Co-Channel TV Reception - AVS Forum
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post #1 of 9 Old 11-15-2013, 11:38 AM - Thread Starter
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Long time lurker here. Appreciate all of the valuable information on these forums. I currently have a Radio Shack U-75R on a DiSEqC rotor mounted in the attic which I'm moderately happy with but it's been a long term goal of mine to upgrade. Most of the time my reception is fine, usually between 75-100% but some are weak enough that when a light switch is flipped it cuts out momentarily, or a severe electrical storm will make things unwatchable. Most of the stations I watch are either due north or due east. The house is a two story and we have TVs in a few different rooms so it's inconvenient to have to be rotating the antenna all the time. So I'm looking at getting maybe a DB8e. Already have an amplifier with separate UHF/VHF inputs on it. I have two channels on high VHF that I want. I currently have an FM band yagi on there that takes care of FM radio and manages to pick up channel 8 fine too. I plan on adding a join-tenna and a VHF high yagi for channel 12 which comes from the southwest.

Now, here's my problem. I think I would be quite happy with just my plan above, but it's nagging me that I won't be able to get channel 35 anymore in the off chance I want to watch it. The issue with channel 35 is that there's an analog low power 35 station coming from the north who's slated to flash cut to digital but is merely a translator for channel 29 which I get as clear as day so I have no use for it. The 35 I want to receive is coming from the south, almost 180 degrees and the signal is also quite weak being ~70 miles away but the U-75R picks it up fine when pointed directly at it. A notch filter would be difficult to find if not expensive that would be EXACTLY for channel 35 only. There's a channel 36 I'd have to keep so any filter solution would have to be very tight indeed! So after some thinking, I thought maybe it would be possible to point a yagi directly at the desired channel 35 and downconvert channel 35 to another frequency before combining it with the coax? What about using an old cable box? Tune it to channel 86, the CATV equivalent to OTA 35, then pump that signal down the coax on channel 3 or 4, being low VHF so unused OTA, combined with everything else. Would this work? Has anyone tried using a really old cable box to tune an ATSC station watching it on your TV on RF channel 3 or 4? What do you think? Any ideas for my situation?

Thanks!
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post #2 of 9 Old 11-15-2013, 01:04 PM
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Not sure if this helps much, but I used a RS U-75R in my attic for a number of years. The distant stations are at 35 miles, UHF was OK with an amplifier and I needed a VHF Yagi for channels 12 and 13. I replaced both antennas with single channel master 8200HD and got better reception without the need for the amplifier. If you are thinking about replacing the UHF Yagi, you should look at the Channel Master as it has a nice physical shape for attics.
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post #3 of 9 Old 11-15-2013, 01:28 PM - Thread Starter
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Hi Joel, thanks for the reply. I'm trying to get rid of the rotor altogether. The bulk of my stations are in the same spot almost due north, then there's a second group almost due east. I'd like to pick up both groups simultaneously without having to rotate anything. If I go the yagi route, it'll have to be two yagis and the gain of the two will have to be at least 3dB better than the U-75R to make up for the loss in combining. Optimally, I'd like the gain figure to be significantly more than 3dB better to get a stronger signal to carry me through the electrical storms and people flipping on and off lights in the house. I could get an antenna that's both VHF and UHF for my northerly channels, but looking at most of the specs it seems that standalone VHF and UHF antennas tend to have better gain. I only have a need for VHF high and that's only for two stations - one to the north and one to the southwest. I use the same cable line to feed my Sangean HDT-1 HD Radio so the FM broadcast band is a must. I have a 5 element FM yagi tied into the VHF side of the amp by itself right now, thinking of expanding that by adding a VHF high only yagi pointed southwest with the join-tenna for channel 12. Channel 8, the other station, is strong enough that it comes in anyway even if the FM yagi is less than optimal. I'm afraid without the join-tenna that combining the two will make channel 8 worse.

The big question in my mind is how to get this channel 35 in there. It would be a real bonus getting it tied in somehow but after some searching it almost seems like uncharted territory doing it without an A/B switch and doing it without a really expensive single channel notch filter. I'm thinking this cable box idea *may* work. Not with the newer ones which have actual tuners in them. Anything with a built in OSD definitely won't work. I'm talking 1980's vintage cable converter box. Will it work? Then next question would be if so, how well would it work since this signal is fairly weak. I'm sure if no one's tried it before someone must have the gear in their basement or something and able to try. If I don't hear anything, next hamfest I go to I'll pick one up for a dollar and try it on a strong station. Since low VHF is empty here, throwing that on the VHF side of the amplifier seems like a solution! Then again I'd hate for a 30 year old converter box to blow a capacitor and catch fire in my attic!
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post #4 of 9 Old 11-16-2013, 09:32 AM
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Quote:
Originally Posted by vo1one View Post

Hi Joel, thanks for the reply.
The big question in my mind is how to get this channel 35 in there. It would be a real bonus getting it tied in somehow but after some searching it almost seems like uncharted territory doing it without an A/B switch and doing it without a really expensive single channel notch filter. I'm thinking this cable box idea *may* work. Not with the newer ones which have actual tuners in them. Anything with a built in OSD definitely won't work. I'm talking 1980's vintage cable converter box. Will it work? Then next question would be if so, how well would it work since this signal is fairly weak. I'm sure if no one's tried it before someone must have the gear in their basement or something and able to try. If I don't hear anything, next hamfest I go to I'll pick one up for a dollar and try it on a strong station. Since low VHF is empty here, throwing that on the VHF side of the amplifier seems like a solution! Then again I'd hate for a 30 year old converter box to blow a capacitor and catch fire in my attic!

I have used an old cable box to add in a channel but that was 20 years ago back in the analog days, and it was VHF. I lived in a small town in New Mexico that had all UHF translators, but no NBC. I could barely pick up NBC on channel 9 direct from El Paso and did not want a switch due to the use of a VCR. The rf 9 was so weak that simply adding it to the UHF channels with a splitter/combiner weakened it considerably. Back than they had no UVSJ's at RS and that was before internet orders. I had seen one in a Los Angles electronics store and planned for it eventually. So, I found an very old cable converter at a thrift store, put it on channel 9 and then could combine the rf 3 output with my UHF. It worked until I moved on to another small town that was different.
Not all old cable boxes will go up to 86, many cut off about cable channel 36, not even in the UHF band (starting at 65). Also, make sure it has some "fine tuning" or off-set switch as the cable channels and UHF are not an exact match. The big question is , will it convert a digital channel?
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post #5 of 9 Old 11-16-2013, 06:53 PM
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W35AX has applied to convert to digital on channel 16, not 35, so WOUC won't be damaged by its conversion to digital. Or am I misunderstanding your question?

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post #6 of 9 Old 11-19-2013, 11:14 AM - Thread Starter
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Originally Posted by Mister B View Post

Not all old cable boxes will go up to 86, many cut off about cable channel 36, not even in the UHF band (starting at 65). Also, make sure it has some "fine tuning" or off-set switch as the cable channels and UHF are not an exact match. The big question is , will it convert a digital channel?

Yeah, I'll probably have to look for one that's just new enough to have the higher channels. If I recall correctly from messing around with one in the 80s that if I tuned a channel onto channel 4, I could also see the next channel up on channel 5 and the next channel down on channel 3, albeit slightly weaker in both cases so maybe the filter is wide enough on its own to accommodate the 2MHz difference in frequencies and more importantly hopefully the TV would be able to capture it anyway with AFC. I know the really old boxes had fine tuning and that would probably be best provided I could find one that had the higher channels as well. It'd be an interesting (to me!) thing to try.
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post #7 of 9 Old 11-19-2013, 11:24 AM - Thread Starter
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Originally Posted by Trip in VA View Post

W35AX has applied to convert to digital on channel 16, not 35, so WOUC won't be damaged by its conversion to digital

Aha! Their sister station 29 is staying on the same channel, guess I should've checked to make sure 35 wasn't doing the same. However, this will probably not happen until September 2015. Knowing how low budget they are they'll likely wait until the last possible second before making the switch. It'll be sad to no longer have any analog stations in a sense. It's a lot easier to figure out what's going on with one, i.e. easier to determine what type of atmospheric conditions are taking place for DX or instant feedback when you're making antenna changes or modifications.

That being said, is it worthwhile essentially combining three UHF antennas together? Looking at the DB8e specs, the radiation pattern when used in a 90 degree split configuration shows a gain of about 10dB (I assume 10dBd??) gain in those 90 degrees. Combining in another antenna would bring that gain down to approximately 7. Would it be pointless adding in another amplifier to mitigate the losses?

73!
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post #8 of 9 Old 11-19-2013, 04:09 PM
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Looking at the DB8e specs, the radiation pattern when used in a 90 degree split configuration shows a gain of about 10dB (I assume 10dBd??)

If you read the spec sheet, they say everything is dBi (page 1, note 3).
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post #9 of 9 Old 11-20-2013, 07:14 AM - Thread Starter
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If you read the spec sheet, they say everything is dBi (page 1, note 3).

Thought at first they meant everything on the first page. That'll teach me for skimming! Just didn't believe that there'd be such a huge drop between having it pointed in a single direction and having it split at 90 degree angles but the more I think about it, it makes sense. Like having two 4-bays phased together, you'd get +3db from a single 4-bay, however if you combine two 4-bays pointing different directions, you lose 3dB from a single 4-bay, so total 6dB difference. Might be better after all to just combine two really good antennas instead of using this.
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