Might try this with my Pi, though with a couple modifications. Btw, do you have any way to measure the transmitted power?

SDR sure has made it easier to play around with RF these days. Bitch as some people might, there are many great things about living in our times.

[photofly]

When did I say that?

Go ahead, argue this is the worst way to do it. It's about one thousand dollars cheaper than any other wheel I've seen

Your English comprehension sucks. That doesn't mean something can't be built for less than $1000; it means that the off the shelf ready built options are limited. Regardless of your idiocy, using a $5 single board computer as a crystal controlled synthesized RF source is a cool hack.

I'm still waiting for an intelligent contribution on this topic from you.

[photofly]

Photofly - I, for one, am interested in a little more detail about how you synthesize the wav files. Might try this with my Pi, though with a couple modifications. Btw, do you have any way to measure the transmitted power?

SDR sure has made it easier to play around with RF these days. Bitch as some people might, there are many great things about living in our times.

I'll post the code tonight. I don't have any way to measure the ERP unfortunately.

[CID]

I'm still waiting for an intelligent contribution on this topic from you.

photofly, that's exactly what I was thinking about you and your posts. I'll leave you to discuss your "hack". Arguably one of the most awkward uses of a Raspberry Pi I've seen so far. But...whatever.

[photofly]

For Posthumane, here's the code that churns out the baseband signal.

It's based on the code from this webpage: http://soledadpenades.com/2009/10/29/fa ... ve-module/

The wikipedia page on VOR was mostly unhelpful, because it makes something very simple sound very complicated. This reference was much more use: http://www.nist.gov/calibrations/upload/tn1069.pdf

Let me know what you try and how it goes.

produce_VOTwav.py 2.zip

(848 Bytes) Downloaded 55 times

[iflyforpie]

Thanks for the info, photofly. Don't let the pedants discourage you.

[photofly]

There are about a million and one ways to improve this; I'm as usual vastly amused by the particular nits people choose to pick. Hoping Posthumane finds something interesting to do.

[NeverBlue]

If it's designed to give a 0 degree radial From indication...or whatever...and that's what it does, then why isn't it a valid test?

What's the difference from using 114.80 Mhz VOT? ...you're not calibrating anything. It's just a check.

[photofly]

Because we value something only in proportion to the cost and difficulty of obtaining it. If a test is done with a $5 part and something you already own and carry in your pocket every day, it's impossible for it to give results as valuable and good as a device that costs $1000 from Aircraft Spruce.

[NeverBlue]

makes something very simple sound very complicated

Actually a VOR signal is kind of complex...the most of any aircraft navigation signal that I've seen.

[Rookie50]

You know, speaking as one who is horrible incompetent with electronics -- must have failed shop class -- I'm impressed with PF's initiatives, even though I doubt I could replicate them. I'm a bit scary with tools......

Two thoughts that came to me: First, we can all choose to live our lives as creators or critics,

And -- if one chooses to work and create (in aviation or elsewhere) solely for money as a motivation -- that will be the only reward given.

Follow your passion, and money will follow as a byproduct, along with many more rewards.

Kudos to those who create and innovate!

[CpnCrunch]

According to the webpage, the range is 100m with a simple wire antenna. It's also not a perfect square wave:

http://raspi.tv/2013/rpi-gpio-0-5-2a-no ... -to-use-it

so it won't just generate nice harmonics at multiples of 108Mhz. The only way to know for sure is to check with an RF spectrum analyzer.

[photofly]

makes something very simple sound very complicated

Actually a VOR signal is kind of complex...the most of any aircraft navigation signal that I've seen.

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.

According to the webpage, the range is 100m with a simple wire antenna. It's also not a perfect square wave:

http://raspi.tv/2013/rpi-gpio-0-5-2a-no ... -to-use-it

so it won't just generate nice harmonics at multiples of 108Mhz. The only way to know for sure is to check with an RF spectrum analyzer.

It will just generate harmonics at multiples of 108MHz. It may not be a square wave exactly, but it's still periodic with a very stable frequency, so it can only contain frequencies that are integer multiples of the fundamental. If it's a symmetric waveform then it can only contain odd harmonics: 1st (fundamental), 3rd, 5th etc.

As far as energy content in the unwanted harmonics goes, square waves are pretty bad. Something trapezoidal will be better.