People are frequently advised to combine two antennas via a jointenna if the same channel can come in via both antennas. The jointenna attenuates one of these thus allowing a tuner to distinguish the proper signal.

This is kind of a dumb question but since 5th generation tuner chips are supposed to pick out the best signal from among competing signals why not simply join two antennas through a splitter/combiner and let the tuner handle the problem?

If 5th generation chipsets are supposed to handle multipath problems, why have a jointenna in the case of multiple antennas?

The JoinTenna is used for those situations when you need to add a second antenna to pick up a broadcast station in another direction but do not wish to use a single antenna and rotator.

The JoinTenna blocks all frequencies but the one it is tuned for, eliminating the ghosting and reflection that can happen when you connect two antennas together.

The JoinTenna creates a space for the channel/station you want to insert with the 2nd antenna. There is significant attenuation on either side of the channel the JoinTenna is tuned for. do not recommend using a JoinTenna if you are also trying to receive a channel immediately adjacent...+/- 5 channels for uhf.

The tuner has nothing to do with the issue.

The JoinTenna is used for those situations when you need to add a second antenna to pick up a broadcast station in another direction but do not wish to use a single antenna and rotator.

The JoinTenna blocks all frequencies but the one it is tuned for, eliminating the ghosting and reflection that can happen when you connect two antennas together.

The JoinTenna creates a space for the channel/station you want to insert with the 2nd antenna. There is significant attenuation on either side of the channel the JoinTenna is tuned for. do not recommend using a JoinTenna if you are also trying to receive a channel immediately adjacent...+/- 5 channels for uhf.

The tuner has nothing to do with the issue.

If the tuner has nothing to do with the issue, then why do tuner designers and manufacturers state that the 5th generation tuner/chipset combats multipath by being able to pick out the best signal?

Don't ghosting and reflection occur because of multipath (aren't these effects of multipath)?

If signals for the same channel arrive from two different sources (out of phase), where does the problem occur - before the tuner or at the tuner? If at the tuner (ie. the tuner cannot distinguish between competing signals for the same channel), then the tuner is indeed involved in signal distinguishing and selection. If the two signals physically distort each other before the tuner, then the problem occurs in the wire before the tuner.

I understand the use of the jointenna (I have one myself and use it) but I'm trying to undertsand the theory where the problem lies. And why 5th generation chipsets claim to combat multipath. What is the difference between one antenna and two antennas delivering competing signals to the same tuner that requires a jointenna for two?

There is significant attenuation on either side of the channel the JoinTenna is tuned for. do not recommend using a JoinTenna if you are also trying to receive a channel immediately adjacent...+/- 5 channels for uhf.


The jointenna not only attenuates adjacent channels, it also attenuates to some degree all channels - in my experience. I use the Channel Master 0585-2 for channel 39. If I do not join the antennas, I get for example, 29-30 db for physical channels 19 and 27 from the first antenna. When I plug that antenna into the jointenna, the signal to noise ration dips 1-2 db (to 27-28 db). Now channels 19 and 27 are more than 5 channels away from 39.

Thinking that the jointenna was somehow defective, I ordered another one. The first jointenna was 3 years old. The jointennas are from two different sellers (and no doubt from two different manufacturing batches). The new one is just a month old. It exhibits the same behaviour - knocking down the signal strength from 1 to 2 db on non-adjacent channels. This is a problem when the SNR dips to 19-21 db by itself and then the jointenna knocks another 2 db off. Under 20 db the picture starts to fragment.

This is not a case isolated to Channel Master jointennas. I observed the same behaviour in a "jointenna" I purchased from another manufacturer (in Canada). Now I have three! (And the one from Toronto cost 3 times more and was actually worse - the Channel Master gave me a better signal for 39). None of them seem to preserve the original signal strength across the entire spectrum. I didn't think the insertion losses for jointennas would knock of 1-2 db off each channel (in the case of the Canadian one it knocked off 2-3 db on some channels not adjacent).

BTW I use my OnAir USB receiver in observing the db count but my Samsung H260F stb also reflects similar results in percentages.

I noticed issues with the jointennas also. in my case insert ch 56 which attenuates ch 54.

my issue...want to amplify uhf but the system works best not amplified.
-tried amplifying the combined to tv output alone with a winegard hd269 12 db gain
-amplified the ch 56 antenna alone
-amplifying both uhf antennas into the jointenna worked best (2 hdp 269s)

the setup works best without amplification.

even tried retuning .

The jointennas are tuned on a per order basis on a test bench at the plant. I communicated to the individual personally. the jointennas are not of high tolerance and the filters are rather wide. I never thought to examine the entire band for loss. Assumed the attenuation was adjacent.There is insertion loss with the jointenna but it is not published. I will call my contact tomorrow and discuss the issue with him.

There are 3 filter companies here and I explored the possibility of ordering a filter of higher tolerance . It was cost prohibative.

I ordered a channel plus distribution amp with a net gain of 1db for the short runs and 4 db for the long runs. going to remove the preamps and try the distribution amp in their place.

If I am not satisfied, I am going to remove the jointenna from the system and go back to the rotor

If I am not satisdied going to remove the jointenna from the system and go back to the rotor

I'm wondering if there is an alternative to a jointenna - ie putting separate components on a line (not all in one box) - like filters and traps and combiners separately. Could it be that when they're integrated in one box, they don't behave optimally?

BTW I took apart my first Channel Master jointenna just to see what it looks like inside (since I had gotten a second one). Then when the Canadian one performed rather poorly, I took it apart (out of anger and frustration - $100 lost bucks since it wasn't returnable) to see what was inside. I was surprised to see how differently the CM and Canadian "jointennas" are made. I was expecting an identical or similar structure. I guess designers and manufacturers have their own way of putting these things together...

These type of electronics are used in cable head ends to insert channels...doubt they use jointennas

There are 3 filter companies here and I explored the possibility of ordering a filter module of higher tolerance just this past Friday . It was rather expensive and not really worth it since I do not watch the channel much.

If I am not satisfied, I am going to remove the jointenna from the system and go back to the rotor

In my case, I can't go to a rotor. The antenna has to be in another location altogether to get the specific channel - about 8-10 feet away from the first antenna. That's why I went with a jointenna. That channel hardly comes in anywhere else.

In fact I use a CM 4228 for my first antenna (channels 19 & 27) and a 91xg for channel 39 - the antennas six feet apart. The 4228 wouldn't bring in 39 but the 91xg did (and holds it nicely - but only at that location). On the other hand, channels 19 & 27 don't come in well at that location though the 91xg does bring them in at diminished levels).

I started out using the 4228 three years ago and then one day discovered that channel 39 had disappeared (it came in at 15 db when I investigated it). Decided to try the 91xg and it brought in 39 at 19 db (same location as 4228). Then when I moved the 91xg around (it's much lighter to move around than the 4228 tank), I noticed that as I moved it further to the left the signal got progressively stronger. So the 91xg became my channel 39 antenna!

Having an insertion loss of 1dB doesn't weaken your signals any more than lengthening the coax by about 20 feet. Technically superior antenna joiners will commonly have even more insertion loss than cheap ones. Realistically, you aren't going to find or make any product with less of an insertion loss than the Jointennas. What's your zip code?

Are you saying that channels 19 and 27 drop from 27-28dB S/N to 17-19 S/N? Is this antenna indoors or outside? Is the signal likely traveling through vegetation? The receiver signal strength and quality meters are primitive at best and cannot be taken as absolutely reliable indicators of whatever they purport to measure. You need to develop a channel 19-27 antenna or antenna array that is stable before you mix it with your channel 39.

Who in Canada made the filters? I have had quites from Tin Lee but never ordered from them.

Who in Canada made the filters? I have had quots from Tin Lee but never ordered from them.

It was from Tin Lee ($98 for "jointenna" plus $16 shipping). It looks much better built than the plastic CM but in my case performed much more poorly. At it's price I was expecting a lot more!

Having an insertion loss of 1dB doesn't weaken your signals any more than lengthening the coax by about 20 feet.

If the channel is at the border of 20-21 db on a bad day, then a further 1-2 db loss sends it under 20 db and the picture starts suffering. I have seen this happen over and over with channel 39 (zip 30041).

Are you saying that channels 19 and 27 drop from 27-28dB S/N to 17-19 S/N?

Channels 19 & 27 drop by 1-2 db (from 29-30 db to 27-28) consistently when I plug the antenna into the jointenna. Remove the jointenna and the're up to 29-30 db. This is not a worrisome loss for those channels but on other marginal channels that 1-2 db loss causes picture breakup when they dip below 19-20 db.

Is the signal likely traveling through vegetation?

I am in antenna hell. House is in a valley surrounded by 40-60 foot trees (Georgia pines on government land that nobody dares remove). Rows and rows and rows of them sloping upwards. To peer over them from my low location I would need a 100' tower and that ain't gonna happen! That I can get anything at 27-28-29-30 db levels is a miracle people tell me. Only 39 gives me a problem and that is a major station (ABC). But the 91xg (tilted up by 15 degrees) does bring it in 6 out of 7 days at 24-25 db (on a bad day it dips to 19-21 db especially when them trees start swaying as if they were in a religious revival). God bless the 91xg (did He create it on the 9th day?)...

Perhaps Home Depot or Wal-Mart will buy that land one day and level it (along with those trees) for a parking lot thus removing my impediment...

If 5th generation chipsets are supposed to handle multipath problems, why have a jointenna in the case of multiple antennas?

If your using the directional antennas to get sufficient gain rather than reject multipath, coupling them without a jointenna usually results in a gain pattern suboptimal for any direction the individual antennas point.

Realistically, you aren't going to find or make any product with less of an insertion loss than the Jointennas.

I've been trying to find what is the insertion loss for a CM jointenna - can't find any documents at any site. Do you know? Is it at 3.5 (like for splitters)?

BTW can you explain to me why a UHF/VHF splitter-combiner (UHF on one leg, VHF on the other) has only a 0.5 insertion loss (either CM or Winegard) but a normal one has 3.5 (legs non UHF VHF differentiated)?

If your using the directional antennas to get sufficient gain rather than reject multipath, coupling them without a jointenna usually results in a gain pattern suboptimal for any direction the individual antennas point.

And that has been my experience. I can't use an A/B switch because the cables from both antennas go into the jointenna and then from the jointenna to a distribution amp (Electroline DropAmp) serving 4 rooms. The jointenna performance I've observed is regardless of whether I plug the jointenna output into the distribution amp or not - same result.

If I didn't want ABC, then I wouldn't need this setup. (And the only reason I want ABC is because of college football for me and "Lost" for my wife). BTW others in this area have also reported problems with ch 39 reception.

I ordered a channel plus distribution amp with a net gain of 1db for the short runs and 4 db for the long runs. going to remove the preamps and try the distribution amp in their place.

What is the noise figure for the Channel Plus distribution amps? I can't see it quoted anywhere.

How much does the noise of a distribution amp add to the overall system? I read somewhere that this is miniscule after a signal has been properly amplified by a good preamp.

BTW I'm also intrigued by the announcement that the 6th generation tuners will have 30% better reception (http://www.dtvconsultancy.com/news/items/061227lge.htm). Does that mean that instead of a 20db threshold (below which the picture starts to degrade), a 15 db SNR become acceptable thus lowering all these barriers to consistent viewing?

Prior to the 5th gen chipset, my reception was aweful (non-existent for 80% of the channels). Now only one channel is problematic (and only on certain days). Both my 5th gen OnAir GT & Samsung H260F receivers have been working marvelously.

From the center of zip code 30040, all of bwam's digital stations are in the same direction, Atlanta, SSW (201° to 202°) except Pax 41.1 which is broadcast from Rome at 238°, and the SSW UHF ones are all 30 to 35 miles. Rome is a few miles closer.


From the middle of his zip code, with either a single story, rooftop antenna, or even on a 40 ft height mast, Antennaweb says bwam will likely receive signals from digital channel 41 from Rome, as well as Atlanta digital channels

41
51
10
20
27
25

Increasing mast height to 100' gains Atlanta channels 43 and 48. Increasing mast height to 150 feet adds channels 19, 44, 21, and 12. Increasing it to 200 ft gains your Atlanta ABC affiliate, broadcast on channel 39 at 1000Kw.

30 miles is not far for UHF signals to travel. The fact that half the Atlanta channels cannot be reliably received with a rooftop antenna 30 miles away means either: A) there is a terrain problem, or B) half of them are running at temporary low power levels. I checked a few of the channels calculated by Antennaweb to be weaker, but they were all at or near power levels of around 1,000 Kw

I see no reason why someone would use a different antenna for channel 39 in this situation. You more likely would benefit from a better antenna, a taller mast, or mast-mounted preamplification with a low gain (12dB) low noise preamplifier. In fact, at 30 miles over unfavorable terrain, I doubt that you would overload a Channel Master 23dB amplifier.

Are you using a preamplifier at present? Forget about the distribution amp. It is noisier than the preamp and is applied after that signal level has already dropped closer to the noise floor. What are you using for an antenna? Is it roof mounted?

A far as that 30% better performance claim, that is just sales crap and has no technical meaning.

From the center of zip code 30040, all of bwam's digital stations are in the same direction, Atlanta, SSW (201° to 202° deg) except Pax 41.1 which is broadcast from Rome at 238° deg, and the SSW UHF ones are all 30 to 35 miles. Rome is a few miles closer.


From the middle of his zip code, with either a single story, rooftop antenna, or even on a 40 ft height mast, Antennaweb says bwam will likely receive signals from digital channel 41 from Rome, as well as Atlanta digital channels

41
51
10
20
27
25

Increasing mast height to 100' gains Atlanta channels 43 and 48. Increasing mast height to 150 feet adds channels 19, 44, 21, and 12. Increasing it to 200 ft gains your Atlanta ABC affiliate, broiadcast on channel 39 at 1000Kw.

30 miles is not far for UHF signals to travel. The fact that half the Atlanta channels cannot be reliably received with a rooftop antenna 30 miles away means either: A) there is a terrain problem, or B) half of them are running at temporary low power levels. I checked a few of the channels calculated by Antennaweb to be weaker, but they were all at or near power levels of around 1,000 Kw

I see no reason why someone would use a different antenna for channel 39 in this situation. You more likely would benefit from a better antenna, a taller mast, or mast-mounted preamplification with a low gain (12dB) low noise preamplifier. In fact, at 30 miles over unfavorable terrain, I doubt that you would overload a Channel Master 23dB amplifier.

Are you using a preamplifier at present? Forget about the distribution amp. It is noisier than the preamp and is applied after that signal level has already dropped closer to the noise floor. What are you using for an antenna? Is it roof mounted?

A far as that 30% better performance claim, that is just sales crap and has no technical meaning.

Here is my setup:

Two antennas on the roof - lifted 10 feet above. First antenna 4228 gets me 11 (VHF NBC), 19 (UHF CBS) & 27 (UHF FOX). This antenna goes into a CM 7777 preamp (dual inputs VHF & UHF). Second antenna, 8 feet away from the first, a 91xg gets me 39 (ABC) - into a CM 7775 preamp (UHF only).

Outputs from preamps go to a jointenna inside the attic. Output of jointenna (12' cable) goes to DropAmp distribution amp. 4 outputs from distribution amp are dropped into separate rooms from the attic.

All wiring is RG6 quad shielded.

Forget about a 100' or 200' mast (I'm in a subdivision)! Those Georgia pines are 40-60 foot tall (must be there since the civil war) between me and the broadcast towers. And they are on a slope upward - my house is in a valley.

PAX BTW comes in as my best channel. But it broadcasts at twice the power of all the others plus it is not in line with the trees. It's direction is 25 degrees away from the trees. I don't get it now but I aimed the 91xg towards it one day just for fun to see what I would get and it came in at 33 db (the strongest of all my channels). However PAX is not interesting for me because it has no HD programming (in fact PAX has hideously split itself into 4 SD channels 14-1 to 14-4).

A far as that 30% better performance claim, that is just sales crap and has no technical meaning.

Well the 5th gen chips claimed better reception and they delivered on it. I had an MDP-100 and MDP-130 (the gold standards in their day for HD tuners) and my 5th gen OnAir and Samsung receivers beat them hands down in my situation.

What is the noise figure for the Channel Plus distribution amps? I can't see it quoted anywhere.

How much does the noise of a distribution amp add to the overall system? I read somewhere that this is miniscule after a signal has been properly amplified by a good preamp.


The best scenario with the jointenna has been with NO amplification.

Without amplification the signal on channel 54 digital is 90. Signal is worse when I amplify the output of the jointenna...high 60's...better when I amplify both antennas into the jointenna ...high seventies.

I had the best results with No amplification with the jointenna (I do not amplify vhf). I could have gotten away with no amplification on the short runs here but on the long runs the upper uhf was attenuating and needed a little boost.

I purchased the Channel Plus distribution amp because the net gain was low. only 1 db to the short runs and 4 db to the longer runs. I am going to remove the preamps. The distribution amp will amplify the combined output of the vhf and uhf off a cm0549 combiner I have in the setup.

I am hoping to achieve some sort of compromise with this setup. The noise of the channel plus units are about 4 db and not a concern right now.

Output of jointenna (12' cable) goes to DropAmp distribution amp. 4 outputs from distribution amp are dropped into separate rooms from the attic.

Amplification does affect performance with the jointenna as mentioned above and amplifying both antennas works best.

You may want to remove the distribution amp and just use splitters. The gain on the cm7777 and cm7775 should be plenty. Adding your distibution amp may be making the situation worse.

You aren't going to be able to engineer a solution for this. If I were desperate, I'd put two identical high gain Yagis on one horizontal boom and point it exactly at Altanta. I'd couple them with an ordinary. hybrid splitter, keeping the cable lengths exactly the same, and then, with a test TV right on the roof, I'd start sliding them apart a few inches at a time, logging the signal measurements that your receivers self-test develops. At some points along the boom, the reflected signals will be 180 degrees out of phase with one another and cancel each other. Chances are, this array will also get you a reliable 19 and 27, but even that will be something of a crapshoot, because whatever channel 19 and 27 multipath you incur will not have the same 180 degree phase cancellation location as 39. Then you preamplify the combined output. And if you can splurge for a second, identical Channel Master preamp, you might as well do that, but you'd have to find a splitter/combiner that passed power on both legs.

You aren't going to be able to engineer a solution for this. If I were desperate, I'd put two identical high gain Yagis on one horizontal boom and point it exactly at Altanta. I'd couple them with an ordinary. hybrid splitter, keeping the cable lengths exactly the same, and then, with a test TV right on the roof, I'd start sliding them apart a few inches at a time, logging the signal measurements that your rceiver's self-test develops. At some points along the boom, the reflected signals will be 180 degrees out of phase with one another and cancel each other. Chances are, this array will also get you a reliable 19 and 27, but even that will be something of a crapshoot, because whatever channel 19 and 27 multipath you incur will not have the same 180 degree phase cancellation location as 39. Then you preamplify the combined output. And if you can splurge for a second, identical Channel Master preamp, you might as well do that, but you'd have to find a splitter/combiner that passed power on both legs.

Mike,
A stacked array may be a good solution for the OP.Multipath and weak signal it sounds like,to me.

With my arsenal of goodies,I might try another approach.A Triax100 Band A for the lower UHF's which is a whole bunch better than a 4228 in terms of gain and multipath rejection,and the gain curve drops like a rock above 37.Feed this into a Triax A/E combiner which breaks at 37,then feed the XG91 into the high side.The combiner can be used passively or configured to pass power to high side,low side,or both.Might be the silver bullet.Took some pics of the combiner,not sure they're clear enough to read well.

http://community-2.webtv.net/GregBarker/TriaxTMC3739STP/

Feed this into a Triax A/E combiner which breaks at 37, then feed the XG91 into the high side.

This combiner (and your approach) interests me. I'm searching for the price for the Triax combiner but cannot find where it can be purchased. Any indications? Thanks.

Amplification affects performance with the jointenna as mentioned above and amplifying both antennas works best as you have done.

Did you try removing the distribution amp???

Remove the distribution amp and just use a splitter. The gain on the cm7777 and cm7775 should be plenty. Adding your distibution amp may be making the situation worse.

BTW can you explain to me why a UHF/VHF splitter-combiner (UHF on one leg, VHF on the other) has only a 0.5 insertion loss (either CM or Winegard) but a normal one has 3.5 (legs non UHF VHF differentiated)?

The VHF leg has .5 loss on the VHF band and infinite Db loss on the UHF, averaging out to 3.5 loss across both bands. Lkewise for the UHF leg. The normal splitter has the same 3.5 loss but evenly spread on both bands.

This combiner (and your approach) interests me. I'm searching for the price for the Triax combiner but cannot find where it can be purchased. Any indications? Thanks.
Don't waste your money with that combiner until you develop a better antenna signal. It will have an insertion loss comparable to that of the Jointenna and the Tin Lee product.

When you eventually develop an antenna array that reliably gets you everything on channel 39 and above from one antenna, but doesn't get you reliable reception on 19 and 27, then you can try the Triax combiner to combine your new 39+ antenna array with whatever works best for 19 and 27, but the Triax combiner will have some modest insertion loss and, without an antenna improvement, will leave you with your present, spotty channel 39 reception. FWIW, many of the "better quality" antenna filtering and combining products have slightly higher insertion losses than do the cheap ones, because in most situations they were engineered to maximize out of band rejection or sharpness of roll-off, which often slightly sacrifices insertion conductivity.

The VHF leg has .5 loss on the VHF band and infinite Db loss on the UHF, averaging out to 3.5 loss across both bands. Lkewise for the UHF leg. The normal splitter has the same 3.5 loss but evenly spread on both bands.

A splitter sends half the signal to each port. the base ten logarithm of one half is .3010299... A decibel is 10logX, therefore cutting signal in half results in a theoretical signal loss of 3.0102999... which we round off to 3. Because the splitter is a real device with parasitic effects that reduce its efficiency, it tends to lose 3.5dB at low frequencies, and closer to 4dB at higher frequencies.

A UHF/VHF band separator/joiner is a fundamentally different device. It basically splices together the outputs from primitive but fairly deep low-pass and high-pass filters. Because there is a huge gap between the upper edge of the VHF band (216 Mhz) and the lower edge of the UHF band (470 Mhz), a sharp rolloff from one band to the other is not necessary, and so the circuitry needed to develop about 30dB of out-of-band rejection is often no more than a capacitor on the high-pass side and a choke coil on the low-pass side, and each of those "first order" filters is relatively efficient at passing the desired, in-band signals.

Channels 19 & 27 drop by 1-2 db (from 29-30 db to 27-28) consistently when I plug the antenna into the jointenna. Remove the jointenna and the're up to 29-30 db. This is not a worrisome loss for those channels but on other marginal channels that 1-2 db loss causes picture breakup when they dip below 19-20 db.

If you simply use the Triax combiner with the two antennas you have now, it means that your relatively weak channels 43, 44 and 48 are going to come from your channel 39 antenna, and your relatively weak channel 21 will come from the 19/27 antenna. That may make things worse for you.

This combiner (and your approach) interests me. I'm searching for the price for the Triax combiner but cannot find where it can be purchased. Any indications? Thanks.

Looks like my overseas supplier doesn't stock these,or the Triax 100 Band A's any longer. www.cpc.co.uk

If your channels work out on each antenna so this piece may be helpful,send me a pm.I have two on hand.