President Jackson Uniden TX noise...

[Giulia]

Hi ,
i have a problem with a president jackson cb ,
in tx there is about 100hz noise (i tx with car battery no PSU),
the noise there is even if carrier is unmodulted (fm and am mode)....
Can someone halp me ?
Schemtics are aviable and i can use an oscilloscope.........

Giulia

 

[Guest]

are you related to marqueer?

Hi ,
i have a problem with a president jackson cb ,
in tx there is about 100hz noise (i tx with car battery no PSU),
the noise there is even if carrier is unmodulted (fm and am mode)....
Can someone halp me ?
Schemtics are aviable and i can use an oscilloscope.........

Giulia

 

[Telstar Electronics]

Hi ,
i have a problem with a president jackson cb ,
in tx there is about 100hz noise (i tx with car battery no PSU),
the noise there is even if carrier is unmodulted (fm and am mode)....
Can someone halp me ?
Schemtics are aviable and i can use an oscilloscope.........

Giulia

Sounds like audio oscillation. What mic are you using? What happens if
you key the transmitter with no mic? Problem still there?

www.telstar-electronics.com

 

[Giulia]

Telstar Electronics ha scritto:

Sounds like audio oscillation. What mic are you using? What happens if
you key the transmitter with no mic? Problem still there?

i put an612 pin to ground ......so mic is cutted out .....or carrier
oscillator or power control loop from tx power transistors.......

Giulia

 

[an_old_friend]

are you related to marqueer?"Giulia" <[email protected]> wrote in message

Dloyd cyber terroist

 

[Frank Gilliland]

Telspam Electronics ha scritto:

i put an612 pin to ground ......so mic is cutted out .....or carrier
oscillator or power control loop from tx power transistors.......

Giulia

Ignore Brian (Telspam) -- he'll tell you that your ground plane needs
to be nine square feet.

Refer to your schematic and use your scope to trace the oscillation
backwards through the audio chain starting at the audio power amp.
You'll find the problem stage eventually. Don't forget to carefully
inspect the board for bad solder joints and loose pads.

 

[Telstar Electronics]

Telstar Electronics ha scritto:



i put an612 pin to ground ......so mic is cutted out .....or carrier
oscillator or power control loop from tx power transistors.......

Giulia

OK... you have pin2 grounded for no input signal. Now use your scope
and trace backward from the RF output collector... moving back through
the audio chain... noting the origin of the 100Hz oscillation.
Normally those radios have only a single transistor buffer for the
mic... followed by a high power op amp (usually mounted to chassis
wrapper) for the audio. Your signal tracing should take long at all.
Hope that helps.

www.telstar-electronics.com

 

[james]

+++Hi ,
+++i have a problem with a president jackson cb ,
+++in tx there is about 100hz noise (i tx with car battery no PSU),
+++the noise there is even if carrier is unmodulted (fm and am mode)....
+++Can someone halp me ?
+++Schemtics are aviable and i can use an oscilloscope.........
+++
+++Giulia

*************

100Hz?????

That is a subaudible frequency.
How could anyone detect it without a scope?

james

 

[jakdedert]

*************

100Hz?????

That is a subaudible frequency.
How could anyone detect it without a scope?

james

Huh??

 

[Radiosrfun]

*************

100Hz?????

That is a subaudible frequency.
How could anyone detect it without a scope?

james

The range of "normal" human hearing is 20-20,000 Hz. How is 100 Hz
"subaudible"?

 

[Telstar Electronics]

100Hz?????

That is a subaudible frequency.
How could anyone detect it without a scope?

james

If you can't hear 100Hz... you need to get your ears checked Jim.

www.telstar-electronics.com

 

[james]

+++> 100Hz?????
+++> That is a subaudible frequency.
+++> How could anyone detect it without a scope?
+++>
+++> james
+++
+++If you can't hear 100Hz... you need to get your ears checked Jim.
+++
+++www.telstar-electronics.com
+++

**********
Obvisously you lack the knowledge of what is the subtle difference
between audible and audio frequency. Also I did forget that CB radios
are not necessarily well designed radios. In a well designed radio,
any audio frequency below 300Hz is considered subaudible.

Why? Because the power density in the human voice below 300Hz is
negligible. Most well designed receivers for communications purposes
do not have audio response below 300 Hz. Also human hearing threshold
increases as the frequency decreases below 300Hz. That is the source
of the audio freq uency needs to have a larger PSL in order for it to
be heard. Sensitivity to audio frequency in Humans is not flat like
that of speakers and some sound systems. Instead SPL, Sound Pressure
Level, needs to increase as frequency decreases below 300Hz to gain
the recognition. For most Humans the power of a 20Hz signal needs to
be about 30dB higher than that of 100Hz.


james

 

[james]

++++++> On Thu, 05 Apr 2007 19:57:47 +0200, Giulia
+++>
+++>>+++Hi ,
+++>>+++i have a problem with a president jackson cb ,
+++>>+++in tx there is about 100hz noise (i tx with car battery no PSU),
+++>>+++the noise there is even if carrier is unmodulted (fm and am mode)....
+++>>+++Can someone halp me ?
+++>>+++Schemtics are aviable and i can use an oscilloscope.........
+++>>+++
+++>>+++Giulia
+++> *************
+++>
+++> 100Hz?????
+++>
+++> That is a subaudible frequency.
+++> How could anyone detect it without a scope?
+++>
+++> james
+++
+++The range of "normal" human hearing is 20-20,000 Hz. How is 100 Hz
+++"subaudible"?
+++

****************

That maybe true but the Human ear does not perceive sounds with a flat
response for that frequency range. Instead as frequency goes very low
and also very high the power density for a given frequency may have to
increase or decrease. The human ear does not have a flat range of
sensitivity.

Also in communications the Human voice has very little power below
300Hz. Therefore most communications equiptment considered below 300
Hz as subaudible. A well designed receiver for voice communications
should reject frequencies below 300Hz. In fact they should also reject
frequencies above about 3KHz also.

The range of 300 to 3000 Hz is where the ear is most sensitive to
frequencies. Also the Human voice contains most of its power between
this range.

james

 

[Giulia]

OK... you have pin2 grounded for no input signal. Now use your scope
and trace backward from the RF output collector... moving back through
the audio chain... noting the origin of the 100Hz oscillation.
Normally those radios have only a single transistor buffer for the
mic... followed by a high power op amp (usually mounted to chassis
wrapper) for the audio. Your signal tracing should take long at all.
Hope that helps.

Changing in VR5 (some related to modulation) remove the noise ,
i put vr5 more near ground.

Noise seems generated from somewhere feedback at hight swr....
regulation of vr5 remove noise but what kind of effect can it have on
modulation (in am all semms right RF evelope in the scope and audio
received from another cb)?

Giulia

 

[Radiosrfun]

Changing in VR5 (some related to modulation) remove the noise ,
i put vr5 more near ground.

Noise seems generated from somewhere feedback at hight swr....
regulation of vr5 remove noise but what kind of effect can it have on
modulation (in am all semms right RF evelope in the scope and audio
received from another cb)?

Giulia

RF feedback into the microphone? If you feel it is due to high SWR - why not
check and reduce it? Try your tests again. What kind of mic are you using?
If you mentioned it, I didn't see it. I've seen D104s do that. On 2 meters -
I've seen RF get into the power source and do all kinds of weird things to
the signal.

Check your SWR then - go from there. IF it IS high, even if the mic/audio
issue isn't cured, at least another problem will be - and save you from yet
a future one.

Are you using an "Amplifier" with this set up?

 

[Radiosrfun]

RF feedback into the microphone? If you feel it is due to high SWR - why
not check and reduce it? Try your tests again. What kind of mic are you
using? If you mentioned it, I didn't see it. I've seen D104s do that. On 2
meters - I've seen RF get into the power source and do all kinds of weird
things to the signal.

Check your SWR then - go from there. IF it IS high, even if the mic/audio
issue isn't cured, at least another problem will be - and save you from
yet a future one.

Are you using an "Amplifier" with this set up?

I "believe" you said you're running the radio off a car battery. Is it
"Actually" mobile or in the house? If in the house, are you running a
trickle charger in the process? IF the modulation was cranked up all the
way, were you running anything in the background maybe the mic picked up?
Many items can cause a hum - you won't hear - that the mic will pick up. If
it is mobile, any chance something in the vehicle is causing it? With the
modulation cranked up - maybe it was enough to allow "that" to be heard.
I've also seen a transmitter make some weird sounds on key - up - with a
weaker battery. The antenna SWR as you alluded to - the antenna not
grounded - could also create issues along those limes. I've seen lots of
weird things happen to cause noises such as you describe - not always
internal. Recheck your Antenna coax connections too.

 

[jakdedert]

****************

That maybe true but the Human ear does not perceive sounds with a flat
response for that frequency range. Instead as frequency goes very low
and also very high the power density for a given frequency may have to
increase or decrease. The human ear does not have a flat range of
sensitivity.

Also in communications the Human voice has very little power below
300Hz. Therefore most communications equiptment considered below 300
Hz as subaudible. A well designed receiver for voice communications
should reject frequencies below 300Hz. In fact they should also reject
frequencies above about 3KHz also.

The range of 300 to 3000 Hz is where the ear is most sensitive to
frequencies. Also the Human voice contains most of its power between
this range.

james

You're backpedaling.

What you clearly said was that it could not be detected without a scope.
Then you come up with a bunch of gobbledeegook about 'well designed
receivers'. That's not the point, and that's not what you said.

Suffice to say that you were simply wrong. 100 Hz is clearly audible.
It doesn't take a scope to detect. A pair of common ears is all that's
necessary. Whether it should be heard in a CB receiver is debatable,
but if it's there, there's no reason why one shouldn't be able to hear it.

jak

 

[David Brodbeck]

You're backpedaling.

What you clearly said was that it could not be detected without a scope.
Then you come up with a bunch of gobbledeegook about 'well designed
receivers'. That's not the point, and that's not what you said.

Suffice to say that you were simply wrong. 100 Hz is clearly audible.
It doesn't take a scope to detect. A pair of common ears is all that's
necessary. Whether it should be heard in a CB receiver is debatable,
but if it's there, there's no reason why one shouldn't be able to hear it.

To be fair, "subaudible tone" is a fairly common euphemism for CTCSS or
"PL" tones. As you point out, though, they're only "subaudible" because
they get filtered out before the final audio stages.

 

[Frank Gilliland]

**********
Obvisously you lack the knowledge of what is the subtle difference
between audible and audio frequency. Also I did forget that CB radios
are not necessarily well designed radios. In a well designed radio,
any audio frequency below 300Hz is considered subaudible.

Why? Because the power density in the human voice below 300Hz is
negligible.

Hogwash. The .3-3kHz limits were standardized (by the military)
because researchers discovered, over half a century ago, that the
bandwidth carried the majority of -intelligibility- in the human
voice. IOW, by limiting the frequency range of the vocal spectrum,
transmitted speech can be understood using much less power than when
transmitting using the full voice bandwidth.

Most well designed receivers for communications purposes
do not have audio response below 300 Hz.

Hmmm..... my Onkyo is a well-designed receiver for communications
purposes and it is flat down to 2 Hz.....

Also human hearing threshold
increases as the frequency decreases below 300Hz.

Huh? When was the last time you looked at a weighted equalization
curve?

That is the source
of the audio freq uency needs to have a larger PSL in order for it to
be heard. Sensitivity to audio frequency in Humans is not flat like
that of speakers and some sound systems. Instead SPL, Sound Pressure
Level, needs to increase as frequency decreases below 300Hz to gain
the recognition. For most Humans the power of a 20Hz signal needs to
be about 30dB higher than that of 100Hz.

That depends on how much you bump up the boom on those 24" JBLs inside
your sub-compact riceburner. The sad thing is that when those kids go
deaf they will collect welfare for their self-inflicted disability.

 

[james]

+++james wrote:
+++> On Fri, 6 Apr 2007 20:10:23 -0400, "Radiosrfun"
+++>
+++>> ++++++>> +++> On Thu, 05 Apr 2007 19:57:47 +0200, Giulia
+++>> +++>
+++>> +++>>+++Hi ,
+++>> +++>>+++i have a problem with a president jackson cb ,
+++>> +++>>+++in tx there is about 100hz noise (i tx with car battery no PSU),
+++>> +++>>+++the noise there is even if carrier is unmodulted (fm and am mode)....
+++>> +++>>+++Can someone halp me ?
+++>> +++>>+++Schemtics are aviable and i can use an oscilloscope.........
+++>> +++>>+++
+++>> +++>>+++Giulia
+++>> +++> *************
+++>> +++>
+++>> +++> 100Hz?????
+++>> +++>
+++>> +++> That is a subaudible frequency.
+++>> +++> How could anyone detect it without a scope?
+++>> +++>
+++>> +++> james
+++>> +++
+++>> +++The range of "normal" human hearing is 20-20,000 Hz. How is 100 Hz
+++>> +++"subaudible"?
+++>> +++
+++> ****************
+++>
+++> That maybe true but the Human ear does not perceive sounds with a flat
+++> response for that frequency range. Instead as frequency goes very low
+++> and also very high the power density for a given frequency may have to
+++> increase or decrease. The human ear does not have a flat range of
+++> sensitivity.
+++>
+++> Also in communications the Human voice has very little power below
+++> 300Hz. Therefore most communications equiptment considered below 300
+++> Hz as subaudible. A well designed receiver for voice communications
+++> should reject frequencies below 300Hz. In fact they should also reject
+++> frequencies above about 3KHz also.
+++>
+++> The range of 300 to 3000 Hz is where the ear is most sensitive to
+++> frequencies. Also the Human voice contains most of its power between
+++> this range.
+++>
+++> james
+++>
+++>
+++>
+++You're backpedaling.
+++
+++What you clearly said was that it could not be detected without a scope.
+++ Then you come up with a bunch of gobbledeegook about 'well designed
+++receivers'. That's not the point, and that's not what you said.
+++
+++Suffice to say that you were simply wrong. 100 Hz is clearly audible.
+++It doesn't take a scope to detect. A pair of common ears is all that's
+++necessary. Whether it should be heard in a CB receiver is debatable,
+++but if it's there, there's no reason why one shouldn't be able to hear it.
+++
+++jak

**************

I stated how could one detect it without a scope? please reread my
post and comprehend better.


100 Hz is hearable or percieved. As I stated before there is a subtle
difference bwetween audible and hearable. Yes you can "hear" 100Hz if
increase the signal power compared to a 1000Hz tone. But at equal
power desity, a 100 Hz tone by most people is not "hearable" or
audible. The same goes for the higher end of the audio spectrum.
Granted some have better sensitivity to a wider spectrum of audiio
frequencies.

Besides this tangent has gone far beyond the scope of the original
post and realy was not my intention. My intention was to discuss the
detection of the offending signal with and without a scope. Not to
discuss what is audible to your ear or the frequency response of your
hearing.

thank you

james