Joining 4 OTA antennas? - Canadian TV, Computing and Home Theatre Forums
 

Go Back   Canadian TV, Computing and Home Theatre Forums > Canadian Internet, Phone, TV and Wireless Service Providers > Over-The-Air (OTA) Digital Television > Antenna Research & Development

Digital Home Helpful Information

Reply
 
Thread Tools Search this Thread Display Modes

Old 2009-08-19, 10:36 AM   #1
ppauper
 
Join Date: May 2007
Posts: 257
Question Joining 4 OTA antennas?

If I wanted to join 4 identical antennas, is it better to use a 4-way splitter or three 2 way splitters ?
and if 4-way is the answer, can someone recommend a good brand/model

Last edited by ppauper; 2009-08-19 at 03:52 PM. Reason: (correct an error pointed out by keef)
ppauper is offline   Quick reply to this message
Sponsored Links
Advertisement
 
Old 2009-08-19, 10:44 AM   #2
keef
 
Join Date: Jan 2009
Location: Minnesota
Posts: 84
Default

You'd need three 2-way splitters. As a 4-way may very well be three 2-way splitters internally, I doubt there's much difference.

If I were determined to join 4 antennas, I'd probably want to join/balance them in pairs, then join/balance the two pairs together; get each pair working well, then get the two pairs working together. Three 2-way splitters would give you that flexibility.

Note: I'd have to be determined. I don't know that I'd even attempt it without some pretty expensive testing and measuring equipment.
keef is offline   Quick reply to this message
Old 2009-08-19, 12:20 PM   #3
roger1818
Veteran
 
Join Date: Apr 2006
Location: Ottawa (Stittsville), ON, OTA (DB4e & VHF-HI folded dipole, AP-2870 pre-amp in Attic), MythTV HTPC
Posts: 6,148
Default

Quote:
Originally Posted by ppauper View Post
If I wanted to join 4 identical antennas, is it better to use a 4-way splitter or two 2 way splitters ?
Will any or all the antennas be pointing in the same direction? This will affect the decision.
roger1818 is offline   Quick reply to this message
Old 2009-08-19, 01:22 PM   #4
stampeder
OTA Forum Moderator
 
Join Date: Jan 2005
Location: North Delta, BC (96Av x 116St)
Posts: 23,994
Default

I was thinking the same thing, Roger - is this for a diamond or quad array, ppauper?

Those 4-antenna configurations are almost always done with channel-cut Yagis for CATV/MATV head ends.
stampeder is offline   Quick reply to this message
Old 2009-08-19, 03:08 PM   #5
ppauper
 
Join Date: May 2007
Posts: 257
Default

Quote:
Originally Posted by roger1818 View Post
Will any or all the antennas be pointing in the same direction?
all in the same direction.
It's a pair of stacked CM4228s, and I was going to try disconnecting the feedlines and using 2 separate baluns on each half of each 4228 (as in the 4228HD hack, to see if there was any improvement) so that I sort of have 4 identical antennas forming a square
ppauper is offline   Quick reply to this message
Old 2009-08-19, 03:27 PM   #6
stampeder
OTA Forum Moderator
 
Join Date: Jan 2005
Location: North Delta, BC (96Av x 116St)
Posts: 23,994
Exclamation 16 and 32-bay arrays not advised

ppauper, Ken Nist says not to bother with a 32-bay (4 ganged 8-bays) and he says to read his 16-bay page first:

http://www.hdtvprimer.com/ANTENNAS/16bay.html

http://www.hdtvprimer.com/ANTENNAS/32bay.html

Note that at the bottom of the 32-bay page he mentions the CM4251 parabolic antenna, but he wrote that page before the various Gray-Hoverman variants came along, so you might want to investigate building something like a GH10.
stampeder is offline   Quick reply to this message
Old 2009-08-19, 03:51 PM   #7
ppauper
 
Join Date: May 2007
Posts: 257
Default

stampeder: It's 16 bay, I've got 2 x 4228's stacked, but I was going to split each 4228 into a pair of 4221's as it were making 4 x 4221

keef: you're right, 3 x 2-way versus 1 x 4-way. I was asleep I guess
ppauper is offline   Quick reply to this message
Old 2009-08-19, 03:53 PM   #8
stampeder
OTA Forum Moderator
 
Join Date: Jan 2005
Location: North Delta, BC (96Av x 116St)
Posts: 23,994
Default

Ken's warnings would apply then. You'd probably hit the law of diminishing returns i.e. reception does not improve with effort expended. Stacking original CM4228s was commonplace, but what you want to do is not.

If you give it a try can you post some before and after signal strength results here?
stampeder is offline   Quick reply to this message
Old 2009-08-19, 04:20 PM   #9
holl_ands
Veteran
 
Join Date: Nov 2008
Location: San Diego, CA
Posts: 2,251
Default

Quad arrays need a low-loss Stripline Coupler (0.2 dB loss, irrespective of matching)
rather than a typical Hybrid Transformer (e.g. RF Splitter) which has 1-7+ dB of loss,
depending on antenna/combiner mismatch wrt amplitude and phase (no-way)...

For instance, if one of the antennas in the Quad Array has a dip in its frequency
response (could be a broken or bent whisker), then it will ALSO degrade the signal
on those frequencies from the OTHER antenna going into the first 2-way combiner.
And THAT imperfectly summed signal will degrade the 2-way combiner trying to
sum the output of the other pair of antennas...a double whammy....

Here is a summary of (mostly partial band) Stripline Couplers:
http://www.avsforum.com/avs-vb/showt...php?p=16072450
holl_ands is online now   Quick reply to this message
Old 2009-08-19, 04:26 PM   #10
ppauper
 
Join Date: May 2007
Posts: 257
Default

it'll be a while before I try it (I'm on the road but thinking about OTA while I'm out of town)
I was thinking about this because if you look at the charts linked in the CM4228HD threads, the hacked CM4228HD with 2 baluns seems to outperform the original 4228 with 1 balun, so I was wondering whether doing the hack to the original 4228 would help.
I may instead buy what appears to be a (from NZ so probably $$$ for shipping) 1:1 balun I posted in the balun thread and again remove the feedlines and hook all 4 "4221s" together to a single 1:1 balun
ppauper is offline   Quick reply to this message
Old 2009-09-06, 01:08 AM   #11
Lineloss
 
Join Date: Aug 2008
Location: Oshawa, On. Canada
Posts: 155
Default

Well I got it working. (see http://www.digitalhome.ca/forum/showthread.php?t=112071 for reference)

I did a fast scan with the top 4228hd connected to the 4 to 1 splitter; two of the inputs were left unconnected since I was only looking for a proper polar response at this point. Connecting both 4228hd's ,in phase this time, only seemed to help increase signal strength on my weak stations from Rochester as all the Buffalo and TO stations are coming incredibly strong. I was pulling in 45 digital channels pointing due south. When I have time I'll get around to a proper comparison. This setup is definitely smoking the single 4221 I used to have mounted in the same spot!

Last edited by stampeder; 2009-09-06 at 01:18 PM. Reason: fixed url link
Lineloss is offline   Quick reply to this message
Old 2009-09-09, 08:34 PM   #12
Lineloss
 
Join Date: Aug 2008
Location: Oshawa, On. Canada
Posts: 155
Default Impedance of all 4

I was pondering if my stacked 4228's (lines removed and baluns added) are impedance matched properly as a whole (75 ohms).

I inserted a 1 to 2 splitter between the antenna and my pre amp input. I only used the splitter input and one output. I know there is some loss here, but the point was to double the so called 75 ohms antenna to 150 ohms and then to lower it to 37 ohms to see the results. Both connections should reduce my signal right? I know an antenna's impedance is not constant with frequency so I picked two middle "real" channels... When the antenna was assumed to be 150 ohms I got higher signal strength???

Any thoughts on this one?

I can't complete any full testing because "this ugly antenna thing is stupid" haha....yep you guessed it, the wife was helping me. I use the word helping loosely..hehe!
Lineloss is offline   Quick reply to this message
Old 2009-09-10, 12:13 PM   #13
ppauper
 
Join Date: May 2007
Posts: 257
Default

so lineloss, does that mean we need to put a 2:1 balun on each antenna or an 8:1 balun ?
ppauper is offline   Quick reply to this message
Old 2009-09-10, 03:22 PM   #14
Lineloss
 
Join Date: Aug 2008
Location: Oshawa, On. Canada
Posts: 155
Default

That would make it four 2:1 baluns.... Something tells me it may be between a 4:1 and a 2:1 somewhere, but this would need a much better investigation than I have done thus far! Hopefully this weekend

Must have more performance
Lineloss is offline   Quick reply to this message
Old 2009-09-10, 05:35 PM   #15
roger1818
Veteran
 
Join Date: Apr 2006
Location: Ottawa (Stittsville), ON, OTA (DB4e & VHF-HI folded dipole, AP-2870 pre-amp in Attic), MythTV HTPC
Posts: 6,148
Default

Lineloss, I am not convinced that leaving one input on a 2-1 splitter open will simulate either a 37 ohm or 150 ohm input. What the exact behavior is will depend on the design of the splitter you are using.
roger1818 is offline   Quick reply to this message
Reply

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Canadian TV, Computing and Home Theatre Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may post new threads
You may 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



All times are GMT -4. The time now is 04:34 PM.

OTA Forum Sponsor


Search Digital Home

Powered by vBulletin® Version 3.8.6
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.