2340 CLIPPER/LIMITER BOARD MOD

[Sonar]

I've two FS 2340's. .
One has the audio clipper/limiter board totally removed, and the other has the board intact, but bypassed.
I saw this one on eBay (it lasted about a day.)
Can anyone tell me what this device added to the audio limiter board might be.
I've had other 2340's, and saw some mods done to boards which went beyond bypassing them, but never this. I notice (in the photos) what appears to be a resistor that's not attached.
Can this cause the rig to have audio issues? Thanks. 73

 

[Onelasttime]

Why not rebuild the circuit and put it back inline and see. Clipper Limiter's if that is what this is limit audio bandwidth to increase average talk power. SOME KNUCKLE DRAGERs like hifi overly broad audio. Problem is you become a splatter box and make less efficient use of your power. I have never worked on one of these but have been told that in stock trim they have nice loud audio.

 

[nomadradio]

The Sonar's audio power was just barely sufficient to modulate the final. The clipper circuit board was meant to hold the audio to a level that wouldn't overdrive the modulator tube.

The "I want more" crowd will bypass it every time.

73

 

[Sonar]

Why not rebuild the circuit and put it back inline and see. Clipper Limiter's if that is what this is limit audio bandwidth to increase average talk power. SOME KNUCKLE DRAGERs like hifi overly broad audio. Problem is you become a splatter box and make less efficient use of your power. I have never worked on one of these but have been told that in stock trim they have nice loud audio.

I do believe bypassing the limiter creates splatter, but in all honesty I've never received a single complaint.
Unfortunately there's only one way to use an amplified mic or in my case the Demco modulator with this rig, and that's to bypass the limiter.
I use my Demco modulator spearingly (@ 10 o'clock) and not only get excellent audio reports, and no reports of splatter. I understand that doesn't mean it's noy happening.
I do believe in not bypassing limiters and or turning up the audio pot but until one hears how these tube rigs sound with the Demco (especially the 2340) as opposed to a non amplifed hi Z (which is all that can be used without the mod) without the modulator I guess you don't know the difference it makes.
I don't know how much extra punch/audio stays on the frequency I'm transmitting on but it's substantial. These Sonar's only have two small 6bq5's (push pull) as opposed to the single large audio tube that's in say a tram d201/a. I'm fairly positive some of that audio is lost, but some must be staying on the operating frequency. I've heard the FS 2340 stock (unmodified) with an unamplified d104 then the limiter bypassed via an added switch with the Demco, and the same mic. The difference was night and day. For the better of course.
I guess it would've been interesting to check out the splatter with the rig working both ways, but I didn't think of it at the time. I'd still like to know what that device is that's hooked up to the limiter Clipper board. I've never seen anything like that on a sonar FS 2340 and I've seen a lot of those rigs. Thanks for your input. 73

 

[Sonar]

The Sonar's audio power was just barely sufficient to modulate the final. The clipper circuit board was meant to hold the audio to a level that wouldn't overdrive the modulator tube.

The "I want more" crowd will bypass it every time.

73

Nomadd. Over the years, and beginning many years ago, I heard that if it was up to sonar they would have released and sold the fs 2340 without that Clipper limiter board installed.
I heard the FCC wasn't happy with what they saw on their test equipment when sonar submitted the fs2340 prior to it's release for sale to the public. Supposedly that's why not limiter/copper board is in there. Most likely folklore, but I wouldn't know for sure. Maybe you could shead some light on that "tall tale." 73

 

[nomadradio]

These days, if you want to sell a CB radio, the FCC requires that your production design is "certificated". A made-up word that means you have a certificate of compliance. That comes from a private company's test lab. The FCC in turn "certifies" the lab's capability to make the critical performance measurements on your product. Once the FCC receives a favorable report from the lab you hired, you get your certificate to sell the thing.

But in the 60s and 70s, the legal term was "Type Accepted". Not sure what the procedure was for that, but sometime between 1973 and 1974 the FCC tightened the rules for type accepting a CB for legal sale. Until then, there was no rule that required a modulation limiter circuit. Weird, but true. Cobra's model 29 mobile radio was originally sold with no limiter at all. Later-production radios had the limiter circuit's parts strung across the solder side of the circuit board. A look at the Sams volume CB56 shows the limiter circuit drawn in dotted lines. The original design lacked the limiter, and the dotted lines showed the components that were "grafted" onto the circuit to do this. But clearly this rule went into effect after Cobra's vendor had begun to build them under the older, looser rules.

Didn't sound all that good, and the limiter was routinely bypassed on that radio. Later radio designs that included this "feature" from the ground up sounded a LOT better.

I don't have any inside info about the Sonar radios, but the clipper board appeared in the FS3023 model around this time, best I remember. The older FS-23 model did not have it at all.

I think.

But that's the best theory I can come up with.

73

 

[Tallman]

I worked in companies that required FCC and FAA approval, I worked in the FAA side of things and lent a hand quite regularly on the FCC side on documentation.
Certificated means the item has been through the wringer electrically and mechanically. Emissions desired and undesirable are noted and documented. Undesirable emissions must be below certain levels and those levels cannot be waived.
Type Certified means that it is a derivative of an approved "Certified" device that has been through the wringer with only minor differences that do not affect the mechanical construction. If the changes are electrical in nature they must be documented by an outside laboratory and must meet the original specifications.
Mechanical testing includes mechanical vibration and shock testing along with the mechanical sympathetic resonance. It is an interesting process to witness.

 

[nomadradio]

"Airworthiness" and "Spectrum worthiness" are not quite the same thing.

If a CB had to pass the FAA tests to be legal, there would not be a single one on the market.

Fortunately for us, a CB only has to pass electrical tests for stray RF leakage from the various connectors, and purity of the transmit signal. Wattage has to be below the limit, too.

Used to ponder out loud renting a high-speed video camera, strapping a CB to an old-style paint shaker and seeing how many parts would fly off.

Seemed like the ideal "final" test for any CB that will be used in a dump truck.

73

 

[TM86]

"Used to ponder out loud renting a high-speed video camera, strapping a CB to an old-style paint shaker and seeing how many parts would fly off.

Didn't Royce advertise that their radios passed "The paint shaker test"?

 

[Riverman]

Didn't Royce advertise that their radios passed "The paint shaker test"?

 

[Sonar]

It's amazing that the CB Hobby was once so tremendous that a company actually advertised their product on television.
That clip actually brought back memories.
I absolutely recall seeing that advertisement run.
Damn I'm old!

 

[Shadetree Mechanic]

I've two FS 2340's. .
One has the audio clipper/limiter board totally removed, and the other has the board intact, but bypassed.
I saw this one on eBay (it lasted about a day.)
Can anyone tell me what this device added to the audio limiter board might be.
I've had other 2340's, and saw some mods done to boards which went beyond bypassing them, but never this. I notice (in the photos) what appears to be a resistor that's not attached.
Can this cause the rig to have audio issues? Thanks. 73
View attachment 21486 View attachment 21487

Hey Sonar, is the one without the clipper board the one that I bought from you?
This FS-2340 is still my favorite AM rig with the D104 and Contex 500 amp. Still getting good reports as always. I am now using a Cobra 148 as a station monitor to make sure the mic gain is set properly. Just need the skip to come back now.

 

[Number#9]

Hi I see this is an old post. Recently purchased a Sonar 2340 and it only deadkeys about 2 watts and swings to maybe 3 at tops 4 watts. Any insight on how to get a little more output would be great. Also see folks bypassing the limiter board. Is there any information available on how to do this modification? I'm somewhat good with the lower deadkey but would like the radio to modulate a little better than what it does. Thanks

 

[Shadetree Mechanic]

Hi I see this is an old post. Recently purchased a Sonar 2340 and it only deadkeys about 2 watts and swings to maybe 3 at tops 4 watts. Any insight on how to get a little more output would be great. Also see folks bypassing the limiter board. Is there any information available on how to do this modification? I'm somewhat good with the lower deadkey but would like the radio to modulate a little better than what it does. Thanks

I am not quite sure what is involved in bypassing the clipper board, mine was already bypassed when I got it. I assume just take the audio wire off the input and output and connect them together. These were not meant to be big power radios, I might get 10 or 12 watts peak. The tubes in the audio chain could be getting weak. Final transmit tubes could be weak too. Replacing the final tubes requires that they be neutralized, which I don't quite know how to do. Will you be running an amplifier?