CM 4228HD built-in balun - Canadian TV, Computing and Home Theatre Forums

uglydukwling · 2009-01-31, 08:52 AM

My 4228 arrrived this week, ahead of schedule (the dealer had said it would be at least mid-February) so it's time to install it and see how it works.
The problem is that it has a built-in balun for a 75 ohm output, and my pre-amp has a 300 ohm input.
Using a second balun to bring the antenna output back to 300 ohms would introduce unnecessary losses (how serious?)
The balun is rivetted to the phasing wires and the rivets are part of the balun, so I won't be able to remove it without destroying it. I'd rather not do that in case I ever upgrade my pre-amp and need a 75 ohm connection. I suppose baluns are cheap enough that I really shouldn't worry, but this one is neater than one dangling from its wires.
Can I leave the balun in place and by-pass it? I won't be able to connect to exactly the same place on the phasing wires as the balun is connected because the phasing wires are tight against the balun. I thought that it was critical that the length of phasing wire had to be the same on both sides of the connection point, but the lengths are different already so maybe an off-centre connection won't matter. Also, will the presence of the balun have any effect on the antenna with only its input side connected?

Tom.F.1 · 2009-01-31, 09:10 AM

I would leave it like it is and use a regular balun to go to 300 to match your amp.
Or change the amp. Have you tried it without the amp?

300ohm · 2009-01-31, 11:25 AM

Quote:

Using a second balun to bring the antenna output back to 300 ohms would introduce unnecessary losses (how serious?)

Fairly high, with two back to back baluns, around 1 to 3 dBi depending on the quality. 3dBi is the halving of the signal. Plus we dont know if the new CM4228HD balun is 4:1, although we assume it may be.

Without looking at it, I dont know what to tell you. Can you post some close up pictures of that balun ?

uglydukwling · 2009-02-01, 08:14 PM

I can't get my camera and computor to talk to each other, so I havn't been able to post a picture.
I hope this description will help. The balun is a plastic box 2 1/2 inches high, 2 1/4 inches wide, 5/8 inches thick. It's connected to ( and supported by) the phasing lines by two hollow rivets 9/16 inches from the left side and 1 9/16 inches apart. The upper phasing line, attached to the upper rivet, is 13 inches long on the left and 9 1/2 inches long on the right. The lower one, attached to the lower rivet, has the dimensions reversed. The 75 ohm connector is on the bottom of the balun.
Left and right are as you would see them facing the front of the antenna. The phasing line lengths are measured from the rivet to the point where the line enters the plastic insulator on the vertical antenna element. Dimensions are somewhat approximate because there are bends in the phasing lines. The upper left and lower right lines are longer because they cross the vertical element and then are bent back in a J to the connection point.
If there are any other dimensions that I should measure, or if any parts of the description aren't clear, let me know.

300ohm · 2009-02-01, 10:09 PM

Quote:

I hope this description will help.

Thanks and we appreciate it, but unfortunately not. We really need a close up picture of the insides and the gauges of the tiny wires inside and the dimensions of the inside ferrite core(s) plus the lengths and turns of the windings. Its going to be pretty tough for someone to describe all that, I know.

uglydukwling · 2009-02-02, 08:35 AM

When you said "close-up pictures", I didn't realize you were talking about the INSIDE of the balun. Unfortunately, it doesn't look like I can get inside without destroying it, and I probably shouldn't do that just yet, in case I need it.
I hadn't considered the possibility of the antenna impedance not being 300 ohms. That may well be the reason they provided a non-removable built-in balun and it may be a unique ratio. That would mean that bypassing the balun and connecting directly to my pre-amp wouldn't work. Also, when I find that out, substituting a conventional 300:75 balun won't work.
Todaty's a business day, so I may end up spending the day on the phone trying to get some information out of ChannelMaster.

300ohm · 2009-02-02, 01:19 PM

Quote:

Also, when I find that out, substituting a conventional 300:75 balun won't work.

Its not that it wouldnt work at all, but if its mismatched, it wont work well. That would be the problem.

uglydukwling · 2009-02-03, 04:52 PM

After trying unsuccessfully to reach the CM tech line, I finally emailed them and got this reply:
"I do not recommend trying to remove or bypass the 75 ohm balun."
No reason given. No answer to my question whether the antenna impedance was 300 ohms or something else.
So it looks like my options are add another balun or change the preamp to one with a 75 ohm input (maybe its time for an upgrade anyway)

300ohm · 2009-02-03, 05:22 PM

Quote:

No reason given. No answer to my question whether the antenna impedance was 300 ohms or something else.

Hmmm, I wonder what they would say if you told them your balun was visibly broken and needed to be replaced ?

uglydukwling · 2009-02-04, 08:19 AM

Probably
"Replacement parts are not available. Buy a new antenna."

2009-01-31, 08:52 AM	#1
uglydukwling Rookie Join Date: Oct 2008 Posts: 27	CM 4228HD built-in balun My 4228 arrrived this week, ahead of schedule (the dealer had said it would be at least mid-February) so it's time to install it and see how it works. The problem is that it has a built-in balun for a 75 ohm output, and my pre-amp has a 300 ohm input. Using a second balun to bring the antenna output back to 300 ohms would introduce unnecessary losses (how serious?) The balun is rivetted to the phasing wires and the rivets are part of the balun, so I won't be able to remove it without destroying it. I'd rather not do that in case I ever upgrade my pre-amp and need a 75 ohm connection. I suppose baluns are cheap enough that I really shouldn't worry, but this one is neater than one dangling from its wires. Can I leave the balun in place and by-pass it? I won't be able to connect to exactly the same place on the phasing wires as the balun is connected because the phasing wires are tight against the balun. I thought that it was critical that the length of phasing wire had to be the same on both sides of the connection point, but the lengths are different already so maybe an off-centre connection won't matter. Also, will the presence of the balun have any effect on the antenna with only its input side connected?

2009-01-31, 09:10 AM	#2
Tom.F.1 Veteran Join Date: Jun 2005 Location: Ajax, Ontario Posts: 1,928	I would leave it like it is and use a regular balun to go to 300 to match your amp. Or change the amp. Have you tried it without the amp? __________________ Samsung TV, Pio-Elite AVR, OppoBD, Wharfedale Speakers, Kicker Subs. Bell EVu, DB-4e OTA:)

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2009-02-01, 08:14 PM	#4
uglydukwling Rookie Join Date: Oct 2008 Posts: 27	I can't get my camera and computor to talk to each other, so I havn't been able to post a picture. I hope this description will help. The balun is a plastic box 2 1/2 inches high, 2 1/4 inches wide, 5/8 inches thick. It's connected to ( and supported by) the phasing lines by two hollow rivets 9/16 inches from the left side and 1 9/16 inches apart. The upper phasing line, attached to the upper rivet, is 13 inches long on the left and 9 1/2 inches long on the right. The lower one, attached to the lower rivet, has the dimensions reversed. The 75 ohm connector is on the bottom of the balun. Left and right are as you would see them facing the front of the antenna. The phasing line lengths are measured from the rivet to the point where the line enters the plastic insulator on the vertical antenna element. Dimensions are somewhat approximate because there are bends in the phasing lines. The upper left and lower right lines are longer because they cross the vertical element and then are bent back in a J to the connection point. If there are any other dimensions that I should measure, or if any parts of the description aren't clear, let me know.

2009-02-02, 08:35 AM	#6
uglydukwling Rookie Join Date: Oct 2008 Posts: 27	When you said "close-up pictures", I didn't realize you were talking about the INSIDE of the balun. Unfortunately, it doesn't look like I can get inside without destroying it, and I probably shouldn't do that just yet, in case I need it. I hadn't considered the possibility of the antenna impedance not being 300 ohms. That may well be the reason they provided a non-removable built-in balun and it may be a unique ratio. That would mean that bypassing the balun and connecting directly to my pre-amp wouldn't work. Also, when I find that out, substituting a conventional 300:75 balun won't work. Todaty's a business day, so I may end up spending the day on the phone trying to get some information out of ChannelMaster.

2009-02-03, 04:52 PM	#8
uglydukwling Rookie Join Date: Oct 2008 Posts: 27	After trying unsuccessfully to reach the CM tech line, I finally emailed them and got this reply: "I do not recommend trying to remove or bypass the 75 ohm balun." No reason given. No answer to my question whether the antenna impedance was 300 ohms or something else. So it looks like my options are add another balun or change the preamp to one with a 75 ohm input (maybe its time for an upgrade anyway)

2009-02-04, 08:19 AM	#10
uglydukwling Rookie Join Date: Oct 2008 Posts: 27	Probably "Replacement parts are not available. Buy a new antenna."