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Thrak1978
New member
Username: Thrak1978
Post Number: 1
Registered: 1-2007
| | Posted on Tuesday, February 06, 2007 - 3:01 pm: | 
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Hello I've been lurking here since I purchased a Magnum S6 about two weeks ago. This is a very informative forum and I've learned quite a bit.
I am having a problem with weak transmission. Just to clear things up I have weak transmit with my galaxy 33 and my Magnum, so I doubt it's the radios.
I just upgraded from a fiberglass antenna to a 102" whip. My SWR is 1.3 on channel 20, I am using a new 18 ft section of mini-8 coax and a new mount. I can get out about 10 miles, but can barely be heard. The TX signal at 10 miles is far worse with these 2 radios as it was on my cobra 25ltd (about 12 watts pep) with my fiberglass antenna.
I have read and re-read this forum and about 5 other forums and tried everything I can imagine or find to solve the weak TX, but nothing has helped.
The antenna is currently mounted on the right rear bumper on a 92 ford ranger. Mounted on the truck box SWR jumped to 2.5 on channel 20.
Any new suggestions?
Thanks in advance for any help. |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 2375
Registered: 9-2004
| | Posted on Tuesday, February 06, 2007 - 11:14 pm: |
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if you are sure that the installation went smoothly, and you didnt have to "MacGyver" anything; that the coax isnt getting smashed, bent, or kinked in any way shape or form, then i am going to say its probably either of two things.
improper use/ improperly working SWR meter, or a grounding issue.
you see, a 1/4 wavelength antenna, such as a 102" whip is the most resonant, perfect type of antenna there is-provided it has a good ground plane to work against-.
so if the installation is clean, and you are sure that all ground connections are clean shiny bare metal against clean shiny bare metal; then suspect a bad ground connection from the bumper to the bed, and/or the frame.
the best way to ensure this is to make or buy some ground straps like you see at the auto parts store.
the silver braid looking kind with the hole connectors at each end.
using a bunch of these, go from a known good bumper bolt to the metal of the bed, the bumper to the frame, the frame to the bed, the bed to the cab(VERY IMPORTANT!), the cab to the frame, the doors to the cab, the hood to the cab, and make sure that the negative cable on the battery going to the frame is 2ga. or bigger.
seems like a lot of work, and it is a bit time consuming, but the rewards are great.
i will tell you that the bumper is not a good place to mount your antenna, as there is metal within very close proximity of the first few feet of the antenna, causing distortion of the waveform, and also SWR issues.
if its possible, it would be much better to mount it to the truck box. (i know, i know, but trust me, once you do the grounding thing, and also make sure that the truck box is well grounded to the bed; as long as the install is clean, you will have an SWR of about 1.5 across the band, which is darn near perfect, and as close as anyone ever needs to worry about. DO NOT EVER CUT A 102" WHIP TRYING TO TUNE IT! they do not need tuning if they are installed correctly)
if you must leave it on the bumper, still do the grounding, and checking, and hope for the best.
now for the second possibility:
what kind of SWR meter are you using?
how is it hooked up?
i will lay out for you how it should be done, and you can check your system from there.
first you need a coax jumper that you can trust.
the way to know that you can trust it, is that you bought it new.
better to buy it at a CB shop or a truck stop than at a radio shack, but most important is that its new and un-messed with.
get the best one you can find, and RG8 mini is much preferred over RG58.
speaking of coax, what is the story with your 18' of coax?
did you put the ends on yourself?
did you cut one end off to use the ball mount?
does the mount have an SO-239 connector on it?
if you put the end(s) on yourself, suspect that first.
no offense, but its pretty involved to get them right, and there are alot of things you need to know how to look for. what might look great to the eye, could be horrible for the RF signal.
ok, hook your good jumper up to the radio, and set it on ch.19 (27.185mhz) mode to AM, and mic gain all the way CCW (down) so it doesnt confuse the readings. top gun, echo, etc... off.
hook the other end of the jumper to the SWR meter where it says, RADIO, TX, or TRANSMITTER.
hook the antenna coax, (with a known good connector on it) to the SWR meter where it says, ANT, or ANTENNA.
look at the switches on the SWR meter.
there will be one that has these two markings on it. SWR, and CAL. it might also have POWER, or PWR if the SWR meter is also a wattmeter, but we're not conserned with that right now.
place the switch in the CAL position and key the mic. the needle should move to the right, and should go all the way over to the right depending upon the position of the knob.
while holding down the mic button, adjust the knob so the the needle sits right in the spot marked CAL, or CALIBRATE on the right side of the meter face.
unkey the mic and wait a few seconds.
place the switch in the SWR position, and key the mic, making sure not to bump or touch the knob.
read the reading on the meter.
the less the needle moves to the right, the better, with no needle movement at all being perfect. (pretty unobtainable)
make a note of the reading.
if it is 1.5 or less, you are good.
if it is 2 or less, you can leave it if you want to, as this difference will not be noticable in your transmitting distance.
if it goes up to 3 or more, then you have a grounding issue; meaning that your antenna has no proper ground plane to work against, which would also account for the lack of range.
(if a van and a honda both had a 102" whip installed on the center of the roof, with the same radio, the van would get out further because of the bigger ground plane.)
now go to ch. 1 and repeat the SWR calibration process, making a note of the reading.
do the same on ch. 40, re-calibrating the meter each time you change channels, or power output on the radio. make a note of the SWR on ch. 40.
ok, read through this post two or three times, and see whats the story with your install.
answer my questions and post your results here.
grounding is the most important thing here.
good luck,
matt |
Thrak1978
New member
Username: Thrak1978
Post Number: 2
Registered: 1-2007
| | Posted on Wednesday, February 07, 2007 - 9:52 am: |
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That's one heck of a response Kid Viscious! I appreciate the fact that your helping me out like this. The short answer to all your questions is I have done everything you mention with the exception of the grounding methods you mentioned. I have the straps, I need the 2awg battery to frame cable. I'll put the straps on it today and put the battery to frame ground as soon as possible.
The long answer is below.
I double checked my coax for any breaks, kinks and smashed areas, it isn't coiled up at all. Nothing appears to be wrong with it. There is no continuity between the center of the coax and the sleeve. The mount is new and I am using a pl-259 connector. I know I don't have the skill to put a 259 on my coax and do it right so I generally just buy new plug and play coax.
I purchased my coax from a truck stop with the ends already attached. I haven't modified it at all. I have my antenna mounted on a mirror mount that is bolted directly onto a sanded portion of the bumper. I checked for continuity between the mount and the bumper, the bumper to the bed, bed to cab and the threaded sleeve on the end of the coax straight to the negative on the battery and all had continuity.
The SWR meter I am using is a new radio shack meter. The coax is hooked up properly and the jumper is new. I normally check SWR on channel 20 because I primarily use channel 19 but do not wish to interfere with the truck drivers communication.
I rechecked my SWR last night in the proper manner ,using channel 1, 19 and 40. I also made sure no objects were near by to affect the reading. My more accurate SWR is between 1.7 and 1.8 across the band.
I have noticed that the SWR changes depending on where I set the power. I set the knob to 12 o'clock for testing. Should I set the power to a diferent position? |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 2377
Registered: 9-2004
| | Posted on Thursday, February 08, 2007 - 1:05 am: |
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thanks for the compliment thrak!
i have been on this forum for a while and i have answered ALOT of troubleshooting questions.
i try to make my answers very detailed for two reasons.
one is that i know that many people in the future will be searching the forum for answers to their problems, and my details might help them.
also, i do not know how much you know so i try to cover all the bases.
now that i know your situation better, we can try some different directions.
first, yes, your SWR will increase along with your output power. that is normal, but it shouldnt increase much.
if your SWR is at 3 when the power is at full output, then you have a problem with the antenna system. (you must recalibrate the SWR meter each time you change the power output.)
you have done a great job on your install!
sounds like everything is good.
your SWR is just fine, and your antenna is acting like it should. there is no point in trying to lower your SWR by grounding. no one will ever know the difference between 0.5 difference in SWR readings. (trust me!)
the reason you are not getting out very far is because the antenna is located on the bumper.
you see, with the antenna mounted there; the whole system is very directional.
since your antenna is on the rear right corner of the vehicle, the maximum signal radiation is pointing towards the front left of the vehicle.
so wherever you point the drivers side front of your truck is the direction that your signal will get out furthest.
anyone in the right rear direction of you will barely hear you.
this coupled with the distorted signal pattern due to the antenna's close proximity to the bed, is the reason you cant get out very far.
put that antenna back up on the truck box and watch your signal strength increase quite a bit.
the 2.5 SWR was because of a bad ground somewhere.
you have a great radio, and the best mobile antenna design around.
you are just not getting full potential out of them because of the mounting location.
best of luck to ya,
matt |
Thrak1978
New member
Username: Thrak1978
Post Number: 3
Registered: 1-2007
| | Posted on Thursday, February 08, 2007 - 8:55 am: |
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Thank you much. I'll move my mount back to the box. I bought the 2awg cable to ground the battery directly to the frame and will go ahead and put that on today.
I did notice while talking to a buddy of mine that has basically the same setup, except he has an f-150, that he would turn and his signal would go to crap, then he would turn another direction and it would sound like he was right next to me.
I'll be moving the antenna today and running the final ground. Any high SWR and I'll put a bullet in this problem by buying some premium quality mini-8 coax and using it.
Thanks again Matt. |
Thrak1978
New member
Username: Thrak1978
Post Number: 4
Registered: 1-2007
| | Posted on Thursday, February 08, 2007 - 1:55 pm: |
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Heya Just as a side note I found another topic covering a similiar issue in another place on the forum and noticed you recommended to that person to use a spring and ball mount. Well my boss just gave me a 4inch spring and it lowered my swr down to more acceptable levels on channel 19, an even 2.0:1 so I'm going to see about getting a ball mount or a 6 inch spring. I am thinking my SWR will be between 1.5 and 1.8 then.
I swapped the 102" out with my old K40 for the sake of testing and my SWR was down to 1.5 with no adjustments, and I managed to get about 15 responses to a check, some so far/weak I could barely hear them. Then the drivers started talking about big expensive radios for about 3-4 minutes afterwards.
It might be time for me to invest in a pre amp so I won't be "all talk,no ears"
Thanks for the 3rd time.
Reggie |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 2379
Registered: 9-2004
| | Posted on Monday, February 12, 2007 - 11:24 pm: |
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hey reggie, no prob man, i like to try and help if i can.
yep, your buddy with the F150 was unknowingly showing you how directional his antenna system is.
now you can see why my first response was so long.
i try not to make any assumptions, and i did it anyway.
i didnt ask you about the mount you are using.
very important!
i assumed you were already using a spring.
YOU MUST USE THE CORRECT SPRING FOR THE 102" WHIP TO WORK RIGHT.
it must be the most heavy duty one they sell.
it will be about 6" and will have a sort of a "belly" in the middle. im sure you can picture it.
without that spring, your antenna is not resonant.
you see, at 27 mhz, a 1/4 wavelength is about 108", so the 102" whip plus the 6" spring equals 108".
any other spring will not work right, and the 4" spring will allow the antenna to sway way too much because it is not stiff enough for such a long antenna.
mount the 102" whip on the truck box, make sure the box is well grounded to the truck bed, cab, and frame, use the 6" spring, and you will be fine.
in fact, you will be more than fine; you will have the most efficient, furthest reaching mobile antenna setup available.
the only thing better would be if you had a van and could mount the 102" whip right smack dab in the middle of the roof.
how practical is that these days?
ONE NOTE!!!!!!!!
do not mount the antenna right up against the cab, when you mount it to the truck box.
make sure that wherever you mount it, that it is more than a foot away from the cab.
preferrably on the tailgate side of the truckbox, right in the middle. (if possible)
trust me, and dont believe all the hype you are sure to hear about antennas.
many, many truckers have been fed a line of bull from a slick talking salesman about the "best" antenna, and when they paid as much as they did; they do not want to hear that they got ripped off.
your 102" whip will outperform ALL other mobile antennas, if installed correctly.
now, their radio or amp may be causing their signal to go further, but with the same amp or radio, your antenna would get out further.
this includes the K40, which is a good antenna.
as for the preamp; dont bother with one.
they just increase the background noise along with the signal, so instead of S2 of noise, you have S6 of noise.
the way radio works; you can usually hear further than you can talk, so a preamp is not much use.
what good is it to hear them if they cant hear you?
once you operate this setup for a few months and get comfortable with it; come back here and we'll talk about a linear amp for you!
matt |
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