This is somewhat off topic; I apologize, but it seems like the people
that hang out here might actually be able to help me with my problem.

I fly radio control gliders. I recently purchased a new transmitter
(a Royal Evo 9 with synth module, for those that might care). I'm in
the US so this broadcasts on 72MHz.

I have problems with this transmitter at one particular flying site
that's right next to a military base. The xmitter is fine at other
locations, and all the gliders respond just fine to my 'old' xmitter
at this site. I've done a bunch of things and it really is just the
new xmitter at this particular flying site.

It seems like there must be an interference problem with some signal
being broadcast from the military base. I've tried to shield the
transmitter without much improvement. That makes me think the
offending signal may be coming in through the antenna.

Being relatively naive electronically, it seems like I could simply
insert a filter between the antenna and the rest of the transmitter
that passes through the 72 MHz signal but blocks everything else.
However, I'm smart enough to know I'm not that smart. That's why I'm
here.

Is it as simple as finding a filter that passes 72 MHz along and
splicing it in to the wire going to the antenna? Is that likely to
cause other problems (transmitting on the wrong frequency, overheating
the RF module due to impedance mismatch, sudden death)? Assuming I
can't find a filter that passes along precisely the frequency I want,
is it OK to put filters in series (like a high-pass plus a low-pass)?
And finally, am I just totally missing the boat here with this idea?
I'm open to other suggestions.

P. Venkman wrote:

This is somewhat off topic; I apologize, but it seems like the people
that hang out here might actually be able to help me with my problem.

I fly radio control gliders. I recently purchased a new transmitter
(a Royal Evo 9 with synth module, for those that might care). I'm in
the US so this broadcasts on 72MHz.

I have problems with this transmitter at one particular flying site
that's right next to a military base. The xmitter is fine at other
locations, and all the gliders respond just fine to my 'old' xmitter
at this site. I've done a bunch of things and it really is just the
new xmitter at this particular flying site.

It seems like there must be an interference problem with some signal
being broadcast from the military base. I've tried to shield the
transmitter without much improvement. That makes me think the
offending signal may be coming in through the antenna.

Being relatively naive electronically, it seems like I could simply
insert a filter between the antenna and the rest of the transmitter
that passes through the 72 MHz signal but blocks everything else.
However, I'm smart enough to know I'm not that smart. That's why I'm
here.

Is it as simple as finding a filter that passes 72 MHz along and
splicing it in to the wire going to the antenna? Is that likely to
cause other problems (transmitting on the wrong frequency, overheating
the RF module due to impedance mismatch, sudden death)? Assuming I
can't find a filter that passes along precisely the frequency I want,
is it OK to put filters in series (like a high-pass plus a low-pass)?
And finally, am I just totally missing the boat here with this idea?
I'm open to other suggestions.

First, you can really mess things up by playing the filter game, so
don't do it unless you need to.

Second, it may be that the transmitter has a weaker signal, or that it
is a bit off frequency. Since your average military base has about a
gazillion different transmitters it's likely that there is some spur
being generated at 72MHz, or a valid signal at your RX's image
frequency. If your transmitter is a bit weak than such a signal from
the base would have an easy time getting into your RX.

If you can get the receiver out of the plane (or if you can get to the
antenna) do a range check with the RX antenna rolled up but with the TX
antenna extended. I'd do this at some _other_ flying site. Check the
range with the suspect TX and with a known good one. If it's
significantly lower with the suspect TX then you can do all the
filtering in the world and it won't help you -- but having the new TX
fixed (or selling it and getting another brand) may help a lot.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Tim Wescott wrote in message ...
P. Venkman wrote:

SNIP

Is it as simple as finding a filter that passes 72 MHz along and
splicing it in to the wire going to the antenna? Is that likely to
cause other problems (transmitting on the wrong frequency, overheating
the RF module due to impedance mismatch, sudden death)? Assuming I
can't find a filter that passes along precisely the frequency I want,
is it OK to put filters in series (like a high-pass plus a low-pass)?
And finally, am I just totally missing the boat here with this idea?
I'm open to other suggestions.

First, you can really mess things up by playing the filter game, so
don't do it unless you need to.

Second, it may be that the transmitter has a weaker signal, or that it
is a bit off frequency. Since your average military base has about a
gazillion different transmitters it's likely that there is some spur
being generated at 72MHz, or a valid signal at your RX's image
frequency. If your transmitter is a bit weak than such a signal from
the base would have an easy time getting into your RX.

If you can get the receiver out of the plane (or if you can get to the
antenna) do a range check with the RX antenna rolled up but with the TX
antenna extended. I'd do this at some _other_ flying site. Check the
range with the suspect TX and with a known good one. If it's
significantly lower with the suspect TX then you can do all the
filtering in the world and it won't help you -- but having the new TX
fixed (or selling it and getting another brand) may help a lot.

When I first had the problem I sent the transmitter back for service -
they didn't find anything wrong, but tuned it anyway and sent it back.
The problem still existed, so I got them to replace the transmitter.
Still the same problem.

At other flying sites the new transmitter actually range checks better
than the old transmitter when checked against multiple different
receivers. For these two reasons I don't think it's that this TX has
a weaker or off-frequency signal.

Lots of other people fly at the same location with a variety of
equipement with no trouble. I've flown a variety of different gliders
there with my old transmitter and never had a problem. I really don't
think there's a conflicting 72 MHz signal.

It really is just this transmitter at this particular site - other
transmitters at the same site are fine, and this transmitter at other
sites is just fine.

Is there any way to make this work?

P. Venkman wrote:

Tim Wescott wrote in message ...

P. Venkman wrote:


SNIP

Is it as simple as finding a filter that passes 72 MHz along and
splicing it in to the wire going to the antenna? Is that likely to
cause other problems (transmitting on the wrong frequency, overheating
the RF module due to impedance mismatch, sudden death)? Assuming I
can't find a filter that passes along precisely the frequency I want,
is it OK to put filters in series (like a high-pass plus a low-pass)?
And finally, am I just totally missing the boat here with this idea?
I'm open to other suggestions.

First, you can really mess things up by playing the filter game, so
don't do it unless you need to.

Second, it may be that the transmitter has a weaker signal, or that it
is a bit off frequency. Since your average military base has about a
gazillion different transmitters it's likely that there is some spur
being generated at 72MHz, or a valid signal at your RX's image
frequency. If your transmitter is a bit weak than such a signal from
the base would have an easy time getting into your RX.

If you can get the receiver out of the plane (or if you can get to the
antenna) do a range check with the RX antenna rolled up but with the TX
antenna extended. I'd do this at some _other_ flying site. Check the
range with the suspect TX and with a known good one. If it's
significantly lower with the suspect TX then you can do all the
filtering in the world and it won't help you -- but having the new TX
fixed (or selling it and getting another brand) may help a lot.


When I first had the problem I sent the transmitter back for service -
they didn't find anything wrong, but tuned it anyway and sent it back.
The problem still existed, so I got them to replace the transmitter.
Still the same problem.

At other flying sites the new transmitter actually range checks better
than the old transmitter when checked against multiple different
receivers. For these two reasons I don't think it's that this TX has
a weaker or off-frequency signal.

Lots of other people fly at the same location with a variety of
equipement with no trouble. I've flown a variety of different gliders
there with my old transmitter and never had a problem. I really don't
think there's a conflicting 72 MHz signal.

It really is just this transmitter at this particular site - other
transmitters at the same site are fine, and this transmitter at other
sites is just fine.

Is there any way to make this work?

Not without more information, which was why I suggested a test.

Did you do the range check against the other transmitters with the TX
antenna collapsed? If so, then you've done a fine test of how well your
TX will work compared to others -- with everyone's antennas are
collapsed. If you normally fly it with the antenna _out_ then you need
to test it that way, and find some other way of attenuating the signal
to the receiver -- like rolling up _it's_ antenna.

You obviously have a problem with that particular TX, which is why I'm
suggesting a look at the TX first. Another question you can ask is does
the TX have the same problem with other receivers? On other
frequencies? Do you have another plane with a different brand receiver,
or a buddy with same, that you can try at the problem site? This may be
a valid thing to try.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Tim Wescott wrote in message ...
P. Venkman wrote:

Tim Wescott wrote in message ...

P. Venkman wrote:


SNIP


Is there any way to make this work?

Not without more information, which was why I suggested a test.

Did you do the range check against the other transmitters with the TX
antenna collapsed? If so, then you've done a fine test of how well your
TX will work compared to others -- with everyone's antennas are
collapsed. If you normally fly it with the antenna _out_ then you need
to test it that way, and find some other way of attenuating the signal
to the receiver -- like rolling up _it's_ antenna.

You obviously have a problem with that particular TX, which is why I'm
suggesting a look at the TX first. Another question you can ask is does
the TX have the same problem with other receivers? On other
frequencies? Do you have another plane with a different brand receiver,
or a buddy with same, that you can try at the problem site? This may be
a valid thing to try.

I've done the range check with the antenna in; under normal
circumstances the range is further than I can see with the antenna
out. I can try rolling up the receiver antenna.

I've tried the transmitter with 5 different receivers (4 different
brands) on 5 different frequencies, all with the exact same problem.

At one point I had two different receivers (different brands) on the
same frequency turned on, and when they glitched they both glitched in
exactly the same way (rudder went hard right on both models, for
example). This isn't proof, but in general you wouldn't expect two
receivers to glitch in exactly the same way if the problem is
interference at the receiver.

P. Venkman wrote:

Tim Wescott wrote in message ...

P. Venkman wrote:


Tim Wescott wrote in message ...


P. Venkman wrote:


SNIP


Is there any way to make this work?

Not without more information, which was why I suggested a test.

Did you do the range check against the other transmitters with the TX
antenna collapsed? If so, then you've done a fine test of how well your
TX will work compared to others -- with everyone's antennas are
collapsed. If you normally fly it with the antenna _out_ then you need
to test it that way, and find some other way of attenuating the signal
to the receiver -- like rolling up _it's_ antenna.

You obviously have a problem with that particular TX, which is why I'm
suggesting a look at the TX first. Another question you can ask is does
the TX have the same problem with other receivers? On other
frequencies? Do you have another plane with a different brand receiver,
or a buddy with same, that you can try at the problem site? This may be
a valid thing to try.


I've done the range check with the antenna in; under normal
circumstances the range is further than I can see with the antenna
out. I can try rolling up the receiver antenna.

I've tried the transmitter with 5 different receivers (4 different
brands) on 5 different frequencies, all with the exact same problem.

At one point I had two different receivers (different brands) on the
same frequency turned on, and when they glitched they both glitched in
exactly the same way (rudder went hard right on both models, for
example). This isn't proof, but in general you wouldn't expect two
receivers to glitch in exactly the same way if the problem is
interference at the receiver.

If two receivers are receiving exactly the same interference at exactly
the same time they may glitch the same way.

Since it's a synthesized module and should be easy to do, have you tried
it on a different frequency (with appropriate RX, of course)? Obviously
something screwy is going on, if it's limited to one frequency you may
be able to just switch to a more benign frequency and have fun.

You could switch to flying control line, but that gets difficult with
gliders.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

P. Venkman wrote:

Tim Wescott wrote in message ...

P. Venkman wrote:


Tim Wescott wrote in message ...


P. Venkman wrote:


SNIP


Is there any way to make this work?

Not without more information, which was why I suggested a test.

Did you do the range check against the other transmitters with the TX
antenna collapsed? If so, then you've done a fine test of how well your
TX will work compared to others -- with everyone's antennas are
collapsed. If you normally fly it with the antenna _out_ then you need
to test it that way, and find some other way of attenuating the signal
to the receiver -- like rolling up _it's_ antenna.

You obviously have a problem with that particular TX, which is why I'm
suggesting a look at the TX first. Another question you can ask is does
the TX have the same problem with other receivers? On other
frequencies? Do you have another plane with a different brand receiver,
or a buddy with same, that you can try at the problem site? This may be
a valid thing to try.


I've done the range check with the antenna in; under normal
circumstances the range is further than I can see with the antenna
out. I can try rolling up the receiver antenna.

I've tried the transmitter with 5 different receivers (4 different
brands) on 5 different frequencies, all with the exact same problem.

At one point I had two different receivers (different brands) on the
same frequency turned on, and when they glitched they both glitched in
exactly the same way (rudder went hard right on both models, for
example). This isn't proof, but in general you wouldn't expect two
receivers to glitch in exactly the same way if the problem is
interference at the receiver.

If two receivers are receiving exactly the same interference at exactly
the same time they may glitch the same way.

Since it's a synthesized module and should be easy to do, have you tried
it on a different frequency (with appropriate RX, of course)? Obviously
something screwy is going on, if it's limited to one frequency you may
be able to just switch to a more benign frequency and have fun.

You could switch to flying control line, but that gets difficult with
gliders.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Tim Wescott wrote in message ...
P. Venkman wrote:

Tim Wescott wrote in message ...

P. Venkman wrote:


SNIP


Is there any way to make this work?

Not without more information, which was why I suggested a test.

Did you do the range check against the other transmitters with the TX
antenna collapsed? If so, then you've done a fine test of how well your
TX will work compared to others -- with everyone's antennas are
collapsed. If you normally fly it with the antenna _out_ then you need
to test it that way, and find some other way of attenuating the signal
to the receiver -- like rolling up _it's_ antenna.

You obviously have a problem with that particular TX, which is why I'm
suggesting a look at the TX first. Another question you can ask is does
the TX have the same problem with other receivers? On other
frequencies? Do you have another plane with a different brand receiver,
or a buddy with same, that you can try at the problem site? This may be
a valid thing to try.

I've done the range check with the antenna in; under normal
circumstances the range is further than I can see with the antenna
out. I can try rolling up the receiver antenna.

I've tried the transmitter with 5 different receivers (4 different
brands) on 5 different frequencies, all with the exact same problem.

At one point I had two different receivers (different brands) on the
same frequency turned on, and when they glitched they both glitched in
exactly the same way (rudder went hard right on both models, for
example). This isn't proof, but in general you wouldn't expect two
receivers to glitch in exactly the same way if the problem is
interference at the receiver.

Lots of other people fly at the same location with a variety of
equipement with no trouble. I've flown a variety of different gliders
there with my old transmitter and never had a problem. I really don't
think there's a conflicting 72 MHz signal.

It really is just this transmitter at this particular site - other
transmitters at the same site are fine, and this transmitter at other
sites is just fine.

Is there any way to make this work?

You didn't say, but if that "military site" is an airport, there's a
localizer beacon that's probably just off the end of the runway and is on 75
MHz. Could readily be strong enough to give your receiver trouble.

W4ZCB

"Harold E. Johnson" wrote in message news:vIbic.12068$IW1.760683@attbi_s52...
Lots of other people fly at the same location with a variety of
equipement with no trouble. I've flown a variety of different gliders
there with my old transmitter and never had a problem. I really don't
think there's a conflicting 72 MHz signal.

It really is just this transmitter at this particular site - other
transmitters at the same site are fine, and this transmitter at other
sites is just fine.

Is there any way to make this work?

You didn't say, but if that "military site" is an airport, there's a
localizer beacon that's probably just off the end of the runway and is on 75
MHz. Could readily be strong enough to give your receiver trouble.

W4ZCB


It's not an airport, but who knows what they have blasting away on any
number of frequencies. I don't have the equipment to check it out.