new..cobra 200GTL..HELP...NEEDED...INFO..NEEDED....

[frogger]

could somone please help. i have a cobra 200( new one with talkback ) and live in the uk .the radio is fine.untill i try to tune in to uk cb band..like 27.781.2 is channel (19 fm in the uk) when i turn the claffier to tune in. the freq display shows 27.781.2 but its no where near that it wont tune down to freq... with the fine tune and claffier to the left.....but on 27.555.0 its smack up with both freq display....but on fm its out on rx to the tx on fm....i no the freq display is not accurate...but thats a common problem..and theres no where to align it..... any help please......also is there a mod for the audio to put a bit of bass...on...as its very tinny....on usb .....any help ....please :?:alot of faults for a new radio.... and very little info.... :?:

 

[bob85]

hmm, quick look at the schematic c90 looks like its in series with the audio signal from the mic amp to ballance modulator ic,
imho this capacitor is too small and should be nearer .047uf to .1uf but there is also an att resistor that is omitted in the radio,

they sound way too thin on tx ssb regardless of where the offsets are set, sounds like a 1.5kc ssb filter and a tinny microphone but mic amp passband while not been hifi wide is acceptable on fm and not imho what is causing the total lack of fidelity on ssb tx,

ssb rx bandwidth sounds about average for this type of radio with the stock export filter bandwidth so i doubt its caused by wrong filter terminating impedance,
strange radio for sure,


if i was going to experiment i would start with c90 and inject a swept tone into the mic socket and scope the audio after the capacitor and monitor rf output as i sweep from 300hz to 3000hz, then i would reduce mic gain to a low level so as to ensure no overdriving the ballance mod ic when i try different caps in the c90 location, next i would change the cap for a .047uf or thereabouts and scope the output from the capacitor untill i had acceptable bandwidth for decent fidelity then add the missing resistor of the correct value to get audio level back to the same or slightly lower than the stock cap and see how it sounded,

what do you cobra guys think?,
has anybody had a play with ssb tx bandwidth ???
( please dont say they did that to compensate for a screwup somewhere else in the radio's design and opening up the audio is gonna cause the radio to warble its ass off and spew harmonics everywhere ),
and whats going on with the kcshift/clarifier very odd unless somebody at the factory screwed up wiring the clarifier?

i have only heared three cobra 200's in my area and they all share the same problems before and after they have been aligned by supposedly competent techs, are they all the same unless you do some modifications?

thanks.

 

[frogger]

mmmm only one reply.....loads of views ......thats says it all about these radios.......

 

[bob85]

look on the bright side, it does actually sound decent on fm with the astatic and not bad on am

 

[frogger]

yes m8 sorted it now aligned it with the 10khz pushed in and it s sorted i can tune to legal uk fm now everthing seems cool now...could do with a mod for receive on fm ....as it is very harsh on the edges....needs a bit off base ..and less...tx...tone on ssb.....so any cobra peeps out there could help please let me no........im starting to like it.....alot of radio for the money.....cheers