Combining two antennas

[miguelaqui]

So, I thought no had the concept of combining 2 different antennas pointed in opposite directions figured out, but I might have been wrong.
I have tried to combine two of the same type antennas , with the same length of the exact same coax, but something odd happened.

As soon as I counted the secod antenna to the splitter , the other signal became much lower.

Why? Shouldn't it have been -4 dB before the second antenna was connected and then stayed that way? Why did the signal drop so much when the second antenna was connected?

I ended up using a directional coupler , putting the strongest one on the -8 dB side to make up for the difference.

 

[primestar31]

Each antenna receives signals from the same tower/channel, but slightly out of phase. That causes them to cancel each other out, even if the signals are very low on one antenna. RARELY can you combine antennas through a splitter, and make it work properly, it's out and out voodoo. IF it works for you, you MUST at least have them pointed at towers a minimum of 120 degrees apart.

It may never work right for you, you just have to keep playing with it and hope for the best. One thing you can try IF it's possible, is have one antenna blocked from the other one by some part of your roof or something else, or try placing it much higher or lower, but don't forget the 120 degree difference, that's still important, though it still might not be good enough in any particular case.

Or, you can use an A-B coax switchbox, OR have each antenna wired to a different tuner. Say one to your tv, and the other to a dvr, things like that.

 

[Tower Guy]

Your directional coupler was a great idea.

I’ve been thinking about ways to combine antennas using coax stubs as filters. Can you tell me which channels you were trying to combine?

 

[primestar31]

I've bought from this guy several times before. He's located overseas, so if you buy something, he makes them up and tunes them to YOUR specs. That means you'd have to tell him via email you want it for US ATSC tv, and the exact RF frequencies(s)/ Channels range you need. All of those frequencies are available to look up through any search engine for the particular channel(s) you need. Make SURE if you do this, you are ordering for the correct RF channel frequency, which is NOT necessarily the actual channel number that shows on your tv anymore! I have one of these on my present antenna system now, and one stashed for when they change frequencies next year in our area. jan_jenca | eBay

Or:

Jan Jenca antenna components

P.S. English is not his first language, so go easy on him! Oh yeah, these aren't waterproof, so you'll need to put them in a waterproof box if you mount it up at the antenna. Home Depot sells some good cheap ones.

 

[cpalmer2k]

I've bought from this guy several times before. He's located overseas, so if you buy something, he makes them up and tunes them to YOUR specs. That means you'd have to tell him via email you want it for US ATSC tv, and the exact RF frequencies(s)/ Channels range you need. All of those frequencies are available to look up through any search engine for the particular channel(s) you need. Make SURE if you do this, you are ordering for the correct RF channel frequency, which is NOT necessarily the actual channel number that shows on your tv anymore! I have one of these on my present antenna system now, and one stashed for when they change frequencies next year in our area. jan_jenca | eBay

Or:

Jan Jenca antenna components

P.S. English is not his first language, so go easy on him! Oh yeah, these aren't waterproof, so you'll need to put them in a waterproof box if you mount it up at the antenna. Home Depot sells some good cheap ones.

How do you get around the spacing issue between channels with those filters, or have you just been lucky enough to not encounter it? In my case I need the following, which jan jenca says they can't make because they need a two to three channel "buffer zone" between input channel groups. In my case antenna #1 needs to cover channels 18, 19, 23-25 and antenna #2 needs to cover 17, 20 and, 30

I've wondered if it would be doable if I used multiple filters instead of one to do both antennas?

 

[primestar31]

How do you get around the spacing issue between channels with those filters, or have you just been lucky enough to not encounter it? In my case I need the following, which jan jenca says they can't make because they need a two to three channel "buffer zone" between input channel groups. In my case antenna #1 needs to cover channels 18, 19, 23-25 and antenna #2 needs to cover 17, 20 and, 30

I've wondered if it would be doable if I used multiple filters instead of one to do both antennas?

You can't get around the needed spacing issue with any filter, as they aren't "tight" enough. HOWEVER, you could use a different TUNER for each antenna. Something like the HdHomerun that hooks to your router. Get two of those, and wire them to separate antennas. I don't know your specific needs/wants, so it gets hard to recommend anything else. Just think of all sorts of different ways, and pick whatever seems likely to work. A-B switchbox, Old school antenna rotator, 3-way splitter and prayer/good luck, multiple tuners, etc.

If it MUST go into a single tuner, such as a dvr, then you'll have to try the splitter/prayer method. Maybe you'll get lucky and it'll work for you good enough.

P.S. Make SURE of the RF channel of your wanted stations, do NOT do anything based on the Psip channel number. The Psip channel number may not (usually is NOT) the same as the actual RF frequency they are broadcasting on.

 

[harshness]

I can't conceive of an economically feasible passive tank circuit/notch filter can cut two adjacent channels apart. I expect that it would require something on the order of a tuner to null out an adjacent channel. primestar31's separate system scheme would seem to be the only practical way to separate them such that you can get both channels 17 and 18 as well as 19 and 20.

The front-to-back ratio of an antenna is an issue in a 180 degree arrangement as what little signal the back side of the away-facing antenna picks up subtracts from the front signal of the other antenna. I do wonder what might happen if you turned one of the antennas upside down such that they were both rowing in the same direction.

 

[cpalmer2k]

I've considered trying the dual antenna setup but currently I have the back side issue you described. Pointing at one set of stations (at about 80 degrees) I can pick all of them up perfectly but I get the other market (at about 280 degrees) off the backside with some stations strong enough for viewing all the time but others stable only some of the time. I would almost have to have two highly directional antennas with great back side rejection to have a shot at combining. I'm kind of waiting to see what happens in August when most of the stations here repack. Many are changing antenna patterns and increasing power so I'm hoping the dynamics might change a bit.

Right now I point at "Market A" and "Market B" is the backside market. I've also considered flipping the antenna and pointing towards "Market B" because overall the bulk of the stations in Market A are stronger. The additional strength might be enough for those to come in on the back side like the other market almost does now. This might require me to sacrifice one station but I don't watch them much anymore, so I might just have to do that.

 

[primestar31]

I've considered trying the dual antenna setup but currently I have the back side issue you described. Pointing at one set of stations (at about 80 degrees) I can pick all of them up perfectly but I get the other market (at about 280 degrees) off the backside with some stations strong enough for viewing all the time but others stable only some of the time. I would almost have to have two highly directional antennas with great back side rejection to have a shot at combining. I'm kind of waiting to see what happens in August when most of the stations here repack. Many are changing antenna patterns and increasing power so I'm hoping the dynamics might change a bit.

Right now I point at "Market A" and "Market B" is the backside market. I've also considered flipping the antenna and pointing towards "Market B" because overall the bulk of the stations in Market A are stronger. The additional strength might be enough for those to come in on the back side like the other market almost does now. This might require me to sacrifice one station but I don't watch them much anymore, so I might just have to do that.

What antenna brand name and model EXACTLY do you have? I want to look it up.

 

[cpalmer2k]

Right now I’m using a Winegard HD-8800 with a Channel Master pre amp (I believe it’s the older 30db 7778 or 7777 version)

 

[primestar31]

Right now I’m using a Winegard HD-8800 with a Channel Master pre amp (I believe it’s the older 30db 7778 or 7777 version)

That preamp is probably too powerful and swamps out more than it helps. I highly recommend the Kitztech KT-200-Coax preamp. As for your antenna, I see two options:

1: Drill out the rivets and remove the reflector rods completely to get both directions at the same time. If it doesn't work, rivet or metal screw them back on.

2: Leave the reflector rods on, AND get a piece of screen door screen with very tiny holes and use black wire ties to wire-tie it to the back of the reflector rods covering them.

That might help more to completely reject signals from the back. If so, then you can use a second yagi style antenna to aim the other way, and hopefully get it while helping to null out any signal combination issues with the other antenna.

 

[Tower Guy]

Consider converting your B market stations to VHF using several Blonder Tongue MCX-Uz channel converters.

https://www.fullcompass.com/common/files/3872-zSeriesDataSheet.pdf

I found one on eBay for 17.99.

Add the outputs of the converters in a backwards splitter. Next, combine the two markets using a UVSJ and then rescan your TV sets.

 

[cpalmer2k]

Consider converting your B market stations to VHF using several Blonder Tongue MCX-Uz channel converters.

https://www.fullcompass.com/common/files/3872-zSeriesDataSheet.pdf

I found one on eBay for 17.99.

Add the outputs of the converters in a backwards splitter. Next, combine the two markets using a UVSJ and then rescan your TV sets.

That's an interesting idea. What does that do to virtual channel numbers- make them all just match the real VHF channel it sends it out on, or does it preserve the originals I wonder? That would be a non starter for TiVo, but it could work with HDHomeRun because they match for guide data based on virtual channel and the channel name.

 

[harshness]

In theory, the virtual channel numbers remain unchanged so nobody would know the difference in daily use. DVRs and the like should work with the virtual channel numbers.

Moving all the channels around so that they could coexist could get expensive and may create significant insertion loss when added up.

 

[cpalmer2k]

It may be a moot point. I can't seem to find those things available anywhere except for the one on eBay anyway :-(. I would only have to move two channels really, so it might be feasible. In "Market "B" CBS, ABC and PBS are all VHF anyway. There are three UHF Stations, and one has plenty of spacing on both sides. I could go with the Jan Jenca filter, then move the other two using these units.

 

[Tower Guy]

The MCX-Ub may also work. There are several available from one online vendor.

The converters have gain, so the losses in the backwards splitter and UVSJ don’t matter.

If you choose to convert to channels 2 through 6 you could use an HLSJ instead of a UVSJ.

 

[Tower Guy]

The one product that I know of that looked for RF channels instead of virtual channels is Windows Media Recorder. Yet it is possible to edit the channel table manually. There was discussion of this issue years ago on the greenbutton forum. It makes me wonder if the channel tables are promptly updated during the repack.

 

[cpalmer2k]

The MCX-Ub may also work. There are several available from one online vendor.

The converters have gain, so the losses in the backwards splitter and UVSJ don’t matter.

If you choose to convert to channels 2 through 6 you could use an HLSJ instead of a UVSJ.

In my case I'd almost have to use the low VHF to make it work. We will already have VHF stations on 8, 11, 12 and 13 after the repack is complete so that wouldn't give much "buffer space" to feed them into the system in the VHF range.

 

[primestar31]

In my case I'd almost have to use the low VHF to make it work. We will already have VHF stations on 8, 11, 12 and 13 after the repack is complete so that wouldn't give much "buffer space" to feed them into the system in the VHF range.

Don't forget that low VHF is especially sensitive to interference, so unshielded power bricks, noisy LED light bulbs, noisy power transformers out on the pole in front of your house, battery tenders in the garage or shed, ALL things like that can cause you issues. I had a power tender and a noisy Dell laptop power brick. The battery power tender could be picked up on my car radio set to AM, 250 feet down my driveway!

It's very important for starters that you use good coax, and it MUST be grounded properly to the house ground.

 

[Tower Guy]

This Holland agile processor looks like it does the same thing as the Blonder Tongue.

Holland Electronics HPH-860 Agile Processor #5138 X | eBay