Cutting D11 on Realistic TRC-492
 

Will there be a problem if I cut out the D11 diode to increase modulation?

Cutting D11 on Realistic TRC-492
 

Thanks "Big Joe"! That circuit at cbcintl.com looks just like what I'm
looking for.


"Big Joe" wrote in message
...
Yes, you will screw the radio up. Clipping diodes to increase Modulation
is a thing Hicks, or CB shops do for a fast buck.

Get a real Audio processor,
One is a Audio compressor,

here : http://www.telstar-electronics.com:80/:

and the other is a Audio clipper.

Here : http://www.cbcintl.com/dsp.htm

your choice

Cutting D11 on Realistic TRC-492
 

On Sep 8, 1:54 pm, "Froggie" wrote:
Thanks "Big Joe"! That circuit at cbcintl.com looks just like what I'm
looking for.

If that's the one you want... you can get it cheaper if you buy on
ebay
http://cgi.ebay.com/SAVE-30-SPEECH-P...QQcmdZViewItem

Cutting D11 on Realistic TRC-492
 

On Sep 8, 3:53 pm, "Big Joe" wrote:
I really like both combinations, a little compression to maintain the voice
p-p levels , then a small amount of clipping to cut off the peaks.
Sounds Just right on the other end.

So I guess what you're saying is you like the distortion of clipping?
www.telstar-electronics.com

Cutting D11 on Realistic TRC-492
 

It's actually going to cost me a lot less than that. I already have all the
parts I need hanging around on my workbench.:-)

"Telstar Electronics" wrote in message
ups.com...
On Sep 8, 1:54 pm, "Froggie" wrote:
Thanks "Big Joe"! That circuit at cbcintl.com looks just like what I'm
looking for.

If that's the one you want... you can get it cheaper if you buy on
ebay
http://cgi.ebay.com/SAVE-30-SPEECH-P...QQcmdZViewItem

Cutting D11 on Realistic TRC-492
 

On Sep 8, 4:43 pm, "Froggie" wrote:
It's actually going to cost me a lot less than that. I already have all the
parts I need hanging around on my workbench.:-)

I hope you have better luck than I had with that design. Let us know
if you could stop the squealing.
www.telstar-electronics.com

Cutting D11 on Realistic TRC-492
 

On Sep 8, 8:05 pm, "Big Joe" wrote:
Sure I like the sound of clipping to a small amount.
As you know all Commercial, and Ham FM radios since the begging, has had
a CLIPPER built in followed by a Low pass filter ( Motorola used to call it
a splitter filter ) . This goes to a Deviation adjustment to feed the
modulator. Does a good job at two things. It holds the deviation (
Modulation ) to a fixed point and also clips off some of the Voice P-P
levels to help increase the average voice level.

So it Seems to sound OK to all the other FM radio users.
If I needed a Broadcast Radio quality sound then Sure I would use a
Compressor throughout the system.
Looking at your board it looks like you are using a somewhat fast Audio agc
which is OK and the noise gate is then even more important.

If the modulation system used in a FM radio was used in a AM CB radio (
without using all the audio feedback crappy AGC systems they use now ) the
audio could be adjusted to 100% and then what ever mic was used the radio
would not overmodulate. Doing so it could be too loud with all the
background noise coming up if the mic had too much gain.
So like I said I like a little of both. Similar to adding a Compressor to
a FM transmitter driving it using the mic gain to a little of clipping.

OK... thanks for your response. I'm just kind of surprised you prefer
audio with distortion. I guess everyone has a personal preference for
audio quality.
www.telstar-electronics.com

Cutting D11 on Realistic TRC-492
 

"Big Joe" wrote...
Sure I like the sound of clipping to a small amount.
As you know all Commercial, and Ham FM radios since the begging, has had
a CLIPPER built in followed by a Low pass filter ( Motorola used to call it
a splitter filter ) . This goes to a Deviation adjustment to feed the
modulator. Does a good job at two things. It holds the deviation (
Modulation ) to a fixed point and also clips off some of the Voice P-P
levels to help increase the average voice level.

So it Seems to sound OK to all the other FM radio users.

What you have to remember is that other FM users have much
more bandwidth to play with than CB users. The broadcast
stations have shed-loads of bandwidth to play with.

If you are using AM or SSB CB, I would certainly recommend
speech processing. But I would recommend that you avoid it
with FM CB, the 10KHz between channels is not really enough
for FM.

With a multi-mode set, I would fit one and disable it for
FM mode. I believe that would be better than lowering the
maximum deviation to allow for the increased average.

But, speaking of broadcast stations, do you know the other
trick used to get greater distance on FM broadcast? It
works a treat on FM CB, without the adjacent channel
splatter of other devices.


If I needed a Broadcast Radio quality sound then Sure
I would use a Compressor throughout the system.

Unfortunately, to get broadcast quality FM, you would need
FM broadcast bandwidth. One channel would take up most
of the CB band.

If you want a Pint, you must first get a Pint container.
But you will never get quality while the barman is giving
you the dregs and slops.


If the modulation system used in a FM radio was used in
a AM CB radio ( without using all the audio feedback crappy
AGC systems they use now ) the audio could be adjusted to
100% and then what ever mic was used the radio would not
overmodulate.

AM, FM and SSB each have their good and bad points. One
big problem with FM is that the bandwidth requirement
really doesn't suit the small CB channel spacing.
Here in the UK, we have had FM CB for over 26 years... and
the splatter has been hell. It's still going on now, even after
the government reduced the maximum allowed deviation.

I have just been listening to someone giving me a signal
of just 7 on his channel... and jumping to 6 on each of the
adjacent channels with every sound he makes.
Oh yes, and he sounds crap on the channel he is supposed
to be on. So much of his signal is going outside of the
receiver bandwidth, that the needle bounces about like
a yo-yo and far too much of his audio is lost.


So like I said I like a little of both.

The choice over which of the two systems to use really
comes down to price and either proven long-term reliability
or trust in the name.

Lou's product is reasonably priced and has proved itself
over a long time but, let's face it, it is only a basic circuit
designed to meet the needs of the majority of CB users... cheap
but effective.
Telstar's product may cost a little more and boasts better
quality**, but it is a new product without the years of
tests in the real world.

Even large manufacturers find problems with their design after
batches have gone out. I have spent many hours fixing design
errors so that a batch of products could leave by the deadline.


Similar to adding a Compressor to a FM transmitter driving
it using the mic gain to a little of clipping.

All FM transmitters are NOT born equal. What works on
one FM system may not be suitable on another.
Speech compression is fine for broadcast FM, but not for
CB FM with only 10KHz channel spacing.


Regards,
Peter.

** I have only had Lou's product on the bench. I have never
tested the Telstar product, so cannot comment on whether
it really is worth any extra cost.

Cutting D11 on Realistic TRC-492
 

Why Do You Need a Speech Processor for Your CB Radio?
Two-way radio communication relies on the modulation contained within
the signal. Maintaining a high modulation level is crucial in
providing the highest possible efficiency from any transmitter
operating on AM, FM, or SSB modes. Two-way radios also rely on
microphones that inherently change audio levels delivered to the
transmitter. This causes transmitter modulation to fluctuate greatly
depending on voice level and pitch. The average modulation of a
typical voice signal is only about 40%. This low percentage applied
to
the transmitter, results in less than optimal transmission range.

Other Processors Have a Problem...
Other speech processors use a low-cost "audio clipping" approach to
achieve compression. While this method is economical for the
manufacturer, clipping distorts the original signal and sounds fuzzy
on the air. What these types of audio processors gain in volume, they
lose in voice intelligibility.

VoiceMax is Different...
VoiceMax uses a sophisticated AGC (Automatic Gain Control) circuit
that installs inside your transceiver to hold the audio level
constant, with less than 1% harmonic distortion. No "clipping" type
processor can come close to this low distortion level. Whether you're
whispering or shouting, VoiceMax holds your transceiver at 100%
modulation allowing you to punch through heavy channel traffic
without
sacrificing voice clarity. VoiceMax incorporates a feature not
offered
on other processors. The adjustable noise gate allows the user to
block unwanted ambient background sounds. This feature is especially
helpful in mobile environments where wind and road noise can be an
issue. VoiceMax works with your non-amplified dynamic microphone to
give you tremendous audio punch without all the background noise
associated with power microphones.


www.telstar-electronics.com

Cutting D11 on Realistic TRC-492
 

On Sat, 8 Sep 2007 20:05:04 -0500, "Big Joe" wrote:

|Sure I like the sound of clipping to a small amount.
| As you know all Commercial, and Ham FM radios since the begging, has had
|a CLIPPER built in followed by a Low pass filter ( Motorola used to call it
|a splitter filter ) . This goes to a Deviation adjustment to feed the
|modulator. Does a good job at two things. It holds the deviation (
|Modulation ) to a fixed point and also clips off some of the Voice P-P
|levels to help increase the average voice level.
|
|----------------

It is called a splatter filter. Besides any time you use clipping you
must follow the clipper stage with a low pass filter in order to
restore the clipper o utput to the original bandwidth. Otherwise y ou
have splatter.

There are many techniques to insure the maximum deviation without
exceeding the allowed bandwidth.


|So it Seems to sound OK to all the other FM radio users.
|If I needed a Broadcast Radio quality sound then Sure I would use a
|Compressor throughout the system.
| Looking at your board it looks like you are using a somewhat fast Audio agc
|which is OK and the noise gate is then even more important.
|
|------------

If one wanted broadcast quality sound you would need far more than
10KHz bandwidth. With 10KHz bandwidth your audio response is going to
be in the 2 to 2.5 KHz range. While this is adequate for voice
communication, it is far to poor for music.


james