How exactly to use/tune a signal combiner? (grabbing OTA in 61874 with two antennas) - AVS Forum
Forum Jump: 
 
Thread Tools
post #1 of 20 Old 09-03-2012, 07:17 AM - Thread Starter
Member
 
sacrophyte's Avatar
 
Join Date: Jun 2008
Posts: 16
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
I have an older indoor passive antenna (phillips MANT something or other) that does an awesome job of picking up most channels in my area, although it struggles with stations that are 25+ miles away (understandably) - I am impressed that it works so well when $50 so-called "HDTV" antennas sold at walmart and Radio Shack have the exact same things inside. I also recently purchased on of those $50 so-called "HDTV" antennas from Radio Shack because I wanted a yagi to point to a particular station (WCCU, 24 miles at 45 degrees) and wanted to see how it did with the others. It does an excellent job, and even a decent job at pulling in a 32-mile signal (WAND) at a very odd angle (256 degrees, almost 160 degrees).

At the advice of a hobbyist, I acquired a amplified signal combiner. My hope is to use the old antenna and tune it for WAND (which seems to work pretty well when I play around with it) and combine it with the Yagi for all the other channels. However, the signal combiner came with no instructions and I cannot find anything online. Still waiting for the vendor to get back to me.

So I am wondering if anyone has experience with a Eagle Aspen Amplified Channel 4 Signal Combiner (SC-4A). Before I climb back up to my attic to attach this thing, how do I "attenuate" it such that I know I will be pulling in WAND and mixing it with everything else from the Yagi? Also, I already have a 18.8db amp that sits in between my antenna and a 3-way splitter. Do I take that out since the combiner already has a 15db amp? Keep it in?

Thanks for your time and attention.
This forum is an awesome resource for the rest of us.
sacrophyte is offline  
Sponsored Links
Advertisement
 
post #2 of 20 Old 09-03-2012, 09:39 AM
AVS Special Member
 
kenglish's Avatar
 
Join Date: Jan 2000
Location: Salt Lake City, UT, USA
Posts: 5,406
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 10 Post(s)
Liked: 31
That combiner is used to combine the output of a VCR (or similar device) on VHF Channel 4, with other channels. It's designed to "patch in" the RF modulated output of the VCR, so you can tune it along side of the other channels.
It has some strong bandpass filtering, so it won't pass anything else.....I think WAND is on UHF channel 17.

You might find a converter box that could be used to tune to WAND, and gives an NTSC analog output on channel 4, and mix that in, but you'd be watching the analog down-conversion of WAND on your TV set.

Ken English, Sr. Engineer, KSL-TV.
"The postings on this site are my own and don't necessarily represent the Company positions, strategies or opinions."
kenglish is offline  
post #3 of 20 Old 09-03-2012, 09:52 AM - Thread Starter
Member
 
sacrophyte's Avatar
 
Join Date: Jun 2008
Posts: 16
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Hmm.... so I cannot use the signal combiner as I had planned. That sucks. How does one capture signals from two different sources when a single omni- or yagi directional antenna won't do the trick?
sacrophyte is offline  
post #4 of 20 Old 09-03-2012, 10:23 AM
Advanced Member
 
JJkizak's Avatar
 
Join Date: Oct 2005
Location: TWINSBURG, OHIO
Posts: 601
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 7 Post(s)
Liked: 11
Electronically at the audio cathode level the two antennas with two receivers would be hooked together and you could realize a 3 db gain but they must be in perfect phase and the antennas must be placed about 50 feet apart with one antenna 50 ft ahead of the other.(Dual diversity) This is basically cost prohibitve unless you are Bill Gates. There are some industrial applications that combine the receivers at the IF level but you must remember that the AGC circuits control which receiver is sharing the most or whether both have equal signals. Or you could use a parametric amplifier for the front end of one receiver which would only cost about 100K. Your 20 db quieting point will be somewhere around -99dbm for the received signal at approximately 900 mhz. I believe (I am speculating and not sure) that you normal TV receiver 20 db quieting spec is around -20 dbm.
Some people have said that using a splitter backwards will combine the two antennas and that it works most of the time ($3.00) but this is really too simple a solution.
JJK
JJkizak is offline  
post #5 of 20 Old 09-04-2012, 05:45 AM
AVS Special Member
 
kenglish's Avatar
 
Join Date: Jan 2000
Location: Salt Lake City, UT, USA
Posts: 5,406
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 10 Post(s)
Liked: 31
Like JJK says, a backwards splitter MAY work in many instances.
All you can do is try.....

Best way to do it is, try one antenna at a time, and see how all your signals look. Pay close attention to whether the station that you want on one antenna looks on the "wrong" antenna. If the "wrong" antenna gets much signal on that station, it means the two antennas might interfere with each other...."multi-path", in other words. If they seem to be isolated from each other, go ahead and try combining the two. This usually works best when the stations are offset from each other by a good bit in azimuth (one is in the main lobe of the antenna, the other is in the null, or "weak" direction).

The unit you have now is only good for the one channel on the "combined" input. A full-blown combiner like a "Join-Tenna" just uses specific filters to separate out the different channels. It's customized to whatever situation you have, and usually needs a "gap" of a couple or three channels between what you want, and what you don't, on each input. The advantage of this is, you don't get addition and subtraction of the signals on the two inputs, which is what causes that evil multi-path (the stuff that makes signals come and go, seemingly randomly).

Ken English, Sr. Engineer, KSL-TV.
"The postings on this site are my own and don't necessarily represent the Company positions, strategies or opinions."
kenglish is offline  
post #6 of 20 Old 09-04-2012, 11:27 AM - Thread Starter
Member
 
sacrophyte's Avatar
 
Join Date: Jun 2008
Posts: 16
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by JJkizak View Post

Electronically at the audio cathode level the two antennas with two receivers would be hooked together and you could realize a 3 db gain but they must be in perfect phase and the antennas must be placed about 50 feet apart with one antenna 50 ft ahead of the other.(Dual diversity)

First, I confess I dropped my class on digital signal processing. But I did complete the class on physics. smile.gif 50ft apart?!? I didn't get that. The absolute lowest end of the VHF spectrum has a wavelength of 10 meters (approx 32.8 feet). So let's say my antennas are (pulling a number out of thin air) 20 feet apart, I have to offset one waveform by 12.8 feet (I could go back 20 feet, but....) or more practically, introduce a phase shift that represents that wavelength of 12.8 feet. At that is the worst case scenario. UHF is from 1 meter to 1 decimeter, making the offset all that much shorter.

From where I sit, the hard part is actively phase shifting various different signals. In my case, I only have about 6 to worry about. It just doesn't seem like it would be that hard. But I do confess, I am a small fish in a big pond and having said "not that hard", I know I can't do it. smile.gif
sacrophyte is offline  
post #7 of 20 Old 09-04-2012, 11:38 AM
AVS Special Member
 
kenglish's Avatar
 
Join Date: Jan 2000
Location: Salt Lake City, UT, USA
Posts: 5,406
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 10 Post(s)
Liked: 31
I think JJK was just teasing us.wink.gif

Ken English, Sr. Engineer, KSL-TV.
"The postings on this site are my own and don't necessarily represent the Company positions, strategies or opinions."
kenglish is offline  
post #8 of 20 Old 09-05-2012, 05:42 AM
Advanced Member
 
JJkizak's Avatar
 
Join Date: Oct 2005
Location: TWINSBURG, OHIO
Posts: 601
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 7 Post(s)
Liked: 11
The 50 ft. distance is for the UHF spectrum. VHF? Don't know. This stuff I threw at you is based on the old UHF tropo systems that used "Quad" diversity setups on the Dewline. The phasing was accomplished with Tektronic scopes comparing at a reference receiver and adjusting the length of the RG-58 IF cable of the receiver in question under good received signal conditions. between sites. Each receiver had a combiner circuit in the audio band with each combiner hooked together at the cathode point and each receiver having it's own AGC controlling the signal applied. This could mean both receivers combined with the same signal giving you a 3 db reduction in noise level or if one receiver has no signal then it is cut off with the good receiver still operating but no reduction in noise level. This was later redesigned to operate at the IF level. Using this old technology with digital signal would be a problem as when a digital signal fades it looses sync and it's a done deal. The analog stuff is instantaneous so it works. So as long as the digital signals don't fade sync should be maintained as long as you can combine the "Synced Signals".I don't know how you would combine two digitally synced signals.
If in fact you can increase the front end sensitivity of the tv set then there is the problem of one tv station trouncing the other if they are on the same channel with one of them being 100 miles more distant than the other. The new LCDs don't handle this very well and get confused. The dual antennas would not help this at all. It's been 40 years since I maintainened this Tropo stuff so I might have left out some details.
JJK
JJkizak is offline  
post #9 of 20 Old 09-05-2012, 05:50 AM
AVS Special Member
 
kenglish's Avatar
 
Join Date: Jan 2000
Location: Salt Lake City, UT, USA
Posts: 5,406
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 10 Post(s)
Liked: 31
It's been a while since I thought about Space Diversity reception for DTV. I talked to some of the ATSC guys several years ago, about the possibility of using it for places like Cable head-ends and larger MATV systems, when they are located near airports.

You can also space antennas at specific distances apart, for specific channels, to null-out signals (on that specific frequency) from a partcular direction, or simply combine identical antennas that are closely spaced, to get a narrower beamwidth. That's not Space Diversity, but just a trick to direct the beam, when signals are steady.

Ken English, Sr. Engineer, KSL-TV.
"The postings on this site are my own and don't necessarily represent the Company positions, strategies or opinions."
kenglish is offline  
post #10 of 20 Old 09-05-2012, 08:36 AM - Thread Starter
Member
 
sacrophyte's Avatar
 
Join Date: Jun 2008
Posts: 16
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Hmm... all very interesting, but I still feel like we are discussing theory. smile.gif So let me bring some laser focus to my question (probably should have done this first, my bad).

I have one antenna that does great 95% of the time. The other 5% of the time, NBC drops out. I want to use an additional antenna to boost NBC. I know for a fact this is possible, I just do not have all the science figured out on how to do it.

I can easily figure out exactly which frequency NBC is being broadcast locally (zipcode 61874, local station WAND, low end of the UHF spectrum, real channel 17, NM 58dB, Pwr -32.8dB according to tvfool.com). Going to guess close to .8 meters for the wavelength. It seems to me that if I have an antenna that is parallel to the signal source, it would be possible to:
  1. capture signals from both antennas at the same frequency for channel 17 that are perfectly in phase (either by way of having an exact geospatial placement and/or forcing compliance via hardware), and
  2. block all other frequencies from antenna 2 such that it does not interfere with antenna 1

(EDIT: So I learned that channel 17 is 489.25MHz, which translates to 0.61276 meters, or just a smidge over 2 feet)


I thought a signal combiner would do that. But the one I have is beyond me, even though it is quite old (I took it apart to look inside because I was curious).

So if you happen to know the specifics of combining signals in this fashion and have some practical knowledge, I would LOVE LOVE LOVE to hear from you. smile.gif Not that all this other background information is not helpful - it is. I just want to focus in on what is most practical at the moment.
sacrophyte is offline  
post #11 of 20 Old 09-05-2012, 10:27 AM
Advanced Member
 
JJkizak's Avatar
 
Join Date: Oct 2005
Location: TWINSBURG, OHIO
Posts: 601
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 7 Post(s)
Liked: 11
There is someone on the Cleveland HDTV section of this forum that uses combiners so you might talk to him. He says it works most of the time.There are several older threads about this subject.
JJK
JJkizak is offline  
post #12 of 20 Old 09-05-2012, 11:27 AM
Advanced Member
 
George Molnar's Avatar
 
Join Date: Jan 2001
Location: South Bend, Indiana
Posts: 522
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Liked: 11
Quote:
Originally Posted by sacrophyte View Post

Hmm... all very interesting, but I still feel like we are discussing theory. smile.gif So let me bring some laser focus to my question (probably should have done this first, my bad).
I have one antenna that does great 95% of the time. The other 5% of the time, NBC drops out. I want to use an additional antenna to boost NBC. I know for a fact this is possible, I just do not have all the science figured out on how to do it.
I can easily figure out exactly which frequency NBC is being broadcast locally (zipcode 61874, local station WAND, low end of the UHF spectrum, real channel 17, NM 58dB, Pwr -32.8dB according to tvfool.com). Going to guess close to .8 meters for the wavelength. It seems to me that if I have an antenna that is parallel to the signal source, it would be possible to:
  1. capture signals from both antennas at the same frequency for channel 17 that are perfectly in phase (either by way of having an exact geospatial placement and/or forcing compliance via hardware), and
  2. block all other frequencies from antenna 2 such that it does not interfere with antenna 1
(EDIT: So I learned that channel 17 is 489.25MHz, which translates to 0.61276 meters, or just a smidge over 2 feet)
I thought a signal combiner would do that. But the one I have is beyond me, even though it is quite old (I took it apart to look inside because I was curious).
So if you happen to know the specifics of combining signals in this fashion and have some practical knowledge, I would LOVE LOVE LOVE to hear from you. smile.gif Not that all this other background information is not helpful - it is. I just want to focus in on what is most practical at the moment.

Using two antennas merged together is complicated because one can pick up unwanted signals that can interfere with desired signals coming from the other. But you can use one all-channel antenna with a second only for the NBC channel. Aim them appropriately, then combine the two antennas together using a 2-way splitter backwards. However, you must use a special filter to notch out (eliminate) the NBC spectrum from the all channel antenna, and a second filter to only pass the NBC spectrum from the NBC channel antenna. Bandpass and notch filters are commercially available. Channel Master once provided an all-in-one solution called the Join-Tenna. Not sure if you can find one available for UHF ch.17 anymore. The filters are necessary to keep undesired signals from the "wrong" antenna from interfering with the desired NBC signal from the other antenna.
George Molnar is offline  
post #13 of 20 Old 09-05-2012, 11:29 AM - Thread Starter
Member
 
sacrophyte's Avatar
 
Join Date: Jun 2008
Posts: 16
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by JJkizak View Post

There is someone on the Cleveland HDTV section of this forum that uses combiners so you might talk to him. He says it works most of the time.There are several older threads about this subject.
JJK

Does "someone" have a handle?

"most of the time" sounds like a reverse splitter. Unfortunately, I need something I can really put my trust in, something that is reliable. Else the wifey ain't gonna be happy.
sacrophyte is offline  
post #14 of 20 Old 09-05-2012, 11:34 AM - Thread Starter
Member
 
sacrophyte's Avatar
 
Join Date: Jun 2008
Posts: 16
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by George Molnar View Post

Using two antennas merged together is complicated because one can pick up unwanted signals that can interfere with desired signals coming from the other. But you can use one all-channel antenna with a second only for the NBC channel. Aim them appropriately, then combine the two antennas together using a 2-way splitter backwards. However, you must use a special filter to notch out (eliminate) the NBC spectrum from the all channel antenna, and a second filter to only pass the NBC spectrum from the NBC channel antenna. Bandpass and notch filters are commercially available. Channel Master once provided an all-in-one solution called the Join-Tenna. Not sure if you can find one available for UHF ch.17 anymore. The filters are necessary to keep undesired signals from the "wrong" antenna from interfering with the desired NBC signal from the other antenna.

I specifically want to boost NBC, though. Neither antenna that I currently own does NBC very well. And I would hate to go out and buy a new yagi and point it towards NBC and then do all this filter notching and bandpassing. Or perhaps what you imply is that I can't do what I want to do, I must use two directional antennas and filter and pass.
sacrophyte is offline  
post #15 of 20 Old 09-05-2012, 11:46 AM - Thread Starter
Member
 
sacrophyte's Avatar
 
Join Date: Jun 2008
Posts: 16
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Crap, I just uncovered another half-baked misconception; WAND is broadcasting on a range of frequencies, not a particular frequency. Apparently the audio, chromacity and something else each take up different frequencies within a 8MHz wide band allocated for the channel.

*sigh*

If only it were easy....

I did find an article on ganging antennas, but it is leaving me feeling even more discouraged. smile.gif
http://www.hdtvprimer.com/ANTENNAS/ganging.html#TAT
sacrophyte is offline  
post #16 of 20 Old 09-05-2012, 01:32 PM
Advanced Member
 
George Molnar's Avatar
 
Join Date: Jan 2001
Location: South Bend, Indiana
Posts: 522
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Liked: 11
Quote:
Originally Posted by sacrophyte View Post

Crap, I just uncovered another half-baked misconception; WAND is broadcasting on a range of frequencies, not a particular frequency. Apparently the audio, chromacity and something else each take up different frequencies within a 8MHz wide band allocated for the channel.
*sigh*
If only it were easy....
I did find an article on ganging antennas, but it is leaving me feeling even more discouraged. smile.gif
http://www.hdtvprimer.com/ANTENNAS/ganging.html#TAT
According to the FCC website, WAND is transmitting with maximum 1,000 kilowatts on UHF channel 17, 488-494 MHz. from 390-meters above average terrain. This is a blowtorch and you can't get it? WAND has permission to change to UHF ch.18, 494-500 MHz with same power and height. How far from the station are you? Any possibility this station is overloading your receiving antenna system??
George Molnar is offline  
post #17 of 20 Old 09-05-2012, 01:41 PM - Thread Starter
Member
 
sacrophyte's Avatar
 
Join Date: Jun 2008
Posts: 16
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by George Molnar View Post

According to the FCC website, WAND is transmitting with maximum 1,000 kilowatts on UHF channel 17, 488-494 MHz. from 390-meters above average terrain. This is a blowtorch and you can't get it? WAND has permission to change to UHF ch.18, 494-500 MHz with same power and height. How far from the station are you? Any possibility this station is overloading your receiving antenna system??

The problem is not that I am not receiving the signal, but rather that I have one antenna pointed to WCCU (less of a blowtorch) and I have another super-cheap 30-year old antenna. Both of these antennas picked up WAND at about decent but not perfect signal strength (keep in mind, WCCU is about 155 degrees away from WAND at my location). Sure, yes, I could point my first yagi at WAND and pick it up just fine, but then I lose WCCU.

Does that help?
sacrophyte is offline  
post #18 of 20 Old 09-05-2012, 02:17 PM
Advanced Member
 
George Molnar's Avatar
 
Join Date: Jan 2001
Location: South Bend, Indiana
Posts: 522
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Liked: 11
Quote:
Originally Posted by sacrophyte View Post

The problem is not that I am not receiving the signal, but rather that I have one antenna pointed to WCCU (less of a blowtorch) and I have another super-cheap 30-year old antenna. Both of these antennas picked up WAND at about decent but not perfect signal strength (keep in mind, WCCU is about 155 degrees away from WAND at my location). Sure, yes, I could point my first yagi at WAND and pick it up just fine, but then I lose WCCU.
Does that help?
Well if you don't want to go to the expense of filtered combining, how about a second downlead from the second antenna to a switch at the back of your TV set so you can select between antennas? Or, have you considered an antenna rotor?? As you have learned, misaiming the antenna or merging two antennas aimed in different directions onto one downlead will lead to reception blackouts.
George Molnar is offline  
post #19 of 20 Old 09-05-2012, 02:22 PM - Thread Starter
Member
 
sacrophyte's Avatar
 
Join Date: Jun 2008
Posts: 16
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by George Molnar View Post

Well if you don't want to go to the expense of filtered combining, how about a second downlead from the second antenna to a switch at the back of your TV set so you can select between antennas? Or, have you considered an antenna rotor?? As you have learned, misaiming the antenna or merging two antennas aimed in different directions onto one downlead will lead to reception blackouts.

Funny, my TiVo doesn't have an option to support a rotor or a a/b switch. smile.gif

I don't even know how much filtered combining is, so it is hard for me to even consider the expense. I do know it sounds complicated and I fear I am getting in over my head. As I mentioned, the combiner I already have (note, already paid that expense) was pitched to me as doing the trick, but it has no instructions and I am a newbie in this field. Willing to learn, but I am not going to get a bachelor's degree in electronics.
sacrophyte is offline  
post #20 of 20 Old 11-25-2012, 10:02 AM
Member
 
vogon13's Avatar
 
Join Date: Jun 2005
Posts: 63
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
I have had fair to good luck using a 2 way splitter backwards, and I always use a high frequency splitter too. 2.4GHz (or better) units seems to have far less port to port losses.

Above suggestion about connecting one antenna at a time, and verifying signal strength is a good idea too.

If your antenna pointing at NBC is very directional, it probably won't pick up too much ghosting signal on the channels you are getting on the other antenna.

I have had more luck, if I need an RF amp to drive several TVs, of just using one on the combined feed rather than one on each antenna. I don't know why that is, maybe non-linearity in the amp stages makes for heterodyning and that causes interference on the desired frequencies.

I use the high frequency splitters to add modulator channels too, that always works well.
vogon13 is offline  
Reply Local HDTV Info and Reception

User Tag List

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page


Forum Jump: 

Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off