Jingling key test and noise

D

Dummy

Guest
There are two VHF (136-174MHz) radios and two UHF (438-470MHz) radios.
For UHF radios, some kind of noise appeared at receiver radio's
speaker when key chain is jingled at the transmitting radio. This
happened even when the microphone was disabled/unplugged from the
transmitting radio. I don't see any way that the noise could be
coupled to the microphone. The noise amplitude (as audible) was much
more lower when antenna was detached. What actually happened there? No
such peculiar phenomena was been observed in VHF radios though. I
suppose it's the interaction between the key chain and RF radiation
field, and caused VCO pulling?
 
It's ESD. The a similar trick can be performed with
a zip-lock bag of coins. just jingle and you'll see
some interesting effects. if you want more info, check out
http://www.emcesd.com/pdf/uesd99-w.pdf

sams

Rich Grise wrote:

On Wed, 03 Nov 2004 04:25:05 +0000, Leon Heller wrote:


"Dummy" <ahkit1021@yahoo.com> wrote in message
news:74bb84c0.0411021808.24369694@posting.google.com...

There are two VHF (136-174MHz) radios and two UHF (438-470MHz) radios.
For UHF radios, some kind of noise appeared at receiver radio's
speaker when key chain is jingled at the transmitting radio. This
happened even when the microphone was disabled/unplugged from the
transmitting radio. I don't see any way that the noise could be
coupled to the microphone. The noise amplitude (as audible) was much
more lower when antenna was detached. What actually happened there? No
such peculiar phenomena was been observed in VHF radios though. I
suppose it's the interaction between the key chain and RF radiation
field, and caused VCO pulling?

Perhaps there is a microphonic capacitor in the Tx. Many ceramic capacitors
are microphonic.


I'd be more likely to think it's actually the keys in the RF field.
I seriously doubt if a microphonic capacitor would act like an acoustic
microphone with the kind of sensitivity that you'd need to pick up
the jingling of keys. If that were the case, you wouldn't be able to
carry on a conversation in the room. And I've seen a very sensitive
UHF receiver that would trigger on jingled keys without even a
transmitter nearby, albeit there were transmitters in the vicinity -
it was USAF tech. school. :)

Cheers!
Rich
Click to expand...
 
Boris Mohar <borism_-void-_@sympatico.ca> wrote in message news:<sdggo0d0e4mk98rf7c6numatufe0la04eg@4ax.com>...
On 2 Nov 2004 18:08:53 -0800, ahkit1021@yahoo.com (Dummy) wrote:

There are two VHF (136-174MHz) radios and two UHF (438-470MHz) radios.
For UHF radios, some kind of noise appeared at receiver radio's
speaker when key chain is jingled at the transmitting radio. This
happened even when the microphone was disabled/unplugged from the
transmitting radio. I don't see any way that the noise could be
coupled to the microphone. The noise amplitude (as audible) was much
more lower when antenna was detached. What actually happened there? No
such peculiar phenomena was been observed in VHF radios though. I
suppose it's the interaction between the key chain and RF radiation
field, and caused VCO pulling?

Vibrating keys causing Doppler modulation in the near field if the Tx
antenna. Are the receivers FM?



Regards,

Boris Mohar

Got Knock? - see:
Viatrack Printed Circuit Designs http://www3.sympatico.ca/borism/
Click to expand...
Well...I just don't understand why it didn't happen at VHF radios.
Maybe it's frequency dependent?
Or perhaps I really should check types of capacitors used in VCO.
Since VHF radios are doing fine, they should be taken as a reference
in the process of finding the root cause on UHF radios. But there are
too many variables. Still do not know which particular area that had
potentially caused the problem.
 
ahkit1021@yahoo.com (Dummy) wrote in message news:<74bb84c0.0411021808.24369694@posting.google.com>...
There are two VHF (136-174MHz) radios and two UHF (438-470MHz) radios.
For UHF radios, some kind of noise appeared at receiver radio's
speaker when key chain is jingled at the transmitting radio. This
happened even when the microphone was disabled/unplugged from the
transmitting radio. I don't see any way that the noise could be
coupled to the microphone. The noise amplitude (as audible) was much
more lower when antenna was detached. What actually happened there? No
such peculiar phenomena was been observed in VHF radios though. I
suppose it's the interaction between the key chain and RF radiation
field, and caused VCO pulling?
Click to expand...
It has nothing to do with the radio being UHF or VHF, and the keys are
not interfering with the RF signal, nor are they generating
significant EMI.

The analog wireless microphones employ varying degrees and quality of
audio compression. The ultrasonics from the keys confuse the circuit /
algorithm. This works for some bells and chimes too.

This is known as the "key test" among wireless microphone
manufacturers.

Frank Raffaeli
http://www.aomwireless.com/
 
On 3 Nov 2004 07:30:10 -0800, Frank Raffaeli wrote:

ahkit1021@yahoo.com (Dummy) wrote in message news:<74bb84c0.0411021808.24369694@posting.google.com>...
There are two VHF (136-174MHz) radios and two UHF (438-470MHz) radios.
For UHF radios, some kind of noise appeared at receiver radio's
speaker when key chain is jingled at the transmitting radio. This
happened even when the microphone was disabled/unplugged from the
transmitting radio. I don't see any way that the noise could be
coupled to the microphone. The noise amplitude (as audible) was much
more lower when antenna was detached. What actually happened there? No
such peculiar phenomena was been observed in VHF radios though. I
suppose it's the interaction between the key chain and RF radiation
field, and caused VCO pulling?

It has nothing to do with the radio being UHF or VHF, and the keys are
not interfering with the RF signal, nor are they generating
significant EMI.

The analog wireless microphones employ varying degrees and quality of
audio compression. The ultrasonics from the keys confuse the circuit /
algorithm. This works for some bells and chimes too.

This is known as the "key test" among wireless microphone
manufacturers.

So why does it happen with the mic unplugged?
Click to expand...

--
Best Regards,
Mike
 
Frank Raffaeli wrote:
ahkit1021@yahoo.com (Dummy) wrote in message news:<74bb84c0.0411021808.24369694@posting.google.com>...

There are two VHF (136-174MHz) radios and two UHF (438-470MHz) radios.
For UHF radios, some kind of noise appeared at receiver radio's
speaker when key chain is jingled at the transmitting radio. This
happened even when the microphone was disabled/unplugged from the
transmitting radio. I don't see any way that the noise could be
coupled to the microphone. The noise amplitude (as audible) was much
more lower when antenna was detached. What actually happened there? No
such peculiar phenomena was been observed in VHF radios though. I
suppose it's the interaction between the key chain and RF radiation
field, and caused VCO pulling?

It has nothing to do with the radio being UHF or VHF, and the keys are
not interfering with the RF signal, nor are they generating
significant EMI.

The analog wireless microphones employ varying degrees and quality of
audio compression. The ultrasonics from the keys confuse the circuit /
algorithm. This works for some bells and chimes too.

This is known as the "key test" among wireless microphone
manufacturers.
Click to expand...
Your explanation does not explain why he saw the effect with the
microphone unplugged.
 
What actually happened there?
Click to expand...
Betcha the radios are microphonic.

Sit one UHF radio on top of the other, disconnect the microphones,
turn the volume up all the way, and enable the transmitter on one.
They will probably howl and sing to each other nicely.

It can be observed with two radios, or when one radio sings to itself.
Speaker vibration - modulates Rx LO VCO - amplified by audio amp -
back to speaker - etc... yuck.

Try tuning one at max volume to a CW carrier. It might not be as
quiet as you think.

UHF radios are more susceptible because the RF frequency is higher.

Less mechanical vibration required to induce the required delta-C
into the Tx VCO circuit. If the VCOs are built on fiberglass FR-4,
it's hard to get them mechanically stable enough.

Higher end radios will usually use a ceramic hybrid VCO to gain
higher performance and better mechanical stability.
 
jswenson@mailcity.com (John Swenson) wrote in message news:<29fdb49a.0411031546.575d790d@posting.google.com>...
What actually happened there?

Betcha the radios are microphonic.

Sit one UHF radio on top of the other, disconnect the microphones,
turn the volume up all the way, and enable the transmitter on one.
They will probably howl and sing to each other nicely.

It can be observed with two radios, or when one radio sings to itself.
Speaker vibration - modulates Rx LO VCO - amplified by audio amp -
back to speaker - etc... yuck.

Try tuning one at max volume to a CW carrier. It might not be as
quiet as you think.

UHF radios are more susceptible because the RF frequency is higher.

Less mechanical vibration required to induce the required delta-C
into the Tx VCO circuit. If the VCOs are built on fiberglass FR-4,
it's hard to get them mechanically stable enough.

Higher end radios will usually use a ceramic hybrid VCO to gain
higher performance and better mechanical stability.
Click to expand...
Another UHF radio with different design did not show any problem as
mentioned.
'Good' UHF radio uses resonator at VCO tank circuit while the 'bad'
one uses large High Q coils. VHF radio uses chip inductor at VCO tank
and all VCO circuits are shielded. Any chance of coil's magnetic field
interaction with shield and RF caused problem? I'm totally bewildered.
It's good if RF is visible to our eyes so that I could see what
actually had happened between the 'good' and 'bad' radio. How do we
make sure the VCO is mechanically stable?
More shielding? I have no idea of any solution since I do not know the
root cause yet.
 
SNIPrf_man_frTHIS@yahoo.com (Frank Raffaeli) wrote in message news:<2c8119eb.0411030730.4e67de19@posting.google.com>...
ahkit1021@yahoo.com (Dummy) wrote in message news:<74bb84c0.0411021808.24369694@posting.google.com>...
There are two VHF (136-174MHz) radios and two UHF (438-470MHz) radios.
For UHF radios, some kind of noise appeared at receiver radio's
speaker when key chain is jingled at the transmitting radio. This
happened even when the microphone was disabled/unplugged from the
transmitting radio. I don't see any way that the noise could be
coupled to the microphone. The noise amplitude (as audible) was much
more lower when antenna was detached. What actually happened there? No
such peculiar phenomena was been observed in VHF radios though. I
suppose it's the interaction between the key chain and RF radiation
field, and caused VCO pulling?

It has nothing to do with the radio being UHF or VHF, and the keys are
not interfering with the RF signal, nor are they generating
significant EMI.

The analog wireless microphones employ varying degrees and quality of
audio compression. The ultrasonics from the keys confuse the circuit /
algorithm. This works for some bells and chimes too.

This is known as the "key test" among wireless microphone
manufacturers.
Click to expand...
We use the "key test" to show that our current wireless microphone
systems don't employ an audio compandor while all others do. However,
I think what is being described here has nothing to do with this,
since the mic is not hooked up. I would guess that the keys are
reflecting/affecting the RF from the transmitter, then the transmitter
case is picking it up, which then affects the transmitted signal.

Karl Winkler
Lectrosonics, Inc.
http://www.lectrosonics.com
 
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