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Dual Predator 10k's

D

distortion

Active Member
Jan 1, 2006
106
1
26
atlanta, ga
I have a 98 sonoma. I have 2 dual coil predator 10k's, both 22" shank's. One is currently mounted on the roof, another I just got. Would I benefit by mounting a 2nd antenna on a bracket on the center of my tailgate (if I could make it work)?

Thanks,
Josh
 

Josh,
The benifit of any dual antenna set up is that they provide a sort of directional radiation pattern. Just how directional it is depends a great deal on the distance between the two antennas, not to mention the 'joys' of matching/phasing the things. If that's what you are looking for, or if you think having dual antennas 'looks' great, then have at it! Otherwise, it just isn't worth the trouble as far as realizing better performance on HF (doesn't really matter what the antennas are).
The draw-backs to any dual HF antenna set up are;
Cost (twice as much).
Installation (where and how they are mounted, distance between them being important).
Phasing/matching (lots of 'fun').
Directianality (at least half the time you'll be pointed the wrong way).
Looks (just depends on wht you think is 'nice').
Gas milage (increased drag, and sort of a 'stretch' really, but thought I'd mention it anyway).

Sound like I'm trying to talk you out of it? Well, I am, sort of. But, not very hard, and if you wanna do it, then do it.
- 'Doc

PS - Completely beside the point, you have one of, if not the best small trucks ever made! I had one two years older than yours till someone decided to "T"-bone me. Worst thing that ever happened as far as what I drove. They don't make them anymore (stupid!) and if you can find another one (impossible around here) you'd better get it. Ended up with a truck eight years newer (S-10) and while it ain't 'bad', it certainly isn't as good! If/when I get the @#$ thing paid off, you wanna trade??
 
I understand.. I don't really mind being directional.. Before I had this setup I had a 102" whip off the back left corner of my camaro. I'd turn my 2x4 up and people would get 4 lbs on me 20 miles away.. turn the car around and I'd be hitting them with 9+. I'm usually parked when really throwing down so I don't mind turning around in order to key on someone, or just talk to someone distant.

But there is a stipulation to this.. I don't want to go directional and not receive much gain. The idea is to be able to key out people who are on single antenna systems with less power. Maybe not alot less, but a couple hundred more watts less.

How much gain does adding a second antenna add in the direction of the signal. Is it an extremely noticable difference.

Also, how do you go about matching/phasing 2 antenna's? Do you have any documents I can use to try and set this up.

FWIW: I'll trade all day long :) I love the hell out of my truck.. but I got an insane deal on it, and I only got about $800 in it ;)

Peace,
Josh
 
Josh,
Gain? Extremely noticable, no. Noticable, yes, probably. As for the phasing/matching, it's basically two electrical 1/4 waves of 75 ohm coax, one running to each antenna, then 50 ohm coax from where they join to the radio. That's the simple explanation. For your particular set up it gets sort of more complicated. One of those electrical 1/4 wave sections isn't going to be long enough, so, you make it three of those lengths long. The extra 2 lengths add up to a 1/2 wave which is sort of electrical 'neutral' (like it isn't there). If that isn't long enough then as long as it's an 'odd' multiple then it'll work (3 - 5 - 7 etc.). A 'T' where the two join works just fine, or, simply splicing them will work too (water proof them though). I'm not aware of any pictures showing how it's done, so sorry 'bout that. Bet others do know and will show you.
- 'Doc

PS - If I had the $800 I'd take it off your hands!
 
Not sure if I'm understanding, is distortion going to co-phase or just use the rear antenna as a director? is this is the case there's no need for phasing or matching just fine tuning the antenna that's radiating, correct?
 
"How much gain does adding a second antenna add in the direction of the signal. Is it an extremely noticable difference?"

when done correctly the additional gain in the favored direction/s can be as much as *3db.. that would be roughly equivalent to doubling your current power output with the single antenna. how noticable would that be? how much more expense would that involve when compared to increasing the gain of the antenna system, even if only in certain pre-determined directions?

the problem with a conventional phasing configuration with both antennas in the same plane front to back on the vehicle is that the signal advantage would be to the sides of the vehicle, within the usual 1/8 to 1/4 wavelength spacing.

depending on the distance between the 2 antennas at the roof and the tailgate a parasitically energized 2 element array may be possible (and providing an increase in performance in generally ONE of the two dections) but the problem here is that the spacing between the 2 antennas is going to affect the input impedance of the driven antenna. ideally the distance of the antenna on the tailgate (from the driven antenna) could be altered to facilitate the proper match of the driven antenna on the rooftop, difficult to to with fixed mounting. for a conventional phased array, (and since newer vehicles don't lend themselves very readily to mirror mounted antennas) usually a light rack/roll bar installed at the cab bed/roof will provide the necessary spacing for a pair of antennas at each end of the cab and the job is fairly straight forward from there.

a properly phased pair of antennas will produce *gain over a single antenna in the directions that are at right angles to the plane of the antennas. the ground mass geometry of the vehicle itself enhances the increase in signal to the front and rear simply by virtue of the fact that the longest paths of body or frame metal in the case of an antenna system so configured are present in those directions as opposed to the sides of the vehicle. and also, since this is the case, another added benefit is that signals arriving from the sides of the array are attenuated when compared to the front and the rear and reception is also enhanced to the same degree. the array produces measurable levels of front to side rejection, which should come as no surprise because that is how antenna gain is achieved in the first place, regardless as to whether we're dealing with the (-) azimuth or (|) elevation planes.
 
Good information freecell. Makes it very tempting to do, I'm gonna start collecting parts and testing in the next few weeks.

What kind of gain can I expect on the receive side of things?

Thanks,
Josh
 
Antenna gain works the same both ways, so if you have a 3 dB gain on the transmitting side, you should see a 3 dB increase in received signal strength.

How much is 3 dB? About half of an S-unit.
 
Beetle said:
Antenna gain works the same both ways, so if you have a 3 dB gain on the transmitting side, you should see a 3 dB increase in received signal strength.
How much is 3 dB? About half of an S-unit.
Click to expand...

Seems like alot of expense and hassle for 1/2 an S unit.
 
Back in the late 60's, or early 70's, Antenna Specialists, or Hygain made a switch box for mobile use of two antennas. As I recall, it had three positions: Omni, Left-Right, Forward-Back. Not sure just how it was configured. Anyone else remember these?

Rich
 

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