How to Put Talk Back in a Cobra 148
| Author | Message |
     Kevster | I have a Cobra 148 GTL and looking to tune it up a bit and "talkback." I have the links to the modification pages but it doesn't tell a lay-person how to do it. Can anyone help? Thanks! |
| Barakuda318 | Here kevster" see if this will help you, Cobra 148-gtl. General Tune Up: |
| Jyd | r-131 is the one you clip for modulation,it is by the front i think. |
| Kevster | Thanks for the help guys! I even got this thing to do talkback! It works great now! And to think I was going to blow $200 on a 2950, I think I'll stay with the 148GTL for now! 73's!!!! |
| Barakuda318 | Yes that is true but I do not recomend clipping unless you are never goin to run a power mic or echo mic, even then its still not the best idea in my opinion, clipping cause your radio to have spuriouse emittions, witch will cause alot of electrical interference and over modulation, the 148 is plenty loud by just turning up the pot vr5 just crank it to max then back it off a hair, strap on a power mic and let her rip... 73's barakuda318 p.s. of course if you wanna clip thats fine, just thought I would give you my opinion. |
| Taz | Yeah, dont clip it cause it it causes those spurious emmisions cause you might go over 100 percent. anything over 100 percent is distortion and is not needed! it will only give you one thing. problems with your neighbors. |
| Jyd | opinions vary,you can run a power mic when it is cliped,and alot of radios sound better cliped,my vr-9000 is cliped plus i have a speech prossecor and i use a astatic 575-m6 power mic,i get nothing but complements.truck drivers say they here me 45 miles before they reach miami. |
| Sonoma | on the 148 if you use sideband clipping will make it hard for any one to understand you if you use a power mic.am is not near as bad. |
| Barakuda318 | Yeah but check those modulation peaks on a scope, you won't bellieve the negative peaks, all you want is positive peaks going up to or barely past 100 percent if the negative goes up then its totally defeating the purpose, clip all you want but I can honestly tell you that 148 will not need it, just turn up the pot and strap on a power mic, and nothin but crystal clean loud very loud audio. |
| Taz | It might sound better clipped but if you go over 100% your neighbors might have a visit. |
| Denny1820 | Hey Barakuda318. Is it L54 or L45, I can't seem to locate a L54 in mine. Of course a magnifying glass might come in handy. Found all of the others easy. I also assume this will work on a Grant XL. |
| Barakuda318 | I'm sure it is L45 sorry must be a typo, and yes a magnifying glass will help, and yes the grant xl is the same... good luck 73's |
| Denny1820 | Thank's 'Kuda. My 148 has a 1994 board, so I thought maybe there was a difference. Actually, just getting the Mod to just a hair under 100% will help this unit a bunch. Thank's again, 73's |
| Barakuda318 | No problem one of the best radio's ever built in my opinion, especially if it is pre 1999 with uniden board, the newest ones are disposible radio's in my opinion and drift very badly on ssb, good luck with yours i'm sure you will be very happy, I am getting lots more information on the 148 I have one that I am working on right now, I call it project 148 almost a total overhaul except that it turn on transmits and recieves but the channels were added wrong, the extra ones that is, and lots of other hacking, gonna try and get it working properly then add channels and other stuff, if you want more info just email me I have lots of info for the 148 now but not everything that I need so if anyone has the schematic for this radio please email me a copy of it if you don't mind, good luck and happy easter to all 73's |
| Kevster | Barakuda318... Defpom's site shows: VR7 = AMC Is this right? |
| Kevster | Heres what I've found on another site. Seems to be correct:: Cobra 148 GTL Power Tweek and Modulation 1) Change R126 to a 2.2k ohm resister. I do not recommend cutting R131 which limits the modulation. If you "clip" or remove R131, you'll have increased modulation on AM, but severe "garble" on SSB. I recommend getting a good aftermarket powermike. You can also adjust VR7 for a little increase in modulation, but watch it on SSB. Extra Channels Find the MB8719 PLL chip. Wire a SPST switch from pin 10 to ground. Wire another SPST switch from pin 11 to pin 12.( Sorry, I don't have a channel map as of yet.) If you don't want to "Hack" your radio up, you can use the ch9-19 switch and the NB/ANL switch. Just remember to solder jumper wires on the NB/ANL to engage those functions. Unlocking the Clarifier 1) Clip one end of R44 and D52. Let the radio "sit" for about 2 hours, with the clarifier knob set at "12-oclock" to get used to the new modification. This will give you about 6 kz of slide.(1kz up- 5kz down) |
| Barakuda318 | Yes Kevster that is right I don't know what happened to the one I posted up on top they are wrong, or at least the one you asked about and the power ssb power is vr7 and modulation is vr5 both of these pots run modulation but vr5 is for am and vr7 is for the ssb modulation hence power cause that is what ssb power is, MODULATION! lol, good luck |
| Sparkomatic | I have a Texas Ranger 296 which is the same radio as a 148. Does anyone have any experience with Expander 100 kits...........some like them some don't, I would welcome everyone's spin on this. |
| Sparkomatic | Cut R131 OR remove TR24 (Modulation limiter) Replace R126 with a 4.7K Ohm resistor Replace R124 with a 2.2K Ohm resistor VR10 adjusts AM carrier Cutting out the limiter opens up the SSB also Cutting the limiter out does NOT cause distortion or garble on SSB I know a lot of CBers that have the Cobra 148 and if it is tuned properly a power mic will be COMPLETELY unnecessary..........maybe a noise canceling mike would be OK. |
| Weakeststation | Ya say you want talk back ey..... use a 100ohm (or higher... you can play with it for quality) connect to speaker jack tip---to ground.. wham talk back |
| Bronzepony New member Username: Bronzepony Post Number: 4Registered: 12-2005 | ARE THESE MODS THE SAME FOR THE 148F MADE IN MALAYSIA |
| Patzerozero Senior Member Username: Patzerozero Post Number: 2057Registered: 7-2004  | the xmit & rcv mods work on all the different chips, for the most part. it's the freq expansion that doesn't work on 8734 chip & SOME of the freq expansion doesn't work on MMB8719. MB8719 & RCI8719 should do all the tricks. which chip is in the radios made after 96 or 97 seems to be a case of what was available the day they made a particular radio. have seen real cobra 148fgtl with BOTH 8719 & 8734(not DX) in 'em.... |
How to Put Talk Back in a Cobra 148
Source: http://www.copperelectronics.com/discus4/messages/3847/15635.html?1134764052