setup for 2 antenna system on mobile

[Mr Fort Worth]

Can anyone offer an opinion about what the best way to set up a two antenna system ( 1 hot and 1 reflector ) on a mobile is???

 

[W5LZ]

Best generalized way I can think of is to decide which direction you want the thing to point. Put the two antennas the 'right' distance apart, which can vary quite a bit. Make the 'reflector' something like 10% longer than the driven element. Match feed point impedance to the feed line and radio.
A good starting point for 'spacing' would be a typical two element beam. Adjust from there to suit your requirements.
Sounds simple till you start doing it, then it turns in to quite a guessing game.
Have fun.
- 'Doc

 

[Mr Fort Worth]

"right" distance

I am getting a lot of differing opinions about the "right" distance. I am beginning to think I would do better playing the Lotto!!!! The problem is I only have one roof up there and I would like to get the holes correct on the first try. This pipe dream is what has led me to these forums trying to get all the info I can. I am beginning to see I may have to put more than hole until I get it correct. If anybody has a pretty good starting point or something they know will work on top of a 2003 Ford E250 extended cargo van I am all ears.

Thanks!!!!

 

[GunSlinger338]

72-86 inches is where 99% of these type setups are mounted.
no matter the spacing.. when tuned the rear antenna will end up 4-8 inches longer than the hot antenna.

 

[W5LZ]

You'll get about as many opinions as there are people talking about it. If you should come up with the best solution for you on the first try, would you buy me one'a them lottery thingys too??
I'm not aware of any 'perfect' set up. I seriously doubt if there is just -one- for all occasions. One'a them "one size fits all" thingys, meaning that it's only going to 'fit' one particular instance well, the rest are just possibilities. If you happen to have that 'one instance' where it's just 'perfect', fine! Don't count on it though. Same old story, put the thing on, then tweak it till it's more better.
Good luck.
- 'Doc

Maybe one 'work around' is to put that reflector on a mag-mount till you find what suits you best. Then drill the hole. Is that a good way of doing it? I sort of doubt it, but...

 

[GunSlinger338]

i did this comparison of 3 different antennas a few months back
here are the results

86" vs. 72"


( Disclaimer ; your results may vary )
All test with Cobra 29 @ 12 RMS bird watts dead key with mic gain at zero
measured with Bird43 w/ 25 watt slug and Fatboy digital field strength meter
all test were from same suburban , same mounts , same location , same day , ect...ect...


2- 27 " 10ks at 72" --------------- 102 on the field strength
2- 27" 10ks at 86" ---------------- 82 on the field strength

2 FatBoy R4's at 72" ------------ 68 on the field strength
2 Fatboy R4's at 86" ------------ 99 on the field strength

2 adjustable 102's @ 72" ---- 123 on the field strength
2 adjustable 102's @ 86"----- 104 on the field strength