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

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?

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

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

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

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

In article ,
P. Venkman wrote:

| 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.

You haven't actually told us what the problem is.

Is the computer in your transmitter crashing? (interfering with the transmitter)
Are the servos in your plane jittering? (interfering with the receiver)
Are you seeing reduced range or something? (interfering with the receiver)

| 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.

We'll need to know what the actual problem is. Shielding your
transmitter isn't going to do much unless the interference is actually
affecting your transmitter (possible, but unlikely) rather than your
receiver.

| 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.

If the problem is interference to your receiver, doing this at your
transmitter won't help at all. You'd need to do it at the receiver.

Some people have had good luck simply wrapping their receiver (just
the receiver, not the antenna) in tin foil. Twisting the servo and
power wires round and round can also help reduce interference to the
receiver as well, and you can get chokes to wrap your servo wires
around as well.

Very very few people put additional filters on their R/C receivers.

Are there any pager towers nearby? Pager companies use the spaces
between the R/C channels to talk to pagers, and can use hundreds of
watts -- this has definately been known to overload R/C receivers and
crash planes. (In that case, the fix would be to 1) do the tin
foil/choke thing and 2) try a different frequency. (Your transmitter
is synthesized, so all you need is a new receive crystal.)

| However, I'm smart enough to know I'm not that smart.

That's a pretty good sort of smart to be!

| Is it as simple as finding a filter that passes 72 MHz along and
| splicing it in to the wire going to the antenna?

Probably not, unless your problem really is with the transmitter
computer crashing.

Which receiver are you using? The cheap park flier ones don't handle
interference well at all.

Do other people fly at this site? Your radio should be able to talk
to any plane, so try switching frequencies and picking the proper
shift and see if you can do a proper range check with their plane.
(Or another plane if you have more.)

You might also try asking in rec.models.rc.air, though they'll
probably tell you the same things I did.

(And yes, I fly R/C too.)

--
Doug McLaren, Reserve your bear to right arms.