Gjtatters wrote:
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?

It's certainly possible ham signals would be strong enough to activate
your equipment. The 1.8MHz band is nowhere near the most popular ham
radio band, but it does see a fair amount of use, including in Brazil.

However, the 1.8MHz band is not good for work over any distance of more
than a few dozen km during the day. There is VERY little daylight
activity on this band - it is used almost entirely at night.

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!

The 182-208MHz frequencies are used by VHF TV channels 7-13:
182 & 184MHz fall in TV channel 8; 206 & 208MHz in channel 12. It is
concievable that TV stations outside the area you're working in are
"propagating" in via various atmospheric phenomona. (however, that kind
of thing tends to be more common right around sunrise and in the
evening, not in the middle of the day)

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!

http://www.labre.org is the national organization for Brazilian hams.
If there is a ham in the area who might be able to help, they should be
able to find them. (and even if the problem doesn't have anything to do
with ham radio, hams are more likely to know what frequencies are used
by broadcast stations in your area - or what other localized sources of
interference are possible)

Two other things you might check...

- How selective is your equipment? (how close does a signal have to be
to 1.8MHz to cause problems? Might 1.5MHz or 1.6MHz be close enough?
In which case it might be an AM broadcast station that's involved?)

- The timing is suspicious. I'm having a hard time thinking of any
radio service that transmits only between 11am and 3pm. Hams typically
operate erratic schedules and more likely at night. Broadcast stations
operate all day long.

I wonder if your equipment is sensitive to heat and drifts off frequency
or otherwise malfunctions in the heat of the day, then returns to normal
operation as the sun goes down and it cools off?

Or, some other transmitter (most likely an AM broadcast transmitter that
operates all day) is drifting with the heat and causing your problem?
--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com