Major 102" whip disappointment

[NeoHam]

I got a 102" whip to trim for 10 meters but thought I'd check it with the CB before I started. First I checked SWR with my old mag mount and it was 1.1. I installed the whip (phenomenal job I must say). Bumper mount on the corner of my full size work van. Hooked up some RG8. SWR ridiculous.. something like 2.5 to 4 I think. I ohmed the ground and it's good. My question is could the metal of the van be throwing it off? No spring.

I cannot leave it on there since it was swinging wildly and almost slapping the cars next to me. They must have been laughing.

 

[Se7en]

I got a 102" whip to trim for 10 meters but thought I'd check it with the CB before I started. First I checked SWR with my old mag mount and it was 1.1. I installed the whip (phenomenal job I must say). Bumper mount on the corner of my full size work van. Hooked up some RG8. SWR ridiculous.. something like 2.5 to 4 I think. I ohmed the ground and it's good. My question is could the metal of the van be throwing it off? No spring.

I cannot leave it on there since it was swinging wildly and almost slapping the cars next to me. They must have been laughing.

Lmfao running a spring on the whip is really funny u could almost smack cars forsure.
Bad piece of coax ? LOL make sure to check vswr when standing still. Don't try it while driving.

Sent from my Xoom using Tapatalk 2

 

[Robb]

This is the perfect example of why I won't mount an antenna on a bumper. . .

 

[KC9Q]

Neoham,

Using the 102” whip without the spring leaves the antenna 7” short of where it should be for resonance on 11 Meters. Your antenna will probably be closer to resonance at 10 Meters without the spring.

Mounting on a bumper is OK if there is minimal metal from the rear of the trunk to the bumper area, and the antenna should also be mounted about 6” or more away from the rear of the trunk of the car (if that’s what we’re talking about). If you’re mounting it on a bumper of a SUV/van, the SWR can be adjusted, however the bandwidth will be extremely narrow. That is why you will see many bumper mounted HF installations on SUV/van’s use a screwdriver antenna.

Case in point: I installed a Hustler CG-144 7’, 2 Meter whip on the rear trunk deck of my car and got 1.1:1 to 1.3:1 across the 2 Meter band. Place the same antenna on a trailer hitch mount and the SWR jumped up to 3:1 and higher. Placed the whip back on the rear deck and low SWR again

Hope I made my point understandable.

Mike

 

[BOOTY MONSTER]

too much metal too close to the antenna . i'd use a shorter antenna on top of the van myself ........
when you had the 102 on the mag mount , where was it at on the van ?
i

 

[Marconi]

too much metal too close to the antenna .
when you had the 102 on the mag mount , where was it at on the van ?

Back in the day we use to run our 102" whip on the rear bumper of our P/U trucks, and they were never a problem sitting a few inches from the tailgate.

The band width is so wide with a whip, even if it is resonant above the CB band a little, your SWR meter should still show a good match for channel 1-40.

Some guys ran their whip on top of the truck too, and they probably worked fine up there too. Installed right, the whip is a very versatile and effective, even when using only the 102" whip with no spring or spacer. Guys that ran springs did ok too, but their antenna were always laying down when on the move.

With mobiles, I suspect the problems are most often a lack of ground plane affect. Just because the 102" might be a bit high in frequency, the difference will not cause the SWR to be unworkably high like you claim just about anywhere in the <2.00:1 bandwidth, and the antenna is probably not resonant fully up into 10 meters anyway.

 

[BOOTY MONSTER]

hes using a "full size work van" so hes got about 6 ft of sheet metal a few inches from his antenna with only a few feet of antenna above it . seems like a lot more reflect than 2 ft of tailgate .

a 102 didnt wanna tune on top of my montero in the same stud that my 10k tuned to 1.3 on the mfj259 60 seconds earlier .
i was told "check the swr on the whip @ 28.6 Mhz. if you're looking for a lower swr. don't forget the hd spring and ball mount next time. have fun."

http://www.worldwidedx.com/cb-antennas/30479-10k-tunes-1-3____102-3-0-a.html

 

[cbradiomagazine.com]

Yeah - bumper mount on a full size work van is like mounting 6" from a steel wall, no surprise on the SWR readings.

 

[Charlie Brown]

i'm running a 102" whip on my bass boat with 3' coax. SWR is 1.3 and it'll talk skip on the water barefoot lol..^^ ab v c^^

 

[The DB]

The disappointment in this case is not in the antenna. Among the most important parts of an antenna setup, location, location, location. The rear bumper of a full sized van, bad bad bad location, even for such a long antenna. You would be far better off with a much smaller roof mount antenna.

Yes, assuming the same mounting locations the 102" plus riser should outperform any other mobile antenna. However, mounting the 102" so much lower and near so much metal really hurts it performance wise.


The DB

 

[mackmobile43]

Use a Wilson 5k and you'll be very happy but stay out of McDonald's.

 

[W5LZ]

Antennas 'like' to be above metal not beside metal, and they are not happy being under metal. Looking at it with that in mind it isn't too surprising to find your placement on the bumper of a van didn't produce very nice results. It would be the same with a car, just with less 'unhappiness' on the antenna's part.
It amounts to what's practical for you. If that bumper is your only option, well, it's just not going to be a very 'happy' set up. It won't make any difference which antenna, of whatever size, you put there it ain't gonna be 'happy'. The best result would be to mount the antenna where it isn't 'beside' any metal. But then you run into all the complications that would bring about (hitting things), and that just isn't going to be very practical at all. That means that you have to find a compromise that's 'livable' for you. (Like all the rest of us.)
Good luck.
- 'Doc

 

[jazzsinger]

why use a top class antenna in a third rate mounting position? might as well just use it lying inside the van.

 

[The DB]

why use a top class antenna in a third rate mounting position? might as well just use it lying inside the van.

Ain't that the truth.


The DB

 

[Marconi]

Eznec models in various locations on a mobile.

You guys are right, mounting the whip on the bumper of a full size van is probably not a good idea.

A while back Henry sent me his Eznec model of a mobile. I thought maybe I could model using his mobile, and see what Eznec suggested about a 102" whip in different locations on the body.

Here are several models and a recap of the results I got.

These are not modeled for accuracy and the only tweaking I did for the models was to set the radiator at 102", and changed the frequency for each so the model showed close to resonance with X=0<>.

The recap shows the maximum gain and angle at the two lowest lobes for the pattern produced, and the values for the match R=, X=, and SWR=. I should have added the resonant frequency to this recap too, but just check it out on each model...how this 102" radiator seems to be effected by different locations on the auto body. Maybe that happens in the real world too, and maybe that accounts for issues we hear folks complain about and maybe their not thinking frequency changes going on. I was a surprised to see this, but I can't really explain why, except to say again that these different mobiles all show the antenna a very different ground plane pattern. So, maybe that is what Eznec is showing us...a varying ground plane with changes in location.
At some point I will take one of these models and try tweaking the radiator length and see if I can't get a similar match as shown when changing the frequency. For me, that would be interesting, but of course with a 102" whip that doesn't happen very often, and if it did we might have to go both shorter and longer to get the tune.

Seeing this much variation, it seems obvious to me that in these mobiles we may be dealing with the vehicle body really acting as a part of the antenna, even more so...than with base antenna's feed line and mast.

View attachment Notes on Mobel .25 whip location..pdf

View attachment Mobile 102'' at various location..pdf

Don't depend on these models for your ideas without considering...your mileage may vary.