3 elements on a 4 door sedan

[bigred222]

i want to add a 3rd element to my 1998 audi a4 i am constructing something to mount a patroit 12ft base antenna off the back of the vehicle at a particular length and then use my 102'' whip on my trunk an the wilson 1000 on the roof of my vehicle. i want to make this setup directional and worth my gain so when i park up at the beach i can set this up and be much more efficient than just using the 102'' whip as my hot antenna. so i guess it would make it so the 102 and wilson 1k mag are directors. i just want some thing that is as effective as possible using VERTICLE elements

 

[M0GVZ]

My advice is to stop messing around, make a drive on stand that will support a telescopic pole and use the pole to support a Moxon beam or a dipole. It'll work far better than the half assed affair you're trying to use currently. Quite why you're fixated on vertical antennas I do not know. You want something effective yet seem to be just randomly placing them on the vehicle. They need to be at specific spacings and need to be specific lengths. You can't just go randomly whacking on whatever you think wherever you want.

Here's an example of a drive on stand.

http://www.sotabeams.co.uk/drive-on-car-stand-for-scaffold-type-poles/

 

[RatsoW8]

The 102" whip is the best choice without any other antennas mounted near it...especially a base antenna. Your plan won't work. It might get you a photo shoot on Ham Sexy though Follow M0GVZ's advice.

 

[bigred222]

i think im just gonna mount the 102'' and leave it at that. see if i can get the swr good and thats it. then crank up the horsepower and call it a day.

 

[Captain Kilowatt]

My advice is to stop messing around, make a drive on stand that will support a telescopic pole and use the pole to support a Moxon beam or a dipole. It'll work far better than the half assed affair you're trying to use currently. Quite why you're fixated on vertical antennas I do not know. You want something effective yet seem to be just randomly placing them on the vehicle. They need to be at specific spacings and need to be specific lengths. You can't just go randomly whacking on whatever you think wherever you want.

Here's an example of a drive on stand.

Drive-on Car Stand for Scaffold Type Poles - SOTAbeams

It's not so much the use of vertical antennas that bothers me as much as it is the dog's breakfast of antennas. Three different antenna types and lengths is going to be a nightmare to set up and run the way you want too. Pick the best performing antenna and go with it and it alone. At the very best you may gain half an S-unit IF you do everything right. The effort and :headbang is not worth it properly. It is however quite easy to do if you don't know what you are doing. :blink:

 

[Road Squawker]

... It is however quite easy to do if you don't know what you are doing. :blink:

I don't think I understand everything I know about that

 

[The DB]

I don't think the directional effects will be as you presume, if they are even significant enough to be noticeable.

I modeled a half wavelength antenna next to a quarter wavelength antenna at various distances apart, weather the quarter wavelength antenna was fed or not it had almost no impact on the radiation pattern produced, which was almost perfectly omni-directional. In either case the shorter antenna had to be pretty close to the length of the longer antenna before it had any significant effect on the radiation pattern. By pretty close I'm referring to about 10% or so size difference.


The DB

 

[Captain Kilowatt]

It is however quite easy to do if you don't know what you are doing. :blink:

I don't think I understand everything I know about that

LOL What I meant was that just like anything that you don't understand, it's always easy to go through the motions not understanding the degree of details that somethings require to be correct. Think tuning up a radio.

 

[Marconi]

I don't think the directional effects will be as you presume, if they are even significant enough to be noticeable.

I modeled a half wavelength antenna next to a quarter wavelength antenna at various distances apart, weather the quarter wavelength antenna was fed or not it had almost no impact on the radiation pattern produced, which was almost perfectly omni-directional. In either case the shorter antenna had to be pretty close to the length of the longer antenna before it had any significant effect on the radiation pattern. By pretty close I'm referring to about 10% or so size difference.


The DB

I see about the same thing in my models DB. If the antenna bandwidths are not overlaping the same bandwidth or real close...modeling shows little effect from being close. At least not near a much as many claim.

In my real world testing around here I see far more ill-effects of having my antenna set too low to the ground and below the peak of my house and those around me. This is where the house is obscuring part of the antenna at the bottom.

I have seen the bad SWR effect with mobiles however...on passing a large truck with a big body on the freeway, so I know stuff closeby does effect antennas, but I tend to believe the size of the obstruction has more effect than a skinny wire relative to the wavelength.

Look around as commercial communications setups and you'll often see multiple antennas that are very close together. Look on the roofs of building and towers too, antennas everywhere.

Unlike all these guys that can see RF and give us all the "woe' is' me," I'm just going by what my models show, and as usual...it ain't near as much of a problem as we hear claimed.

Now if we are tuning, testing, and comparing antennas it is common sense to get as much open space as possible.

 

[wa1knx]

multi tune, or beam

You can feed a cpl antennas in phase, not for pattern gain. but a decrease in
loading coil losses if the antennas are say shortened and a bit lossy. I've done
this on 75mtr mobile with success. The arrl antenna handbook has this under multiple-tuned antennas.
You could make a 3el yagi vertical beam for the beach, if you don't run out of ground-plane, with the audi. you can shrink the boom
length of a beam down to .15 or even .1 wavelength per element.
say 3 102 whips, lengthened or shortened as needed. ohmic losses pile
up the shorter you get, but it would play. you wouldn't want coil loaded
antennas for this project.

 

[bigred222]

What if I were to get 3 ss102'' whips at the same height and mount a boom that went off of my roof and used the spacing of a maco 3 element bean and worked out some input matching network? I don't mind doing extra work or would it be more effective to build something that hoists a 3-5 element Yagi of any angle polarization?
-222

 

[222DBFL]

There is a certain length that needs to be applied when mounting those 3 whips, why are you so dead set on becoming so directional? It is not going to be as easy as you think. But hey to each his own. IMO I would mount 1 102" ss whip, get the swr as low as possible and call it a day. If anything, make sure you use some good coax and a good hard mount. But that's JMO. God bless

 

[wa1knx]

vehicle as boom

Getting a parasitic beam to work isn't fussy, but you can't do it casually.
reading up on them is worth it plus one needs some instruments. I do like
the idea, as I almost put one together on my f-150 PU for 10mtrs - not an audi! - years back. For my old truck, if were armed with only a SWR
analyzer I'd do it this way. put a ball mount in front, one behind the cab,
one at the rear. ONE 102" whip at a time, tune the front +5% of the operating
frequency. (might need pruning) take it off. Put the middle one up, tune
for the operating frequency, take it off. Put the rear one up, tune for -5%
operating freq. (might need adding). ground the front and rear mounts.
Put all 3 whips on and connect up the rig to the middle. I'd probably be
seeing gain where ever I pointed my truck on the receiver! next I'd make
up a L match for the swr as the impedance may be much lower. arrl
antenna manual tells how to use them. an audi?? not sure what I would do..

 

[bigred222]

with all of this know said and discussed i think ive come to the conclusion that the best option is to setup a mount for a "portable" yagi antenna to see the most gain in signal for least amount of headache. so i will be posting up pictures of what i will work on tomorrow at work if i have time and look into purchasing a maco 103 or learning how to build my own yagi that proposes best gain for my budget. any more input on this specific thing "putting up a portable yagi" would be helpful
thanks
-222

 

[w9cll]

First thing you need to sell the Audi and buy a Suburban