are dtv signals fickle?

[RBW]

I took a drive to the top of Mt. Greylock last weekend, armed with a Haier portable (DTV) TV, and a Terk indoor UHF-VHF directional antenna. At the summit of the mountain is the tower for WCDC-19 (their DTV antenna is there too isn't it?) plus a couple of translators. I stood with the TV in search mode, adjusting the position of the antenna in small increments... NOTHING... it continued to scan... NOTHING! I was soooo disappointed :'(

First off... why wouldn't I receive WCDC? Was I too close to the tower??? (is that possible?) And second, why would nothing ELSE come in? Nothing from neighboring NY... or southern Vermont. For heavens sake I was 3,600 ft up! I would've thought something would've come through! What a bummer.

 

[RBW]

OK, before any questions are asked;

Since I added this post I did some analyzing of the process. And it's possible that the TV might've been in the wrong mode. Everytime a scan is performed on this TV, it asks whether or not the scan is for CABLE or OTA reception. I recall when setting it up that it was difficult seeing the screen in the sun angle I was in. So yes, it could've been on cable setting! -- (which didn't occur to me at the time), and I only did 1 scan.

The next chance I'll have in the area is in 3 weeks. I'll have to give it another shot.

 

[fybush]

It does indeed seem likely your TV was in the wrong mode.

But to answer the question you asked before - "is it possible to be too close to the tower?" - the answer is a qualified yes. TV antennas, especially UHF antennas, are designed to send much more signal out toward the horizon than straight down toward the ground, so it's at least theoretically possible that WCDC-DT's signal might have been shooting right out over your head.

In general, though, there's usually enough downward radiation to make reception possible right at the tower base.

Does the Haier TV allow direct entry of RF channel numbers? If so, when you're next up there, punch in "36" if a scan doesn't get 19.x to show up, and see what happens.

In addition to WCDC, Greylock should give you easy line-of-sight reception of the Albany TVs, and depending on the day and the quality of your receiver, you ought to have a pretty good shot at everything from Boston to Utica from up there.

(That "quality of the receiver" part is important - it's also possible to have so much RF at a transmitter site that the front end of your receiver simply overloads and can't get much of anything at all.)

 

[RBW]

Does the Haier TV allow direct entry of RF channel numbers? If so, when you're next up there, punch in "36" if a scan doesn't get 19.x to show up, and see what happens.

Yes, I’m aware of RF overload since I remember doing the same thing up there years ago with an analog set-up, and WCDC appeared on more channels than were desirable.

And yes, the channels CAN be entered directly which I did after the scan. I couldn’t recall where 19 was digitally, but entered 19-1 (and got nothing). Now this could have been the result of the mode still being in “cable”. I’m not sure if that setting affects direct entry, but it probably does. The TV is odd though; sometimes even when a channel is 100% receivable, it won’t display it through direct entry, if it isn’t already in the database. It must be scanned (and added to the db) first.

Better luck next time! :-\

 

[necrat123]

From Greylock, digitally you should get Albany, Springfield, and Hartford without much issue, even with WCDC there.

If your TV is portable, the best place to stand is at the monument, oriented so the WCDC/WAMC tower is behind the tower from you. It can shield against the tower's RF.

That's how I fight the RF overload from WAMC up there when I bring portable radios.

 

[w9wi]

And yes, the channels CAN be entered directly which I did after the scan. I couldn’t recall where 19 was digitally, but entered 19-1 (and got nothing). Now this could have been the result of the mode still being in “cable”. I’m not sure if that setting affects direct entry, but it probably does. The TV is odd though; sometimes even when a channel is 100% receivable, it won’t display it through direct entry, if it isn’t already in the database. It must be scanned (and added to the db) first.

WCDC's RF channel is 36. And that's what you would have had to enter to get WCDC through direct entry.

(Is it possible the channels that don't come up through direct entry are the ones whose RF channel is different from their virtual channel? )

 

[RBW]

WCDC's RF channel is 36. And that's what you would have had to enter to get WCDC through direct entry.

(Is it possible the channels that don't come up through direct entry are the ones whose RF channel is different from their virtual channel? )

No. I've experimented with that. Either/or can be entered. If an RF channel is entered, it'll display the virtual channel. Same goes with entering the virtual. Either way, the RF channel will be tuned.

 

[pqgeorge]

DTV signals are somewhat fickle. You have to have a very strong signal for a station to decode and to STAY decoded. That's the "cliff effect". You either have it, or you don't. That's the nature of the beast, when it comes to DTV. Having the right antenna is half the battle. Since I live in a rather strong area for DTV with both Boston and Providence signals coming in pretty well (with a couple of exceptions), most stations in both markets come in and stay in. As for DTV DX'ing, that's another issue. Last night, with a very strong tropo opening to the southwest toward Hartford and New York City, I was able to decode WFSB-TV (PSIP 3/RF 33) with their three virtual channels and WGGB (PSIP 40/RF 40) with their two virtual channels. Both stations are about 100 miles away from my home QTH (Whitman, MA). Saw the signals (with no decoding) of WVIT/35, WCDC/36 and WWLP/11. Both WFSB and WGGB were visible for over two hours with some fades (dropouts) at times.

I was using and fringe corner-reflector for UHF and used my FM antenna for VHF (yeah, I know.... cheating a little bit). The receiver was an Insignia DTV box, connected to RG/6 with an all-band RF amp (18 db. gain) with an in-line rf amp. Total gain, about 30 db. The FM was wide open to NYC with stations at local strengths, even some HD's made it through.

DTV is the method of television in the USA now. We're all getting used to it now. I still miss the analog DX of VHF and UHF.

73,
Peter Q. George (K1XRB)
Whitman, Massachusetts

 

[KML0224]

WFSB-DT of Hartford has three subchannels:

3-2 CBS 3 (geared towards Springfield with their own newscast and ads)
3-3 Eyewitness News NOW
3-4 WFSB Fairfield County (bit starved and looks horrible)

Their transmitter is on Avon Mountain to the west-southwest of Hartford. WUVN-DT (UNI) channel 46 (virtual channel 18) is next to them.

Any luck with WTIC-DT (FOX) on channel 31 or WTXX-DT (CW) on channel 20? I know two of the Boston stations are using those same frequencies. WTIC and WTXX both transmit from Rattlesnake Mountain in Farmington, with WEDH-DT (PBS) channel 45 (virtual channel 24) coming off the same tower. WVIT-DT (NBC) channel 35 (virtual channel 30) is on their own Rattlesnake Mountain tower.

 

[Skynet74]

DTV doesn't work well with VHF frequencies. That much I know. WHDH had a major problem with people not able to receive the station anymore when they switched to a VHF Frequency. So they had to actually revert back to UHF.

 

[RBW]

DTV doesn't work well with VHF frequencies. That much I know. WHDH had a major problem with people not able to receive the station anymore when they switched to a VHF Frequency. So they had to actually revert back to UHF.

WRGB 6 (Schenectady) is a perfect example of that. They remained on digital 6 after the analog shutdown and could barely be seen by anyone without cable. They raised their power... no better. Now they're running piggyback to their CW afilliate on RF 45-3, but still keep their initial signal on 6. They also carry "This TV" on 6-2. Incidentally, Albany's Fox aff. (virtual 23) makes their digital home on ch. 7 and I believe WNYT (NBC) virtual 13, wound up on ch. 12

 

[RonTheEngineer]

You guys are also forgetting two things, multi-path and receiver desensitization (de-sense)

Yes most of that signal is shooting straight out, and yes there should be enough downward radiation to get a good signal, but, that very strong, most of the power, signal shooting straight out, is reflecting off the next mountain top, straight back at you. This would have looked like a ghost on analog, its a mess or nothing on digital.

Fun Fact: At WTXX we had a "backup demod" which was a corner reflector on the roof and a cheap demod. In case something happened to the real one. Guess where this antenna was pointed... at the nearby water tower, not up at the transmitter antenna. To point it there gave us unacceptable multipath.

On de-sense: True its not alot of signal coming down at the transmitter site, but define "not much". Its still within ANSI exposure levels, but is the strongest signal that receiver has ever seen. Without going into complex discussion on such things as intermodulation distortion, compression and the like... it will essentially knock down the strength of all your far-off stations, in layman terms.

Fun fact: As I would drive by WEBE on RT 95 every day, no matter where my FM car radio was tuned, would take a noticable dip in signal strength and quality. Of course the closer to 107.9, the worse it was.

Another Fun Fact: I got a call from Charter Cable in Newtown complaining that my analog output power was fluctuating, their Chief even showed me on his spectrum analyser. I called my assistant and he parked at the output meter, which didn't budge as I saw my signal go up and down by about 10db. I widened out the spectrum analyser display and watched a 900 MHz paging transmitter nearby come on and go off in perfect time with the fluctuations.