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Fusebreaker
Intermediate Member
Username: Fusebreaker
Post Number: 205
Registered: 3-2004
| | Posted on Saturday, September 24, 2005 - 12:36 am: | 
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no one seems to know how to do the 5kc switch mod on the cobra 148gtl any one know how? |
Yankee
Advanced Member
Username: Yankee
Post Number: 930
Registered: 7-2003
| | Posted on Saturday, September 24, 2005 - 12:37 pm: |
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As some of you know, my Grant XL has it working with the CB/PA switch and 2 wires to the PC board. It was done on many 148s, 2000s, and Grant LT/XLs,was being done by a gent in his 50s who retired from the Air Force after 26 years a radio repair man. He passed on close to 3 years ago now, and I think he took the 5 KHz. mod with him.
In and around the Oklahoma City area there are many of these radios with the mod, but many of the people are hanging onto those radios. |
Fusebreaker
Intermediate Member
Username: Fusebreaker
Post Number: 206
Registered: 3-2004
| | Posted on Saturday, September 24, 2005 - 6:46 pm: |
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Yankee im bound and determind to find it its gotta be out here somewhere im sure and it looks like a very nice mod. |
Fusebreaker
Intermediate Member
Username: Fusebreaker
Post Number: 207
Registered: 3-2004
| | Posted on Saturday, September 24, 2005 - 6:55 pm: |
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It gives me the idea that maybe its the 10kc down switch mod principle with a resistor or something going to ground or maybe something in the clarifier circut i have no idea but im not going to give up on it.Its not that i need the mod its that my compititive personality wont let me quit tell i find it and i will be botherd until i do LOL |
Kid_vicious
Advanced Member
Username: Kid_vicious
Post Number: 691
Registered: 9-2004
| | Posted on Saturday, September 24, 2005 - 8:57 pm: |
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i found it in a secret cb book.
vol. 18 i think.
the reason this mod is not more popular is because it involves switching a crystal, and they are harder to come by these days.
you build a circuit to switch between the 11.3258 crystal and another freq. which gives a 5kc drop.
i would like to have this mod but crystal switching in these radios is very tricky.
matt |
Fusebreaker
Intermediate Member
Username: Fusebreaker
Post Number: 209
Registered: 3-2004
| | Posted on Saturday, September 24, 2005 - 10:38 pm: |
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basicly i just need the crystal value i can do the rest thx kid |
Kid_vicious
Advanced Member
Username: Kid_vicious
Post Number: 693
Registered: 9-2004
| | Posted on Sunday, September 25, 2005 - 1:04 am: |
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the mod i have is for the 142gtl/washington chassis
using the 11.1125 crystal.
the new crystal value for the 5khz drop is 11.1108.
so in the 148/2000gtl chassis with the 11.3258 crystal the new value would be 11.3241.
the mod is not that simple though.
first you have to make sure you get the right load capacitance when ordering your new crystal, if not, you wont be able to tune it in.
also, you cant just switch the crystals mechanically. you have to use some form of electronic switching like diodes or transistors.
the circuit shown in the secret CB book uses diodes, and each crystal has its own trimmer cap.
there is also a mini 10 turn pot behind the clarifier for tuning center slot.
you should really take a look at the mod before trying it, just for referrence.
i got the whole set of secret CB books and the 7 tune up manuals on the auction site for 10.00
on CD. its a great deal. i have most of them on paper which is nice, but the CD is nice to have for using the computer.
hope this helps,
matt |
Yankee
Advanced Member
Username: Yankee
Post Number: 932
Registered: 7-2003
| | Posted on Sunday, September 25, 2005 - 1:26 am: |
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I was thinking it's in the control crystal circuit myself.
I've traced the circuit where the 5 KHz. wires connect to the PC board and from the looks of things nothing has been added or subtacted.
Although, I could have missed even the smallest change in the circuit, and a resistor or cap. is being bridged with the switch.
Matt, what does secret CB say about it?
Allen, The radio still has the factory original crystal in the circuit, I was thinking that the crystal had been changed to get the 5 KHz. drop, so one of the times I had the radio open to play with the clarifier range I checked the crystal, the frequency is printed on the crystal and it is factory.
Matt, From what you have said, I think that the frequency of the crystal is somehow being dropped 5 KHz. When I flip the switch the counter reads dead on zero frequency, and the circuit has only the one stock control crystal. |
Yankee
Advanced Member
Username: Yankee
Post Number: 933
Registered: 7-2003
| | Posted on Sunday, September 25, 2005 - 9:24 am: |
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Another thought: The Redco model 400 or the UFO Digi-Scan, if you can find one operates the radio in steps of 5 KHz.
Digi-Scan is just another term for VFO. Don't confuse the Redco RDS-1 with the 400 or UFO.
The RDS-1 only works with certain PLL circuits and only operates in steps of 10 KHz. And controls the in circuit PLL chip and the 40 channel selector is no longer functional. The RDS-1 tunes the full 200 channels of the in circuit PLL chip.
And the 400 or UFO is programable with dip switches in the unit, has it's own PLL circuit and doesn't use the in circuit PLL chip.
I have only used the RDS-1, so I don't know the operating range of the 400 or UFO. |
Fusebreaker
Intermediate Member
Username: Fusebreaker
Post Number: 211
Registered: 3-2004
| | Posted on Sunday, September 25, 2005 - 11:20 pm: |
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ok thanks guys |
Fusebreaker
Intermediate Member
Username: Fusebreaker
Post Number: 212
Registered: 3-2004
| | Posted on Monday, September 26, 2005 - 6:36 am: |
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i think a superslide clarifier mod and a ten turn pot would be a lot easy`r to do now that i looked into it |
Hollowpoint445
Advanced Member
Username: Hollowpoint445
Post Number: 768
Registered: 6-2004
| | Posted on Monday, September 26, 2005 - 7:09 am: |
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Yankee - It sounds like your 5k switch is changing the capacitance of the oscillator circuit just like the clarifier does but with a switch that directly adds capacitance rather than a pot that varies the voltage to the varactor diode (which changes capacitance with voltage).
Interesting modification - does it go up and down or just one direction? Is coax used from the board to the switch? |
Yankee
Advanced Member
Username: Yankee
Post Number: 935
Registered: 7-2003
| | Posted on Monday, September 26, 2005 - 9:21 am: |
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It drops down 5 KHz. and it's wired with just a short piece of twin wire,(two non-shielded wires in a clear plastic caseing), the likes of wiring in some computers. |
Yankee
Advanced Member
Username: Yankee
Post Number: 936
Registered: 7-2003
| | Posted on Monday, September 26, 2005 - 10:59 am: |
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Think I've posted something along this line before.
Seems to me that this 5 KHz. mod would be common place in other countries that have channeling on the zero frequency. In order to use radios made for the United States, people in those countries have to be dropping 5 KHz. to operate on their channels.
And BTW: England for one has 80 legal channels, but only AM or FM and I believe it's 1-40 AM and the upper 40 FM, with all channels on zero frequency.
I don't think sideband CB, as we know it here in the United States, is legal in many countries. |
Fusebreaker
Intermediate Member
Username: Fusebreaker
Post Number: 213
Registered: 3-2004
| | Posted on Monday, September 26, 2005 - 4:22 pm: |
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you are correct yankee SSB is not legal in europe or most country`s i guess we are just specail LOL |
Yankee
Advanced Member
Username: Yankee
Post Number: 937
Registered: 7-2003
| | Posted on Monday, September 26, 2005 - 11:44 pm: |
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Sorry: I made a mistake on England, CB radio in England is FM only. And it's Sweden and New Zealand that operate on the zero frequency.
I did a search and found the world CB frequency allocation chart.
Sweden's CB band is- 26.910.0-27.410.0
New Zealand's CB band is- 26.330.0-26.770.0.
Although after reading the world chart I have found that several countries allow AM, FM and sideband.
Australia even has a 70 centimeter CB band, FM only, 476.425.0-477.400.0.
The countries that do allow SSB other than the United States are, Brazil, Argentia, Canada, Germany, (France, allows AM,FM but only upper sideband), Ireland, Spain, (Portugal offers FM without being licensed, but for AM and sideband a license is required in Portugal).
South Africa , Switzerland, New Zealand, Australia, and Namibia are the remainder of countries that allow sideband legally. |
Kid_vicious
Advanced Member
Username: Kid_vicious
Post Number: 704
Registered: 9-2004
| | Posted on Monday, September 26, 2005 - 11:46 pm: |
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i agree with hollowpoint, unless there is a crystal wired right to the back of the switch. (probably wouldnt work too well)
if his switch is switching in some capacitance then i would guess there has to be a trimmer cap added somewhere. i cant believe someone found the exact ammount by trial and error.
the secret cb mod is just a crystal switch; just like the one you would build to switch in another 40 channel band.
if we can find out how yankee's is done, that's the mod im doing to mine.
so what do you say yankee?
ready to take that radio apart so we can do an autopsy?
just kidding! (it's my nature)
we know how much you love that radio. |
Fusebreaker
Intermediate Member
Username: Fusebreaker
Post Number: 214
Registered: 3-2004
| | Posted on Tuesday, September 27, 2005 - 1:05 am: |
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where could i get a crytal switch with the trimmers and such already on it? |
Yankee
Advanced Member
Username: Yankee
Post Number: 938
Registered: 7-2003
| | Posted on Tuesday, September 27, 2005 - 10:16 am: |
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I Know nothing has been added to the circuit, but I will one day when my hands are not as stiff as they are right now, take the radio apart and investigate the 5 KHz. mod.
The other evening I was told by my friends on 37 LSB, that the Cobra 138 XLR has louder transmit audio than the Grant XL.
Both radios are well engineered, but there's just something about the uPD-858 PLL chassis having louder audio. I'm using the same microphones on both radios.
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Yankee
Advanced Member
Username: Yankee
Post Number: 939
Registered: 7-2003
| | Posted on Wednesday, September 28, 2005 - 3:13 am: |
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Hollowpoint has much pinned down the mod., it is in the control crystal circuit and ties in with the variactor diode, (R188 has been removed, but I'm not sure if R188 has anything to do with the mod.)
Sorry: I missed one addition, a three red color band resistor has been added to a point close to where R188 was removed and the other wire from the switch ties in next to where D-52 was removed.
This is about all I can see, and I figure that a voltage is being lowered to the variactor diode thru the resistor that has been added.
I'll stop here and let someone that knows a lot about these circuit designs figure out the mod.
I've done the best I know how to trace the 5 KHz. mod. Hope this is of some help. |
Kid_vicious
Advanced Member
Username: Kid_vicious
Post Number: 709
Registered: 9-2004
| | Posted on Wednesday, September 28, 2005 - 4:48 pm: |
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thats it yankee!
its got a resistor(2.2K) in in series with the varactor that lowers the voltage and in turn, the capacitance.
im just surprised that a standard value resistor was the exact right ammount of voltage drop for 5khz drop.
i'll have to try this with my spare 148gtl.
matt |
Fusebreaker
Intermediate Member
Username: Fusebreaker
Post Number: 215
Registered: 3-2004
| | Posted on Wednesday, September 28, 2005 - 6:55 pm: |
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HEHE i am wanting to try it now |
Yankee
Advanced Member
Username: Yankee
Post Number: 942
Registered: 7-2003
| | Posted on Wednesday, September 28, 2005 - 8:40 pm: |
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None the less, it works and works best with the standard PLUS or MINUS 7 KHz. unlocked clarifier.
At one time my clarifier range was minus 14 KHz. and plus 8 KHz. and not the easyest to keep on frequency after the radio has sat powered up. Now with PLUS or MINUS 7 KHz. the frequency is stable.
With the PLUS or MINUS 10 KHz. mod. all that's needed is the 7 KHz. clarifier range. It's either R-144 or R-147 being put back in circuit, that regulates the 7 KHz. clarifier range, can't remember which resistor I put back in circuit without taking the radio apart again. Anyway Matt, you have the clarifier mod. info.
Have fun and keep me posted on your 5 KHz.progress. |
Fusebreaker
Intermediate Member
Username: Fusebreaker
Post Number: 216
Registered: 3-2004
| | Posted on Friday, September 30, 2005 - 1:59 am: |
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hum? now im wondering if you put the right resistor in the varacter if you could drop the hole radio down one band just wondering. |
Yankee
Advanced Member
Username: Yankee
Post Number: 944
Registered: 7-2003
| | Posted on Friday, September 30, 2005 - 2:27 pm: |
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Allen: To drop a whole band, you would have to add a second control crystal and I believe retune the VCO circuit, although the Expo crystal kit, model L for the 2000,148 GTL and Grant LT/XL and like radios, uses three crystals. Low band, regular 1-40, and high band, and also works well with the PLL pin switching method for extra channels. I have never used an Expo kit, I only know what they can do, and how they work. |
Fusebreaker
Intermediate Member
Username: Fusebreaker
Post Number: 218
Registered: 3-2004
| | Posted on Friday, September 30, 2005 - 10:48 pm: |
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I had one in a cobra 29 and it worked fine but i did not use them much some people claim the channels never line up right but mine did |
Patzerozero
Senior Member
Username: Patzerozero
Post Number: 1567
Registered: 7-2004
| | Posted on Saturday, October 01, 2005 - 4:37 pm: |
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they didn't line up right because they hooked it to the wrong leg of the can, left out the diode when needed or just plain didn't adjust the coils correctly. only had 1 that ever that wouldn't work right, removed & replaced with another & it was fine... |
Fusebreaker
Intermediate Member
Username: Fusebreaker
Post Number: 222
Registered: 3-2004
| | Posted on Sunday, October 02, 2005 - 2:13 am: |
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well i think they are not doing something right for sure cuz those work great when set up right |
