One scanner, multiple antennas

[jaskel]

Sooo guys, I have attached a drawingof what I plan to do, I have an existing Discone on my roof and want to add a Airband antenna and maybe a UHF antenna and combine all 3 to feed my Uniden 996XT, does this diagram look right?? I live a fair hike from the main Airport in Sydney and the discone does ok but my main goal is to get better airband reception. I also use a Airnav Systems radar box and would like to mount an antenna for that as the cellular antenna I am currently using doesnt do too well,

what antenna do you guys suggest for a dedicated Airbnd and also a radarbox antenna?

Thanks guys

I know this is an old thread but hey it is still relevant

 

[WA1ATA]

I'm pretty sure that there will be slightly more than 6dB loss between each of the antennas and the scanner.

A perfect 4 way splitter will have 6dB loss in each path --- the 6 dB corresponding to the 1/4 of the power that is sent to each port. Since the splitter operation is symmetrical, it will also have 6dB minimum loss working in the opposite direction, as in your diagram.

If you want to eliminate the effect of the splitter loss, you would have have a preamplifier for each of the antennas. Ideally, each preamplifier would be located at the antenna so it would also compensate for any loss in the coax run.

Of course, if 6 or 7dB loss is acceptable for each antenna, just use the splitter by itself as you have drawn.

 

[andy1974]

well i have found this thread interesting.......however i have a question about this whole process about separate band antennas being set up and ran through a spliter, combiner, diplexer, duplexer, triplexer every what you want to call them. Un less the scanner can determain which signal to listen to at any given time and i am refering to triple trunking scanner that can can multi bands and systems at once. whats the point? why not just use a multiband antenna. maybe i am just not understanding. someone clear it up for me? just seems like it would be signal overload to the scanner and case intermod? and yes i realized i bummed on a OLD post

 

[jaskel]

well i mainly scan 1 band at a time, mainly air band.

 

[jaskel]

ok thanks champ, any ideas what preamp?? again I am only RX, no TX

 

[WayneH]

Please do not cross-post. I've taken the two discussions and merged them in to your own thread.

 

[LtDoc]

If I understood you correctly, you're using a cell antenna now. Before you go to a lot of trouble, why not try just an antenna for the lowest band of interest? Compare that to what you have now, any better? And if so, is it 'good enough' to satisfy you? Seems reasonable to me.
- 'Doc

 

[Nap]

Those splitters have at least 4dB of loss, whatever gain will be produced by a particular antenna will be annihilated by the splitter. Not to mention phase issues when adding signals.

You have about two options:

- buy multiple scanners and connect each one to its own antenna, program them according to each antenna's capabilities

- buy a scanner capable of "diversity reception" such as this one:

IC-R2500 Communications Receiver - Features - Icom America

 

[Turbo68]

Hi Jaskel why not use seperate antennas for each band u wil get beter reception and if u live a fair hike from sydney airport highly recomand the Polar-214A Dipole/Rfi-Gp3 Groundplane both are commercial airband antennas not cheap use both and they do an excellent job using RG213 coax cable.

Regards Lino.
ALINCO DJ-X11,ALINCO DJ-X2000,ALINCO DX-R8
AOR-8200MK3
GRE-PSR400,GRE-PSR500
GRUNDIG SATELLIT-750
ICOM-R3,ICOM-R20,ICOM-R71,ICOM-R75,ICOM-R2500,ICOM-R7100,ICOM-PCR1000,ICOM-PCR1500
ICOM-RX7
PALSTAR-R30A
REALISTIC-PRO2035
TEN TEC320D
UNIEN-245,UNIDEN-396,UNIDEN-780
YAESU-VR500

 

[n5ims]

well i mainly scan 1 band at a time, mainly air band.

Instead of using the three antennas through a splitter and suffering the splitter loss and distortion, phase loss, and other issues from having three antennas active, just use a coax switch and eliminate those issues. When on that single band, simply switch the antenna for that band and go. When you switch bands, simply switch the antenna for that band.

You could go fancy (and expensive) with one of these remote 5 way switches Ham Radio Outlet | AMERITRON RCS-8V | REMOTE COAX SWITCH 5 POSITION or something as cheap and simple as this 3 - Way Coax Coaxial DSS CATV TV F ABC Switch Push-Button

 

[W2PMX]

If you do use a 4-way splitter for 3 antennas, you'll get a lot more than 6db loss on each one, unless you terminate the 4th one with a non-inductive resistor of the same resistance as the system impedance (the coax, antennas and splitter should all be the same impedance - mismatches cause standing waves which increase loss). You should be able to fins a 3-way splitter, which will have less loss. But a switch will have still less loss than any splitter.

 

[Duramaxman]

I have 2 antenna's but, i have them run into there own preamps (Lowes) and then combined into one on top of the scanner, it works perfect. It will work, but youll need a couple preamps, good luck.

 

[prcguy]

For the OPs original intent a diplexer or triplexer will properly combine the different frequency antennas with very low loss onto one feedline. As mentioned, a 4-way TV splitter has at least 6dB textbook loss but its more like 7 to 10dB loss depending on brand.

Usually a scanner type Discone works about as well as a separate ground plane for VHF air band but if there is a gain type UHF antenna available you will really notice a difference by combining it with your Discone using a diplexer.

In this case the Discone can work for VHF air, 2M amateur and VHF commercial up to maybe 200MHz then the separate higher gain UHF antenna can take over above 400MHz.

You just need to find the appropriate diplexer or triplexer that will work best with the combination of antennas you have.
prcguy