RumpRot (oops, I mean RugRat) has it right. Tune the pre-driver coils for best carrier, then modulate and tune L21 for best PEP. It really helps to have a 'scope, because you can make sure you're not getting a slightly "fuzzy" peak, which can happen with the 200 if you're not careful.
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Mods for the Cobra 200GTL
- Thread starter DTB Radio
- Start date
You don't need to. Just set your low key level for what you need for the external amp, and do at least the AMC timing cap mod, and you should be ok.
Hi ! DTB I did this mod's R181 SMT (824) and removed C154. Low power i good audio report , Hi power is to noise.sssssssssbzbzzbz. so what is the ploblem thank you.
C158 IS 47UF NOT (a 4.7uf cap for the C158 mod )
C158 IS 47UF NOT (a 4.7uf cap for the C158 mod )
my one local has one on am its clean but definately not
a audio monster.on ssb its sounds clean but has kinda a
pinchy sound.like if your holding your nose while talking.
overall my opion the radio is not bad but definately needs
a few mods.we tested it against a 2970dx with smd technology
both were pretty much stock expect conversion and a slight
peak up.the 2970 beat it in every aspect.everything else
was the same coax,mic,antenna,powersupply.
id rate it on a scale of 1-10 10 being perfect id give it
a 6 stock with no mods
a audio monster.on ssb its sounds clean but has kinda a
pinchy sound.like if your holding your nose while talking.
overall my opion the radio is not bad but definately needs
a few mods.we tested it against a 2970dx with smd technology
both were pretty much stock expect conversion and a slight
peak up.the 2970 beat it in every aspect.everything else
was the same coax,mic,antenna,powersupply.
id rate it on a scale of 1-10 10 being perfect id give it
a 6 stock with no mods
rodgerbird i have not experimented with the 200 yet but i looked at the schematic when i heared how thin they sound on ssb regardless of where you set the carrier offset,
the passband of the mic amp is fairly normal for a modern cb radio and the ssb rx is pretty ordinary but the ssb tx is horrible,
if you look at the mic amp and follow it into the ballance modulator theres a coupling cap that imho is way too small to pass any bass,
right beside it is a unused place for a resistor which if fitted would make a resitive divider,
if i was to play with one i would change the value of the cap to something larger and keep an eye on levels at the ballance modulator, you may need to add the resistor if boosting bass gives too much audio into the ballance mod,
theres another cap on the same line to ground close to the ballance modulator on the schematic that imho is too large and shunts too much trebble, i would make that smaller too,
its clear the audio passband on ssb is way too narrow, everybody round here hates the sound of the 200 on ssb,
i can only think of 2 possible reasons why they would make them like that,
1, for some reason using a more normal audio passband caused problems further down the chain with ballance mod levels,
2, the makers dont have a clue what they are doing,
looking at the other faults with the radio i am guessing number 2 is likely but it would not surprise me if making the ssb tx passband wider causes problems and the narrow it down idea was a fast bodge/fix,
we wont know untill somebody mods one and somebody that knows what they are listening for in a ssb transmission has a real good listen,
good luck.
the passband of the mic amp is fairly normal for a modern cb radio and the ssb rx is pretty ordinary but the ssb tx is horrible,
if you look at the mic amp and follow it into the ballance modulator theres a coupling cap that imho is way too small to pass any bass,
right beside it is a unused place for a resistor which if fitted would make a resitive divider,
if i was to play with one i would change the value of the cap to something larger and keep an eye on levels at the ballance modulator, you may need to add the resistor if boosting bass gives too much audio into the ballance mod,
theres another cap on the same line to ground close to the ballance modulator on the schematic that imho is too large and shunts too much trebble, i would make that smaller too,
its clear the audio passband on ssb is way too narrow, everybody round here hates the sound of the 200 on ssb,
i can only think of 2 possible reasons why they would make them like that,
1, for some reason using a more normal audio passband caused problems further down the chain with ballance mod levels,
2, the makers dont have a clue what they are doing,
looking at the other faults with the radio i am guessing number 2 is likely but it would not surprise me if making the ssb tx passband wider causes problems and the narrow it down idea was a fast bodge/fix,
we wont know untill somebody mods one and somebody that knows what they are listening for in a ssb transmission has a real good listen,
good luck.
yea ive heard several on ssb they sounded awful.guys tried numerous mics
no prevail.just mho these radios straight out of box are junk.roger check out
the mods posted by DTB in earlier posts.seemed to bring up the power but
as far as the pinny sound on ssb i dont know.that pinny sond is becoming
popular on these 200s.guess ya get what ya pay for
just play with T 715 ( USB ) AND T 714 (LSB ) I AM TRIEND TO FIND THE WEB SIZE I'LL GET BACK TO YOU
Pinchy Audio
Bob,
You were right on! I replaced C90 with a different value, and SSB audio came up slightly and the bass response was much better. I have to determine what value I ended up with.
C90 is a 2200PF, I tried a 220 pf cap but had no notable change, I have bag of SMT Caps and used one of those, Not sure of the value (Aa5 = 1uf?). But it improved, and worked with the Stock mic and the Desk power mic and Hand Powermic. I did not need to add the resistor to R692 position.
Thanks for steering me in the right place.
Roger
Bob,
You were right on! I replaced C90 with a different value, and SSB audio came up slightly and the bass response was much better. I have to determine what value I ended up with.
C90 is a 2200PF, I tried a 220 pf cap but had no notable change, I have bag of SMT Caps and used one of those, Not sure of the value (Aa5 = 1uf?). But it improved, and worked with the Stock mic and the Desk power mic and Hand Powermic. I did not need to add the resistor to R692 position.
Thanks for steering me in the right place.
Roger
thats good news roger,
i have wanted to try that since i first heared a cobra 200 and looked at the schematic to see why there was such a large difference between audio passband on fm vs ssb, nobody local has one anymore for me to experiment with,
thanks for letting me know it works
.
i have wanted to try that since i first heared a cobra 200 and looked at the schematic to see why there was such a large difference between audio passband on fm vs ssb, nobody local has one anymore for me to experiment with,
thanks for letting me know it works
.