cb mod advice

jturner0829 · Aug 22, 2011

hey guys. i have used a cobra 29 for a few years and it got to where it wasnt performing good enough anymore. i just bought a new cobra 29 night watch, wx, and bluetooth. iv been trying to do some research on the modulation. from what i have read 100% modulation is what you want and they come from the factory with 70 to 80%. could anyone give any advice from experiance. any info on this or any other mods would be very helpful. im wanting to learn as much as i can about the radios. i also have a Astatic 600 5000 Watt SWR/Mod/ Power Meter which will help when i set up this radio.
thanks for any info.

W2NJS · Aug 23, 2011

You won't gain much, if anything, if you turn the modulation up to one hundred percent. Common practice in AM radio is to run it between fifty and seventy percent. At full bore, so to speak, you will get distortion and signal splatter as an almost guaranteed result. Or go to SSB where you can run a bit more power and the net effect is an eight times stronger signal being transmitted.

K9WG · Aug 23, 2011

In AM mode modulation does not get you anymore distance, only makes you louder at the receive end. Unless the modulation is really low keep it at the factory specs.

LtDoc · Aug 23, 2011

M odulation percentages change, it isn't constant by any means. A typical high average is probably around 80 - 85 percent. That typically works just fine. The modulation percentage varies around that figure, both higher and lower, it's an 'average'. That sort of compensates for the variations in loudness, tone, with the typical persons voice. Get excited, or yell and the percentage 'bumps' higher. Anything over 100% amounts to wasted power, and being 15 - 20% lower than 100% isn't 'hearable'. Modulation doesn't equate to more range. High tire pressure doesn't mean going further either...
- 'Doc

WouffHong · Aug 23, 2011

Beware

jturner0829 said:
hey guys. i have used a cobra 29 for a few years and it got to where it wasnt performing good enough anymore. i just bought a new cobra 29 night watch, wx, and bluetooth. iv been trying to do some research on the modulation. from what i have read 100% modulation is what you want and they come from the factory with 70 to 80%. could anyone give any advice from experiance. any info on this or any other mods would be very helpful. im wanting to learn as much as i can about the radios. i also have a Astatic 600 5000 Watt SWR/Mod/ Power Meter which will help when i set up this radio.
thanks for any info.

Transmit-Audio Mods will usually do nothing but splatter and distort to the point that you cannot be understood. I assume your 5000 Watt Power meter will be used on some type of "so-called" "Linear" (rarely) Amp in order to get the needle even off the left peg, so you are already almost in deep yogurt for FCC fines and equipment seizure, and we respectfully suggest you avoid all Mods and study for a ham ticket - Not difficult these days.:roll:

summary; beware mods - They are a road to trouble, my friend...

73 (no "s")

da Wouff

KC4RAF · Aug 23, 2011

What the previous posters

have written is correct. Best to leave the factory setting as it is. When you up the percentage factor, your signal suffers. Here's what WILL do you good, buy a GOOD-GREAT antenna and coax. The cheaper the antenna and coax, the more LOSS you're find.

jturner0829 · Aug 24, 2011

ok thanks for the replies. i understand a little better now. i dont know anything about the ham radios. are they still on cb channels? because thats what i want is cb channels. as far as the 5000 watt meter has 3 settings. up to 10, up to 100 then up to 5000. i think thats the right numbers. i do have a linear that was givin to me by my uncle. i was not sure if i wanted to use it or not.

now... what about coax and the anntennas. i was thinking about going with a wilson or a firestick. either a 4 or 5 foot. it will be mounted on the toolbox on my truck. i had a radioshack anntenna on my last setup, that may have been part of my problem. i couldnt get my swr to a comfortable range. it was at 2 at the least. when i checked the watts on it it was only putting out 2 watts. i then checked my father in laws cobra 25 with a mag mount and it was pushing 4 watts. both are stock radios.

any suggestons on coax and anntennas. also i will be intalling a scanner in my truck too and wanted a matching anntenna for it.

thanks again for the help.

RES51CUE · Aug 24, 2011

where can i buy a cobra HH38WXST and a lapel mick and the long range att. for a good price

W4BOZ · Aug 24, 2011

jturner0829 said:
now... what about coax and the anntennas.

You mentioned Wilson and Firestik. Personally, I'd go with the Wilson but Firestik makes a fine antenna as well. I've used both before (including a 5ft or so Firestik with their indoor ground plane system) and currently use a Wilson 1000 which has always given me good results. You'd be better off going with whichever Firestik is a bit longer than 4-5ft. Heck, if you could handle a 108" whip on your vehicle and don't mind the length go with that. If you can use a mount that makes a good electrical connection to the body of the vehicle then that would be your best bet and that would be a lot better than a magmount. When it comes to radio installs I've always been told and stood by the idea that you should put as much into your antenna system as you can. An expensive radio can end up being useless with a POS antenna system.

As for testing the power output of the radios, and someone correct me on this if I misread or am flat out wrong in this situation, you'd be better off using a dummy load connected to the meter instead of an antenna.

jturner0829 · Aug 25, 2011

I will more than likley run a 5 foot. My truck is already tall and do go in and out of the the woods so I think the 108 whip may be out of the question for me. If I run a ground wire from the anntenna mount on the toolbox to the truck frame, that should be good right?
How much do dummy loads run?

fischlerpromo · Aug 30, 2011

kg4ivt said:
You mentioned Wilson and Firestik. Personally, I'd go with the Wilson but Firestik makes a fine antenna as well. I've used both before (including a 5ft or so Firestik with their indoor ground plane system) and currently use a Wilson 1000 which has always given me good results. You'd be better off going with whichever Firestik is a bit longer than 4-5ft. Heck, if you could handle a 108" whip on your vehicle and don't mind the length go with that. If you can use a mount that makes a good electrical connection to the body of the vehicle then that would be your best bet and that would be a lot better than a magmount. When it comes to radio installs I've always been told and stood by the idea that you should put as much into your antenna system as you can. An expensive radio can end up being useless with a POS antenna system.

As for testing the power output of the radios, and someone correct me on this if I misread or am flat out wrong in this situation, you'd be better off using a dummy load connected to the meter instead of an antenna.

I ran a FireStik with my SSB Radio.. modified with 120 "illegal" extra freqs above the normal CB band. 100K "illegal" linear with a locked clairifier to get between those freq. where it's very quiet..
It worked fine with that antennae.

OCO · Aug 30, 2011

Just curious, why put illegal in quotes - the out of band op and the "linear" (most likely not linear) were illegal.......

fischlerpromo · Sep 3, 2011

old_CJDC_ops said:
Just curious, why put illegal in quotes - the out of band op and the "linear" (most likely not linear) were illegal.......

OH God.....curious peeps want to know....WHY, simple, BECAUSE I COULD, THAT'S WHY.

James_Bond_007 · Sep 3, 2011

in broadcast you want 90-95% modulation to get it you use a AGC / Gain rider followed by a compressor then an asymmetrical limiter but since voice is asymmetrical you wont need the asymmetrical just a straight limiter.

thats the best thing you can do and for just voice this can be accomplished on a single board with just a few IC's and discrete components and can be made to fit right inside radio.

my recommendation would have been to have the old 29 worked over by someone and brought back to factory specs. a lot of these newer radios are built like cheap crap.

JayMojave · Sep 4, 2011

Hello Jturner:

There is some justification in getting to 100% modulation from say 70%, as this is a 3dB increase.

However in most all electronic trouble shooting you need to measure what you have before heading off into a direction not knowing what you have. Many CB and Ham Radio Enthusiasts have gone the wrong direction not knowing all needed info.

One other consideration here that has not been covered, is the design and componets used in the radio, as many manufactures do not use a design or componets that would allow say 100% modulation. Because the Modulator Circuit simply runs out of poop not having the power needed to make the 100% modualtion level. The manufactures save money and you get stuck with a lower than 100% Modulation.

Many times I have looked a Oscilloscope modifiying a radio to get to the 100% Modulation Level, I have gotten close, as the radios modulator runs out of power. I know there are some radios than can make or get real close to the 100% modulation level, but I don't work on radios as a living so I don't have all the answers.

Suggest you measure your radios modulation percentage before doing anything about it.

Hope this helps a little.

Jay in the Great Mojave Desert, ....just down the road aways from the fillin station.

jturner0829 said:
hey guys. i have used a cobra 29 for a few years and it got to where it wasnt performing good enough anymore. i just bought a new cobra 29 night watch, wx, and bluetooth. iv been trying to do some research on the modulation. from what i have read 100% modulation is what you want and they come from the factory with 70 to 80%. could anyone give any advice from experiance. any info on this or any other mods would be very helpful. im wanting to learn as much as i can about the radios. i also have a Astatic 600 5000 Watt SWR/Mod/ Power Meter which will help when i set up this radio.
thanks for any info.

Token · Sep 4, 2011

fischlerpromo said:
I ran a FireStik with my SSB Radio.. modified with 120 "illegal" extra freqs above the normal CB band. 100K "illegal" linear with a locked clairifier to get between those freq. where it's very quiet..
It worked fine with that antennae.

I am not sure what this 100K illegal linear thing is, never seen that reference before. And the linear thing, it had a locked clarifier, if it was locked how did it allow you to adjust it?

T!

LtDoc · Sep 5, 2011

Not in any particular order.

As 'Jay' said, all radios are not 'equal' in how they are built. Most can be made to produce 100% modulation, but, at the expense of producing lower power outputs. Which isn't all that bad if you think about it. Another 'catch' in that is that if you don't have the proper equipment to measure that 'modulation', AND the knowledge of how to do it, you have a much better chance of winning the lottery without buying a ticket. (Knowledge and equipment. One can counter balance the other a tiny bit, but that 'tiny' really is TINY.)
An additional "ground" wire connecting tool box, and chassis. If that tool box is properly tied/bolted to the truck bed, and if that bed is properly tied/connected to the truck's frame, any additional 'ground' connection is not only a waste of time/money, it can cause problems because of 'ground loops'. The 'cure' is worst than the 'problem' to start with. Sounds a lot like 'snake oil', doesn't it?
[Something to keep in mind is that RF is not DC. It's AC, and a 'ground' at AC ain't the same thing as a 'ground' at DC. Howz that for a 'nasty' thought??]
Output power amplifiers.
Very simply, no matter what the power output is increased to, they are illegal in the USA. making any significant changes in the transmitter of a CB radio in normal CB service, is illegal in the USA. That's just the way it is, it's called law/rules. Wanna do it "cuz I can!"? Knock yourself out with it! Just don't whine when you get caught, you know? "Can't do the time, then don't do the crime.", that fit's real nice and is simple to understand.

- 'Doc

KC9ICE · Dec 28, 2011

jturner0829 said:
any suggestons on coax and anntennas. also i will be intalling a scanner in my truck too and wanted a matching anntenna for it.

If you want to run matching antennas I would look at the 4' Firestik. They make fine CB antennas but also make 4' antennas that are tuned as 5/8 wave VHF antennas. There are 2meter ham(144mhz), MURS(151/154mhz), and railroad (161mhz) versions. For receive only any of these would work as well as the next, but if you were to ever get your ham license, I'd get the 2m as it'll have low SWR on that band. Even though they're mono-band VHF antennas (which is what most fire/rescue is on, which they will receive well), a 5/8 wave VHF is close to a 1/4 wave VHF low-band do it'll RX ok there and most police UHF repeaters are strong enough that it'll likely receive just fine there too. What this all means is you can have two different antennas (one CB and one scanner) that appear to be a co-phased dual CB antenna setup. For coax, standard RG-58 will be just fine.

Check out Firestik Antenna Company Home Page for more info.

fischlerpromo · Dec 28, 2011

KC9ICE said:
If you want to run matching antennas I would look at the 4' Firestik. They make fine CB antennas but also make 4' antennas that are tuned as 5/8 wave VHF antennas. There are 2meter ham(144mhz), MURS(151/154mhz), and railroad (161mhz) versions. For receive only any of these would work as well as the next, but if you were to ever get your ham license, I'd get the 2m as it'll have low SWR on that band. Even though they're mono-band VHF antennas (which is what most fire/rescue is on, which they will receive well), a 5/8 wave VHF is close to a 1/4 wave VHF low-band do it'll RX ok there and most police UHF repeaters are strong enough that it'll likely receive just fine there too. What this all means is you can have two different antennas (one CB and one scanner) that appear to be a co-phased dual CB antenna setup. For coax, standard RG-58 will be just fine.

Check out Firestik Antenna Company Home Page for more info.

I used a Firestik way back when and loved it. Perfect SWR and it handled power.... just sayin'

KC9ICE · Dec 28, 2011

fischlerpromo said:
I used a Firestik way back when and loved it. Perfect SWR and it handled power.... just sayin'

Yeah, I've used a number of the CB versions (2', 4', 5' all as singles and 4's as co-phased) and currently run a single 4' and I've always been happy with them although I've never run any real kind of power through them (standard peak & tune). I did for a while run one of the 5/8 wave 2meter ones on my Yaesu FT2800 which was 65 watts FM. The only thing I didn't like about that antenna was when I went to a Part 90 radio (so I could run public safety VHF and 2meter in the same radio) it wasn't quite wide-banded enough for me to be happy with it transmitting on both bands, but it always received well.

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