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Old 19-Nov-2010, 6:28 PM   #1
MikeInEburg
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One 'challenging' off-air station

Greetings,

We maintain a private cable system for a small retirement community in Hanover PA. We have a mix of satellite and off-air channels. Prior to the digital change, we were able to get an OK off-air signal from the Baltimore stations. Now that conversion is finished, we have chronic troubles with reception of WJZ 13 from Baltimore. Here is link to tvfool report:


Pre transition, we were using WJZ's analog broadcast RF 13 and signal was OK. During transition, WJZ was broadcasting digital in UHF and all was good.
Since June 2009 transition date, WJZ moved their digital back to CH13 RF space - and we've been fighting it ever since. Signal level on 213MHZ at antenna mast as measured on my Sadelco meter is -24dBmV. Much of the time, signal is fine. Then we get tiling and picture breaks up. Digital demod indicates a 20dB SNR - which should be OK. I suspect that combo of marginal signal and multipath are to blame. All the residents know is that it used to work fine and now it doesn't. And it's my fault!

Hardware setup is as follows:
-Blonder Tongue BTY-10HB single-frequency antenna (for channel 13) roughly 40' above ground level.
-Blonder Tongue CMA-HB VHF preamplifier on mast
Roughly 250' of RG11 to headend
-Blonder Tongue PS-1536 Preamp power supply
-Toner 3-way splitter:
Leg 1 to Drake DAD860 digital demodulator for WJZ (RF13) (converts to baseband, then we re-modulate on our in-house cable plant)
Leg 2 to Blonder Tongue 8VSB to QAM transcoder (we transmit same signal on QAM on our private cable plant)
Leg 3 to a Drake DAD860 digital demodulator for WBAL (RF 11) that is broadcast from the same tower as WJZ. No problems with this channel!

Drake (digital demodulator mfr) says that I should try a newer consumer-grade set-top box to see if newer chipset better deals with multipath. So - any recommendation on a newer set-top box that has tuner that may be better than others? It appears that the set-top box market has fallen off a cliff in the past year...

We are considering a second stacked antenna to help eliminate multi-path, however that's a fairly large nut to crack.

Due to FCC regs, we can't simply get this station off of satellite because we're in a different market area.

So, advice on set-top box and any other suggestions are welcome.
Thanks!
Mike
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Old 19-Nov-2010, 7:23 PM   #2
No static at all
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This is probably a stupid question, but is FM trapped on the channel 13 antenna?

WJZ's directional signal is really hurting you & that location is only seeing about 7 kw's over somewahat difficult terrain.

Last edited by No static at all; 19-Nov-2010 at 7:25 PM.
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Old 19-Nov-2010, 7:49 PM   #3
MikeInEburg
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Quote:
Originally Posted by No static at all View Post
This is probably a stupid question, but is FM trapped on the channel 13 antenna?

WJZ's directional signal is really hurting you & that location is only seeing about 7 kw's over somewahat difficult terrain.
FM is NOT trapped off at this point. We discussed internally and decided that it was better to not put another widget in the line, especially since antenna is single-channel variety.

What the residents don't understand is that, in the old days they saw snow and maybe slight ghosting. What they're seeing now is the modern-day equivalent...
Mike
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Old 19-Nov-2010, 9:51 PM   #4
mtownsend
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Quote:
Originally Posted by MikeInEburg View Post
Signal level on 213MHZ at antenna mast as measured on my Sadelco meter is -24dBmV. Much of the time, signal is fine. Then we get tiling and picture breaks up. Digital demod indicates a 20dB SNR - which should be OK. I suspect that combo of marginal signal and multipath are to blame.
Quote:
Hardware setup is as follows:
-Blonder Tongue BTY-10HB single-frequency antenna (for channel 13) roughly 40' above ground level.
-Blonder Tongue CMA-HB VHF preamplifier on mast
Roughly 250' of RG11 to headend
-Blonder Tongue PS-1536 Preamp power supply
-Toner 3-way splitter:
Leg 1 to Drake DAD860 digital demodulator for WJZ (RF13) (converts to baseband, then we re-modulate on our in-house cable plant)
Leg 2 to Blonder Tongue 8VSB to QAM transcoder (we transmit same signal on QAM on our private cable plant)
Leg 3 to a Drake DAD860 digital demodulator for WBAL (RF 11) that is broadcast from the same tower as WJZ. No problems with this channel!
Your setup seems sound. A 20 dB SNR from the demodulator means that you should have about a 4 dB margin for handling multipath/interference/fading. You might be able to squeeze out another dB or two by switching to an amp with a lower noise figure. The CMA-HB noise figure is 5.0 dB, while something like the Winegard AP-3700 has a noise figure of 2.6 dB (the Winegard also has a built-in selectable FM trap).

Do the pixellation events correlate to certain conditions like rainy weather or windy conditions? You might want to check for antenna wobble and tree blockage.

Multipath does seem to be the most likely cause of the occasional breakups. You might want to try aiming the antenna a little off-axis to see if things get any better/worse. If you have a strong multipath reflection coming off of a hill or building, you might be able to de-tune your sensitivity to it by adjusting the antenna aim. It would help if you had access to a spectrum analyzer and could look at the flatness of the modulated channel while you are adjusting the antenna.



Quote:
Drake (digital demodulator mfr) says that I should try a newer consumer-grade set-top box to see if newer chipset better deals with multipath. So - any recommendation on a newer set-top box that has tuner that may be better than others? It appears that the set-top box market has fallen off a cliff in the past year...
Yep, the demand for set-top boxes has gone away since all new TVs have built-in tuners, and TV's keep coming down in price. Without the $40 coupon program, it probably makes more sense to upgrade an old TV rather than to spend $60 out of pocket on a set-top box.

Most electronics retailers still carry at least 1 model of converter boxes. Set top boxes are still available, but your selection might be limited to just the 1 model that the store carries. I recall seeing them at Walmart and Radio Shack, and there are probably others.

The LG chipset used in many of these boxes is known to be pretty good (so-called 6th generation chipsets). Broadcom also has a pretty good chipset. These newer chipsets are known to do a better job of dealing with multipath. You might want to check out this list on Wikipedia (http://en.wikipedia.org/wiki/Comparison_of_CECB_units).

BTW, these "low-end" converters downconvert everything to NTSC quality (should be the same as the DAD860), so they will not be able to deliver HD content in their native resolution. Do you have any plans to support HD content in the future?



Quote:
We are considering a second stacked antenna to help eliminate multi-path, however that's a fairly large nut to crack.
The set-top converter box definitely seems like the easier and cheaper route to try first.
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Old 19-Nov-2010, 10:25 PM   #5
John Candle
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Television Reception

http://www.barrel-of-monkeys.com and http://www.ramelectronics.net , have consumer grade hard to find tuners and etc. And I typed in professional grade ATSC or 8VSB tuners , or , cable headend ATSC or 8VSB tuners in the google search box and found several.
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Old 19-Nov-2010, 10:54 PM   #6
John Candle
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Television Reception

DVD player/recorders with a built in ATSC tuner is a way to get the latest chips , http://www.panasonic.com has three of these. . Also check out http://www.hauppauge.com , Also check out what http://www.avermedia.com has now days. . Also check out ,http://www.kworld-global.com , SA290-QDVI and SA290-QLE , ATSC/QAM tuners. . Also check out http://www.lg.com for DVD recorder with ATSC tuner

Last edited by John Candle; 20-Nov-2010 at 8:33 AM.
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Old 19-Nov-2010, 11:31 PM   #7
John Candle
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Television Reception

Also check out http://www.channelmasterstore.com , The CM7000 and CM7000PAL . The last of the ghost killer antennas that were made by antennacraft , channelmaster , the last one being made now is winegard HD7210P . Ok check this out http://www.markertek.com , Americas Broadcast Supply House , Check out the Totevision ATSC 100 and other ATSC tuners. In the markertek search box type in atsc modulator or atsc tuner.

Last edited by John Candle; 20-Nov-2010 at 9:18 AM.
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Old 20-Nov-2010, 8:41 AM   #8
John Candle
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Television Reception

With ATSC when on the edge of clear reception and a blocks in the picture. The Lower the Noise Figure the better. Here are ultra low noise amps. . http://www.kitztech.com and http://www.researchcomms.com/hdtv.html

Last edited by John Candle; 20-Nov-2010 at 4:47 PM.
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Old 20-Nov-2010, 9:10 AM   #9
John Candle
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Television Reception

Stacking 2 identical tv antennas vertical or horizontal is easy. Vertical stacking is often done around airports , the large bodies of the planes make great reflectors. and in the case of diffraction , vertical stacking is done when a hill or mountain or something else is in line with the receiving antenna and the transmitter. With vertical stacking one antenna is fixed in place and the other antenna is moved up and down to reduce the vertical multipath. Horizontal stacking is done when signals are reflecting off of buildings , trees , mountains/hills etc.. For horizontal stacking the antennas are side by side , one antenna is in a fixed position and the other antenna is moved closer and further away to find the sweet spot , the desired result of multipath reduction or elimination. For horizontal stacking the mounting is often made of steel pipe like water line pipe or even gas line pipe. The pipes are very strong and do not bend. There is way to much information on the net about tv antenna stacking.

Last edited by John Candle; 20-Nov-2010 at 6:08 PM. Reason: Clarify the information.
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Old 20-Nov-2010, 9:34 AM   #10
John Candle
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Television Reception

http://www.silicondust.com , HD Homerun Tuner TECH , has dBmV signal level display , dB signal quality (MER) display , and is compatible with TS reader for stream analysis.

Last edited by John Candle; 20-Nov-2010 at 6:11 PM.
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Old 20-Nov-2010, 1:28 PM   #11
MikeInEburg
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Hi all,

Thanks for the many replies. I will probably start by replacing the preamp with something that has lower noise - a couple of dB may do the trick. Next try a set top box. John - thanks for the reminder about DVD players - they're probably easier to find than quality set top boxes these days. Looking carefully at the coverage map, it is clear that this location is hidden behind a small rise - essentially located directly toward the transmitter tower.

Stacking - I've read a fair amount and could add the second antenna on the mount that I have - although I"d be pushing my luck. My antenna is roughly 18' above the closest roofline - and those rooflines are shaped such that I doubt they're reflecting the signal. More likely multipath source is the hill a mile or two off. If John's overview is correct, then I'd need a side-by-side "stack" to address this - logistically much more difficult. I'd need to replace my monopole mast with a tower. I have a flat roof (but nothing can touch/penetrate the flat roof) and an eight-foot parapet for mounting. No guy wires. Hence, I'm working thru the electronic possibilities first.

Thanks again!
Mike
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Old 21-Nov-2010, 10:40 PM   #12
Tower Guy
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Quote:
Originally Posted by MikeInEburg View Post
FM is NOT trapped off at this point. We discussed internally and decided that it was better to not put another widget in the line,
I'd suggest that you try an FM filter anyway. The preamp or the DAD860 itself could create a second harmonic of WGTY on 107.7. That harmonic would fall on 215.4 which is within channel 13.

A CMA-B preamp tuned for channel 13 would reduce the FM and also have a 2.5 db lower NF spec.

Last edited by Tower Guy; 21-Nov-2010 at 10:55 PM.
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