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reciever sensitivity??

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Old 05-09-2003, 05:25 AM
  #1  
tunnelvishon
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Default reciever sensitivity??

Hi there, I was looking at the specs for my JR reciever and for sensitivity it is listed as 5 micro seconds. After talking with an electrical engineer specializing in wireless systems he had informed me that sensitivity is either shown as micro volts or Dba. Micro seconds apparantly have nothing to do with reciever sensitivity and as he put it "Its like measuring your tire pressure in yards". Is this specific ation erronious or is this something special for rc recievers that both of us are missing?
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Old 05-09-2003, 12:25 PM
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wildnloose
 
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Default reciever sensitivity??

You should have done a search in the "RC Radios-Receivers-Servos" forum. I did it for you. This is "Danny from JR"s answer to your question (it was asked before).

That is just a choice that they make. They have selectivity and sensitivity listed, and they have selectivity listed as a db value.

I do have a question for you. I have been in the RF industry for 14 years. I see people asking this question all the time, but I never knew why they bother (You cannot change it, modify it, or do anything about it). So, why do you want to know????
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Old 05-09-2003, 01:59 PM
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Default reciever sensitivity??

So that he can rub it in on guys with "sensitivity envy."

That, or as a crash excuse. "Rats, sure could have used those two extra micro-seconds just then."
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Old 05-09-2003, 05:33 PM
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Default reciever sensitivity??

To say that "selectivity" and "sensitivity" are interchangeable and can be used either way is wrong. The people taking this liberty and validating their position by saying its their choice are promoting their ignorance of the subject or the ignorance of being accurate...especially for specifications. As to why I would want to know something if I cannot change or modify it...maybe the tutors in your youth should have told you that the sun moves at 3 miles to the gallon and actually does not exist when it is past the horizon....AFTER ALL....YOU CANNOT MODIFY, OR CHANGE IT.

1. I could use the proper information in selecting my equipment and as a comparison of value and quality.

2. I could use the proper information for calculations to determine effective range over various conditions of interferance and meteorology.

3. If an auto manufacturer specified a vehicle to have a gas milage of 36 psi and to have a tire pressure or 20 mpg and then state that it was their "choice" to state it as such (ie. not a misprint) I would truly wonder what else was screwy with the vehicle.

I was aware of some of the previous threads on this discussion and only asked the question again because the answer was vague, and somewhat arrogant.
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Old 05-09-2003, 07:21 PM
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Rodney
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Default reciever sensitivity??

I have to disagree with wildnloose, sensitivity is very important. All manufacturers should specify what it is as it is an important parameter for determining range . Low sensitivity, short range, i.e. check out the Feather versus FMA M5, worlds of difference in acceptable performance.
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Old 05-09-2003, 07:45 PM
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Steve Lewin
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Default reciever sensitivity??

O.K. pardon my ignorance but what exactly does a sensitivity figure in microseconds mean. I'm used to uV for a given S/N etc but for uS the only thing I can think of is some sort of capture time. But what ?

BTW wildnloose, some people just like to understand things. It's like the difference between being educated and just "monkey do this" trained.

Steve
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Old 05-09-2003, 07:52 PM
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Default reciever sensitivity??

wildnloose, maybe some people just want to know. besides what is wrong with asking that question here?
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Old 05-09-2003, 08:27 PM
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frank@simrex.co
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Default reciever sensitivity??

The 5us receiver sensitivity spec is probably a misprint... perhaps they meant 5 uV (equivalent to -100 dBm). Not a great spec for a radio, but probably OK if you only need a mile or 2 of range and it is free space between antennas.

Receives are commnly specified as some quantity of signal required at the receiver input (usually measured in dBm or uV) to acheive some specific metric of performance depending on the application. eg.

eg. 2uV for 3% rms full scale error.

Alternate meteric for recivers are:

Like % full scale RMS servo error for RC

1e-6 BER (Bit Error rate) in data communications (applicable in PCM RC).

12 dB SINAD for voice communication.
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Old 05-09-2003, 08:39 PM
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Default reciever sensitivity??

Just a quick follow up. Many of these radios are FM based and an RF service monitor will easily measure the 12 dB sinad sensitivity if you connect to the discriminator output (if you can get at it). Alternately badger your vendor until they give you a sensitivity spec that is at least measured in the right "dimensional" units. your class of reciver should be 0.5 to 5 uV or -100 to -115 dBm.

When you have the senesitivity spec, go to my website at http://www.aria-glb.com/wireless/som.php4 and run the range and signal loss calculator. Plug in you freq in MHz and use 0.5 dB for the line losses and 0 dB for your TX and RX antenna gains. Your 1W radio is +30 dBm. Plug in different miles miles until you run out of operating margin and you get your maximum theoretical gain.

Of course you never want to run at the limit and most systems want to see 15 to 20 dB of safe operating margin so that if the plane banks , you can withstand an antenna directivity induced loss. Happy to answer any questions....
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Old 05-10-2003, 02:43 AM
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Default reciever sensitivity??

Wow, just too many type A personalities here...

Sorry for asking the question, I just wanted to know if I was missing something..I did'nt mean to p**s anyone off, just asked a simple question (why??).

Oh, and I just love this one:
wildnloose, maybe some people just want to know. besides what is wrong with asking that question here?

My thoughts exactly, thats why I asked...

Once again, my apologies...
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Old 05-10-2003, 05:21 AM
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frank@simrex.co
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Default reciever sensitivity??

wilnLoose... i just followed back on the thread... you can change almost any aspect of the link budget after the fact except perhaps the RF power as there is probably an FCC rule regarding this. The simplest change is an RF preamp with better noise figure than the existing one... or replace the transistor... improve the preselector... .Get yourself a surface mount rework station and go to town.... Other items are better receiver antenna configuration or higher gain TX antenna.

Actually the point that I took issue with was the same as the other post where the spec was posted in us ... this is a completely useless spec and I challenge anyone to unravel any meaningful significance (in the context of a reciver performance metric) from it as stated.. Perhaps there is some specmanship among the vendors but my gut tells me it has to be a typo.
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Old 05-10-2003, 12:19 PM
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Default reciever sensitivity??

Frank,

I agree with you. I know all about link budgets (spent 3 yrs designing/optimizing pcs systems for Sprint). I just didn't see the benefit of knowing why nupeswv was asking. That is why I asked him why he wanted to know (like I stated, I thought I may have been missing something).

Thanks for your reply though. Nupeswv had already answered my question to him (albeit a little snippy about), but I guess he thought I was being a smart a** to him for asking...
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Old 05-10-2003, 02:02 PM
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Default reciever sensitivity??

I apologize for my snippetyness....guess I just had a bad day or something. As for being a smart a**...I can live with that...seemed appropriate at the time in response to the "crash excuse" comment.
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Old 05-17-2003, 06:03 PM
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frank@simrex.co
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Default reciever sensitivity??

Hmm no posts in a week... I guess there is no rational explanation for the 5 uS receiver sensitivity spec.
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