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

Cutting D11 on Realistic TRC-492
 

On Thu, 13 Sep 2007 05:24:23 +0100, " Peter"
wrote:

|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.
|
|-------------------

Actually they don't have loads of bandwidth to play with. In most
cases 15KHz is the highest frequency respone that they can have
without exceeding the peak diviation with Stereo FM. About 10% of the
modulating power is reserved for the 19KHz pilot carrier for stereo
FM. Commercial FM broadcast stations need the bandwidth for
transmitting higher fidelity music. Here in the US they are limited to
75KHz peak deviation. Besides tranmitting stereo music with FM is far
more complex than that of voice with FM.


james

Cutting D11 on Realistic TRC-492
 

"james" wrote...

Actually they don't have loads of bandwidth to play
with. In most cases 15KHz

James,

That is AUDIO bandwidth of the input signal, not the
bandwidth allowed for the transmitted radio signal.
For CB, the audio bandwidth is just 3KHz.

I'll bet you would consider that ratio significant if
it was applied to a pay-rise... and I bet you would find a
way to spend 5-times the income :~)
We are greedy creatures. Give us more and we will manage
to use it, wonder how we ever managed, and demand
another increase.

Here in the US they are limited to 75KHz peak
deviation.

Now we are getting closer... that is much better than the
2KHz deviation now allowed for UK FM CB.

Broadcast station deviation is the same here, 75KHz.
With an audio bandwidth of 15KHz, the total bandwidth
required for a basic mono signal of that quality is around
120KHz.

12 CB channels in each direction just to match the quality
of the mono signal.

The CB channels, and the 10KHz spacing, were set back in
the days of AM. But then we in Europe took this spacing
and decided to put an FM signal in there.
It took some squeezing and some careful balancing tricks,
we even had to reduce the deviation from the original
2.5KHz down to 2KHz.


Regards,
Peter.

Cutting D11 on Realistic TRC-492
 

"TelSpam Electronics" The Griffter Man wrote...
Why Do You Need a Speech Processor for Your CB Radio?

The simple answer is that you don't. You need air, you
need water and you need food... but you will survive
without a speech processor.

The word "need" is used by salesmen to create a feeling of
urgency, so you rush out and buy their product without too
much thought or product comparison.

A speech processor is *useful* for AM and SSB CB, but
you really can take your time and shop around for the
best product for your needs.
Here are just a few alternative products:

Lou Franklin's DSP:
http://www.cbcintl.com/dsp.htm
Bobs CB speech processor - kit, pre-built or boxed:
http://bobscb.com/kits/tr_kits.htm
Spectrum Communications speech processor:
http://www.spectrumcomms.co.uk/cbkits.htm#SP1000
Build your own:
http://www.rason.org/Projects/speech/speech.htm

Maintaining a high modulation level is crucial in providing
the highest possible efficiency from any transmitter

Transmitter efficiency is set by the output biasing, not
the audio levels.

operating on AM, FM, or SSB modes.

Speech compression is NOT suitable for FM CB - there are
only 10KHz between channels.
Compression works on broadcast FM because they do have
the bandwidth - equal to 30 CB channels for one transmission.

If you want broadcast quality FM, you require broadcast
quality bandwidth. This would make the whole Citizens'
Band just one single channel.

You cannot put a Pint in a 1/2 Pint jug. Those who tell you
otherwise are selling something, and really don't care how
they make the sale.

When deciding which product to buy or use, trust is
important. In deciding trust, people may wish to take notice
that the above linked pages make no reference to use
on FM CB.
Do you think they just don't want to sell their product, or
that they are simply not willing to mislead people just to
make a sale?

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.

Except in the case of FM (NBFM) CB, where it makes it
possible to fit your transmission on a single channel.
Increasing average audio on an FM CB transmission increases
the average adjacent channel power. This is then picked up
by people on the next channel, but clipped by those trying
to listen to you on your channel.

clipping distorts the original signal and sounds fuzzy
on the air.

Fuzzy at best, large amounts of clipping cause severe
distortion and difficulty undestanding the person.
This is a common problem when people try to increase
their peak or average deviation on FM CB.

VoiceMax holds your transceiver at 100% modulation
allowing you to punch through heavy channel traffic

This does not apply to FM.
The output amplitude of an FM transmitter is constant,
extra deviation will NOT boost your signal above
the "traffic".

VoiceMax works with your non-amplified dynamic microphone

Another issue with FM CB, is that they use very little audio
power to modulate the transmitter. There is not a UK FM CB
made that does not have all it needs to give far more audio
than required... without additional add-on devices.


Regards,
Peter.