Graters,

Sorry to hear about your problems.

The frequencies you are using for telemetry aren't in the ham bands, they
are in the TV broadcast bands. It would be unlikely for hams to be causing
interference in those frequencies.

I am not familiar with the atmospheric background noise levels in Brazil,
but many of the VHF bands get noise like this during the day. Perhaps at the
equator it is worse than what you may have found with your testing in
Canada.

Can you tell us what the power output is on your lizards, and what the
distance is you are listening from ?

You may be able to improve your signal to noise ratios by using a
directional antenna such as a Yagi aimed toward the lizards, or adding notch
filters tuned to the correct frequencies.

The interference seems to cover a very large bandwidth....suggesting this
may not be a ham or aviation transmitter on your frequencies. Hams would
transmit on a discrete frequency, such as 146.940 mHz. A TV station could
cover 2 of the frequencies at a time though.

Could the problem be in the selectivity of your receiver ? Perhaps there is
an FM radio transmission at 91 - 104mHz that is swamping your receiver. Do
you have another radio (such as a scanner) capable of listening to the
frequencies involved to see what you are hearing....is interference really
there at those frequencies, and if so what does it sound like. If the
equipment has a signal level indicator you might get an idea of the
interference pattern.

The 1.8mHz signal burst is unlikely to be your problem. Do all 4 lizards
turn on and off ? It would be an unusual station that transmits once to turn
off your lizards at 11am , and once again at 3pm to turn them back on. If
there was such interference, I would expect the lizards to be turning off
and on continuously from 11am to 3 pm. It sounds more like a signal/noise
problem, and you are getting swamped with noise.

If there are any hams out there near your experiment site, they would
probably be interested in helping you find out the problem, even if they
aren't the ones causing it.

And be sure to mention them in the credits if you get your research
published,

Good luck,

*Watt



"Gjtatters" wrote in message
om...
This may at first seem like a strange post to a Ham Radio newsgroup,
but I am hoping someone can help us out. We (Canadian Scientists) are
currently conducting research in Brazil near the city Rio Claro in Sao
Paolo state. We study lizard physiology and hibernation, and are
currently conducting a year long study using radio telemeters
implanted inside lizards. These telemeters allow us to monitor heart
rate, breathing rate and body temperature, and all of this information
is uploaded via radio frequencies and recorded to computer.

The telemeters themselves work in the high MHz range. Each animal (we
are currently looking at 4 animals) has a unique telemeter with a
unique transmission band. The 4 frequencies we are looking at a
182, 184, 206 and 208 Mhz. This radio frequency information is then
decoded with a demodulator, and the information stored as a voltage
signal on a standard computer acquisition system.

The problem we are finding is that typically, between 11am and 3pm
during the day, our telemeters are encountering massive interference
from some external source, and we cannot make any meaningful
recordings. Our signal strength goes to pot, and all we get is noise.
Strangely enough, during the evenings, the recordings seem fine.

To add to the story, all the telemeters can be turned on or off (they
have a battery that should last about 1 year) using a 1.8 Mhz burst
(we have a small battery powered wand-like antenna that we wave over
the lizards for this express purpose!). Once we started to encounter
our interference problem, we began to think that perhaps our
telemeters are being turned on and off intermittently by an external
source of 1.8 MHz. That was when we realized that Ham Radio operates
from about 1.8 to 30 Mhz.

What I wanted to ask the newsgroup was whether anyone thinks that the
signal strength from a local ham radio operator would be enough to
turn our telemeters on or off (I doubt you would know the answer to
this question, but thought I'd ask). Do Ham Radio operators typically
use 1.8 Mhz?

Otherwise, does anyone out there know what could possibly be
interfering at the higher frequencies (182-208 MHz)? There is a local
airstrip and flying club that flies overhead where we are conducting
this research, but I do not know if they typically transmit within out
frequency range!

But more importantly, if the Ham Radio signal could be the source of
our interference, we wanted to know if anyone could help us find out
if there is anyone in Rio Claro that is a Ham Radio operator?!! If
so, would they be willing to help us troubleshoot this problem!

Thanks for your time. Please reply directly to this email if you can.

Gjtatters