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4 antennas to 1 radio

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#2
Well you could run them into a switch and then choose which port you want opened depending on what you're listening to at that moment. That would make it so you dont have to constantly disconnect and reconnect
 

thewenk

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#3
BillQuinn said:
is it possible to hook up 4 antennas into one scanner? Low,vhf,uhf, and 800MHz? thanks!
It might be more trouble than it's worth. Use a good multiband antenna for vhf and uhf and a specific antenna for 800 (2 antennas total) would be my suggestion. Then use a diplexer to filter the 800 frequencies out of the multiband antenna. Numerous threads exist on this subject if you do some searches.

Dave
 

kb2vxa

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#5
Yeah, and you still have considerable overlap and phase cancellation making reception on certain band segments iffy at best. Theoretically a "quadplexer" is doable but requires considerable RF electrical engineering design skills and then manufacturing a brand new product.

Simply put in the New York vernacular; fogitit buddy, jus' git yerself a good anteena. (You'll save money on a lot more coax than you need too.)

Shine on you crazy Diamond; welcome to the RR machine.
 
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#7
Don_Burke said:
The antennas usually figure out a way to interact badly.

A single multiband antenna will almost always outperform a multiple antenna setup.
I notice you say "almost always". Is there any way to overcome this? I mean, if I have something with a roof the size of a Suburban or Excursion, can I overcome the interaction problem with distance, or is it more of a phasing thing that occurs regardless of antenna proximity?

As discouraging as it is, I keep coming back to this question because the performance difference between a multi-band antenna and a single bander is really profound, so it would seem worth it to find a way to make this work.
 
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#8
af5rn said:
I notice you say "almost always". Is there any way to overcome this? I mean, if I have something with a roof the size of a Suburban or Excursion, can I overcome the interaction problem with distance, or is it more of a phasing thing that occurs regardless of antenna proximity?

As discouraging as it is, I keep coming back to this question because the performance difference between a multi-band antenna and a single bander is really profound, so it would seem worth it to find a way to make this work.
Some wicked things can happen when two versions of the same signal meet up in the cables. Sometimes they will add and sometimes they will cancel. There is also the effect of one of the signals going up the cable to another antenna and bouncing back to the receiver. The lengths of the cables come into play here.

If I had my heart set on a multiple antenna setup, I would take a page from the cable TV systems and use a small preamp on each antenna, not for the gain, but for the isolation. A triplexer or quadplexer would probably be a good idea, although I suspect it would be a PITA to get right.

At work I use dedicated scanners on dedicated antennas. The antennas do work after a fashion on the other frequencies, but only as a backup. I consider that to be a simpler way to go.
 
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#9
If you have a Suburban or Excursion roof to play with you can certainly arrange seperate gain type antennas for VHFl o, hi, UHF and 800 with little or no interaction. That coupled with an off the shelf Triplexer or a combination of Diplexers will give you way better performance on all bands compared to the best single multiband antenna. That's assuming you will be using all the antennas and combining parts within their normal operating parameters. I do this at home with a broad band military 30-90MHz ground plane combined with a VHF hi band 4-bay dipole array, an 8-bay UHF dipole array and a large 10dB gain 900MHz omni. It actually overloads many of my scanners and sometimes I end up just connecting the antenna for the particular band of interest.
prcguy
Don_Burke said:
Some wicked things can happen when two versions of the same signal meet up in the cables. Sometimes they will add and sometimes they will cancel. There is also the effect of one of the signals going up the cable to another antenna and bouncing back to the receiver. The lengths of the cables come into play here.

If I had my heart set on a multiple antenna setup, I would take a page from the cable TV systems and use a small preamp on each antenna, not for the gain, but for the isolation. A triplexer or quadplexer would probably be a good idea, although I suspect it would be a PITA to get right.

At work I use dedicated scanners on dedicated antennas. The antennas do work after a fashion on the other frequencies, but only as a backup. I consider that to be a simpler way to go.
 
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#10
prcguy said:
It actually overloads many of my scanners and sometimes I end up just connecting the antenna for the particular band of interest.
prcguy
Like I said, wicked things can happen.

If I was going to use all the antennas you are using, I would look into dedicating a scanner or two to each antenna.
 
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#11
Aside from the occasional cable tv applications, I just don't know of anyone in the professional world who uses multiple antennas to one radio without tedious engineering and calculation, which includes the cable lengths involved, and the physical spacing between the antennas. Antenna stacking is done all the time, but it's for a single band, if not a single frequency. What you're wanting to do is generally considered unworkable.

I would suggest a single wide band antenna, such as a discone, and if performance is unsatisfactory, use a high quality low noise amplifier.If you really want to do it right, and money is no object, separate receivers for each antenna/band.
 
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#12
Cable lengths are not critical when using specific frequency antennas into a diplexer or triplexer. The roof of the vehicle mentioned is plenty large enough to arrange several antennas with minimal interaction. A Discone mobile? I've seen that and its not very pretty.
prcguy
zz0468 said:
Aside from the occasional cable tv applications, I just don't know of anyone in the professional world who uses multiple antennas to one radio without tedious engineering and calculation, which includes the cable lengths involved, and the physical spacing between the antennas. Antenna stacking is done all the time, but it's for a single band, if not a single frequency. What you're wanting to do is generally considered unworkable.

I would suggest a single wide band antenna, such as a discone, and if performance is unsatisfactory, use a high quality low noise amplifier.If you really want to do it right, and money is no object, separate receivers for each antenna/band.
 
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#13
prcguy said:
Cable lengths are not critical when using specific frequency antennas into a diplexer or triplexer. The roof of the vehicle mentioned is plenty large enough to arrange several antennas with minimal interaction. A Discone mobile? I've seen that and its not very pretty.
prcguy
I must have missed something. I was focusing my responses toward the OP, who didn't mention a mobile installation at all. Other than that, I agree... a diplexer provides isolation so critical length cable isn't necessary. And mobile discones ARE ugly. But I was referring to a fixed installation.

I didn't really express myself well enough... When I wrote that, I was thinking about applications where an omni antenna and, say, a yagi, were harnessed together to provide a unique radiation pattern on a single frequency band, which is the only application I can think of off hand where I've seen anyone use multiple receive antennas to one receiver on a single feedline, outside of this website.
 
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#14
Ah, now we're getting onto the same page here! Being primarily a mobile scannist, I never even thought about utilising multiple antennae on one scanner in my home. I mean, at home I can use a gigantic farking amplified multi-band antenna that sucks up every signal for 75 miles, so there is really no need for phasing multiple antennae together. But in the vehicle, with eight or so radios running, the ability to draw in maximum signal strength through the use of narrow band antennae is a potentially MAJOR benefit. I know for sure that I can get MUCH better performance from two or three single band antenna than I can from even the best multi-band scanner antenna. The question remaining is whether I can do so without creating more problems than I solve.

I was starting to think the question was definitively answered here already, but now I'm starting to think I may have to just pony up the dinero and experiment myself for the answer.

Two big questions though: Can I run a diplexer or duplexer backwards, attaching the scanner to the input and the antennae to the outputs?

And can I duplex a scanner and a transceiver into the same antenna? They make devices to run a CB transmitter and your AM/FM radio off the same antenna, so I would think so...?
 
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#16
af5rn said:
Two big questions though: Can I run a diplexer or duplexer backwards, attaching the scanner to the input and the antennae to the outputs?

And can I duplex a scanner and a transceiver into the same antenna? They make devices to run a CB transmitter and your AM/FM radio off the same antenna, so I would think so...?
The operation manual for my Comet CFX-514 gives three examples of use:
1- Multiple radios into one antenna.
2- One radio with multiple antennas.
3- Long coax run, using two triplexers.
Three radios into triplexer> one long coax> triplexer> three antennas.
 
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#17
You know what I would do? I would run a single 18" whip to the scanner with an Advanced receiver Research wideband low noise preamp with the ability to bypass it and run straight to the antenna. The performance would be more than adequate, you could bypass if it was getting over loaded, and you wouldn't have the expense and clutter of multiple antennas.
 
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#19
Where ZZ (and I) live were surrounded by 5,000ft and higher mountains on several sides and thats where lots of mainline public safety and amateur repeaters are located. Don't need to run a big mobile antenna in some areas around here.
prcguy
QUOTE=af5rn;810459]You live in the IE and really think an 18" whip is adequate for wide area, all band scanning?

If it's mounted on a mountaintop tower, maybe.[/QUOTE]
 
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#20
I live in the Flatlands of NC . I ONLY use a 19" whip for VHF HI and Lo, UHF, Milair 800 and 900 systems with very good results. I don't have a problem with overload and I hear lowband from all over the state. I hear Milair activity for a good 70 to 80 miles away. Keep it simple and you'd be surprised how well it will work.

EDIT: I forgot to mention that I use the 19" whip for MOBILE scanning. At home is a different story....
 
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