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Kwhubby
Junior Member
Username: Kwhubby
Post Number: 14
Registered: 12-2004
| | Posted on Thursday, September 29, 2005 - 1:39 am: | 
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Hi, my cobra 148gtl (new make) transmits off frequency and frusterates me that there is no nob to correct this. I am looking for detailed information on how i could adjust the frequency of the transmitter to be on frequency internally. I am also looking for a "clarifier" mod I believe, I want a SEPERATE nob that I can use to adjust the OUTPUT frequency by a few khz. The clarifier mods I see confuse me as it seems like it takes away functionality from an existant nob. I don't want to destroy a current feature of my radio as I use them all. I think this consists of using some kind of variable capasitor but I am clueless. I would also appeciate any information on how to make this radio more stable on frequency and not drift around occasionally if any exist.
Thanks |
Fusebreaker
Intermediate Member
Username: Fusebreaker
Post Number: 217
Registered: 3-2004
| | Posted on Friday, September 30, 2005 - 2:22 pm: |
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if its the new one i think it has the RCI8719 not the MB8719 and i cant swear to this but on the dx-959 RCI8719 wires p5 and p6 control channels but i would look into it before you do it cuz im not 100% sure if it will work on yours. |
Kwhubby
Junior Member
Username: Kwhubby
Post Number: 15
Registered: 12-2004
| | Posted on Monday, October 03, 2005 - 11:34 pm: |
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how would i figure that out? somebody I talked with said that the board number is under the channel selector. I looked under there and it says KEPC-332-E3. The back label says model no: 148GTL D and made in china ( although the front says just plain 148gtl, not dx. It is the one sold here on copperelectronics.com right now). If there is any other numbers that I am looking for please tell me. I just looked and found VR5 says txfreq next to it which i assume tweaks the output frequency. This radio seems to drift from about 27.3845 to 27.3849 at different times. (I tested with a calibrated drake r8 short wave reciever). It seems to make a significant different in frequency when I ground or disconnect ground from the case of the radio. The clarifier mods I assume make the voicelock change output frequency along recieve. I was wondering maby I could just connect a certain pot resistor in paralel to the tx adjust and then retune the tx to be on frequency, then I could go up or down by adjusting this external pot. |
Vanillagorilla
Intermediate Member
Username: Vanillagorilla
Post Number: 250
Registered: 4-2005
| | Posted on Tuesday, October 04, 2005 - 8:25 am: |
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If thats the extent of your "drift" I seriously would not worry about it! A waver from .3845 to .3849 is NOTHING anyone will ever hear. I know its upsetting to see but trust me...it's not serious enough to worry about. Damn those 6 digit counters! 
Now,if you received on .384 but transmitted on .386..THEN you could scratch yer head and think about it. |
Dave1
Member
Username: Dave1
Post Number: 70
Registered: 9-2005
| | Posted on Tuesday, October 04, 2005 - 9:23 am: |
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there is a quick fix for this LOL just buy a Cobra 200 GTL DX and you will be all set because if you like the 148 you will love the 200
Dave |
Hollowpoint445
Advanced Member
Username: Hollowpoint445
Post Number: 794
Registered: 6-2004
| | Posted on Tuesday, October 04, 2005 - 5:39 pm: |
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Vanillagorilla - Apparently you're not a SSB user because frequency drift is a big problem on SSB. 400hz is A LOT of drift! As little 100hz can make enough of a pitch change that you might not be able to understand what someone is saying, and 50hz can be annoying.
The most I've ever seen a Uniden SSB chassis drift from cold to warm is a few hundred hertz, and very little once they're warm.
The radio with the least drift I've ever seen was a Teaberry Stalker IX (Uniden chassis naturally - same chassis as an 8719 Washington) that drifted only 30 hz from cold to warm and it was ROCK SOLID once warm. The clarifier was opened but the range was stock.
Of course a modified clarifier with too much range can drift a great deal and they're also hard to tune well unless a multi turn pot or a fine control pot is added. |
Vanillagorilla
Intermediate Member
Username: Vanillagorilla
Post Number: 251
Registered: 4-2005
| | Posted on Tuesday, October 04, 2005 - 6:31 pm: |
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Well,
I'm not a BIG sideband user but I thought it was a general question....generally meaning AM. Suppose your right about the sideband thing...I don't do enough of it to go further with this discussion...not enough time "IN" to offer an opinion on that end.
My only radio that does not drift that little was the S9. Everything else I have (or had) alway had some sort of drift until fully warmed. Never enough to move the 5th digit though. So far was never told I was off freq once (on AM anyways)I found a happy center.
Perhaps I need to pay more attention for the sake of my fellow sidebanders |
Hollowpoint445
Advanced Member
Username: Hollowpoint445
Post Number: 795
Registered: 6-2004
| | Posted on Tuesday, October 04, 2005 - 7:17 pm: |
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You can be WAY OFF on AM and it doesn't matter. Why do you think Galaxys are so popular among AMers while SSBers don't touch them with a 10 foot pole?
Don't get me started on the frequency counters built into radios. The oscillator in them drifts more than the radio's oscillator does. Depending on them to give you an accurate reading is like predicting the weather with an almanac. |
Vanillagorilla
Intermediate Member
Username: Vanillagorilla
Post Number: 254
Registered: 4-2005
| | Posted on Wednesday, October 05, 2005 - 9:09 am: |
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What then would be an accurate way of seeing ACTUAL freq reading on RX/TX? Is yer "average" external meter that much more accurate or are we splitting hairs here? Not looking to "get you started" here Hollowpoint...just like to know if I could be doing something better for myself.
"Ifsofactso" I won't need to buy anymore radios with freq counters built in...much cheaper 
Sorry this thread got a little off track. Lets see if anyone can answer the original question.
Lemme look through my notes...I'd think there ought to be an adj for TX freq. |
Hollowpoint445
Advanced Member
Username: Hollowpoint445
Post Number: 796
Registered: 6-2004
| | Posted on Wednesday, October 05, 2005 - 2:04 pm: |
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Most people use CB frequency counters as frequency displays, and for that they work just fine. Just don't think that they're dead accurate because they aren't. With resolution of only 1,000 or 100 Hz and a cost of only about $50 they really can't be.
An analogy for their accuracy would be shooting at a slow fire pistol target at a distance of 25 yards. CB frequency counters are only as accurate as a gun that'll hit the target each time, while a decent frequency counter used for radio service work will be as accurate as a gun that'll hit the bull's eye every time.
Why? Because a reasonably stable frequency counter will have either a temperature compensated crystal oscillator and/or a crystal oven, while the CB frequency counter has an oscillator that's not even as good as the oscillator in the radio.
The way I adjust frequency on my CBs is to synchronize them to my HF rig which is synchronized to the WWV frequency. After that I don't worry about their frequency because I know that once they're warm they're going to be in the ballpark and that's about all I can ask of a radio that cost me less than $200. |
Patzerozero
Senior Member
Username: Patzerozero
Post Number: 1604
Registered: 7-2004
| | Posted on Wednesday, October 05, 2005 - 8:29 pm: |
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my $150 XL does use a $50 fc347 to help me find approx location quickly. doesn't really matter who is on what freq, me or the station i'm talking to, just turn clarifier til i understand 'em & all's well |
Kwhubby
Junior Member
Username: Kwhubby
Post Number: 16
Registered: 12-2004
| | Posted on Thursday, October 06, 2005 - 2:03 am: |
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Well thanks for all the response this is interesting. Well Hollow said, that kind of drift is very significant with ssb, specially when certain people use very acurate radios and when lower bandwidth is used. 500hz off frequency makes me simply garble noise to somebody who is on frequency. My reference like I said was a drake r8 short wave reciever (was something like 1000$ new -no its not mine) tuned to wwv so I trust this. It actually has a 7 digit counter on it but I can't remmeber the exact number I took down but I rounded it.
Dave said to get that 200 gtx which would solve my crappy sounding kl200p (class C) amp issue (with its extra power) but would it be more stable? or would its design be similar and drift without a way to adjust. I'd like to get my stuff working before I just upgrade.
Anyways back to the main question, does anybody have any modificatiom information on an output frequency adjustment. I rather it not adjust with the voiclock nob if posible, as then certain issues would be very frusterating trying to tune somebody in without changing myself for them creating this unending loop of tuning. Either way I would like some information and explanation. The cut blah and connect blah although tells me what to do, this type of thing doesn't tell what its going to do or how its going to work unless I do it and see or guess by looking at things. Thanks |
Dave1
Member
Username: Dave1
Post Number: 74
Registered: 9-2005
| | Posted on Thursday, October 06, 2005 - 10:17 am: |
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KW
My Cobra 200 dont drift at all it seems to be a very stable radio it has a 6 diget Freq counter and it dont move unless you move it yourself
dont know if this helps you any but GL with the radio you have ask around to outher owners of the 200 and see what they say I bet they all love the radio
Dave |
Vanillagorilla
Intermediate Member
Username: Vanillagorilla
Post Number: 258
Registered: 4-2005
| | Posted on Thursday, October 06, 2005 - 2:15 pm: |
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Not sure how much this will help as I'm also not sure how similar your radio is to the old one.
Check this out..hope it helps.
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Vanillagorilla
Intermediate Member
Username: Vanillagorilla
Post Number: 260
Registered: 4-2005
| | Posted on Thursday, October 06, 2005 - 7:38 pm: |
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Oops...guess I can't send you to a Mods site?
I'll shoot you a PM |
Patzerozero
Senior Member
Username: Patzerozero
Post Number: 1606
Registered: 7-2004
| | Posted on Friday, October 07, 2005 - 4:51 pm: |
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my point, was, basically, EVERYBODY, or almost EVERYBODY on this forum has an SSB radio that is 100% stable & on freq, except mine & Kwhubby's, i guess, which is close enough for my purposes-and everybody who's heard me. the REST of the CB world uses radios with poor stability and/or are a bit off center slot. yes, there is a point where that becomes annoying because it's TOO FAR off, but a couple hundred Hz or less on a radio that most likely cost less then $300 is the norm. then, take a 'real' CB with a locked clarifier, even LESS then 100 Hz off & those of us with open clarifiers(as well as those with duals) start tuning with the open clarifier, & the next thing you know, everybody is all over the place. & of course as i've said before, there are those (including me) whose ears prefer to listen to a signal that just MAY not be where that stations voice is intended to be-but for ease of copy, that's where we tune.
i THINK what Kwhubby's initial post was saying was, that yes, his NEW 148 IS a bit off freq & his clarifier is still locked, & what he'd like is a dual clarifier, 1 locked & 1 unlocked. like on the exports... |
Kwhubby
Junior Member
Username: Kwhubby
Post Number: 17
Registered: 12-2004
| | Posted on Tuesday, October 11, 2005 - 2:18 am: |
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I think thats exactly what I want patzeroxero, I want something so I can fine tune both RX and TX frequency and seperatly (like any ham radio equipment always has a way to varry tx and rx frequency in smaller then 10khz jumps hehe). If nobody knows on this mod, I have an idea on how to mess with it but testing my "idea" is going to be a pain. |
Patzerozero
Senior Member
Username: Patzerozero
Post Number: 1650
Registered: 7-2004
| | Posted on Tuesday, October 11, 2005 - 7:41 pm: |
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there is a way to make a dual clarifier on these chassis', but i've never done it, nor even looked into how... |
Hollowpoint445
Advanced Member
Username: Hollowpoint445
Post Number: 810
Registered: 6-2004
| | Posted on Tuesday, October 11, 2005 - 8:19 pm: |
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It doesn't exactly work that way with this design. Amateur radios track transmit and receive out of the box. The RIT (Receiver Incremental Tuning) then varies the received frequency.
The 148's design is exactly opposite. If you've ever aligned one of these radios you know that you adjust the frequency of USB, LSB, and then AM - all with different controls and all on RX. After that's been done you adjust a single pot to synchronize the TX.
Yes - that control can be moved to an external pot so you can control TX. But unlike an amateur radio when you adjust the TX it doesn't change the RX. So you don't know if you're synchronized with the the other party in the QSO. You can't get "dead on" with the TX and then adjust the RX to the tone you want because you won't have any way to tell where the TX is in relation to the received signal. That's why the common mod is to unlock the clarifier so it tracks TX on almost exactly the same frequency as RX.
But if you still want to try it, the TX control pot is VR5 according to Sams 249.
Patzerozero - I know that all radios drift from cold to warm unless they have a very sophisticated mechanism to prevent it - and no CB that I know of has a TCXO or crystal oven. So you can include me with you and Kwhubby in having a radio that drifts.
However, I part ways with you about frequency. I KNOW my radios are darn close to frequency when they're warm because I take the time to get them there and I have a very good way of doing it. I believe I've described my method in great detail before, so I'll spare everyone from that here, but it's an excellent method if I do say so myself. |
Patzerozero
Senior Member
Username: Patzerozero
Post Number: 1654
Registered: 7-2004
| | Posted on Wednesday, October 12, 2005 - 3:52 pm: |
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the dual clarifier setup on the 148's involves using a dual pot & putting 1 before the 'open' mod & the other after. it's a bit trickier then that because you need to actually rebuild a 2nd portion of the clarifier circuit...i've never been sufficiently annoyed to even think about it though. especially in the mobile. i suppose if i used it consistently SSB as a base, it would get to me, but...
'on frequency' being a relative term, as you state yourself, hollow, 'darn close to frequency'...and that's not the problem, that's why there's a clarifier, it's the radios that are just a bit farther then where you wanna hear 'em AND those of us with ONLY an open clarifier that start tuning to those that ARE a tad off, & that vicious cycle begins where each person can tune 50 or more Hz til we have 5 guys spread out over a couple of KC's. it's going to be more of a problem on a roundtable-type contact then DX or just a couple guys shooting the breeze. |
Hollowpoint445
Advanced Member
Username: Hollowpoint445
Post Number: 812
Registered: 6-2004
| | Posted on Wednesday, October 12, 2005 - 6:12 pm: |
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I've never heard of that dual clarifier modification - got a link?
About the only way a round table discussion can happen on SSB is with open clarifiers unless they all take the time to accurately adjust their frequency. I don't think I know anyone who primarily uses a CB on 11m SSB that doesn't have an opened clarifier. Of course most of the folks I know who use 11m SSB use an HF rig.
I really haven't ever experienced that kind of problem with open clarifiers. Do you have a hearing loss that prevents you from listening to someone on frequency?
By darn close to frequency I mean within 10 Hz - which is the smallest step my TS450 uses. I zerobeat my TS450 to WWV and then I zero beat my CB to my TS450.
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Patzerozero
Senior Member
Username: Patzerozero
Post Number: 1662
Registered: 7-2004
| | Posted on Friday, October 14, 2005 - 3:28 pm: |
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zero beat/wwv, that is how i tune my 'stuff' as well, the ic735 to my HANDHELD(!) so when i check my 'work' i don't accidentally overload any of MY radios when keying up...maybe not 10kc, but i'm close.
yes as a matter of fact i do have 'measurable' hearing loss to 1 ear & even 'more'(30%+) in the other, & at times i find it easier to copy signals 100-200hz UP. i also know people, who may or may not have the problem, that also seem to tune SSB signals to the 'high' side for ease of copy.
as for the dual clarifier mod, i have NEVER been able to locate it on the web. however, a shop that has long since gone out of business 'copied' an export dual setup into a cobra 148 YEARS ago & it worked fine. if you compare a schematic to a YUK galaxy schematic, i doesn't look all that intimidating, you just have a few extra parts flying in the breeze...i've thought about it once or twice, but never felt it worth the time... |
Hollowpoint445
Advanced Member
Username: Hollowpoint445
Post Number: 816
Registered: 6-2004
| | Posted on Friday, October 14, 2005 - 5:19 pm: |
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I was looking around and found a modification using two different pots, but that modification starts with unlocking the clarifier and just switches pots with a relay - one for transmit and one for receive.
I'm not sure I understand the point of using a handheld. The reason I use the HF rig is because it's very frequency stable, it covers both WWV and CB, and it's multimode so I can sync up USB, LSB, and AM with proper offet. |
Patzerozero
Senior Member
Username: Patzerozero
Post Number: 1684
Registered: 7-2004
| | Posted on Saturday, October 15, 2005 - 6:40 pm: |
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whoops!-'maybe not 10kc, but i'm close'-i meant Hz...
wwv gets my ic735 & my 101e(which has its own builtin 25/100kHz calibrate) dead on, or as close as i can. my handheld zero beats to the icom, so i use the handheld to check & make sure mods are on, on AM at least. using the handheld, if i key up the 'being tuned' radio, i don't worry about any damage, & the handheld has been right next to 100 watts & keeps on tickin'.
as for the clarifier mod, like i said , look at a schematic for a dual/coarse-open radio, & you add the extra circuitry that's before the open part, compare an XL to exports' schematic, or you could probably add the 2nd control before the modded circuit somehow...i've NEVER really even looked into it, though it could be interesting to examine. |
Hollowpoint445
Advanced Member
Username: Hollowpoint445
Post Number: 828
Registered: 6-2004
| | Posted on Saturday, October 15, 2005 - 8:09 pm: |
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I use my HF rig as my reference because I can switch back and forth to the WWV signal to make sure I'm still on frequency. I guess I just consider a 3rd radio an opportunity for more error - especially handhelds which are never very stable in my experience.
I had a friend who used a Cherokee AH-100(?) SSB handheld and that thing constantly drifted during use. It was as bad as an old Galaxy. Of course for AM you can be pretty far off and it'll still work fine.
I don't think I'll ever work out the details of that modification because I prefer to keep my equipment legal. I certainly understand why some folks open clarifiers and I don't personally think it's evil to do so as long as you're using it to match someone else's frequency error and not sliding between channels.
If I were converting a Grant to use on 10 meters I would definitely open the clarifier because that would be the only way I could use it well on SSB. |
Kwhubby
Junior Member
Username: Kwhubby
Post Number: 18
Registered: 12-2004
| | Posted on Tuesday, November 01, 2005 - 6:51 pm: |
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Thanks again for the info everybody. Lately my radio seems to be behaving when there aren’t higher temperatures or hours being on. It took me a while to get back. I think I may have found the mod I am looking for http://www.radiomods.co.nz/cobra148gtlmods.html (doesn't look like a competitor website to me after checking for once) you see the scanned text of the mod for dual clarifiers. I would like to build this IF this is the way to do it for MY version of the 148 as I think I posted earlier. Is it? I also don't know were I am going to get that funny part (dual pot). Anybody know? I could simply use another pot externally to do this but its not as elegant. Does anybody know what the current value of the pot resistor in there is?
I may just do the single open clarifier if I can't do that mod. The mentions from various people about certain mods (like the relay thing and galaxy ideas etc)- I'd like to see actual schematics or instructions if you can link here or in pm.
Thanks again!
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Kid_vicious
Advanced Member
Username: Kid_vicious
Post Number: 771
Registered: 9-2004
| | Posted on Wednesday, November 02, 2005 - 12:36 am: |
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kwhubby,
the mod that you are looking for is in one of the later issues of "secret CB". i dont remember which, but i'll check when i get home and if i have the mod, i'll post it.
the part may be very hard to get these days, but just FYI, the value is 20K for the coarse control and 1K for the fine tune. both are linear taper.
i put a 10 turn pot in mine and i get 17khz of slide and its all fine tuning. i love it!
later,
matt |
Kid_vicious
Advanced Member
Username: Kid_vicious
Post Number: 782
Registered: 9-2004
| | Posted on Friday, November 04, 2005 - 12:02 am: |
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i cant post the whole mod, but it is in Secret CB volume 18, on page 29.
if you cant find a paper copy; you can order the whole set on the auction site for about $10.00
hope this helps,
matt |
