On Mon, 28 Jul 2003 10:19:13 +0100, "Hans Summers"
wrote:


Back to your interference problem. Is your operating
channel frequency smack in the middle of the 40 Mhz band?
If so, maybe you could try a different set of crystals, so
that you operate as far away from everyone else as
possible. Or simply just borrow a different set of crystals
in case there is a weird mix going on, just to eliminate
that possibility.

We've recently got wise to that one and I've ordered a pair of xtals
from the *last* channel of the band. That's what we'll be running with
come the last week in August, when we're due up for the next filming.


Not necessarily the solution, I got bitten by that one once some 9 or 10
years ago when I used to fly radio controlled aircraft (in the UK on 35MHz).
It bothered me when someone else at the flying field had the same crystal as
I did and I had to wait for them to finish flying before I could fly. So
bought another pair of crystals, the highest I could find, if I recall that
was channel 83 (35.230MHz). Everything was fine for a while but a few weeks
later I crashed after losing radio contact with my plane.

A little investigation (in between gluing the aircraft bits back together)
found the cause. A channel vs frequency listing, compared with the MHz
printed on the crystal case revealed that the receivers were single
conversion superhets with 110KHz IF. Channel separation was 10KHz. Clearly
with that setup, image rejection is practically negligible. So someone
transmitting on channel 61, 220KHz away, interferes with channel 83. After
that I went back to my crystals on 76 smack in the middle of everyone elses,
learnt to be patient if someone was already using the channel, and had no
more problems ;-)

Hans G0UPL
http://www.HansSummers.com


Hello Hans,
what brand/make was that R/C set that you had?

You have reminded me of a silly incident at my model
flying club decades ago. One of the wealthier club
members was having all sorts of trouble with his
model, engine and radio gear so he flung heaps of
money at a ready made, ready to fly model with an
expensive four stroke engine, and a new expensive
all singing and dancing radio control set. First day
out with the new model and everything is going well
for him, he was doing stunts all over the sky.

My models were el cheapo sticks and tissue construction,
I couldn't afford nice covering film/material. I was
more interested in home built radio control gear. Radio
assisted free flight was more my style.
When the fuel ran out in my models I didn't mind
walking a few hundred yards if necessary to retrieve
my model. So I am off for a long walk with my transmitter
still switched on as one would. (The receiver gets
switched off first then the transmitter.)

The rich guy is stunting around and decides to buzz
me at low level about 20 feet above the ground.
His model flies over me and then nose dives into
the ground near by. I could here his servos twitching
away as I walked past the wreckage.
After I retrieved my model and switched off my
transmitter, I stopped by the little gathering at the
wreck site. The rich guy was operating his servos OK
and scratching his head. " I spend thousands on
my model and that ******* John Crighton comes
here every weekend with 50 dollars worth of homebuilt
junk and flies. It just isn't fair." "Moan...grumble..moan."
I didn't try to explain that his receiver got swamped. His
mates put the crash down to pilot error at low level, and
that was that.

Fun and games, eh! :-)
Regards,
John Crighton
Sydney