Cobra 19DX4 pops when going under squelch...
 

Yesterday, someone brought me a radio to install one of my VoiceMax
beta-test units. I fired up the radio before the installation... and
noticed that the speaker made an annoying loud pop sound when the
signal fell under the squelch. This is the second unit I have noticed
this on. Anyone know what is causing this? Sounds like a big DC pulse
when the squelch kicks in. I haven't had time to look at this issue
with a scope. Anybody else experience this? Any fixes?

www.telstar-electronics.com

Cobra 19DX4 pops when going under squelch...
 

On Apr 2, 6:27 am, "Telstar Electronics"
wrote:
Yesterday, someone brought me a radio to install one of my VoiceMax
beta-test units. I fired up the radio before the installation... and
noticed that the speaker made an annoying loud pop sound when the
signal fell under the squelch. This is the second unit I have noticed
this on. Anyone know what is causing this? Sounds like a big DC pulse
when the squelch kicks in. I haven't had time to look at this issue
with a scope. Anybody else experience this? Any fixes?

www.telstar-electronics.com

I've identified the problem. It seems that the squelch transistion on
this model is on the order of 500uS. That is unecessarily fast and
causes a fast spike to the speaker when the receiver dips under the
squelch. I need to slow the squelch response time to eliminate this
problem. This shouldn't be a big deal... but I ran out of time last
night. I will be posting a fix for this issue in a day or so. Shame on
Cobra for allowing this annoying problem to get into production.

www.telstar-electronics.com

Cobra 19DX4 pops when going under squelch...
 

On 3 Apr 2007 04:59:32 -0700, "Telspam Electronics"
wrote in
.com:

On Apr 2, 6:27 am, "Telstar Electronics"
wrote:
Yesterday, someone brought me a radio to install one of my VoiceMax
beta-test units. I fired up the radio before the installation... and
noticed that the speaker made an annoying loud pop sound when the
signal fell under the squelch. This is the second unit I have noticed
this on. Anyone know what is causing this? Sounds like a big DC pulse
when the squelch kicks in. I haven't had time to look at this issue
with a scope. Anybody else experience this? Any fixes?


I've identified the problem. It seems that the squelch transistion on
this model is on the order of 500uS. That is unecessarily fast and
causes a fast spike to the speaker when the receiver dips under the
squelch. I need to slow the squelch response time to eliminate this
problem. This shouldn't be a big deal... but I ran out of time last
night. I will be posting a fix for this issue in a day or so. Shame on
Cobra for allowing this annoying problem to get into production.


Shame on YOU for not seeing the obvious problem. That gating time
isn't abnormal in the least. Instead of chasing insignificant time
constants you should be checking each audio stage (tracing back from
the speaker) for DC offset with squelch on and off, the likely culprit
being a shorted cap between the audio line and the gating signal. You
should have learned THAT much already..... but then again, what should
someone expect from a self-proclaimed "professor" who bought his first
proto-board less than six month ago?


Oh yeah..... where's that schematic, Brian? LOL!!!

Cobra 19DX4 pops when going under squelch...
 

On Apr 3, 6:59 am, "Telstar Electronics"
wrote:
On Apr 2, 6:27 am, "Telstar Electronics"
wrote:

Yesterday, someone brought me a radio to install one of my VoiceMax
beta-test units. I fired up the radio before the installation... and
noticed that the speaker made an annoying loud pop sound when the
signal fell under the squelch. This is the second unit I have noticed
this on. Anyone know what is causing this? Sounds like a big DC pulse
when the squelch kicks in. I haven't had time to look at this issue
with a scope. Anybody else experience this? Any fixes?

www.telstar-electronics.com

I've identified the problem. It seems that the squelch transistion on
this model is on the order of 500uS. That is unecessarily fast and
causes a fast spike to the speaker when the receiver dips under the
squelch. I need to slow the squelch response time to eliminate this
problem. This shouldn't be a big deal... but I ran out of time last
night. I will be posting a fix for this issue in a day or so. Shame on
Cobra for allowing this annoying problem to get into production.

www.telstar-electronics.com

The fix for this problem is to add a 100UF/6.3V capacitor from the
base of QR1 to ground.

www.telstar-electronics.com

Cobra 19DX4 pops when going under squelch...
 

On 4 Apr 2007 04:08:09 -0700, "Telspam Electronics"
wrote in
. com:

On Apr 3, 6:59 am, "Telspam Electronics"
wrote:
On Apr 2, 6:27 am, "Telspam Electronics"
wrote:

Yesterday, someone brought me a radio to install one of my VoiceMax
beta-test units. I fired up the radio before the installation... and
noticed that the speaker made an annoying loud pop sound when the
signal fell under the squelch. This is the second unit I have noticed
this on. Anyone know what is causing this? Sounds like a big DC pulse
when the squelch kicks in. I haven't had time to look at this issue
with a scope. Anybody else experience this? Any fixes?

www.telspam-electronics.com

I've identified the problem. It seems that the squelch transistion on
this model is on the order of 500uS. That is unecessarily fast and
causes a fast spike to the speaker when the receiver dips under the
squelch. I need to slow the squelch response time to eliminate this
problem. This shouldn't be a big deal... but I ran out of time last
night. I will be posting a fix for this issue in a day or so. Shame on
Cobra for allowing this annoying problem to get into production.

www.telspam-electronics.com

The fix for this problem is to add a 100UF/6.3V capacitor from the
base of QR1 to ground.


Gee Brian, it might help to tell what model you are talking about. But
it really doesn't matter since if this QR1 is in the audio line your
added cap will work like a low-pass filter and make the audio "boomy"
(actually, it will be -really- boomy with that big of a cap on the
base of a transistor). If it's part of the squelch gating circuit then
you are going to have 1) a really long time constant on squelch which
may interfere with audio, and 2) the same DC offset problem as before
which may very well cause another fault down the road.

So where's that schematic, Brian?