Swing kit / cap resitor mod?

[805 california]

Does anyone know if after doing the swing mod in a cobra 29 ltd that it changes your transmit frequency? I am under the impression that it does but it doesn't seem like the swing kit is in the transmit frequency stage. Anybody have any words of enlightenment?

 

[222DBFL]

Shouldn't change the transmit frequency. All it's for a to lower the AM carrier as far as I know. Unless some has messed with the 54mhz trap. Just some food for thought.

 

[Tallman]

Does anyone know if after doing the swing mod in a cobra 29 ltd that it changes your transmit frequency? I am under the impression that it does but it doesn't seem like the swing kit is in the transmit frequency stage. Anybody have any words of enlightenment?

It should not affect your frequency. Unless you got into the PLL circuits.

 

[543_Dallas]

No change to frequency with that mod. Even if the tvi trap that 222 mentioned has been tampered with it will not put the radio off frequency.

 

[805 california]

Excellent thanks for the info!

 

[Onelasttime]

You should have a high power and low power pot in the radio. Set it to deadkey 2 watts rms swinging to 8 and get your modulation to 98% and call it a day! Set the swing to peak at 4x the carrier. You can exceed that a bit on mosfet final radio's and still sound good. The power output was just an example not an absolute the 4:1 rule still holds true. Just know that reduced carry high swing modulation mod's seldom win in the end. They do well in a very narrow spectrum of use and seldom do so in a clean fashion. I am not against them just think they are over used and seldom properly applied in field use.

 

[9C1Driver]

Most 40 channel AM only cb sets do not have the AM Power pot like you described, now AM/FM Export radio's or SSB cb sets do have this.

 

[222DBFL]

Also I don't see a mention of it but I am sure it's known. Use a 50 ohm dummy load and not your antenna for performing these mods and testing of the radio. Like I said, I am sure this is known, but just in case it was missed somehow. Hope it all works out for you.

 

[Robb]

If the radio is off center freq; then you tuned the wrong coil. If you are starting out aligning radios, it is best to take your time and be certain of which coils are to be tuned in each step.

Time to hook up your freq counter. IIRC, think the test point is R61 and L24 adjusts it and are located in the left/rear of the chassis in front of the driver . . .

 

[sonoma]

after reading your 1st post do you have a freq counter to check for proper freq on transmit?

 

[wavrider]

I do not like the "swing kit" in a 29, I install 2 more diodes on the Center tap of the transformer this lowers the dead key and allows great forward swing, and is clean on the scope,
most swing kits just make the radio owners happy looking at the watt meter, then again the band is saturated with shit sounding splatter boxes any wayYMMV

 

[222DBFL]

100 watts, a good antenna system, and proper filtering is all that is truly needed.
If you are trying to get on channel 6, then by all means have at it. Just don't move too close to me.

 

[wavrider]

I doubt if you are off frequency, probably over modulated to the point you can not be understood.

Undo the mod check the radio stock. see if it is indeed off freq, from your posts it seems you have limited test equipment so when all else fails, undo the mod and make sure the radio is still good.

 

[805 california]

I doubt if you are off frequency, probably over modulated to the point you can not be understood.

Undo the mod check the radio stock. see if it is indeed off freq, from your posts it seems you have limited test equipment so when all else fails, undo the mod and make sure the radio is still good.

Yeah I have limited test equitment. I only have two fluke 1910 and 1911 frequency counters, a tektronix 465 scope, a hp 8640b signal generator, a VU meter, a fluke true rms multimeter and a Bird 43p watt meter.

 

[wavrider]

Then if you know how to use them should have been able to troubleshoot and repair the problem your having.

Swing kit has nothing to do with PLL circuit UNLESS YOU have installed something incorrect and are loading down the voltage on the whole circuit board.

As said before , undo the mod, see if you still have the problem.

With all that TEST equipment you have you should be able to diagnose your problems.

http://www.cbtricks.com/radios/cobra/29ltd_29ltd_st_29wx_st/index.htm

There ya go, factory service manual, schematics, alignment procedures,

NOW put all that equipment you have to use,