102" whip vs the rest

[brandon7861]

Any idea why I could lowered the SWR to 1.0 with the radial compared with 1.3 with the rear gate opened? What’s involved here ?

That is not a simple question and there is no single answer. There are so many factors that come into play with RF, from parasitics and ground loops to resistive losses and pattern distortion pushing current into materials they don't belong. What career PCB designers struggle with on a hand-sized scale using complex modeling software like HFSS, you are doing on a vehicle-wide scale with simple test equipment and no modeling whatsoever. There will be unanswered questions.

This is why I would like to see you settle for a configuration that is not only permanent, but one that offers a predictably useful pattern. What you are doing (playing with that tailgate and that ground rod that is poorly attached) is just slowing you down from achieving something that you will be happy with long term. It's up to you what you want to do, but if you want my advice... Shut the tailgate, get rid of the ridiculous counterpoise rod, and get the antenna matched. Be done with it.

Edit: Or, to keep it simple, measure the swr (with the antenna and vehicle as you want to use it), calculate the voltage on the coax with that swr to ensure there will be no (literal) fire in the wire with that gigawatt amplifier (you're probably ok skipping that step), then install a tuner at the radio end to keep the radio happy with said mismatch (oh crap, did I just trigger the "tuner theory" people????)

 

[Alexis Mercado]

Brandon, the whip tunes to 1.1 on the middle of the roof. I know for sure that’s the better spot for any antenna.

I just want to take advantage of the directivity of the whip mounted on the rear.

And for sure, the counterpoise looks extremely ridiculous.

Isn’t it to achieve the goal to get the lowest SWR ? As you could see on the analyzer readings, you can see all those results are fine.

I don’t mind the ridiculousness of the counterpoise rod. It is a shut out competition where we will have fun. As long as I can get the whip to work on the lowest SWR, it will be OK.

 

[Alexis Mercado]

Bu the way, why the length of this whip mounted on the rear is way longer than 108 “( in my case 117 inches long ) ? Is it because of the position ?

 

[brandon7861]

I am not one of the people here proficient in modeling software, but if I had to guess, I would say it has to do with the area of the ground plane underneath (and very close to) the antenna base. Ignoring the metal far away and only considering the metal near the portion of antenna with greatest current (the base), cutting it in half (placing the antenna at the back) would mean the other capacitor plate (the antenna element) would need more surface area to achieve the same capacitance as it would have had in the center of the roof.. However, I have no experience with modeling software, never even used it, so I am probably wrong. Just tossing a guess out there.

 

[Alexis Mercado]

Hi again. This is an update. I bought a 3 magnet mount to replace the 1 magnet mount in order to achieve more surface area. Also, I moved it 1 foot towards the center of the roof. I upgraded the coax with RG-400 ( Belden 84142 ).

It improved the SWR. Since I move it, I had to cut 1 inch from the tip of the whip. Now it is 116 inches long ( it was 117 inches long ).

One friend ( who used to compete on key downs) of mine told me that it is normal for any antenna to get longer when it gets close to the rear of any vehicle.

A- Here are some pics of the SS whip mounted on the new 3 magnets mount.





1- Readings with the rear gate closed



2- Readings with the opened gate



3- Readings with the opened gate on channel 7 ( where the key down competition will be )





B- I also tested a telescopic aluminum whip from an old antenna . It is 117 inches long. Here are some pics



1- Here are the readings with the closed gate


2- With the opened gate


3- Opened gate on channel 7


4-

 

[Alexis Mercado]

And the last reading from the aluminum whip on channel 7



I was wondering something. Since these antennas are longer than they are supposed to be, ( probably because they are not on the center of the roof ) Will they perform the same, better or worse than a 108 inches long whip ?

The idea to place the whip close to the rear is because I want the signal to be directional. Remember, it will be a key down competition. I will use the whip only once. Then I’ll replace it with a Stryker trucker antenna.

 

[338_MtRushmore]

And the last reading from the aluminum whip on channel 7

View attachment 59882

I was wondering something. Since these antennas are longer than they are supposed to be, ( probably because they are not on the center of the roof ) Will they perform the same, better or worse than a 108 inches long whip ?

The idea to place the whip close to the rear is because I want the signal to be directional. Remember, it will be a key down competition. I will use the whip only once. Then I’ll replace it with a Stryker trucker antenna.

Is this a mag mount specific competition? If not, you will likely lose to anyone not using a mag mount. Your ground losses must be massive for a whip that long.

 

[Alexis Mercado]

Is this a mag mount specific competition? If not, you will likely lose to anyone not using a mag mount. Your ground losses must be massive for a whip that long.

I can add a half inch ( about 1 feet long ) strap to the rear hinge. Will it resolve the ground looses ? I tested them with the ground strap as well with no noticeable differences. The three magnets have aluminum foil to improve capacitive ground.

 

[338_MtRushmore]

I can add a half inch ( about 1 feet long ) strap to the rear hinge. Will it resolve the ground looses ? I tested them with the ground strap as well with no noticeable differences. The three magnets have aluminum foil to improve capacitive ground.

I'd guess it wouldn't help much, but I am no mag mount expert. It's been over a decade since I've used one.

 

[hotrod]

should have never cut the 102-108 whip. its a perfect lenth as is..adding a ground wire could help...or could make things worse ..from ya pics you posted id say leave it be

 

[Alexis Mercado]

What do those readings tell you? Remember, I will run only 800 to 1,000 watts for this competition. After that, I will run the driver at around 200 watt with a center loaded Stryker SR-A10 antenna

​

 

[Alexis Mercado]

What I want to know if the stretched ( around 117 inches ) whips would be detrimental to the signal . I think I will be the only one using a whip. The other competitors will be using center loaded antennas like Predator 10k, Monkey made, and other center loaded ones.

Since my antenna will be the longest one, by logic, I am supposed to have a slight advantage over those 1/4 wave center loaded antennas.

Some swear that those antennas 5/8 but that’s an advertisement gimmick.

 

[AudioShockwav]

I would not worry much, you have good numbers on the analyzer.
This is a one time thing.
I have seen guy's do this before.
It's what you get running a mag mount when you just can not drill.
Run it and have fun.

73
Jeff

 

[Marconi]

Alexis, I agree with AudioShockwav.

I would like to know what were your Mini VNA readings you got on your mobile with the tail gate closed and the 1/4 wave antenna you used during the field strength test you did with your buddies?

I'm looking for a reading that does not show "OUT-OF-RANGE" condition on your Mini VNA when you were using the Striker SR-A10 antenna (78” long). This out-of-range message is still bothering me.

Reminder: also, what radio signal meter results did you get on your end of the signal testing you did with your buddies at 25 miles?

Marconi

 

[Alexis Mercado]

I wrote the data somewhere. as soon as I find it, i’ll provide it to you.