CM 4228 and multipath Help needed!

[markmanxp]

I recently moved my Channel Master 4228 from it's ground location to the chimney on my house. I basically use it to pull in my big 3 (soon 4) networks from about 30-35 miles out. My NBC and FOX are basically on the same tower. The ABC one is like 25 miles west of that. I point towards the middle. From the ground and now with summer a tree has caused problems with multipath, mainly because it is part of the path to the ABC tower.

Anyways I moved it up to the roof. I get a much better signal on all three. But multpath seems to be worse (not all the time but more it seems) and if you look at the attachment it will help you understand. I put the 4228 facing SE (so the right side of the chimney in the picture). The mast is 9 feet but only 5 feet is above the last top bracket/or top of the chimney. (I am not counting the metal tube, whateer that part is called). SORRY I didn't have a AFTER installation picture! )

Anyways that metal part I think is causing reflection and multipath? Would that be a fair accessment? Since this is "behind" the antenna or direction of the towers could I put a piece of cardboard on the backside of it to block the reflection? Since this chimney is for a fireplace we don't use I could do something like that or even take the metal part off? Any other ideas? Am I understanding multipath correctly? I am guessing that is the cause instead of trees or something else between the towers and myself. The signal meter (tivo) on two of the three bounces from 80 to 71 to 68 and sometimes 0.

Also since I am using an HD Directv Tivo it isn't as nice when it comes to handling multipath as my 2006 HD tv. But everything is recorded / comes through the tivo so I really need help! Thanks everyone who has some ideas!

Sincerely,

mark

 

[Tower Guy]

View attachment 16802

I moved it up to the roof. I get a much better signal on all three. But multpath seems to be worse (not all the time but more it seems)

mark

I doubt that the metal behind the 4228 screen is causing multipath. Take a look at a UHF analog signal that is in the same direction as the digitals. If you see ghosting, your guess may be right, but the reason may be an aiming error, not the chimney. Perhaps the 4228 has a beamwidth that is too narrow for your location and the attempt at aiming "down the middle" worked in the attic only due to serendipity reflections through the roof.

When trying to pick up signals from a spread of more than 15 degrees, the 4221 is a better choice than a 4228.

 

[markmanxp]

Perhaps the 4228 has a beamwidth that is too narrow for your location and the attempt at aiming "down the middle" worked in the attic only due to serendipity reflections through the roof.

Thanks for your reply!

Actually it has never been in the attic. It was on the deck which is at ground level. Now it is on the other end of the house on the chimney. Basically it was, at least until this spring, getting those three channels from the two towers with little multipath issues. I will try to fine tune it to see. I always thought if your signal meter is bouncing somewhat wildly and even hitting zero it was for sure multipath.

 

[bhelms]

I use the 4228 for signals coming from different directions and it works reasonably well. Check the link below. It describes the process of stacking two 4228s. I'm not suggesting that for you, but when you look at the gain patterns shown in this article you get that idea that the 4228 has it's best gain on-axis as expected, but has some reasonable gain in the two significant lobes that are about 45 deg. off-axis on each side. (The pattern for a single antenna would be about the same as for stacked antennas but with lower gain figures.) Those lobes can be used to advantage, or they can hinder if the mulipath is aligned with either of them. The point is that perhaps you can improve your situation by rotating your antenna off-axis from the primary direction. Also - Cardboard is transparent to radio signals in these frequencies. It is possible that any metal at about the same height as the receiving elements might be contributing to a multipath problem. If you can remove that chimney piece at least for a trial that might be worth the effort. Good luck!

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

Best. Welcome, BTW...!

 

[Rick0725]

You need to first determine if you actually have multipath, need to make sure your antenna is properly aimed, and be aware of the fact that it may be a challenge to find a sweetspot (antenna aimed down the middle so to speak) reception wise with your current antenna.

multipath diagnosis
-examine your analog stations for ghosting and minimize as best you can with antenna peaking.
-if you are unable to minimise the ghosting to your satisfaction you may then need to experiment with location and height.

look at a resonable sampling of stations.

 

[Tower Guy]

I always thought if your signal meter is bouncing somewhat wildly and even hitting zero it was for sure multipath.

That sounds more like mis-aiming to me. Could also be made worse by trees blowing in the wind or airplane flutter.

 

[Jhon69]

Thanks for your reply!

Actually it has never been in the attic. It was on the deck which is at ground level. Now it is on the other end of the house on the chimney. Basically it was, at least until this spring, getting those three channels from the two towers with little multipath issues. I will try to fine tune it to see. I always thought if your signal meter is bouncing somewhat wildly and even hitting zero it was for sure multipath.

To see if you have mutipath issues go to www.antennaweb.org .Good Luck!.

 

[Jim5506]

Multi-path is caused by the receiver getting two copies of the same signal at slightly different times (off by nano-seconds or more).

There must be something between your antenna and the station towers (off to one side or the other) that is large enough to reflect the signal back toward your antenna slightly time delayed. When the antenna was lower, it may have been out of the path of the multi-path.

Try re-orienting your antenna, maybe moving the antenna around on the roof. You may need a tripod mount instead of mounting it on the side of your chimney.

BTW the symptoms DO sound like multi-path to me.

You may need a more directional antenna. The 4228 is known for being more prone to multi-path than yagi style antennas like the RS U-75R and the Antennas Direct 91XG and 43XG.

What is the angle between the group of stations and the ABC station?