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Great Mic Sound for your CB or Export Radio-part 1

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  #25  
Old 10-31-2010, 06:22 AM
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Quote:
Originally Posted by Robb View Post

The newest crop of export radios soon to be released in the US will have USB. It won't be too long before we will be able to use our computers to TX and RX using software that will give us digital audio enhancements, as well as even being able to use - dare I say it - some digital modes of communications into the CB realm as well.

Digital modes have been on 11 meters for some time now. SSTV, PSK31, RTTY, Pactor have all been observed on 11 meters. More popular overseas than US it seems.

And you can already hook a CB or Export to your computer and use the sound card to tweak audio in/out. You certainly don't need USB on the rig for that, just speaker and mic connections. Not that that isn't cool, but the only functionality is probably just programming the memories / maybe some settings on the rig. Now true rig control would be neat, but I doubt that's what we're getting.
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  #26  
Old 10-31-2010, 06:44 AM
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I think that most any CB or Export that is properly tuned with a good mic sounds great on the air. Mine do. I have no problem with people tweaking their audio to sound good, but the super wide stuff I think is really inconsiderate.
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  #27  
Old 10-31-2010, 06:49 AM
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One thing that has been overlooked in this quest for broadcast quality audio is that all the efforts are pointless if the receiving end cannot accept the wider transmitted bandwidth.Most ham radios and likely most CB radios do not have the required IF bandwidth to take advantage of the wider signals and in some cases make the really wide stations sound worse due to added distortion by the receiver than if they were transmitting normal audio.

The guys on The AM Forum - Index run wide bandwidth AM and sound GREAT if you can actually hear everything being sent. They usually employ boatanchor receivers that have wide bandwidths up to 16KHz. SIXTEEN kilohertz!!

My Kenwood receiver has filters for 2.7, 6 and 12 KHz and there is a world of difference in listening to a station on the 12 KHz setting than from even the 6 KHz setting and as for 2.7 KHz, well that isn't even in the picture.
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  #28  
Old 10-31-2010, 08:59 AM
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Quote:
Originally Posted by jazzsinger View Post
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HIFI audio may well be legal,but it is very inconsiderate towards other users of a mode that was designed to reduce bandwidth and noise.

What does it achieve anyway ? why does audio need to be any better than clear ? out of all the people you talk to how many will have the receive audio bandwidth to even benefit from your wide audio ? outwith the less than 1% who can benefit of the rest their narrow filters will hack most of it away so in 99% of contacts you just wasted a heap of money installing "hifi audio".

Jazzsinger -

Very well stated. As I said in my first post on this thread, the object of CB or amatuer radio is to communicate and to do this by transmitting a signal that is loud and CLEAR.

- 399

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  #29  
Old 11-03-2010, 05:42 PM
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Receive audio bandwidth is just as important as transmit audio. It is useless to have one without the other. But bringing modulation down to 100% and still having great audio is possible. I'm sure those who run radios with an NPC mod might find it confining; or use it to their advantage if set up right.

Is great audio all that important for communications? If it can be cheaper than ever possible, if there is interest, and if it is in grasp of anyone to use - then yes. Some would rather own and drive a Model T Ford; others a 2011 Ford Mustang. One is simple and classic and the other well thought out and still changing for the better.

I know the UK/European radio is different than US in using digital modes. The US might be using it already to some degree on 11m; but I have seldom heard or seen it - despite the fact that it can be done.

Staying in the realm of CB's is where this is going. The points were made to point out these changes come slowly to CB. But TX audio quality is improving and is apparently growing.

I'm sure that this info doesn't surprise or amuse those who have been in the radio hobby for any real length of time. However, for those beginners and even intermediate CB operators that have wondered the 'hows and whys' of hifi TX audio; this is for them...
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  #30  
Old 11-08-2010, 09:44 PM
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I've been running Hi-Fi AM on several bands for over 15 years. The microphone is a cheap electret. The EQ couldn't get any simpler. All you really need to do is notch out some lower mid range around 500 cycles to remove that muddy sound when heavily modulated. I just use a 700 ohm relay coil as the inductor and a .1 mfd cap to make a series resonate notch filter.

In my mind supplying the transmitter with quality audio is the easy part. Getting it to pass the response is another issue. Most people know about increasing the size of coupling caps and emitter bypass caps. They tend to get confused once they hit the modulator IC. Looking at the data sheet for the IC can help. They often have circuit examples showing how to configure the IC for flat response rather then communications audio.

All most all of these chips are configured with an external hi frequency negative feedback loop that kills everything over 3.5 KHz. That needs to be modified to get any hi end out of the transmitter. These chips also use external caps to bypass the emitters of internal transistors. The caps are often too low in value to reproduce bass through the chip.

Many people will tell you that you need to be listening on a wide band receiver to hear Hi-Fi. This is true to a point. Even a cheap receiver with 6 KHz bandwidth can detect the improvement in bass and treble response from a Hi-Fi transmitter. The average CB uses a ceramic 6 KHz IF filter on AM. At the edges of that bandwidth you are only down 3 db and those ceramic filters are far from brick wall filtering.

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  #31  
Old 11-08-2010, 10:09 PM
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I also wanted to comment about those who think Hi-Fi on 11 meters creates an interference problem as a result of wider bandwidth. Hogwash! This is the least of your problems in terms of wide band signals on this band. With 10 KHz channel spacing it's not going to be the Hi-Fi guy giving you bleedover.

Those that run Hi-Fi are concerned with quality transmission and almost never drive their audio into RF cutoff. It's the guy with the 16 pill and clipped AMC with a power mic that causes the real bleedover issues on this band. It's more complex on 75 meter AM. To those who are offended there, I invite you to move away from the AM window and stop complaining like the so called net on 3872.

I do have some sympathy for those who complain about Hi-Fi SSB on 80 meters. SSB was never intended to reproduce Hi-Fi do to it's restricted bandwidth. While it does improve sound quality, SSB receivers have much narrower and sharper filtering. Making much of the effort wasted unless the receiver has a wide filter. At least with AM the wideband operation is mostly confined within a 20 KHz slice of spectrum on 75 meters.

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  #32  
Old 11-09-2010, 01:32 AM
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Well said!!!
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