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Aeroengineer
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Re: RF I/O
Aeroengineer   7/7/2014 7:37:51 PM
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I agree about the title of blogger.  I would love to see that either of the two that you mentioned.

MeasurementBlues
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Re: RF I/O
MeasurementBlues   7/3/2014 8:01:50 AM
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@Adam,

The rankings are really kind of dumb. they are based on the number of comments you make and have nothing to do with the thought behind those comments. When I ran DesignCon Community last year, we had people who were experts on signal integrity ranked as rookies or whatever the marketing people called tham on that site. If I could, I'd eliminate the rankings.

You see, 100 dumb comments count more than one well-though-out comment.

I also dont like the name "blogger." "Contributor" or "author" is better.

We really need to change your user ranking from rookie.

Aeroengineer
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Re: RF I/O
Aeroengineer   7/2/2014 9:26:14 PM
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We really need to change your user ranking from rookie. 

 

I just looked at the datasheet and it is showing 512k on chan 2.  The more interesting thing is that it only shows an arbitrary waveform max frequency of 40MHz, though a pure sine wave max frequency of 160MHz.  This is something that I will have to play with.  I expect the signal out of the transmitter to be close to a pure sine, so we shall see what we can do with the equipment.

 

Your suggested RF coupling methods are very much appreciated. This is still a new environment for me, and there is still a lot of learning to be done.

salbayeng
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Rookie
Re: RF I/O
salbayeng   7/1/2014 2:03:25 AM
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Hi Adam, I was going to suggest some RF coupling methods , but then stopped to read the specs of the WaveStation.

Anyhow, at ~ 70MHz , the 1/4wavelength is ~ 5ft , therefore
  • the actual voltage on the antenna (which is shorter than 5ft)  will be more than the 5v suggested by forcing 0.5W into 50ohm.
  • short lengths of coax (~2ft) singly terminated with ~50Ω won't create issues.
  • Short bits of hookup wire (~1ft) have negligible effects.

Also for napkin type calculations, 60pF and 150nH have reactances approaching 50Ω, so 
  • You can make a Q=10 coupling coil with say 15nH and 600pF (Parallel)
  • You can make a tapped capacitor pickup coil Q=10, with 150nH and 66pf+600pF
  • you can clip a 6pF capacitor to the antenna, and call it a 1: 10 probe.
  • etc etc

The fly in the ointment is the sample width of the WaveStation, it can record 16,000 samples, so at a 160MHz digitisation rate, this is 100uS of waveform. Problem is the modulation frequency of the RC transmitter is something like 2mS per transmit channel (the old fangled digiprop method) ,  I'm not sure what modulation scheme modern RC radios use, but the channel spacing is 20kHz , and the modulation frequency is 2.8kHz for the hitec spectra. To do the testwork you envision you really need something like 20ms - 100ms of recorded RF to get a frame in, with some baseline either side, so you need more like 16,000,000 samples. 

You could alternatively record the baseband signal going into the Hitec Spectra, then play it back to another Hitec Spectra and couple this to your Rx with appropriate attenuators and noise sources.  

Aeroengineer
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Re: RF I/O
Aeroengineer   6/30/2014 8:35:48 PM
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That is a great point, and one that I will have to investigate to see if I can simulate it.  I wonder if on the WaveStation 3000 if I can just scale the output.  This would be an interesting test.

 

Thanks for the idea!

elizabethsimon
User Rank
CEO
RF I/O
elizabethsimon   6/30/2014 8:32:51 PM
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When you test the system by playing a waveform back in on the RF side, it would interest me to know how low a signal level can you generate and still have a faithful reproduction of an ideal signal to the RF chip. In most cases during actual operation, the RF input level is likely to be much lower than the output level and it's always a good idea to test your receive threshold.

 



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