Question: Mixing two antennas

scandiskwindows9x

Moderator of DTV Latino
#1
Hello

Was thinking in mixing two antennas have my old one of 8 elements and my current of 13 elements with corner reflector my question is what I would get if do this ie both antennas are UHF but my idea is put the 8 elements one in another location.

This would improve my poor signal strength or would cause an strong impact on the signals received?

Best regards
Francisco

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nbound-au

The Graveyard Shift
#2
Im assuming you mean with a diplexer/combiner to combine two separate signals from different directions, in which case it wont have any effect on what your already receiving except about 1dBuV insertion loss.

But if you are trying to increase your signal from a single direction (or you have a rotor) you can pair the antennas in a phased array and gain upto 3dBuV over the original antenna's gain, but you need two antennas of the same type to accomplish this properly.
 

Fringe Reception

Super Moderator, Chief Content Editor
Staff member
#3
Im assuming you mean with a diplexer/combiner to combine two separate signals from different directions, in which case it wont have any effect on what your already receiving except about 1dBuV insertion loss.

But if you are trying to increase your signal from a single direction (or you have a rotor) you can pair the antennas in a phased array and gain upto 3dBuV over the original antenna's gain, but you need two antennas of the same type to accomplish this properly.
I have no clue what 1dbuV means but in REAL terms that our readers can understand, if you split a signal two ways it cuts the signal in half. It works very much as garden hoses work. Two water outlets from the same source each deliver half of the available water. Duh!

But IF ... you have enough clean signal 'strength" to start with, dividing it in half makes no difference to your tuners. I split FREE TV 4-ways around my home without using any amplifiers.

However, connecting a second antenna to a coaxial cable with a functioning antenna setup and expecting it to add channels to the existing setup is nonsense 99% of the time. Yes, Low or High band VHF can be easily added to a UHF antenna setup, but combining similar-band signals is very unlikely to work for you.

Jim
 
#4
I have no clue what 1dbuV means but in REAL terms that our readers can understand, if you split a signal two ways it cuts the signal in half. It works very much as garden hoses work. Two water outlets from the same source each deliver half of the available water.
I read somewhere that's just what you would expect from subtracting 3 dB -- half a signal. Something to do with the logarithmic scale per dB. (I'm a math head, but I admit I don't understand it either. Might have something to do with the fact I haven't done my homework. :shrug: )

But IF ... you have enough clean signal 'strength" to start with, dividing it in half makes no difference to your tuners. I split FREE TV 4-ways around my home without using any amplifiers.
Isn't that because (almost) every TV has an amp between the coax input and tuner? I see these big "studies" comparing different antennas, and they just hook them up to a signal meter -- no amp! It can leave the impression you're not going to get those stations below a certain cutoff strength, and that just ain't so.

However, connecting a second antenna to a coaxial cable with a functioning antenna setup and expecting it to add channels to the existing setup is nonsense 99% of the time. Yes, Low or High band VHF can be easily added to a UHF antenna setup, but combining similar-band signals is very unlikely to work for you.
But combining signals from opposite directions (two antennas sufficiently spaced apart), that could work, couldn't it? At least for those channels with no direct conflicts?

Thx,
Rick
 

Fringe Reception

Super Moderator, Chief Content Editor
Staff member
#5
... But combining signals from opposite directions (two antennas sufficiently spaced apart), that could work, couldn't it? At least for those channels with no direct conflicts?

Thx,
Rick
Rick,

Antennas receive and they transmit. If you connect two (X and Y) receiving antennas pointed at two different directions, they might provide useable signals for you to receive, but half (signal level) of the the signals received by each antenna are retransmitted by the other antenna which is coupled in this setup. If the two antennas are not identical, the signals will not easily escape do to a phenomenon known as standing waves. Google it.

Neither antenna collects 'perfect' RF signals and consequently any multipath reception received is also shared and retransmitted by both antennas.

So, on the single feedline to your TV set, you now have competing signals on the same channel: the primary signal from a strong local channel BUT there are delayed (multipath) lower level signals coming in from the second antenna and your tuner is 'seeing' all of them. So, how can it choose which digital stream to decipher, after all ... both streams may be clean enough to decipher, except they cancel each other, meaning no reception at all = black screen.

Jim
 
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nbound-au

The Graveyard Shift
#6
I have no clue what 1dbuV means but in REAL terms that our readers can understand, if you split a signal two ways it cuts the signal in half. It works very much as garden hoses work. Two water outlets from the same source each deliver half of the available water. Duh!
You arent splitting a signal, you are combining it, at best this can give you double the signal strength (+3dB), with properly phased antennas pointed at the same site. With aerials pointed at separate sites, the signal will be fairly dissimilar (unless the aerials are poorly directional), in which case the signals should combine in a relatively coherent manner, calculating gain/loss in that scenario is very hard unti the system is set up. What I can tell you is that most diplexers have a insertion loss of about 1dB (or less than half the signal strength)

I stated dB as stating half the signal is misleading though as signals are logarithmic in scale, and a 10 times weaker signal could still be well above the digital cliff depending on the circumstance.

Yes there will be some multipath issues, but this doesnt necessarily mean there will be problems.

Antennas receive and they transmit. If you connect two (X and Y) receiving antennas pointed at two different directions, they might provide useable signals for you to receive, but half (signal level) of the the signals received by each antenna are retransmitted by the other antenna which is coupled in this setup. If the two antennas are not identical, the signals will not easily escape do to a phenomenon known as standing waves. Google it.
The inputs are isolated from each other and the losses out of each antenna are minimal.
 
#7
Antennas receive and they transmit. If you connect two (X and Y) receiving antennas pointed at two different directions, they might provide useable signals for you to receive, but half (signal level) of the the signals received by each antenna are retransmitted by the other antenna which is coupled in this setup. If the two antennas are not identical, the signals will not easily escape do to a phenomenon known as standing waves. Google it.
Hey, sounds just like feedback in a sound system! Don't want the mic too close to the speaker.

So, on the single feedline to your TV set, you now have competing signals on the same channel: the primary signal from a strong local channel BUT there are delayed (multipath) lower level signals coming in from the second antenna and your tuner is 'seeing' all of them. So, how can it choose which digital stream to decipher,
Well, here's how: There's only one amp (of that type) in the TV, so the stronger signal gets amped to where the tuner can use it, and the weaker signal gets interpreted as noise -- if you're lucky -- which is routinely eliminated. I'd think the distance between the two antennas is crucial.

I'll probly try it when I get my new antenna. Combine it with the little Monoprice HDA-5700. It'll only cost me the price of a reverse splitter.

I'm a demon for disaster. ;)

R.
 
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#8
Something I found while googling "standing wave":

"Rotor ... This author recommends that if your stations are in just two directions, you will be happier with two antennas. A common splitter can be used to combine the two antennas. Doing this will cost you a lot of signal strength (Half of the signal from each antenna gets rebroadcast out the other antenna. Figure a 3.5dB loss at the splitter.). A Join-Tenna is a device that can avoid this loss." [emphasis added]

From Glossary R to Z

I hadn't thought about the splitter connecting the antennas for rebroadcast. I'd read about the Join-Tenna, but thought it was just another splitter/combiner.

[edit: Ah, but the Jointenna is only for one station at a time. Not much help. Then there's the Winegard Antenna Coupler: http://www.amazon.com/Winegard-CC-7870-Antenna-Coupler/dp/B001TK3C82 which features a "low -3.5 insertion loss" so there ya go. Still might work -- amp in the TV, remember? Or an AB switch could work. (Not to say I know what I'm talking about. :daffy: ) ]

R.
 
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Fringe Reception

Super Moderator, Chief Content Editor
Staff member
#9
Rick,

I think you will JoinTennas very hard to find, because they were discontinued several years ago. Two years ago I found someplace online that had a few left and I'll look around to see if I can find it. They are very effective when tying more than one antenna to a single coaxial downlead. An A-B switch works well (I use four A-B-C-D switches) and remote-controlled A-B switches are available, so you don't have to leave your sofa.

Jim
 
#10
I think you will JoinTennas very hard to find, because they were discontinued several years ago. Two years ago I found someplace online that had a few left and I'll look around to see if I can find it.
Jim,

Thanks VERY much, but please don't go to the trouble on my account. There are a couple JoinTennas on eBay, but like I said -- only one station at a time. So for multiple stations you need multiple JoinTennas. Lessee, 10 stations x $20 = $200. Too many $$ and probably too much hassle.

I'm thinking through lots of exotic possibilities, but in the end I like to keep things simple. After all, TV is for relaxation. ;)

I already have an AB switch to switch back and forth between my cable bleed and the little Monoprice HDA-5700 and my tin can reflector. Heh, heh. So I can use that to experiment if I want.

Thanks again,
Rick
 

scandiskwindows9x

Moderator of DTV Latino
#11
If use an VHF UHF mixer my current antenna is UHF and my old VHF and half UHF if combine and my old just put the combiner connected to that antenna to VHF and my current to the UHF and send the mixed signals to my feed line?

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Fringe Reception

Super Moderator, Chief Content Editor
Staff member
#12
Francisco,

I gather you have a UHF antenna and a combination VHF-UHF antenna. If so, they can share a single coaxial downlead using a UVSJ combiner/joiner. The UHF signals received by the UHF antenna will pass through the UHF side of the joiner but only the VHF signals received by your combination antenna will pass through the VHF side of the joiner. If the two antennas are mounted on the same mast they should be at least one meter apart from each other as possible to avoid interaction.

Jim
 

scandiskwindows9x

Moderator of DTV Latino
#13
yeah that was my idea, mix the VHF signal of my old antenna of 8 elements UHF/VHF and my current antenna for get some analogic channels in VHF and my digital ones in UHF and if were possible also connect the radio receiver to the antenna to pick up cleaner FM broadcast
 

Fringe Reception

Super Moderator, Chief Content Editor
Staff member
#14
Francisco,

Try it with a UVSJ and split the VHF side to your FM. NO guarantee it will work, but your FM tuner will (at least) be isolated from your UHF TV reception. Test! Try bizarre ideas and TEST!

Jim
 
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