Re: TI-H: Radio link stuff

[Prev][Next][Index][Thread]

Re: TI-H: Radio link stuff



David Knaack wrote:
 


> Bryan Fields wrote:
> 

> >what freq. is this link on?

> 433Mhz or 418Mhz, but this is dependant on the TX/RX modules used

If i were you i would stay away from 433.92. the reason for this is it
is very close to 434.00 a popular ham TV carrier freq.  i my self run
250 watts sync power on this freq. car keyless entry devices which
operate on this same freq. are made inoperative for many miles because
of my low power transmissions.  i know people who are north and west of
chicago (i am south in calumet city)  that run 5000 watts sync (don't
tell the fcc!)  and high gain antennas who have eirp of 30,000 watts. 
this can make keyless entry systems inoperative for more than 30 miles.

also if the building this is used in has a internal CATV system, channel
59 is on 433.90, and most of internal cable systems are poorly shielded
and run more power than necessary.  in this environment it is easy for
the cable to radiate 5 mW or more.

i did look at the Radiometrix page and i think the 170 MHz system would
be better suited to your application plus up around there the noise
floor is lower than on uhf. plus motorola makes some cool rf power
transistors for that band making it easier to run a couple watts.




> >what chips are you using for the transmitter and receiver?
> Planning on Radiometrix modules, hopefully the RPC-433-A,
> but possibly the BiM-433-F or TX2&RX2.


take a look at the tx1 and rx1 vhf will go further and be less chance of
interference up around 200 MHz.  




> >what power level will this put out?
> Broadcast power is currently in the 10mW range.
> Probably an amplifier could be added as a separate module.

i might be able to help you with an amp if you don't know how to design
one.

 
> >btw, i am not a digital guy, cant stand the 1's & 0's, so please keep
> >that in mind if i stated something that is wrong in this case.

> Weird the way some people prefer analog and some digital...

i like how you accurately have a use for high math with it. no more dumb
problems out of a text book like how many times something crosses that x
axis. mind you i, a person who cant do simple math in his own head said
that!


 

 
> > while we're already working with radio signals,
> > include a headphone jack so we can tune in to our favorite stations; (this
> > one might require some advanced programmers willing to put in a lot of time
> > and effort)
 
> Won't happen, bring a walkman if you want music.

Amen to that! 



 
> > make a flash TINOS to replace the TIOS with most functions built
> > in; any more ideas?-I'll keep thinking.
> 
> Now that would be cool, but hacking the ROM and recalculating the
> checksum would probably be a hell of a lot of trouble.

k.i.s.s.



> > >    Long range (over 30-75 meters in-building).
> >
> > #1 (Could this be done so, that you'd have a knob which you turn to
> > determine the range?
> 
> Yes, by attenuating the signal to the antenna.
> 
> > I myself think I'd easily use 30+ meters of range, but
> > as it might get interference on the way from other radio sources and stuff,
> > it would be great to be able to adjust the range with the knob, so you could
> > try to cut out as much interference as possible, or boost the range, if
> > there was no interference or the other link could not be contacted.)

well how about a decent 7 pole filter on the antenna. a variable
attunator that is 50 j 0 ohms all the time at 430 mhz will cost you.




> With an amplifier module the range could probably be extended
> to somewhere in the range of 300M indoors, maybe 800-1000 outdoors.
> FCC ain't gonna be too happy though..

hell the fcc wont care if you not going to market it. though they are
cracking down more and more.


> From: Nick <zaphod@coe.neu.edu>
> > someone else do the protocol... but any digital protocol plugged into the
> > mic jack of a commercial radio, say one of those nifty Motorola FRS jobs,
> > would give you a range of around 1/2 to 1 mile... and plus, each system
> > would be totally independent of frequency, so just say "channel sixteen" to
> > your friend and you have your own private link w/o interference... also,
> > most FRS radios have "quiet codes" to not activate the audio out unless the
> > code is received.
> >
> > FRS (family radio service) radios are decent, FM, license-free, and cost
> > anywhere from $50 to $150. Cheap enough for my sorry ass, especially when
> > compared to the work of designing FM circuitry myself.
> 
> Very cool, and a definite possibility, this eliminates any FCC issues,
> and only requires the radio, and a microcontroller.  I'll look into
> this, the private channels and voice capability are a huge benefit
> for something not that much more expensive (and that has a warrantee)
> 
> > It's gonna be slow, though.  It's an analog-to-digital system, being put
> > through the voice filters in the FRS radio, so I'd guess that anything over
> > 9600bps would not be possible. Some simple error correction would be
> > necessary, probably in a program on the TI.
> 
> It will likely run slower than that anyway.  This isn't really suited
> to large data transfers anyway.  Its better for ASCII text (chatting,
> test 'assistance' :) etc), and game synchronization messages, etc.

frs radios are not suited to data transmission, and it is illegal to do
so.   

the reason they are not suited is all the voice and receive audio
processing will distort the data coming into and leaving the radio.  if
you tapped the recovered audio at the discriminator, receive might work
but you would have to modulate the radio at the reactance modulator
directly.  even then you would have decent performance, but you would be
limited to around 2400 baud because frs radios use a 2.5 kHz deviation
and that is not good for data transmission.


i have tried this before with bad results, out of the box we could only
get 300 baud data rates. to slow for my tastes.  if you wrote a custom
protocol for the frs radios then it might be possible but with regular
packet the best i got was 300 baud.
 
also they use splinter channels from the grms service so you have a
higher potential for interference.

not to mention if you are in school a lot of them don't take kindly to
students having radios.  i have been arrested for having a fcc licensed
radio in a public school before.  mind you local officials cant do that
with a federally licensed radio service. but tell that to them and it's
"shut the fuck up," "but", "What the fuck did i just say shut the fuck
up". trust me you don't want to be in this position even if you are
right. all this for being safer!


just my 2 cents again,

Bryan Fields


-- 
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
"If there be time to expose through discussion the falsehood and the
fallacies, to avert the evil by processes of education, the remedy to be
applied is more speech, not enforced silence." 
-- U.S. Supreme Court Justice Louis Brandeis, 1927

"Necessity is the plea for every infringement of human freedom. It is
the argument of tyrants; it is the creed of slaves." 
--William Pitt, 1783
References: