Multiple Antennas on a single cable??

[DracosIgnis]

I’m sure I’ll be called crazy for asking, but here goes…

Is it possible combine the signal from two different antennas to a single cable? I’ve seen many people here using RG6, and the standard splitter for TV cable says it can also be used to combine signals. If there is enough separation between the antennas, why not combine them in the attic, and run a single coax down? I understand a switch box can be used, but why not get the best of both worlds at once.

 

[K5MAR]

Yes, that can, and has been done. You need to make sure the splitter/combiner is rated for the frequency ranges you plan to use, for instance, some CATV splitters are only rated to 500 MHz. And there will be some signal loss in the splitter.

There are fancier units on the market made for this purpose, and I'm sure others will be glad to point them out to you. I haven't tried them, so I can't help there, but I have done the basic splitter/combiner trick with good results. I see you're in Dallas, so all you may need is a good multiband omni, but there's no reason not to give your idea a try.

Mark S.

 

[TeRayCodA]

Yes,I tried this once for a mobile application.I used a 18"whip for VHF,a 6"whip for UHF,(RG-58)tied it all together with a common CATV splitter,and it worked great!

The trick to get the RG-58 to fit into an F connector snug,is to "build up"the jacket diameter with a narrow strip of some of that aluminum adhesive tape.

-So good,I ended up keeping this set-up for about a year.

The same applies to a base scanner,I run a scantenna,and a discone,with a CATV switch box(switch between both,for land mobile,and aircraft)

 

[DracosIgnis]

Thanks… As I figured. I’ve got a Diamond discone mounted in a closet that does a great job, but like many others, I wonder if I’m missing anything. I was recently given a scantenna from Antennacraft, and considered moving one or both to the attic to see if I find anything else in the area. It’s a long shot, but I was wanting to pick up Irving which about 25 miles or so and I’m 99.9% sure I’m not having an luck since I can’t get the antenna in the air. (landlord wouldn’t appreciate an antenna 20 feet in the air.)

TeRay-
If you have both a Scantenna and a discone attached to a switch box, why not use a splitter to combine the two rather then pushing a button each time on the box and still get the best of both worlds?

Mike

 

[TeRayCodA]

To compare the antennas,see where each one has the best reception.

I listen to a distant TX,and switch between the two.

It'll really let you know how well each antenna receives this-or-that better.

 

[K5MAR]

While I agree with the idea of comparison testing the two antennas to see which works best for you, there is no doubt in my mind that your main problem is lack of antenna height. The best antenna you can get won't make up for this.

Solution? Move! Find a place where the landlord will allow an antenna. Yeah, I know, easier said than done! BTW, have you asked your current landlord?

Mark S.

 

[Highlander_821]

You could always get a second scanner/receiver and use the discone on one and the scantenna on the other. Program each radio to take advantage of each antenna's strong points. Remember, if one radio is good, two radios are twice as good....

 

[breadtrk]

You could always get a second scanner/receiver and use the discone on one and the scantenna on the other. Program each radio to take advantage of each antenna's strong points. Remember, if one radio is good, two radios are twice as good....

I used to juggle 2 girlfriends and had scanners at both of their houses. I got busted when I asked gf#1 about a conversation I had with gf#2 while listening to a similar event on the scanner.

2 radios is bad.

 

[smason]

I used to juggle 2 girlfriends and had scanners at both of their houses. I got busted when I asked gf#1 about a conversation I had with gf#2 while listening to a similar event on the scanner.

2 radios is bad.

Ouch.

I had a girlfriend who lived across the street from me. I'm normally not suspicious, so when I get to be, it's usually for a reason. One day I decided to monitor a certain device she used that happened to be on 46 mhz or so. Turns out my suspicions were founded. She was juggling too. Not for long....

 

[prcguy]

When using a TV splitter/combiner you will loose 3 to 4dB of signal right away unless you are combining two identical antennas phased properly for gain. You will also have potential problems with signals on one band being picked up by both antennas and arriving out of phase at the splitter, canceling the signal or degrading it further. For combining two or more antennas for different bands a diplexer or triplexer will combine them properly with minimal loss, probably .2dB or less.
prcguy

 

[N_Jay]

When using a TV splitter/combiner you will loose 3 to 4dB of signal right away unless you are combining two identical antennas phased properly for gain. . . .

You do not lose 3dB when combining, only when splitting.

You can get odd gains and losses if the two antenna have overlapping band coverage (and therefore will have the same signals out of phase.

 

[prcguy]

The will be a 3dB loss when combining two unrelated signals. I had to prove this to myself just now by connecting a high quality Angle Linear 440-470MHz Wilkinson power divider/combiner on a scaler network analyzer. Feed the signal into one of the two identical ports and measure at the common, or feed the common and measure at one output its 3dB loss plus a tiny bit more. The unused port was terminated of course.

This means people using a splitter to combine two antennas for different bands are taking at least a 3dB hit in signal from each antenna and probably much more.
prcguy

You do not lose 3dB when combining, only when splitting.

You can get odd gains and losses if the two antenna have overlapping band coverage (and therefore will have the same signals out of phase.

 

[W6KRU]

The will be a 3dB loss when combining two unrelated signals. I had to prove this to myself just now by connecting a high quality Angle Linear 440-470MHz Wilkinson power divider/combiner on a scaler network analyzer. Feed the signal into one of the two identical ports and measure at the common, or feed the common and measure at one output its 3dB loss plus a tiny bit more. The unused port was terminated of course.

This means people using a splitter to combine two antennas for different bands are taking at least a 3dB hit in signal from each antenna and probably much more.
prcguy

Jay is correct. The 3db loss when splitting the signal is obvious since 3db is a doubling of power and -3db would be a halving of power. Now the insertion loss when combining signals is anyone's guess. The really hard part though is predicting the strength of combined out of phase signals.

 

[prcguy]

If you read my last post you will see that I just measured this and there is a minimum of 3dB loss when running a signal through one side of a splitter or combiner and it doesn't seem to matter which way through the splitter. If you have two identical in phase signals that you are combining its a another story but the original post was about combining different band antennas and this will loose at least 3dB from each antenna.
prcguy

Edit: I just added a pic of the test setup in case someone thinks I'm making this up. This is a very high quality combiner/splitter and it shows 3.38dB loss at the minimum using it as a combiner.

Jay is correct. The 3db loss when splitting the signal is obvious since 3db is a doubling of power and -3db would be a halving of power. Now the insertion loss when combining signals is anyone's guess. The really hard part though is predicting the strength of combined out of phase signals.

 

[prcguy]

And one final addition, I measured a high quality TV splitter/combiner using 50ohm cables to feed the signal through it with a 75ohm termination on the unused port. I was surprised it was only 3.95dB loss in the 440-470Mhz range.
prcguy

 

[N_Jay]

The will be a 3dB loss when combining two unrelated signals. I had to prove this to myself just now by connecting a high quality Angle Linear 440-470MHz Wilkinson power divider/combiner on a scaler network analyzer. Feed the signal into one of the two identical ports and measure at the common, or feed the common and measure at one output its 3dB loss plus a tiny bit more. The unused port was terminated of course.

This means people using a splitter to combine two antennas for different bands are taking at least a 3dB hit in signal from each antenna and probably much more.
prcguy

Something was amiss in your set-up.

Your conclusion is in error.

 

[N_Jay]

If you read my last post you will see that I just measured this and there is a minimum of 3dB loss when running a signal through one side of a splitter or combiner and it doesn't seem to matter which way through the splitter. If you have two identical in phase signals that you are combining its a another story but the original post was about combining different band antennas and this will loose at least 3dB from each antenna.
prcguy

Edit: I just added a pic of the test setup in case someone thinks I'm making this up. This is a very high quality combiner/splitter and it shows 3.38dB loss at the minimum using it as a combiner.

THINK!!!!

If in phase signal are added, then there can not be a 3 dB loss on each port.

 

[W6KRU]

Something was amiss in your set-up.

Your conclusion is in error.

If the "high quality splitter" was a simple "T", I think it would measure this way. That is what the measurements seem to indicate. There is a halving of power no matter which way the goesintas and goesoutas are connected. ????

 

[N_Jay]

If the "high quality splitter" was a simple "T", I think it would measure this way. That is what the measurements seem to indicate. There is a halving of power no matter which way the goesintas and goesoutas are connected. ????

Nope, if it is a "T" hen you get out your Smith Chart paper and start sweating like it is your "Waves and Fields" final and your were out pounding beers last night. (Not that I can relate)

 

[W6KRU]

Nope, if it is a "T" hen you get out your Smith Chart paper and start sweating like it is your "Waves and Fields" final and your were out pounding beers last night. (Not that I can relate)

Sorry Jay, that is a little over my head. I've never had to learn smith charts. I know what they look like and thats about it.