LCL-2740 CB Converted
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LCL-2740 CB Converted
Hi all...just bought above cb radio and it was sold as converted to 10 metre Fm
its what i wanted ...i see its had a couple crystal changes and realignment....but has no repeater shift...that i can see...i need to have a 100khz shift for repeater use...
has anyone any info on doing this mod to Cb....
many thanks
paul
its what i wanted ...i see its had a couple crystal changes and realignment....but has no repeater shift...that i can see...i need to have a 100khz shift for repeater use...
has anyone any info on doing this mod to Cb....
many thanks
paul
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Re: LCL-2740 CB Converted
What xtal has been fitted?
Also the hi/lo power switch used to be used to add the repeater shift on tx
So you may have an 18.660MHz xtal for the conversion to 29MHz
and it may also have an 18.560MHz xtal for the repeater offset on tx
Also the hi/lo power switch used to be used to add the repeater shift on tx
So you may have an 18.660MHz xtal for the conversion to 29MHz
and it may also have an 18.560MHz xtal for the repeater offset on tx
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Re: LCL-2740 CB Converted
Hi guys
thanks for your quick reply's...
i will see what freq crystals are fitted and get back to you....also read through the links to posts sent.....this is the best forum for information..
thanks all
paul
thanks for your quick reply's...
i will see what freq crystals are fitted and get back to you....also read through the links to posts sent.....this is the best forum for information..
thanks all
paul
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Re: LCL-2740 CB Converted
We're always glad to help out on here.
Saying that, I know bugger all about this kind of stuff so I can't include myself in the above statement
Saying that, I know bugger all about this kind of stuff so I can't include myself in the above statement
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Re: LCL-2740 CB Converted
Hi guys sorry for delay....my eyes are not brill but the 2 crystals are 16.32400 12.12990 mhz does this help?
ive tested the rx and it seems very sensitive...ch30 shows 29.600 mhz and seems to go 10khz steps up down from there....there does however seem to be no repeater shift....which is what i will need....so any more input on my findings and problems would be great...
thanks agn
paul
ive tested the rx and it seems very sensitive...ch30 shows 29.600 mhz and seems to go 10khz steps up down from there....there does however seem to be no repeater shift....which is what i will need....so any more input on my findings and problems would be great...
thanks agn
paul
- Alucard
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Re: LCL-2740 CB Converted
It seems odd that whoever converted it didn't include a repeater shift.
Probably the easiest way would be to switch an extra crystal in but not the cheapest. You could also use an Eprom probably also overkill.
You could also used logic ICs to get the desired result or if the shift was required on a specific channel then some diode switching to program the n-codes would work.
Probably.
Probably the easiest way would be to switch an extra crystal in but not the cheapest. You could also use an Eprom probably also overkill.
You could also used logic ICs to get the desired result or if the shift was required on a specific channel then some diode switching to program the n-codes would work.
Probably.
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Re: LCL-2740 CB Converted
Hi Alucard tnx for reply....i saw a very old article think it was 1984 in shortwave mag...showing a simple circuit using a cm4001 cmos adder nor gate chip along with a few resistors and bc109 ...this was wired to the mc145106 pll chip...the mod is based on the icom icb1050b..cb...as far as i can see this changed the truth table a bit allowing 100khz shift...via a switch...now the lcl2740 does use the same pll chip...so would this work on my rig?
as i said its a very old article and i wondered if anyone on here as done this...perhaps a diff way....yes a crystal switched in across tx line would work..
but what freq would this crystal have to be? i put in a post above the crystals fitted by a prev owner but cannot see how he arrived at the freqs?
thanks all for your continuing interest and help..
paul
as i said its a very old article and i wondered if anyone on here as done this...perhaps a diff way....yes a crystal switched in across tx line would work..
but what freq would this crystal have to be? i put in a post above the crystals fitted by a prev owner but cannot see how he arrived at the freqs?
thanks all for your continuing interest and help..
paul
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Re: LCL-2740 CB Converted
From the information I have, to give you 29.310 on ch1 to ch40 29.700mastercare wrote: ↑01 Oct 2021, 14:16 Hi guys sorry for delay....my eyes are not brill but the 2 crystals are 16.32400 12.12990 mhz does this help?
ive tested the rx and it seems very sensitive...ch30 shows 29.600 mhz and seems to go 10khz steps up down from there....there does however seem to be no repeater shift....which is what i will need....so any more input on my findings and problems would be great...
thanks agn
paul
The xtals should be RX 16.93500 and TX 12.53500 and 12.48500 for repeater shift.
HOWEVER:
I think looking at your xtal values the person who modified it used xtals he had close at hand and then
adjusted the pll divide by N to give him the difference he required, im not quite sure what has been done,
but because yours has used different xtal values then your repeater shift xtal will have to match the xtals/ pll ratio that yours has used.
Maybe that is why they never fitted a repeater shift.
Im not too sure what value you need. but it could be around 12.0800 it will all depend on what your tx PLL ÷ N is set to etc.
The TX VCO frequency gets doubled to give your final transmit frequency.
Here is a block diagram which should help you see what is going on.
The Frequencies in brackets are the 10m frequencies.
I am no expert on converting these radio's so If you can, I recommend you find a set of articles written by the BURY RADIO SOCIETY called
"FEEDBACK" dated May 1984 they did a Special edition which contained detailed information on converting CB's to the 10m band.
They included icom icb1050, DNT M40, LCL-2740 and cybernet chassis using lc7137 pll's etc.
I am wondering if maybe http://www.spectrumcomms.co.uk have the xtals you need?
I do know he has a few used and new at quite cheap prices.
Hope that helps a little Im off to bed.
73 Mark
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Re: LCL-2740 CB Converted
Hello
From https://www.vintage-radio.net/forum/sho ... ?p=1096531
Steve G4WCS memberlist.php?mode=viewprofile&u=29131
https://www.americanradiohistory.com/Short_Wave_UK.htm
Feb 83 simple conversion method
April 83 repeater shift
Jun 83 Further mods ICB1050
Mar 84 how to convert "unconvertible" rigs
Nov 84 ICB1050 conversion update, LCL-2740 display mod
Dec 84 ICB1050 channel scanner
@+
Claude
From https://www.vintage-radio.net/forum/sho ... ?p=1096531
Steve G4WCS memberlist.php?mode=viewprofile&u=29131
https://www.americanradiohistory.com/Short_Wave_UK.htm
Feb 83 simple conversion method
April 83 repeater shift
Jun 83 Further mods ICB1050
Mar 84 how to convert "unconvertible" rigs
Nov 84 ICB1050 conversion update, LCL-2740 display mod
Dec 84 ICB1050 channel scanner
@+
Claude
Last edited by 14CS06 on 05 Oct 2021, 12:09, edited 1 time in total.
Photo Collector CB RADIO
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Re: LCL-2740 CB Converted
Hi Mark Steve
thanks a bunch for the fantastic info you have both provided....i will have to check around the pll and see if the previous owner has indeed played with the truth table...to use what it seems is strange value crystals...its a shame i do not have the what would be the org cb crystals cos i could start agn with known values as your circuit shows mark...steve i will check out all the links you sent ...
ill prob be back with more questions...
thanks agn
paul
thanks a bunch for the fantastic info you have both provided....i will have to check around the pll and see if the previous owner has indeed played with the truth table...to use what it seems is strange value crystals...its a shame i do not have the what would be the org cb crystals cos i could start agn with known values as your circuit shows mark...steve i will check out all the links you sent ...
ill prob be back with more questions...
thanks agn
paul
- Alucard
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Re: LCL-2740 CB Converted
Hi bud, the circuit would probably work as it was designed for the mc145106. I would meter the pins to work out the truth table first as Digger said they've probably been manipulated to match the Crystal.mastercare wrote: ↑04 Oct 2021, 14:42 Hi Alucard tnx for reply....i saw a very old article think it was 1984 in shortwave mag...showing a simple circuit using a cm4001 cmos adder nor gate chip along with a few resistors and bc109 ...this was wired to the mc145106 pll chip...the mod is based on the icom icb1050b..cb...as far as i can see this changed the truth table a bit allowing 100khz shift...via a switch...now the lcl2740 does use the same pll chip...so would this work on my rig?
as i said its a very old article and i wondered if anyone on here as done this...perhaps a diff way....yes a crystal switched in across tx line would work..
but what freq would this crystal have to be? i put in a post above the crystals fitted by a prev owner but cannot see how he arrived at the freqs?
thanks all for your continuing interest and help..
paul
Don't know if you saw my post in "For sale" but I have shitloads of crystals mostly in the 30Mhz and 8-11Mh range but I may well have some that are of use to you so give us a shout before you buy any.
Never ask a starfish for directions.
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Re: LCL-2740 CB Converted
One thing to be aware of the LCL2740 uses two seperate VCO's one for TX and one for RX. A doubler circuit is used for the TX. therefore doubling the 14.??? MHz vco for final tx frequency.mastercare wrote: ↑05 Oct 2021, 10:52 Hi Mark Steve
thanks a bunch for the fantastic info you have both provided....i will have to check around the pll and see if the previous owner has indeed played with the truth table...to use what it seems is strange value crystals...its a shame i do not have the what would be the org cb crystals cos i could start agn with known values as your circuit shows mark...steve i will check out all the links you sent ...
ill prob be back with more questions...
thanks agn
paul
I think the 1050 uses 18MHz xtals which it mixes with the single VCO and PLL offset and either adds 10.240 to get its TX frequency
or subtracts 10.695 for the RX frequency
So they are quite different.
Its been years since I last played around with 10M modded CB's so I had to try and re-learn how they worked.
Anyway I hope you manage to sort it.
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