IMPROVING RECEIVE PERFORMANCE FOR SUPER DXING

[unit_399]

Sometimes reading a really ridiculous thread can give you a good idea.

One of the posts on the MAULDULATOR Thread suggested using a Hi-Fi Stereo receivier to recover the "broadcast quality" sound from the MUJULATER (thanks, FATTY).

Anyway, this got me to thinking... would connecting a good stereo receiver to my CB improve the receive ?? God knows that the receive audio of a CB radio is anything but hifi, so I decided to give it a try. I tapped into the receive detector output of my TRC-457 and connected it to the AUX input on an old Sansui Stereo (circa 1980) that I had sitting around. It worked OK, but the stereo loaded down the detector output too much. So... I built a copy of the record (line out) circuit used in the Cobra 1000/2000 models and wired it into my 457. (I posted a copy of the circuit in my photo album.) This worked great. Then I connected an old 7 channel graphic equalizer into tape monitors 1 and 2 on the stereo.

WOW !!! The results were outstanding ! With the first two and last two sliders on the EQ set at the full cut position, the noise below 300 Hz and above 3 Khz was down by 24 db !! Stations that were in the "mud" were now loud and clear. The Sansui has hi-pass and lo-pass filters and LO-MID-HI tone controls. Using the MID control; I found that I could "tune in" on specific stations. It was so cool to be able to flip switches or spin dials and pull in stations that I would never have been able to hear before.

You have to hear it to believe it. A block diagram of my station is also in my photo album. Check it out and give it a try. You won't be sorry.

- 399

 

[Moleculo]

That's pretty inventive! It sounds like you've wired in a basic version of what expensive HF rigs do with pass band filtering, except you've done it at the AF stage. I can see how that could work pretty well as accentuating certain audio frequencies helps add to intelligibility of the signal. Well done! I certainly have never thought of trying something like that

 

[15minigrass]

With that in mind, could I just run a stereo jack from my EXT. Speaker on the radio to the Receiver and run it that way? I know Audio feedback will interfere w/it. If I had a Cobra 2000, where wouild I tap in to to run something like yours?

Aloha, Jim....

 

[Robb]

Just a thought...
All you would really need to do is to use a 'DI box'; or 'direct injection box' to get the same effect. Take the speaker out of the radio you want to use and then run it into the DI box. Then, out of the DI box in to the amp/equalizer.

DI boxes are relatively cheap and can be found used. Or can be built - but I don't know where a schematic for one can be found. It is easier to just buy one; I could be wrong. I don't know what they want for the DI boxes these days...

 

[MisterFatty]

Great Idea, MuJu folks could probably use that Seriously, A cool idea which probably yields some nice results!

 

[W5LZ]

So far, nothing has changed with your receiver's performance. You have made changes in the processing of the receiver's audio output, which is not the same thing at all. Basically an audio equalizer, or a much glorified 'tone' control.
As for where the idea came from, that 'MAULDULATOR/MUJULATER' thread, I'm sorry to say that it 'fits'. An unnecessary device used to make another unnecessary device usable, in an unnecessarily complicated fashion, for the simple reason of 'being different', since the 'normal'/usual means of doing the same thing has been around for a very long time and is cheaper anyway.
- 'Doc

 

[BOOTY MONSTER]

i use my sennheiser 555 headphones on my washington sometimes . it has a 1/4 jack on the front that when the headphone plug is fully inserted engauges both left and right channels . anyhow , they do make a positive difference with weak signals and allows me to talk with folks i cant make out with the built in or my regular external speakers . as w5lz said its not changing the performance of the radio , its just simply higher fidelity audio equipment allowing things/details to be herd that lower fidelity equipment cant ....... allong with the signal processing your recievers tone controlls and filters allow . you can get the same effect on a weak AM music radio station . but take too much high frequency static out and it can sound muffled . like a blanket is over the speaker .

but if it helps you hear folks you normaly cant so you can make that contact with them , go for it .

 

[Captain Kilowatt]

Congratulations, you have just demonstrated why trying to transmit wideband audio for two way communications is a bad idea. Sure it sounds good if the signals are very strong and no fading but for normal comms forget it.

 

[unit_399]

15MINIGRASS -

The Cobra 2000 has a record out jack on the rear panel. The circuit I posted is the one that is used in the 2000

- 399

 

[unit_399]

So far, nothing has changed with your receiver's performance. You have made changes in the processing of the receiver's audio output, which is not the same thing at all. Basically an audio equalizer, or a much glorified 'tone' control.
- 'Doc

Doc -
I like to think of the hookup as a glorified noise limiter. By using the Equalizer to remove the noise content from the signal, it is much easier to hear and discern the audio content. Especially weak stations' signals.

As far as the MAULDULATOR is concerned, I think that device is a joke.

- 399

 

[Carl]

your better off just using a better full range speaker and using your eq in between the mic element and the radio.