[2m] Re: [Antennas] mobile ants

[cboone at earthlink.net]

On the "chicken band" the spacing and coax phasing lines were so far off, I am suprised the antennas worked at all..
A single antenna was better! (can you say marketing hype?)......As someone who has done active antenna arrays (especially in AM broadcast) for 30 years, nope, the CB antenna was a joke...sorry but the laws of physics dont work for it....it looked nice but in reality, didnt work worth a flip...(just like the other gadgets sold for truckers, etc...most are junk and doNOT help....the echo boxes, etc! CLEAN clear AM audio travels best....anything else just degrades the range of the signal and reduces audio punch on the air; best thing for good audio is an Optimod 9100 ;).

As for 2mtrs, NOW you are getting to a point where you can get "gain" and directivity (the wavelength is short enough for it to work) but only in two directions (usually)....but again, it takes the proper spacing and coax phasing lengths to do it...is it worth it? Unless you want to lose signal say off the sides of your vehicle (turn and the contact is gone!), its not worth it..

Omni directional antennas are designed for that reason...so you can turn a corner and NOT lose the signal...
(think driving with a yagi on your auto...you REALLY want that?). To keep the signal "tuned in" you would have to electrically change the phase between the two antennas...or change the length of the phasing lines and then there is the SWR matching...tieing two together via a coax T is not doing it right...two 50ohm antennas teed together results in a 2:1 SWR (or 25 ohms at the common point) and thats ONLY if the antennas are 50ohm and the coax lengths are the same lengths.

A 5/8wave is ok for most uses...anything bigger on 2m gain wise would be pretty tall to get decent gain in an omni pattern.

BTW, gain in an omni antenna is done by squeezing the pattern DOWN...take a balloon or donut and squeeze it with your hands on top and bottom...the bulge is the "gain" but you lose signal at top and bottom...in mobile FM vertical antenna use, thats not an issue.

Hope that helps explain it..

Chris
WB5ITT
(ex KDO-2700)
FCC Commercial since 1973

-----Original Message-----
>From: Jonathan Thawley <kc8cpw at gmail.com>
>Sent: Jan 30, 2007 9:32 AM
>To: 2m at mailman.qth.net, antennas at mailman.qth.net
>Subject: [Antennas] mobile ants
>
>I have a weird question... I've seen this done on the "chicken band"
>but never ham radio...
>
>Could I run 2 5/8 wave mobile antennas on 2m and hook them up to my
>radio with a so-239 T adapter?
>
>What, if any improvement would this warrant over just 1 antenna?  Or
>would I risk blowing up the radio?
>
>Curiosity is just killin the cat today.. LOL
>
>Jonathan/KC8CPW
>