[Tim_K]

I've been on the roof for several days now (not consecutively, of course...though sometimes it feels that way) and I need help to resolve a problem w/my OTA digital station reception. Here's my situation:


Dish 6000 w/8VSB.


(2) Radio Shack UHF only attennas mounted on a 5' mast on the roof (2 story Cape).


The antenna leads are joined by a Channelmaster unit that joins the 2 signals (antennas are ponted in the opposite direction from each other) and sends a single signal to the receiver.


100' run of RG-6 cable from the antennas to the receiver.


I am located less than 30 miles from all of the digital station towers (relatively flat terrain as well).


I am able to receive signal strength of 60 or > on all of my local digital stations.


My problem is that I see very significant dropoffs in signal strength across all of my local channels, regardless of how close or far I am from the tower (that is, the dropoff for the closest one is no less than the farthest one). Signal strength of 80+ one minute that drop to zero...back to 75...back to zero, etc. Obviously the dropouts include picture loss, etc.


I have re-pointed the antennas several different times and the problem persists. I've had a taste of these high quality pictures on my Mits 55" ...but it's been a tease to this point.


Any help or recommendations ? Is it a bad cable...bad 8VSB...bad receive...do I need an amplifier...Help!!!



Thanks in advance...


Tim

 

[Bogney Baux]

I suspect that combining 2 separate UHF antennas may be part of the problem. Combining 2 antennas like that is asking for multipath problems. Try each antenna separately and you will probably have much better results.

 

[farvque]

What you have is called "multipath", which means that your signal is bouncing off things and not being consistently recieved directly from the transmitter.


I solved my multipath problems by elevating my antenna about 10 additional feet. I found that within 20-30 degrees of aim, the aim is not very important, unless you are "bending" around an obstruction. Elevation has a far better effect on eliminating multipath than does aiming.


Also, the brand of the antenna and the strength of the preamp has a lot to do with the problem as well. A good, directional channel master with a strong preamp will usually get you a good signal, provided you are high enough.

 

[JasonATL]

TimK,


It would help a lot of people help you if you give us a bit more information:


1. Location (City)

2. Channels you intend to receive from each direction.


I assume that you are using two antennas pointed in either direction since the transmitters are located in two directions? Otherwise, Bogney's suggestions should help out tremendously. If you must aim two separate directions, it is possible that a more elaborate solution is needed. This is where the channel info comes in.


Suppose that you are trying to hit two different transmitters, transmitter 'S' is south of you and 'N' is north of you. If only one channel is transmitted from 'N' (the rest coming from 'S'), then you can try a Channel Master channel "trap" that will filter out all but that one channel. Here's a link to Stark Electronics:
http://www.starkelectronic.com/cmjoiner.htm

I've not used a channel-specific one. However, I do use a channel master joiner that isolates VHF and UHF (I used this because one antenna was causing the behavior you're seeing by interferring with my UHF antenna). In theory, you can use multiple traps, but I've not had experience with this. The main idea is to isolate the signal to come from one and only one of your antennas for each station.


Before spending money (and more time on the roof), you should do the experiment that Bogney suggested: unhook one antenna and verify that the signals from that antenna (i.e., the transmitter that it is pointing at) are stable. Then, try the other antenna in isolation. If this works, then some combination of traps is probably necessary.


Others who have actually done this will/should chime in. Their experiences will be quite helpful -- especially once it is known from what city (or cities) you are trying to get signals.


Good luck!

 

[jonlgauthier]

TimK,


I replied to your identical thread at ***************!

Here's my own experience with combining two UHF antennas without the use of a rotor. YMMV

 

[Tim_K]

First off...thanks to all who responded to my request for assistance, including those who responded across multiple forums.


I'm located in Southern NH, approx. 10 miles north of the Mass border. The "all channel" antenna is pointed South/South West towards Boston/Needham. The channels I am looking to pick up are:


19 WGBH PBS

20 WCVB ABC

30 WBZ CBS

31 WFXT FOX

42 WHDH NBC


The second antenna is pointed North/North West towards Manchester, NH. The channels I want to pick up in this location are:


57 WENH PBS

59 WMUR ABC


If the second antenna must be isolated on a single station, then I can sacrifice WMUR (ABC affiliate) since I would be able to pick up WCVB in Boston (ABC affiliate). I guess the same would apply for the PBS channels except that to date I have been unable to get any signal out of channel 19 during their testing periods.


Thanks in advance for any further assistance !!!


Tim

 

[JasonATL]

I think that you might be fortunate in isolating 57 and 59 from the same location. A reminder of my disclaimer: I haven't done this with isolating one channel -- only isolating VHF and UHF.


Check the Stark Electronics link that I posted previously. You might be able to get a "channel trap" or "cut to channel" filter to isolate the high 50's channels. There are diagrams on that page about how to wire up the channel traps. It says something about not trying to isolate two adjacent channels. This suggests to me that these things are not perfectly precise -- meaning that you might be able to get by with a channel 58 trap in order to pull in both 57 and 59. This is just a guess or idea. Personally, I would at least try this (if not too expensive or if Stark will let you return/exchange items). But, some combination of traps sounds like the best avenue to go.


Good luck and please let us know what works -- others might want to try something similar as more stations start their digital transmissions.