Cobra 148GTL (Twn) diy Tune-up (newbie)?

[Roachman]

First Post. Thank you for your time!

Would anyone be able to post a step-by-step, basic, rundown of the correct order of procedure and potentiometer-adjusting for a d.i.y. Peak/Tune/Frequency-Check to a 148GTL (Taiwan)? Including the SSB settings.

I seem to have located "bits and pieces", VR#-this and LR#-that, from numerous sites but can't seem to find a simple, start-to-finish, basic Tune-Up/Freq-Check for someone wanting to get a little more pro-active with their radios. I'm just not fully comfortable about piecing the procedure together. Would greatly appreciate a low-tech, step-by-step if possible. I realize w/o a tone-generator and other instruments, I may not be able to do all I wish, but I have to start somewhere.

Background: I have a 148 that I use as a base-station with a few years TXing experience, but upon recently having it peak/tuned by someone new (hate having to change) would like to check/learn the procedure myself. I was game for a change, so I requested it to be tuned for "distance etc." (this particular radio will be used for SSB only). But upon mulling over the 6-watt dead-key and whatnot, I'm just not sure about the whole experience/new cb-shop-guy-adjustments and think this may be the time to start learning how to tune-up my radios to my own preferences. It may be set-up perfect as is, but I'd like to learn myself if possible. I believe a few snips etc. have been done (it works), but I don't want to do any soldering/jumping.

For simplicities sake, I cannot spend "any money" and "only have the use of" :
1) basic SWR/WATT/MOD meter (again, let's just assume/accept it is accurate)
2) ParaD PDC356 Frequency counter (ditto)
3) 19amp power supply
4) homemade dipole antenna (we'll save that for diff post)
5) SWR 1.2-1.3
6) non-conductive screwerdriver

What parts of the requested procedure can I do, and how might I do them?
Thank you kindly for taking your time to read/respond and I hope I used the proper protocol...apart from being a bit long-winded of course. Thanks again!

 

[Roachman]

Oops. I have posted a few other times (unrelated topics). Just noticed that. Duh. Ok, so not First Post. My bad.

 

[Dipole]

You really need a Dummy load so your not transmitting a signal while your adjusting. I like to set the AM dead key less than 3 watts and 100 % modulation with the mic gain at full open. SSB transmit power is all modulation there should be no carrier present any thing more than 100% is self defeating.

 

[Roachman]

You really need a Dummy load so your not transmitting a signal while your adjusting. I like to set the AM dead key less than 3 watts and 100 % modulation with the mic gain at full open. SSB transmit power is all modulation there should be no carrier present any thing more than 100% is self defeating.

Thank you. I forgot to mention the 6-watt dead was not on the SSB. That is at zero. My bad again!

 

[sonoma]

here is a link to the factory service manual from cbtricks. self explainatory as it is.

http://www.cbtricks.com/radios/cobra/148gtl/index.htm

 

[9C1Driver]

There really is no short cut or basic way to properly tune a radio when you don't have the proper equipment and know how. If the radio works the most I would do is adjust the AM dead key, SSB peak power, and modulation to what you want or need. There is a reason that good cb techs are very busy. There is also a reason why so many radio's are jacked up, too many golden screwdriver wanna be techs tweeking the wrong VR pots.

If you do want to give it a shot click on the link that sonoma posted, the alignment procedure is in the factory service manual section pages 48-63. You will have to go step by step in prder for a correct alignment. After you read through this you can see why a good tech gets 45-55 dollars for a full alignment.

 

[Tallman]

There really is no short cut or basic way to properly tune a radio when you don't have the proper equipment and know how.

If you don't have equipment and training don't do it. That's a quick way to trash your radio.

 

[unit_399]

Since this is your first attempt to align a radio, I suggest that you first use your counter to verify that the rig is on frequency. If it is on freq, then leave the VCO and Carrier Oscillator adjustments alone. These are the easiest to screw up (especially for a first-timer). Then review the entire procedure to make sure you understand everything, and have all of the equipment necessary before proceeding. For instance, you didn't mention having a digital voltmeter which is needed to set the driver/final bias. Once you feel comfortable with the procedure, go for it.
Good luck and 73s.

- 399

 

[Roachman]

If the radio works the most I would do is adjust the AM dead key, SSB peak power, and modulation to what you want or need.

Thank you. It (tech manual) certainly looks more complex than the 15 minute quickie-tune-ups from 3 diff cb shops I've utilized for previous peak/tunes/radios (which is all I wanted to do myself). Is there a specific order that I need to do what you recommended and/or just crossreference the pots from a schematic and start turning while transmitting ("audio...aah...whistle" etc.)? You wouldn't happen to know/confirm the order and exactly which pots to adjust on the older 148 for the power and modulation adjustments (am/san)? I don't want to screw up what I don't know so b/c it is on-freq (+/- .0004) I am just going to focus on adjusting deadkey/power/mod. I'd like to adjust that .0004 down but probably dont have the equip. Lastly, any suggestions on best SSB "dx" settings for deadkey/swing are welcome. Thanks again to all repliers!

 

[Roachman]

Since this is your first attempt to align a radio, I suggest that you first use your counter to verify that the rig is on frequency. If it is on freq, then leave the VCO and Carrier Oscillator adjustments alone. These are the easiest to screw up (especially for a first-timer). Then review the entire procedure to make sure you understand everything, and have all of the equipment necessary before proceeding. For instance, you didn't mention having a digital voltmeter which is needed to set the driver/final bias. Once you feel comfortable with the procedure, go for it.
Good luck and 73s.

- 399[/QUOTE

 

[Roachman]

Thank you for the kind words of encouragement. I believe I may have set my sights higher than my equip/knowledge can muster. But I am eager to start somewhere...doing at least some of it on my own w/o a PhD in Electronics or an $800 Birdmeter, lol. Thanks again Unit_399

 

[sonoma]

the service manual has every item in order to tune the radio. shows what items to adjust if you have the right equipment hooked up to each section as it calls for to use. unit 399 told you what to leave alone if you do not have the knowledge and equipment to do the adjustments. you do not have to have a bird watt meter to tune with. a good peak reading meter will let you set the out put of the radio.

 

[Dipole]

Everybody has a Smart phone these days go to the Market and get a free App( https://play.google.com/store/apps/details?id=de.guentherkrauss.audio.audiotesttonegenerator) for a Tone generator and use that to adj the dead key. That whistlein AUUUUDIOOO BS is what you get from a TS cb hack Golden screwdriver shop is inaccurate. as is Transmitting Spurious emissions while Whistelin in the wind looking for your AUUUDIIII OOOOOO. To Properly tune a Radio you need a Dummy Load.

 

[Roachman]

Everybody has a Smart phone these days go to the Market and get a free App( https://play.google.com/store/apps/details?id=de.guentherkrauss.audio.audiotesttonegenerator) for a Tone generator and use that to adj the dead key. That whistlein AUUUUDIOOO BS is what you get from a TS cb hack Golden screwdriver shop is inaccurate. as is Transmitting Spurious emissions while Whistelin in the wind looking for your AUUUDIIII OOOOOO. To Properly tune a Radio you need a Dummy Load.

Everybody has a Smart phone these days go to the Market and get a free App( https://play.google.com/store/apps/details?id=de.guentherkrauss.audio.audiotesttonegenerator) for a Tone generator and use that to adj the dead key. That whistlein AUUUUDIOOO BS is what you get from a TS cb hack Golden screwdriver shop is inaccurate. as is Transmitting Spurious emissions while Whistelin in the wind looking for your AUUUDIIII OOOOOO. To Properly tune a Radio you need a Dummy Load.

Saint and a gentleman. Thank you kindly Dipole!

 

[Robb]

Peaking a radio is not done by twiddling the variable resistors. It is done by using a nylon tuning tool on the TX cans in USB mode with a dummy load and a steady hand with a decent watt meter. For AM, the AM Modulation variable resistor is tweaked with a O'scope and a watt meter. Unless you have a MOSFET final in that radio, 6w is too much to set the dead key at for AM . . .