The Defpom Forum, for RadioMods, S&M Software and Music by The Defpom

Alrighty, this is my problem. I bought a "moded" Cobra 29 off ebay. It has echo, talkback and a fancy faceplate. The guy that I bought it from said that he had all the work done on it many years ago. It is supposed to deadkey at 5 watts and swing to 27 watts. I do not have a wattmeter nor anywhere close to take it to to get it checked out. Well anyways, I hooked it up in my Freightshaker with 4' firestiks and found out that I can't talk as far as I could with my old stock Cobra 25 I had in there before. I thought it was the antennas. I bought new antennas. Nope, not that. Coax? Nope, not that either. Everything on the truck is perfectly tuned as I can get it. "Not sure how to tune duals but I think they are pretty good (Maybe someone can give me info on that too)." The guy said he had a wilson lil wil on it. Said he took it to the cb shop and they tuned it in his truck. It receives pretty well, mainly from people with linears talking from other states. I am not sure what the problem is. Maybe it is off frequency. Can someone give me a good idea how far my setup should talk? My old stock 25 talked around 6 miles, this talks about 2 miles.

Well,that all depends.There are alot of variables that have to
be accounted for.Like for one,are you trying to talk during
the day during peak skip times..That matters alot..You can have
a prefectly setup, and during the high skip traffic like weve been
having here lately around here.Youll be lucky if you can talk
2 miles locally.During noisy times like these you have gotta
have some horse power, and then sometimes you still cant
talk 3 miles.You might talk across the country,but cant get out
across town.Also another thing,or you talking mobile to mobile.
Or are you talking mobile to some guy with a set of 8 element
beams 150 feet high 6 miles away.If hes got that big set of beams
looking down on you.You think your talking a long way.But in
reality its his setup thats doing all the work..His recieve,not your
transmit.But to answer your question,,the main thing,,first make for
sure your s.w.r. are set right on your setup.Your antenna system
makes for 90% of your get out.Therefore it is of great importance
to make sure your s.w.r. is set right. 1.5 to 1 or less..No more than
2.0 to 1 at the most.Setting your s.w.r. requires a good s.w.r. meter
If you dont have one,if you have a local rat-shack,they have a
small affordable little meter.That will do just for setting your s.w.r.
They are not very good for tuning a radio,other than just setting
the dead key.Once you have your s.w.r. meter.Attach it with a
small jumper between your radio and antenna.It should be labeled
at the back which so-239 connector to connect antenna/radio too.
Set the meter to s.w.r. check..set the meter to the forward
Then key the tranmitter,and slowly turn the set knob until the needle
on meter is all the way to right to where the set line is.Then set the
meter to the reverse position..This will give you your s.w.r.
If it is high 2.0 to 1 or greater.adjust your antennas.If it is a firestick
or similiar.The adjustment will be at the top of the antenna.It will have
a little plastic cap over the tip.Loosen the allen screw,and slide the
stinger up or down,1/8 of an inch at a time.First check on channel 20.
if it is high.Go to channel 40,check it here,write down the measurement.
Then go to channel 1,check it here,write down measurement.Then say
it is 2.5 to 1 on 40,,and it is 1.5 to 1 on channel 1.slide the tip of
antenna down 1/8 inch and re-check.If it goes down.Let it down alittle
more a check again..If it is high on channel 1 say 2.5 to 1 on channel 1
and 1.5 to 1 on channel 40..Then you loosen the set screw and slide
it up about 1/8 a inch at a time..In otherwords high on the high side
(channel 40) lower the stinger 1/8 inch at a time..High on the low side
(channel 1) raise the stinger 1/8 inch at a time.If for some reason
the s.w.r. wont lower no matter where you set the stinger in the
antenna..You may have a bad ground..Make sure you check your
grounds..You might have to run a ground wire from the base of
your antenna bracket, to a good ground on the chassis of your truck.

The swr is perfect 1:1:1. I am a local truck driver. I make rounds from Houston to San Antonio and back. I mainly talk to other drivers as we are going in opposite directions. This is also normal at night. I run mostly at night and during the mornings when there is little traffic. I know my signal on my old 25 goes pretty far even though it is stock but this 29 is not doing so well. I can switch them out when I am driving and can tell the difference. So what's the deal??

Next you are gonna have to have a watt meter///
I know you said it suppose to be dead key 5 watts and
swing 27..But without a watt meter you cant know for sure.
It is possible that the rf final went O/S. I have seen this
before where the final went out.And it would still get out
a short distance..One thing to check,that is if the radio meter
is working.Does it show any output on the radio meter in TX?????

I have an old radio shack swr/field strength meter. I tuned the antennas with that one before I got the 29. When I key the mike, the field strength meter moves pretty far to the right, about twice as far as when I would key the mike with my stock 25. The meter on the 29 goes to about 9db on the meter or where the green and the red meet. When I say something, it usually stays about right there. On my 25, the needle moves when I talk, usually to the right. Is this usual? Do you have any more suggestions? It has a T C2075 Final. I don't know what rating it is for. Can someone find more info on the final. I have a 1969 final around here from when I was playing with an old radio. I could talk about 1/2 mile when I put that final in an newer style 29 I used to own. I appreciate all the help. thanks!!

O.K. that is better info..The more info you can give us,the better
the chance we can help with your radio problem..The radio meter
indicates the final is O.k. But what is odd..You said earlier that
the radio suppose to be dead keying 5 swinging 27.If that was truly
the case,When you modulated into the mic it should peg the radio
needle in the corner.If the radio meter is working properly.This
may be a stupid question,,But you do have the mic gain turned
up right??If so lets try a p.a. test and see how the audio is here.
If you have a external speaker.Plug the external speaker into
the p.a. jack in rear of radio.Put the radio in the p.a. mode
and speak into mic.And see how the audio is at this point.
Cause if the antenna s.w.r. is fine.And your getting a good dead
key (carrier)..Then that only leaves two things can be wrong.
Either you have a modulation problem.Or the radio is off
frequency.Have you tried a different mic???? Do you have a
frequency counter????

I did the PA test. Works. lots of sound. Back to CB: when I key the mike, I notice the needle swings between the "A" and the "L" on the words CAL or the 3 on +30db(I didn't have my glasses on when I read the needle on the previous post. Sorry...that thing is hard to see). This is with the RF switched up. Not on SWR or CAL. I checked it on my other truck that was sitting about 100ft from it and the it's needle was FAR to the right. Sound was good and clear. I have the MIC GAIN to about 3/4 because at Full it sounds too LOUD to the person I am talking to. What else can you think of? I am still getting lots of long distance talkers from out of state (this is what you call "Skip" Correct???) No, I do not have a frequency counter.

Forgot to mention, I retuned the antennas to about 1.2 to make sure that my meter was working correctly. I think I will leave them at that.

what you were hearing is skip....and 1.2 is a right fine and dandy reading

Well if it sounds loud and clear at close range.Then you
can rule out a frequency problem.Are you sure that the
problem is with your tx,,Or could the problem be with
the other guys rx (the one your trying to talk too)???
The only other thing i can think of,is that the dead key
might need to be lowered some..That would increase your
audio some..One more thing is the radio the only thing you
have changed???

I changed antennas too. I noticed that one of my dual antennas was broken so I replaced both with 4' firestik, which I tuned to about 1:2 to 1:3. I tuned them as a pair. Not sure if that is how you are supposed to do duals. If needed to raise one, I raised them both in equal increments. Anything else? The funny thing is that when I unhook my new 29 and then put my old stock 25 back on there I can go another 3-4 miles on distance so that leaves me to believe that it is the radio but the 29 receives very well. I would say better than the 25.

O.K. dont know if you are aware of this..
But co-phasing your antennas,make your signal
directional..In otherwords your just most shooting
signal forward and rearward..You have very little
side to side reflection.If your gonna use in this
application.Make sure both antennas are tilted
forward,on your mirror mounts.Not straight up.
This will allow you to talk good forward,and your
trailer will act as a ground plane.And you can get
rearward reflection via it.I would try to talk you
through re-tuning and lowering your key on
the radio.But without a watt meter it will make it
more difficult..

Right now, my antennas are leaning back some. I'll see if I can get them to tilt forward tomorrow. Most people I talk to are going the opposite direction as I am so I guess this would help. What do you plan on doing with the key?? I would like to crank it up so that I am putting out more watts to go further. What were your plans??

I have the antennas tilted a tad forward so that we I am driving down the road, the antennas are straight up or just a little bit forward. They work great!!!!! Many thanks!!!!!