UHF antennas

Submitted: Thursday, Nov 28, 2002 at 01:00
ThreadID: 2490 Views:2144 Replies:7 FollowUps:3
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Does anyone know if a "splitter" can be used between 2 antennas. I have a 1.8m antenna with a 6dB throw or pattern. What I'd like to do, is get another antenna with a 4dB gain, which is suitable for hilly terrain.
In other words, what I'd like to do, is to get the best of both worlds, both antennas working at the same time, one for flat terrain, the other for hilly terrain, hanging off a splitter, and connected back to my GME TX3400. Anyone tried this??
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Reply By: Eric - Thursday, Nov 28, 2002 at 01:00

Thursday, Nov 28, 2002 at 01:00
Johnf.
The myth about antenna's for hilly and flat ground must have been started by a antenna salesman, the polar patern of the 4db and the 6db are both suitable for eather terian. The most important thing about mounting your antenna is to get it above the vehicle because the signal is blocked by any metal object more than 1/10th of a wavelenth wide. Look at the police and ambulance antennas, always short and above the roof line and away from the interference generated by the motor. When lives depend on radio many hours of testing is done and the result is there for all to copy.
Eric.
AnswerID: 9093

Reply By: Mike - Friday, Nov 29, 2002 at 01:00

Friday, Nov 29, 2002 at 01:00
I don't know why everybody has large aerials on there vehicles, I have a 13cm uhf 1/4 wave aerial on a magnetic mount thats sits on the rear shelf INSIDE my car and I TX & RX repeaters some 60km away also simplex around 10kms.
AnswerID: 9101

Follow Up By: Bob Y. - Friday, Nov 29, 2002 at 01:00

Friday, Nov 29, 2002 at 01:00
Mike, Maybe people like to get more than 10 km on simplex, we get that from hand helds here, and up to 30 km on simplex in mobiles, as long as you are on high position. Nobody NEEDS long aerials, but when conditions are not optimum, then the better performance of longer aerials can make a vast difference, especially in work/safety issues. But it's like beer and tyres, everybody is right...Catch you later..
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FollowupID: 4550

Reply By: ken d - Friday, Nov 29, 2002 at 01:00

Friday, Nov 29, 2002 at 01:00
Back to the original question.
No you won't be able to get an effective splitter. Signal can be split between 2 antennas however this requires an engineering solution for each particular setup. Reason being that the signal has to have the correct phase relationship at each antenna in order that you don't get cancelation of signal. Dificult to explain but basically where mulitiple antenna are used together they have a splitter and phasing setup in order that they work correctly. eg Have a look at phased arrays for TV. (The setups with multiple antenas one under the other).
You could use a coaxial switch ( has to be a coaxial switch) to selct one antenna or the other (make sure you are not transmitting when you switch, the smoke might come out),

Cheers
Ken
AnswerID: 9113

Follow Up By: Johnf - Friday, Nov 29, 2002 at 01:00

Friday, Nov 29, 2002 at 01:00
Thanks Ken D. What you say makes sense. I might try the switch, because when I'm touring, the terrain changes when you're doing lots of kms, and it's impractical to stop and change antennas all the time. The switch sounds good option.
And also, by the way, thanks for actually answering the question. I've noticed lots of people tend to bounce off into other irrelevant issues, in the forum generally.
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FollowupID: 4570

Reply By: Truckster - Friday, Nov 29, 2002 at 01:00

Friday, Nov 29, 2002 at 01:00
I just carry it in the car and swap ariels when I cant hear anymore.....

Takes a whole 10 seconds
AnswerID: 9127

Reply By: Bob Y. - Saturday, Nov 30, 2002 at 01:00

Saturday, Nov 30, 2002 at 01:00
John, have you had a look at GME website, their 4700 series aerials would suit your requirements. Five whips, from about 400mm up to 2 M, with gains up to 6 dB, all on one spring base. Screw on & off in few seconds.

It's easy to get sidetracked from original query, when others make statements, that might suit them, but wouldn't apply in extreme conditions. Catch you later...
AnswerID: 9140

Reply By: Member - Nigel - Sunday, Dec 01, 2002 at 01:00

Sunday, Dec 01, 2002 at 01:00
A splitter would not help you as even if it was engineered to suit your two different antennas, you would only be getting approx half the signal into each antenna, thereby reducing your useful transmitting range.

Co-phasing is simpler and uses two identical antennas to increase the signal strength in a particular direction (at the expense of other directions) but that's not what you are trying to acheive.
AnswerID: 9158

Reply By: plexus - Tuesday, Dec 03, 2002 at 01:00

Tuesday, Dec 03, 2002 at 01:00
Well, I've welded a tag onto the front of the bull bar on my FJ60 which carries both 2dB and 4,5dB colinear, groundplane-independent antennas. Contrary to what some may think, the radiation patterns *are* different. I use the 2dB for hilly areas and the 4,5dB when things are flat. Definitely makes a difference. I just use a switch mounted under the dashboard where the glovebox is. 1 second job to change over.
AnswerID: 9298

Follow Up By: Johnf - Wednesday, Dec 04, 2002 at 01:00

Wednesday, Dec 04, 2002 at 01:00
Thank you Plexus - this is precisely what I'll be doing, using a switch to flick between the 2 antennas. I can't do what BOB Y suggested, because the original series 6dB antenna I have does not have a lower dB antenna available in the range, so I have to buy the 4700 series, which has a different base. Anyway, I'd rather the convenience of flicking a switch, than screwing antennas on and off every time you go around hills. Yes, I'm lazy, what the heck.
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