• To anyone looking to acquire commercial radio programming software:

    Please do not make requests for copies of radio programming software which is sold (or was sold) by the manufacturer for any monetary value. All requests will be deleted and a forum infraction issued. Making a request such as this is attempting to engage in software piracy and this forum cannot be involved or associated with this activity. The same goes for any private transaction via Private Message. Even if you attempt to engage in this activity in PM's we will still enforce the forum rules. Your PM's are not private and the administration has the right to read them if there's a hint to criminal activity.

    If you are having trouble legally obtaining software please state so. We do not want any hurt feelings when your vague post is mistaken for a free request. It is YOUR responsibility to properly word your request.

    To obtain Motorola software see the Sticky in the Motorola forum.

    The various other vendors often permit their dealers to sell the software online (i.e., Kenwood). Please use Google or some other search engine to find a dealer that sells the software. Typically each series or individual radio requires its own software package. Often the Kenwood software is less than $100 so don't be a cheapskate; just purchase it.

    For M/A Com/Harris/GE, etc: there are two software packages that program all current and past radios. One package is for conventional programming and the other for trunked programming. The trunked package is in upwards of $2,500. The conventional package is more reasonable though is still several hundred dollars. The benefit is you do not need multiple versions for each radio (unlike Motorola).

    This is a large and very visible forum. We cannot jeopardize the ability to provide the RadioReference services by allowing this activity to occur. Please respect this.

Tuning a 102" whip

Status
Not open for further replies.

GoldenEagle17

Newbie
Joined
May 16, 2017
Messages
1
First, I want to thank everyone in advance for any advice, guidance, or help concerning tuning.

Here's what I have:
2006 Jeep Wrangler
Uniden 520XL
102" whip antenna
Astatic PDC7 swr meter
18' coax cable (could be 12')

My antenna is mounted to my bumper with a heavy duty spring and the coax runs under the bumper, up the fender and then routed through the padding of the roll cage.

I connect my swr meter to my CB and start with channel 1 in the FWD position and adjust the needle until it is on SET. Then I switch to the REF while continuously transmitting. The needle remains in the red with something like a 3.5.

I change the channel to 40 and repeat the same process above and I still get the needle in the red with something like a 3.4 or 3.5. Its so small in the change you really can't tell.

I do know that if one reading is higher than the other then it will dictate your next actions, lower or shorten the antenna. However, I can't seem to find the reason why I'm in the red to begin with. Additionally, I am wired into my fuse box with a connector and grounded to the floor.

Any help in this matter would greatly be appreciated. Thank you
 

mmckenna

I ♥ Ø
Joined
Jul 27, 2005
Messages
14,674
Location
SNCZCA01DS0
There's a lot of variables involved, and it'll take some work to narrow it down….

You need to do some basic checks first.
You'll need a multimeter or continuity tester for this:
1. Disconnect the coaxial cable from the back of the radio.
2. Check for continuity between the center conductor and the outer conductor. There should NOT be continuity. If there is, you have a short circuit somewhere, probably in the connector or antenna base. That'll need to be fixed.

Next:
3. Check for continuity between the antenna whip and the center conductor of the far end of the coaxial cable. There should be continuity.

Next:
4. Check for continuity between the outer shield of the coaxial cable and the vehicle body. There should be continuity.

If all that checks out, then we need to look at antenna length.
3.5:1 is pretty high, so that indicates either a coaxial cable issue, connector issue, or an antenna base issue.
You said you have a heavy duty spring on the base. The length of the spring and antenna should be close to 108 inches. This is quarter wavelength on the CB frequencies.

The other issue that is common with Jeeps is proper grounding. You didn't say what bumper this was mounted on, front or rear. Either way, making sure all the body panels are properly grounded is very important. If the antenna is mounted on the back bumper, you need to be 100% sure there is a good RF ground from the tailgate to the rest of the body. That often requires running a ground braid from the tailgate to the body and making a really good connection.
You may need to do the same with the drivers side and passenger side doors as well as the hood.

Having the antenna mounted down low on the bumper can cause issues with reflection from body panels that are close to the whip. Ideally the antenna needs to be out in the open. If it is down low and close to the vehicle body, that can cause issues.
Along these same lines, make sure you are testing the antenna out in the open, away from any metal, such as garage doors, metal fences, lamp posts, etc. These can all impact your SWR readings.

Also, make sure the CB chassis is well grounded. Do not necessarily rely on the negative power lead for a good ground. I've always installed a short jumper between the radio chassis and the vehicle body, as short as possible.

Unfortunately doing a proper job installing on a Jeep can be difficult. Most people just mount the antenna and go, never bother to check the SWR. You're doing it right, so keep working on this.

Pictures can be worth a thousand words. Specifically the mounting location and both sides of the antenna base. If you can post some photos, that can really make life easier.
 

BushDoctor

Member
Joined
Dec 19, 2002
Messages
130
Location
Strasburg, Va
First, I want to thank everyone in advance for any advice, guidance, or help concerning tuning.

Here's what I have:
2006 Jeep Wrangler
Uniden 520XL
102" whip antenna
Astatic PDC7 swr meter
18' coax cable (could be 12')

My antenna is mounted to my bumper with a heavy duty spring and the coax runs under the bumper, up the fender and then routed through the padding of the roll cage.

I connect my swr meter to my CB and start with channel 1 in the FWD position and adjust the needle until it is on SET. Then I switch to the REF while continuously transmitting. The needle remains in the red with something like a 3.5.

I change the channel to 40 and repeat the same process above and I still get the needle in the red with something like a 3.4 or 3.5. Its so small in the change you really can't tell.

I do know that if one reading is higher than the other then it will dictate your next actions, lower or shorten the antenna. However, I can't seem to find the reason why I'm in the red to begin with. Additionally, I am wired into my fuse box with a connector and grounded to the floor.

Any help in this matter would greatly be appreciated. Thank you
It might be the antenna is to close to the metal body before it rises above the body. Try it without the spring just to be sure it doesn't make a difference either way in power reading it should be more without the spring . I noticed when i mounted low band antennas on armored trucks i had to use a longer antenna then mounting on a sedan rear quarter panel Even the rear quarter panel i used the formula 3045/freq in mhz total length including the spring. ON armored trucks mounting on side just behind drivers door were always a problem i used a much longer whip on them to get the reflected power lowered. You might try the front bumper just to see if it is lower then you will know if it is the added metal in the rear. I hope this gives you a place to start. I added springs to make the antenna longer if needed then my 96 inch whip length tester was. When i worked on 2 way radios back in the 50s almost everything was low band we thought taxi. A combo i found handy for CBers was a Motorola low band antenna with a Motorola loading coil (TJB 6071A) above the spring and as i recall an 89 inch whip for cb mounted on the side of a motor coach Greyhound style due to the metal on the side going so high which you might have to resort to using your present antenna. you just have to keep trying i had the advantage of lots of antenna rods various lengths and a whip length tester. An extra spring or 2 might give enough added length to get the swr down.
 

Gniederb

Member
Joined
Dec 27, 2015
Messages
58
Location
WV
I'm far less advanced than the other guys that posted on here but I have one thought for you. It's always best to have your antenna in the location of your vehicle that is centralized based on the metal mass in your vehicle for the sake of the ground plane. Putting it on a corner or a bumper is always inferior to center mass, maybe not too bad though and if you don't want to listen to it bang off of every tree and low sign you go under like I do then the roof is out of the question for a 102 inch whip. But that's exactly were mine is on my 13 silverado and has been for a while and I've hit lots of things at high speeds and my antenna is fine and my truck is fine, it's just noisy. I've even had it on a high lift with the antenna bent in half at the garage and it straighten back up immediately upon exiting.

Now that I've presented you with my roof mount commercial I don't own any super expensive analyzers or even an swr meter but I do have a cb/ham/communications shop in Mineral Wells WV that has all those things and I pay them a token fee to set it all for me and then leave it alone. They even explain to me in detail the hows and why's (which I remember) and the actual physics of it all (which I quickly forgot) But there's no replacement for the type of analyzers that can check your ground plane and make sure your forming proper "lobes" (I think they are called) Apparently your antenna isn't just a stick it makes some big invisible bubble that performed the actual function and it gets drawn and stretched towards nearby metal and will transmit and receive stronger in certain directions and weaker in others depending on where it's mounted and where the major mass of your vehicle is if I understand my tutors correctly.
 

jim202

Member
Joined
Mar 7, 2002
Messages
2,669
Location
New Orleans region
Unless I missed it, one test that wasn't mentioned was to disconnect the center of the coax from the base of your bumper mount. I have seen these mounts where the center was not insulated from the mount. As such, it caused a short on the coax cable. You will end up knocking your head on the bumper in frustration if this is the problem.

Basically the spring and whip antenna should be floating off of ground. If not, your never going to get your antenna to tune. The SWR will stay very high and not move no matter what you do.

Come back and tell the group here just what you found and did to resolve your problem.
 
Status
Not open for further replies.
Top