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Cobra 29 modulation adjustment.
- Thread starter Terry Thornsberry
- Start date
Yeah 10-4, with d-11 snipped it does look like shit on a scope. Spreading coils isn't necessary on every radio. All I'm saying is every cobra radio I've gotten from a pro had the coil spread a certain way and it looked good on a scope. Maybe somebody knows something that you'll don't know.I've had a used hacked up radio from a tech with the mod limiter removed and other mods and it was loud as heck on the air and all the CB guys thought it sounded badass.
If you put that radio on a scope it would have been all over the place.
Although it sounds good, it won't be putting out a clean signal - but that being said you may not care.
If you want a clean signal that isn't splattering then don't touch the coils - any tech that touches the coils is ruining the filter system and isn't a real tech...they are a CB mod specialist who charges you money to do things to the radio so it sounds "loud" on the air.
If you're happy with the result then no harm, no foul. If you're bleeding through your neighbors speakers and TV then at least you'll know why
The best rule of thumb is - don't touch the coils. I've messed with 100's of radios that sounded great on the air and I never touched the coils.
If they were real pros - as both they and you claim - then they wouldn't mess with the 54mhz trap circuit.
Because they would know why it is a useless mod.
I've worked and fixed many SSB radios. Some of these same lame mods end up in them as well - which I had to correct. But I am sure of what I am saying, in that messing with that circuit is a sign that no real pro would do - or even consider to do.
The main fantasy in CB seems to be word of mouth, I have an SDR that I can use as a make shift (while limited) spectrum analyzer to test this coil mod. [to examine this claim]
In the past [CERTAIN SHOPS] peak n' tune involved removing the 54Mhz trap circuit (disable it) this shows more output swing on a meter, but doesn't help to gain anything @ 27Mhz (AFAIK) the increase output reading is not accurate as the watt meter adds any power together that is sent through it, regardless of the individual frequency of the two (or more) signals.
Maybe someone with some more specific knowledge can chime in.
I have seen the "spread X coil for best swing" rhetoric used on DTB's site, he was considered a pro by many, but you won't see me following his websites advice...
I feel as if I must say this: I have seen radios that had fine looking modulation on the 'scope while throwing a nasty 54Mhz spike! (The 1st harmonic of 27Mhz) Later I saw someone had spread the coil and removed the ferrite slug from L13 (I think that's the one).
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I think you are right about 'word of mouth' CB myths. There are real mods out there; but they are beyond the range of the golden screwdriver hacker - which makes up the main body of users. They also require adjustments.
Problem is, there are a lot of technical examples of poor radio mods available on YouTube, most of which are reliable and accurate. It is not really open to debate if the 54mhz filter circuit mod is a junk mod - it is. People trust their wattmeter to be the final judge - not knowing that the wattmeter reads the 54mhz signal summed with the 27mhz signal.
Their #1 desire is to be louder, without any real concept of where to go - other than the myths that have been perpetuated over the decades They go with the fast food solution, because Joe Blow does it. Even though Joe Blow doesn't have a real clue - either.
805 california, please watch this video. Any questions - please ask.
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I 100% agree with you, no debate here on my end. Mods that release the 54 Mhz harmonic are junk, I just want to confirm that toying with L12 will indeed damage the harmonic/tvi filter and show more ghost watts, I need to test this because that is the only way I know how to prove it to someone.
EDIT:
To potential "hackers" @ 2:30 into the video he says "excess power" do not read this as a limiter is holding the radio back from some hidden potential, this is not a 5 H.P. Briggs & Stratton side shaft motor on a go-kart that you remove the throttle limiter from to go faster, the term limiter becomes a misnomer if you associate it with radio, while thinking about engines. The term is not applicable in this sense, I believe some confusion comes from the term "limiter" being used by "street techs" when they explain how cutting D-11 will "wake her up"... An incorrect explanation can be more damaging than no explanation.
73
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AM works a certian way and you can't change that. People that are too cheap to buy a transmitter capable of making the power they want resort to the typical CB hacks. If making a meter dance is your primary goal you can get away with a lot of dumb stuff.
It's the 110% percent truth what all the posters above have said. It's all SNAKE OIL to make the Meter Dance!!! Other than that you don't gain a damn thing adding 5 or 10 more watts when you are peaking at 15-20 already. You would need 60-80 watts to even get an S-Unit of extra power. Might as well get a small 2 transistor amp and keep it clean and mean! That is JMHO. A proper 1:4 dead key to PEP power is what you should be after. And keeping the negative peaks to about 90-95%. Positive peaks at 100% or a touch more. But you'll need a way to monitor your audio that way you don't exceed 100% negative peaks. More toward 95% max IMO. Keeps the signal clean and your audio clean and clear. Like said, want more power, get an amp.
You would think the people that build the radios can get the damn coils made right. I don't think they place wax or glue so you can freely open them or whatever you are talking about. That can't be any good. I would venture to say you bleed over many more freqs than you realize. Not saying you can't get more power. But as others have said, it's not on 27MHz. And the radio probably gets hot at the back due to this and the other mods I am sure are done. That is a straight peak and tweak. Again, just what I get from reading your thinking and also claims of knowing on the matter.
I would find another tech if could are being spread. Again, KEEP IT CLEAN AND MEAN!!
73 and God Bless
222 Daytona Bch., FL
You would think the people that build the radios can get the damn coils made right. I don't think they place wax or glue so you can freely open them or whatever you are talking about. That can't be any good. I would venture to say you bleed over many more freqs than you realize. Not saying you can't get more power. But as others have said, it's not on 27MHz. And the radio probably gets hot at the back due to this and the other mods I am sure are done. That is a straight peak and tweak. Again, just what I get from reading your thinking and also claims of knowing on the matter.
I would find another tech if could are being spread. Again, KEEP IT CLEAN AND MEAN!!
73 and God Bless
222 Daytona Bch., FL
Listen around 28mhz with your SDR when you hear some guys on exports talking. If there close enough to you you can understand some of them.
I have listened to myself on 54 Mhz with a slinky Cobra before!! I'll have to try a dirty export on my test bench next chance I get!
If only we could go back to the hey-day of CB, and stop 30+ years of myths and misinformation from being spread, then the hobby wouldn't have so many issues..
And a lot of radios could have been saved from carnage.
Another myth to explode - is the export radio. It is just as clean as a stock, untouched/unmodded CB radio. In fact, much of the design is exactly the same. Look at the schematics for yourself if you don't believe me. Some Hams gave them a bad rep, and undeservedly so.
The first harmonic for a export radio isn't at 54mhz; it is at 56mhz.
28.000mhz x 2 (1st harmonic) = 56mhz
The first harmonic for a export radio isn't at 54mhz; it is at 56mhz.
28.000mhz x 2 (1st harmonic) = 56mhz
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Isn't this a byproduct of the mixer scheme they use coming through? that's not really the same as harmonics from disabled limiters and filters.
I think that much of export radios bad rep comes from the fact that those who buy them are looking for hotter radios, as such they are more likely to go for the usual hack mods. I've seen some pretty clean ones.
Yes, the export thing is about harmonics in the mixer and doesn't really apply here. Just something for LeapFrog to check out with his SDR.
I have a DX66v I might "swing mod" the hell out of it for a video, I just tried a Cobra 29 right next to the SDR, my audio was very understandable at 54 megahertz, the radio hasn't really been hacked up and I think a lot of it is proximity to the dummy load, If I had a real antenna for the SDR I could put some distance between the d.u.t. and then monitor for any 54 megahertz harmonic by sampling the actual radiated power not just some "capacitive coupling" through the dummy load and nearby SDR like I have been doing.
Even factory condition though the export radios cannot go toe-to-toe with the old Uniden radios of a similar design. (in cleanly-ness of RX performance they are worlds apart i.m.o. ) IMD products have been said to be a major concern with the export radios, I wonder if one could be made clean if it was just set up correctly or does it inherently suffer from some design flaw or poor-quality material?
All that being said ultimately it will come down to the final configuration of a radio, and the qualitg of the components used will play a role.
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Sorry I was kind of referring to the average export that has already been converted for 11 meters, we all know they are not real 10 meter amateur radios.
Even after the conversion does the harmonic remain @ 56Mhz?
Thanks Robb.