Minature AM transmitters - attenuation?

N

naked_draughtsman

Guest
Hello

I'm building a remote control circuit using some miniature AM
transmitters/receivers. This is my first RF project (apart from
making crystal radio sets when I was younger).

The transmitter I'm using is one of these:
http://uk.farnell.com/quasar/qam-tx1/module-transmitter-am-433mhz/dp/1304024
They are pretty basic - they need power, a data input and an aerial.
They are quoted as having a range of 50m, but I have read on other
websites that 100m is possible.

The problem I have is that while I was testing, I had the transmitter
running while I fiddled with parts of the receiver and I am 90% sure
it was triggering the neighbour's wireless doorbell. I heard lots of
cursing and clattering as if they were trying to take the batteries
out, and it stopped ringing as soon as I turned the transmitter
off....

I'd like to reduce the transmitter power a little so I can test the
circuit, but I'm not sure how to do this. Is it as simple as putting
a resistor in series with the aerial?

Currently the aerial is a bit of wire about 200mm long. Could the
antenna be causing the problem?

Any advice would be gratefully received.

peter
 
On Sat, 17 Sep 2011 02:16:22 -0700 (PDT), naked_draughtsman
<googleaddy@petereverett.co.uk> wrote:

Hello

I'm building a remote control circuit using some miniature AM
transmitters/receivers. This is my first RF project (apart from
making crystal radio sets when I was younger).

The transmitter I'm using is one of these:
http://uk.farnell.com/quasar/qam-tx1/module-transmitter-am-433mhz/dp/1304024
They are pretty basic - they need power, a data input and an aerial.
They are quoted as having a range of 50m, but I have read on other
websites that 100m is possible.

The problem I have is that while I was testing, I had the transmitter
running while I fiddled with parts of the receiver and I am 90% sure
it was triggering the neighbour's wireless doorbell. I heard lots of
cursing and clattering as if they were trying to take the batteries
out, and it stopped ringing as soon as I turned the transmitter
off....

I'd like to reduce the transmitter power a little so I can test the
circuit, but I'm not sure how to do this. Is it as simple as putting
a resistor in series with the aerial?

Currently the aerial is a bit of wire about 200mm long. Could the
antenna be causing the problem?

Any advice would be gratefully received.
Click to expand...
---
Remove the antenna for testing.

--
JF
 
On Sat, 17 Sep 2011 05:32:03 -0500, John Fields
<jfields@austininstruments.com> wrote:

On Sat, 17 Sep 2011 02:16:22 -0700 (PDT), naked_draughtsman
googleaddy@petereverett.co.uk> wrote:

Hello

I'm building a remote control circuit using some miniature AM
transmitters/receivers. This is my first RF project (apart from
making crystal radio sets when I was younger).

The transmitter I'm using is one of these:
http://uk.farnell.com/quasar/qam-tx1/module-transmitter-am-433mhz/dp/1304024
They are pretty basic - they need power, a data input and an aerial.
They are quoted as having a range of 50m, but I have read on other
websites that 100m is possible.

The problem I have is that while I was testing, I had the transmitter
running while I fiddled with parts of the receiver and I am 90% sure
it was triggering the neighbour's wireless doorbell. I heard lots of
cursing and clattering as if they were trying to take the batteries
out, and it stopped ringing as soon as I turned the transmitter
off....

I'd like to reduce the transmitter power a little so I can test the
circuit, but I'm not sure how to do this. Is it as simple as putting
a resistor in series with the aerial?

Currently the aerial is a bit of wire about 200mm long. Could the
antenna be causing the problem?

Any advice would be gratefully received.

---
Remove the antenna for testing.
Click to expand...
The neighbor's behavior might be coincidence. So to greatly
reduce the probability of it being explained as coincidence,
I think a LOT more testing of the OP's conjecture is needed
first. The transmitter should be turned on and off through
at least 1000 spaced cycles, with careful observation of the
neighbor during each cycle. :) I might consider reducing
that probability to zero in the limit if I were ornery. ;)

Jon
 
On Sep 17, 12:27 pm, Jon Kirwan <j...@infinitefactors.org> wrote:
On Sat, 17 Sep 2011 05:32:03 -0500, John Fields

The neighbor's behavior might be coincidence.  So to greatly
reduce the probability of it being explained as coincidence,
I think a LOT more testing of the OP's conjecture is needed
first.  The transmitter should be turned on and off through
at least 1000 spaced cycles, with careful observation of the
neighbor during each cycle.  :)  I might consider reducing
that probability to zero in the limit if I were ornery.  ;)

Thanks for the suggestion Jon, however I don't particularly want the
Click to expand...
ghost hunters around and I'd like to stay on good terms with the
neighbours! <g>

peter
 
On Sep 17, 11:32 am, John Fields <jfie...@austininstruments.com>
wrote:

Remove the antenna for testing.
Click to expand...
Thanks John, I hadn't thought of that.

I took the antenna wire out (prototype board) and did a couple of
short transmissions without a problem. I then left the transmitter on
for a few seconds to change the data that was being sent and the
doorbell starting ringing again....

Hopefully they will go out for the afternoon so I can experiment a bit
more.

peter
 
naked_draughtsman wrote:
On Sep 17, 12:27 pm, Jon Kirwan <j...@infinitefactors.org> wrote:

On Sat, 17 Sep 2011 05:32:03 -0500, John Fields


The neighbor's behavior might be coincidence. So to greatly
reduce the probability of it being explained as coincidence,
I think a LOT more testing of the OP's conjecture is needed
first. The transmitter should be turned on and off through
at least 1000 spaced cycles, with careful observation of the
neighbor during each cycle. :) I might consider reducing
that probability to zero in the limit if I were ornery. ;)


Thanks for the suggestion Jon, however I don't particularly want the
ghost hunters around and I'd like to stay on good terms with the
neighbours! <g

peter

Does this only take place while sending the data or does it also
Click to expand...
happen with a carrier only?

If it's data related, see if you have an option to turn down the
drive on the carrier, you could be over driving it and generating
lots of splatter.. (harmonics)

Jamie
 
On Sep 17, 4:30 pm, Jamie
<jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:
Does this only take place while sending the data or does it also
happen with a carrier only?

   If it's data related, see if you have an option to turn down the
  drive on the carrier, you could be over driving it and generating
lots of splatter.. (harmonics)
Click to expand...
Jamie

The transmitter only transmits when it has data going to the 'data'
terminal - it's not continuously transmitting a carrier without any
data. The transmitter modules are pretty 'black box' without much
scope to adjust.

I've tried reducing the supply voltage, but I think next door have
taken the batteries out of their doorbell now (transmitting on full
power when they went to walk to the dog didn't seem to set anything
off) so it's hard to tell if it makes a difference.

peter
 
On Sat, 17 Sep 2011 05:00:36 -0700 (PDT), naked_draughtsman <googleaddy@petereverett.co.uk> wrote:
On Sep 17, 11:32 am, John Fields <jfie...@austininstruments.com
wrote:

Remove the antenna for testing.

Thanks John, I hadn't thought of that.

I took the antenna wire out (prototype board) and did a couple of
short transmissions without a problem. I then left the transmitter on
for a few seconds to change the data that was being sent and the
doorbell starting ringing again....

Hopefully they will go out for the afternoon so I can experiment a bit
more.
Click to expand...
peter,

You might consider purchasing a 433MHz wireless doorbell of your
own. I dimly recall the prices on these things being in the $10-20
range ... Ah! Home Depot has a Heath Zenith Kit for $13, but no
mention of frequency.

The advantage, assuming that the one you find mimics your neighbor's
doorbell, is that you could test with a very short antenna or none
at all and still see whether you were causing a problem. (Ideally
you'd find a doorbell of the same make and model as your neighbor's,
but this might not be the ideal time to ask about this. <grin!>)

This is an area where I'd advise caution, because, as someone
operating radio transmitting equipm,ent (and thus responsible for
the interference caused by it)), it's not just something between you
and your neighbor. First, others may be affected, not just the one
neighbor you know about, and second, if anyone gets ticked off
enough and calls in the FCC, it sounds like the FCC will be able to
figure out fairly quickly who the "interfering" party is.

In the instructions accompanying the transmitter/transceiver module
there should be some sort of note describing the maximum antenna
length. You should check this to make sure you aren't exceeding the
FCC-approved length.

You might also want to review this section of the ARRL 'Web site:

Radio Frequency Interference (RFI)
http://www.arrl.org/radio-frequency-interference-rfi

and the pointers to FCC information here:

FCC RFI Information
http://www.arrl.org/fcc-rfi-information

Sorry... I'm not trying to rain on your parade, but I suspect you'd
be a little ticked off if the situation were reversed -- if, say,
your neighbor's doorbell started triggering loud buzzing sounds from
your 200-watt stereo speakers. <grin!>

Hope this helps...


Frank McKenney
--
You can't wait for inspiration. You have to go after it with a
club. -- Jack London
--
Frank McKenney, McKenney Associates
Richmond, Virginia / (804) 320-4887
Munged E-mail: frank uscore mckenney aatt mindspring ddoott com
 
naked_draughtsman wrote:
The problem I have is that while I was testing, I had the transmitter
running while I fiddled with parts of the receiver and I am 90% sure
it was triggering the neighbour's wireless doorbell. I heard lots of
cursing and clattering as if they were trying to take the batteries
out, and it stopped ringing as soon as I turned the transmitter
off....

Any advice would be gratefully received.

Go knock on the neighbor's door with your transmitter in your hand,
Click to expand...
and tell him that you think your transmitter is triggering his doorbell.
Politely ask him if it's OK to press your button right then to test it.

If it does, then apologize profusely and either tune your tx/rx to
a different frequency, or buy a transmitter that's already on a
different frequency.

And 20 cm of antenna might violate FCC rules, depending on what band
it's operating on; see part 15 of the FCC rules.

Hope This Helps!
Rich
 
On Sat, 17 Sep 2011 14:29:55 -0700, Rich Grise
<richg@example.net.invalid> wrote:


And 20 cm of antenna might violate FCC rules, depending on what band
it's operating on; see part 15 of the FCC rules.

Hope This Helps!
Rich
Click to expand...
Perhaps the FCC doesn't apply where he is.

Tom
 
On 2011-09-17, naked_draughtsman <googleaddy@petereverett.co.uk> wrote:

The problem I have is that while I was testing, I had the transmitter
running while I fiddled with parts of the receiver and I am 90% sure
it was triggering the neighbour's wireless doorbell. I heard lots of
cursing and clattering as if they were trying to take the batteries
out, and it stopped ringing as soon as I turned the transmitter
off....
Click to expand...
Their doorbell should be using a coded signal and be mostly immune to
accidental triggering.

I'd like to reduce the transmitter power a little so I can test the
circuit, but I'm not sure how to do this. Is it as simple as putting
a resistor in series with the aerial?
Click to expand...
that would work.

Currently the aerial is a bit of wire about 200mm long. Could the
antenna be causing the problem?
Click to expand...
The real problem is with the doorbell. but reducing or attenuating
the antenna should stop the accidental triggereing

AIUI the regulations on the 433Mhz band say that signals should be
intermittant, not constant. The band is used for several different
remote-control tasks and while one transmitter is running it's
unavailable for other tasks.

--
⚂⚃ 100% natural

--- Posted via news://freenews.netfront.net/ - Complaints to news@netfront.net ---
 
naked_draughtsman wrote:
Hello

I'm building a remote control circuit using some miniature AM
transmitters/receivers. This is my first RF project (apart from
making crystal radio sets when I was younger).

The transmitter I'm using is one of these:
http://uk.farnell.com/quasar/qam-tx1/module-transmitter-am-433mhz/dp/1304024
They are pretty basic - they need power, a data input and an aerial.
They are quoted as having a range of 50m, but I have read on other
websites that 100m is possible.

The problem I have is that while I was testing, I had the transmitter
running while I fiddled with parts of the receiver and I am 90% sure
it was triggering the neighbour's wireless doorbell. I heard lots of
cursing and clattering as if they were trying to take the batteries
out, and it stopped ringing as soon as I turned the transmitter
off....

I'd like to reduce the transmitter power a little so I can test the
circuit, but I'm not sure how to do this. Is it as simple as putting
a resistor in series with the aerial?

Currently the aerial is a bit of wire about 200mm long. Could the
antenna be causing the problem?

Any advice would be gratefully received.

peter
Click to expand...
You could try putting a reflector between the transmitter antenna
and the doorbell location, close to the transmitter antenna. The
idea is that the waves radiated from the antenna toward the neighbor
are reflected in the opposite direction before they have traveled
even one wavelength (about 28"). See
http://www.northcountryradio.com/Articles/crfl.htm

You should be able to build a simple corner reflector from the
information there.

Ed
 
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