The great jointenna exchange - Page 3 - AVS | Home Theater Discussions And Reviews
Baselworld is only a few weeks away. Getting the latest news is easy, Click Here for info on how to join the Watchuseek.com newsletter list. Follow our team for updates featuring event coverage, new product unveilings, watch industry news & more!


Forum Jump: 
 
Thread Tools
Old 10-03-2012, 10:32 AM
AVS Special Member
 
AntAltMike's Avatar
 
Join Date: Nov 2001
Location: College Park, MD
Posts: 3,691
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 60 Post(s)
Liked: 34
There's an insertion loss of the bandpass filter that might be dropping your signal strength below an acceptable level. It varies from one unit to another. It has been a long time since I seriously experimented with UHF jointennas on a bench, but I think the insertion loss of the bandpass path commonly varied from about 2 to 5 dB.

The other thing is, the band reject filters aren't very narrow, and the channel 23 band reject circuit could attenuate channel 20 on the thru path, and the channel 20 filter's reject circuit could reject the channel 23 on its thru path, so it is important to couple the weaker, problematic signal last in a string of jointennas. You might also benefit from lightly amplifying the channel 23 lead by 10 to 12 dB before inserting it into a filter, but whether you can get away with doing that will depend on the relative strength of the other signals coming off that line. If you only have a 15 to 20dB amplifier available, you can use it to preamplify the channel 23 line, but if you do, you might need to "double up" your two channel 23 Jointennas, using the first one on the preamplifier output just as a bandpass filter and using the second one for coupling.

Do you have a TV fool plot we can look at?
AntAltMike is online now  
Sponsored Links
Advertisement
 
Old 10-07-2012, 08:49 AM
Newbie
 
rptr's Avatar
 
Join Date: Sep 2012
Posts: 6
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
AntAltMike

Thanks again for taking an interest in my problem. I will try to address the issues you raised in your last post. I do have a TVFool plot for my location but I do not know how to send it to you. I can tell you the results. Most of the stations I watch are located to the east which I receive by diffraction due to a ridge between me and the transmitters. Two of these are VHF stations which I receive on an upper band VHF antenna. The signals from the UHF antenna and the VHF antenna are combined through a CM-7777 amplifier. However, I also have two UHF stations located to the north which I receive by line of sight. One of these, channel 20, is so strong that I can receive it on my UHF antenna pointed east. The other, channel 23, is strong but needs an antenna pointed north.

In my last test of the channel 23 jointenna I used an antenna pointed north connected to the CM-7777 amplifier. The channel 20 jointenna was not connected. I tuned my TV to channel 23 and had a good signal. I then inserted the channel 23 jointenna right at the TV set, and got no signal. Does this information give you any ideas as to why it doesn't work?
rptr is offline  
Old 10-07-2012, 12:17 PM
AVS Special Member
 
AntAltMike's Avatar
 
Join Date: Nov 2001
Location: College Park, MD
Posts: 3,691
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 60 Post(s)
Liked: 34
Quote:
Originally Posted by rptr View Post

I do have a TVFool plot for my location but I do not know how to send it to you.

I think this site requires that you have made five posts before it will let you post the hyperlink to your TV fool plot, but your next post will be your fifth.
AntAltMike is online now  
Old 10-07-2012, 12:21 PM
AVS Special Member
 
AntAltMike's Avatar
 
Join Date: Nov 2001
Location: College Park, MD
Posts: 3,691
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 60 Post(s)
Liked: 34
You might try using one channel 23 Jointenna as just a bandpass filter, between the antenna and the preamplifier input, and then, if that preamp output is tunable by your TV, then couple the preamp output into your other antenna line using your other channel 23 jointenna.

What is the published gain of your CM7777? It has been mentioned here that newer Channelmaster preamps have different electronics and different gain figures than do earlier units bearing the same model or part numbers.
AntAltMike is online now  
Old 10-16-2012, 08:17 AM
Newbie
 
rptr's Avatar
 
Join Date: Sep 2012
Posts: 6
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
AntAltMike

I have the old model of the CM-7777 which has separate inputs for VHF and UHF. It has a gain of 26dB on UHF. I did not understand why you are suggesting to use both channel 23 jointennas. Neither one will pass the channel 23 signal on the channel 23 input. Can you explain why that is happening? Thanks again for for your interest and suggestions.
rptr is offline  
Old 10-16-2012, 11:16 AM
AVS Special Member
 
AntAltMike's Avatar
 
Join Date: Nov 2001
Location: College Park, MD
Posts: 3,691
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 60 Post(s)
Liked: 34
Actually, both of them "pass" the channel 23 signal if they did so when Channel Master tested them and if no one has subsequently attempted to retune them.

It is possible for a TV to work when connected to a signal that has passed through a working filter when insertion loss drops that signal below the minimal level needed by the tuner, or when preamplification has degraded it. It is actually easier to deal with the problem of an anemic digital signal because, since preamplifiers all have lower noise figures than do digital TV tuners, a weakened digital signal can be "rescued by "post preamplification" after it comes out of a bandpass filter.

Since you have the two filters and a preamp on hand, you need to just try this and see how it does. If it doesn't work, then the next step would be to try pre and post amplification combinations using a lower gain amplifier.

Last edited by AntAltMike; 04-18-2015 at 05:41 PM.
AntAltMike is online now  
Old 11-08-2012, 05:46 PM
Newbie
 
rptr's Avatar
 
Join Date: Sep 2012
Posts: 6
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Good news. I solved my channel 23 Jointenna problem by buying an Antenna Signal Injector from Tin Lee. It does the same job as the Jointenna. I just connected it to the antennas and it worked. I can now get all the channels from the two antennas.


AntAltMike

Thanks for your interest and all your advice.
rptr is offline  
Old 11-09-2012, 09:05 AM
Advanced Member
 
ADTech's Avatar
 
Join Date: Jun 2010
Location: St Louis
Posts: 526
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 48 Post(s)
Liked: 39
rptr,

If you're interested, I can check out the ch23 Jointenna to see what was wrong with it. Sorry, missed your previous posts or I'd have offered to check it sooner. Shoot me aPM if you're interested.

BTW, how much did the TinLee injector cost? Just curious since we often run into oddball channel locations when talking to customers.

Cheers!

Tech support for Antennas Direct
ADTech is offline  
Old 04-15-2015, 09:26 AM
Newbie
 
OTAzak's Avatar
 
Join Date: Oct 2011
Location: north central CT
Posts: 8
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 5 Post(s)
Liked: 10
Are there any opinions as to whether Jointennas should be used before or after signal amplifiers? I have always used them after amplification.


In my particular case I would like to wire a single secondary antenna through a preamp, then power inserter, then a splitter and into two single channel inlet ports on two separate Jointennas (in parallel), then have the primary antenna (also post preamp, post power inserter) come through the common ports of both Jointennas (in series).


If I recall correctly jointennas are power passive.
OTAzak is offline  
Old 04-15-2015, 09:30 AM
Member
 
bigdaveyl's Avatar
 
Join Date: Nov 2011
Location: Rochester, NY
Posts: 49
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 21 Post(s)
Liked: 10
Quote:
Originally Posted by ADTech View Post
rptr,

If you're interested, I can check out the ch23 Jointenna to see what was wrong with it. Sorry, missed your previous posts or I'd have offered to check it sooner. Shoot me aPM if you're interested.

BTW, how much did the TinLee injector cost? Just curious since we often run into oddball channel locations when talking to customers.

Cheers!
I was quoted $100USD for a 1 channel and $120USD for a 2 channel. Doesn't include shipping. I was debating picking 1 or 2 up next time I was up in Toronto to save shipping....
bigdaveyl is online now  
Old 04-15-2015, 10:38 AM
AVS Special Member
 
AntAltMike's Avatar
 
Join Date: Nov 2001
Location: College Park, MD
Posts: 3,691
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 60 Post(s)
Liked: 34
Quote:
Originally Posted by bigdaveyl View Post
I was quoted $100USD for a 1 channel and $120USD for a 2 channel. Doesn't include shipping. I was debating picking 1 or 2 up next time I was up in Toronto to save shipping....
You'd better call ahead and prepay, because I doubt they have all models in stock.
AntAltMike is online now  
Old 04-15-2015, 10:44 AM
AVS Special Member
 
Calaveras's Avatar
 
Join Date: Jan 2007
Location: Mountain Ranch
Posts: 3,774
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 516 Post(s)
Liked: 150
Quote:
Originally Posted by AntAltMike View Post
You'd better call ahead and prepay, because I doubt they have all models in stock.

I don't think they have anything in stock. AFAIK they custom build everything.
Calaveras is online now  
Old 04-15-2015, 10:51 AM
AVS Special Member
 
Calaveras's Avatar
 
Join Date: Jan 2007
Location: Mountain Ranch
Posts: 3,774
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 516 Post(s)
Liked: 150
Quote:
Originally Posted by OTAzak View Post
Are there any opinions as to whether Jointennas should be used before or after signal amplifiers? I have always used them after amplification.


In my particular case I would like to wire a single secondary antenna through a preamp, then power inserter, then a splitter and into two single channel inlet ports on two separate Jointennas (in parallel), then have the primary antenna (also post preamp, post power inserter) come through the common ports of both Jointennas (in series).


If I recall correctly jointennas are power passive.

If you order from Tinlee I think you can get DC pass wherever you want. Inexpensive splitters that pass DC on one port are available.

The preamp should be first if at all possible because anything between the antenna and the preamp adds loss, which either lowers the effective antenna gain or increases the system noise figure, depending on how you view it.

I think the use of two antenna joiners as you described above is shown in my diagram below. This will work. Otherwise you can put one power inserter just before the TV and you'll need DC pass on the proper device ports.
Attached Thumbnails
Click image for larger version

Name:	Join Antennas.jpeg
Views:	18
Size:	85.2 KB
ID:	668138  
Calaveras is online now  
Old 04-15-2015, 10:53 AM
Member
 
bigdaveyl's Avatar
 
Join Date: Nov 2011
Location: Rochester, NY
Posts: 49
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 21 Post(s)
Liked: 10
Quote:
Originally Posted by Calaveras View Post
I don't think they have anything in stock. AFAIK they custom build everything.
This is true, I believe. They could custom build any 1 or 2 channel inserter. That would make sense because they say no returns/exchanges unless unit is defective.
bigdaveyl is online now  
Old 04-15-2015, 12:35 PM
AVS Special Member
 
rabbit73's Avatar
 
Join Date: Apr 2008
Location: S.E. VA
Posts: 1,034
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 78 Post(s)
Liked: 25
Quote:
In my particular case I would like to wire a single secondary antenna through a preamp, then power inserter, then a splitter and into two single channel inlet ports on two separate Jointennas (in parallel), then have the primary antenna (also post preamp, post power inserter) come through the common ports of both Jointennas (in series).
Why? What is the advantage of using two jointennas to insert the signal from the second antenna twice?

If you can not measure it, you can not improve it.
Lord Kelvin, 1883
www.megalithia.com/elect/aerialsite/dttpoorman.html
rabbit73 is offline  
Old 04-15-2015, 01:34 PM
Newbie
 
OTAzak's Avatar
 
Join Date: Oct 2011
Location: north central CT
Posts: 8
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 5 Post(s)
Liked: 10
Quote:
Originally Posted by rabbit73 View Post
Why? What is the advantage of using two jointennas to insert the signal from the second antenna twice?

Sorry this wasn't clear, they would be inserting two different UHF channels, about 12 channels apart (and roughly 30 deg. angle separation). Figured a splitter is cheaper and easier than setting up a third antenna.
OTAzak is offline  
Old 04-15-2015, 04:59 PM
AVS Special Member
 
rabbit73's Avatar
 
Join Date: Apr 2008
Location: S.E. VA
Posts: 1,034
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 78 Post(s)
Liked: 25
Oh, OK. That might work using a splitter in reverse as a combiner.
Google search for join tenna schematic:

https://www.google.com/search?q=join+tenna+schematic&biw=1093&bih=420&tbm =isch&tbo=u&source=univ&sa=X&ei=S-ouVfjwFfiUsQSj6ICoBQ&ved=0CDEQsAQ

What channels are you talking about? Is this pretty close to your tvfool report?
http://www.tvfool.com/?option=com_wr...f1f0147309a88d

This is the way Channel Master does it:



http://www.warrenelectronics.com/Antennas/Jointennas.htm

And this is another way, using a splitter in reverse as a combiner:



http://webpages.charter.net/themanny/ota.htm

Quote:
If I recall correctly jointennas are power passive.
Maybe one way, but not the other:

Attached Thumbnails
Click image for larger version

Name:	Jointenna6_1.jpg
Views:	64
Size:	25.1 KB
ID:	668794   Click image for larger version

Name:	Jointenna7_1.jpg
Views:	66
Size:	43.5 KB
ID:	668802   Click image for larger version

Name:	Jointenna8_1.jpg
Views:	70
Size:	49.6 KB
ID:	668810  

If you can not measure it, you can not improve it.
Lord Kelvin, 1883
www.megalithia.com/elect/aerialsite/dttpoorman.html

Last edited by rabbit73; 04-15-2015 at 05:07 PM.
rabbit73 is offline  
Old 04-16-2015, 06:44 AM
Newbie
 
OTAzak's Avatar
 
Join Date: Oct 2011
Location: north central CT
Posts: 8
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 5 Post(s)
Liked: 10
Rabbit, thanks for your reply. I have seen the basic diagrams on the Warren Electronics site but had not seen the second schematic (although they never show where a signal amplifier could or should be introduced - if an amplifier overcomes the ~ 12.5 bandstop then I suspect there could be issues).


In my case I want to receive RC 22 and RC 34 from the north, and have an RC 22 jointenna and a second UHF jointenna that I hope to retune to 34. Most of my stations are southerly as the TV report indicates. If this is not feasible the loss of RC 34 isn't very significant. I had hoped to get these off the (primary) antenna backside but have been unsuccessful so far just via aiming of the main antenna.


Thus my question above - split a single antenna input through two jointennas using a splitter. I had not thought about using a combiner on the bandstop side.

Last edited by OTAzak; 04-16-2015 at 06:49 AM.
OTAzak is offline  
Old 04-16-2015, 09:29 AM
AVS Special Member
 
AntAltMike's Avatar
 
Join Date: Nov 2001
Location: College Park, MD
Posts: 3,691
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 60 Post(s)
Liked: 34
Quote:
Originally Posted by OTAzak View Post
Are there any opinions as to whether Jointennas should be used before or after signal amplifiers? I have always used them after amplification....
If I recall correctly jointennas are power passive.
Quote:
Originally Posted by rabbit73 View Post
Maybe one way, but not the other:

I just popped the cases open on an 0579 channel 9 VHF Jointenna and an 0585-1 UHF Jointenna pre-tuned to channel 28.

That schematic above is for a VHF Jointenna, which does not pass power through its single antenna port. The UHF 0585-X Jointennas DO pass power to all ports. I just measured zero resistance from TV Set to All Channels, and 0.5 ohms from TV Set to Single Channel. I am not able to estimate their current carrying capability of the Single Channel circuit, as those current bypass inductors are wound with awfully tiny wire, but they surely can carry whatever amount of current a single preamplifier draws. FWIW, the TV to All Channels path can carry enough current to light a Christmas tree,

In fact, the drawing is either a Low Band Jointenna or a very old one. The channel 9 High Band Jointenna I am looking at right now was likely made in this century, and it has tiny trimmer inductors in series with each of the shunt capacitors. I have not yet experimented with them to see what their tuning range and effects is.

About a decade ago, I opened and examined some low band Jointennas whose packages I had to wipe the dust off to read, and they did not have similar, trimmer inductors. I have no way of knowing whether those trimmers are a modern addition or an inherent design difference between the low band and high band units.

The two big inductors on the VHF Jointennas are wound around the same threaded non inductive core, meaning they function as an air core transformer. Curiously, that core is threaded and slotted and can be turned, but turning it accomplishes nothing electrically, so it was probably used just because it was a readily available item that neatly supports those heavy gauge four turn coils.

On the UHF Jointenna, the similarly circuited inductor coils that also interact to function as a transformer are free standing and appear to have been hand optimized by poking at them. There are also multiturn inductor screw slugs that move the pass band and reject notch through the entire designated ranges of channels 14-30 (0585-1), 31-49 (0585-2), and presumably 50-69 (0585-3), but I don't have an 0585-3 available to test. FWIW, when I adjust those inductor slugs to change the UHF Jointennas from one channel to another, I see no effect of a metal, inductive screwdriver of their performance. Similarly, I could tune the slugs on the old, Tru-Spec BPFs with an ordinary, 1/8" magnetic screwdriver as well.

Last edited by AntAltMike; 04-17-2015 at 12:56 PM.
AntAltMike is online now  
Old 04-16-2015, 01:58 PM
AVS Special Member
 
rabbit73's Avatar
 
Join Date: Apr 2008
Location: S.E. VA
Posts: 1,034
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 78 Post(s)
Liked: 25
OK, I think I got it. Chuck's diagram is correct, if you can keep the power inserters in the places indicated. If you want a power inserter after the second jointenna and just before the TV instead, then it must be able to provide enough current for both preamps, and the jointennas and splitter must be able to pass the current.


Attached Thumbnails
Click image for larger version

Name:	ChuckDiag_1.jpg
Views:	51
Size:	80.0 KB
ID:	669737  

If you can not measure it, you can not improve it.
Lord Kelvin, 1883
www.megalithia.com/elect/aerialsite/dttpoorman.html
rabbit73 is offline  
Old 04-16-2015, 03:50 PM
AVS Special Member
 
rabbit73's Avatar
 
Join Date: Apr 2008
Location: S.E. VA
Posts: 1,034
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 78 Post(s)
Liked: 25
Quote:
Originally Posted by OTAzak View Post
In my case I want to receive RC 22 and RC 34 from the north, and have an RC 22 jointenna and a second UHF jointenna that I hope to retune to 34. Most of my stations are southerly as the TV report indicates. If this is not feasible the loss of RC 34 isn't very significant. I had hoped to get these off the (primary) antenna backside but have been unsuccessful so far just via aiming of the main antenna.
This is your tvfool report for your estimated location

You never did post your tvfool report AFAIK, so I hope my estimate of your location is close enough.

I think you can make it work, but I see a few potential problems ahead. I understand your desire to amplify the signals before the jointennas to compensate for their insertion loss. But, since your signals from the north and from the southwest are already very strong, there is a good chance that the preamps will be overloaded which will create spurious signals in the preamp from IMD that will wipe out your weakest desired signals.

There a few ways you can deal with that problem. You can try just the CH 22 jointenna first without any preamps, you can select a preamp that can tolerate very strong signals, or you can insert an attenuator between the antenna and the preamp input for a compromise between those two extremes that will provide just enough amplification without creating enough overload to damage your weakest desired signal. I favor the first choice as a test.

CH 22 is going to be a lot easier than CH 34, in spite of the fact that CH 22 is 26.5 dB weaker than WSFB on CH 33.

CH 34, WTXX-LP digital virtual 34.1 has co-channel interference (if tvfool is correct) from WTXX analog that is 7.3 dB weaker, co-channel interference from WESA analog that is 15.1 dB weaker, adjacent channel interference from WFSB on CH 33 that is 37.7 dB stronger, and adjacent channel interference from WVIT on CH 35 that is 27.1 dB stronger.

If you can not measure it, you can not improve it.
Lord Kelvin, 1883
www.megalithia.com/elect/aerialsite/dttpoorman.html

Last edited by rabbit73; 04-16-2015 at 03:57 PM.
rabbit73 is offline  
Sponsored Links
Advertisement
 
 
Thread Tools


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