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Author
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Topic: Sony STW-C140GI HI/VI problem
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Ken Lackner
Phenomenal Film Handler
Posts: 1907
From: Atlanta, GA, USA
Registered: Sep 2001
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posted 12-20-2013 09:47 AM
Bob,
Is this a single screen theater? If not, I would try swapping the transmitter with another auditorium. Have you tried more than one receiver?
The recommended placement of the transmitter is parallel to the ground, antenna side facing the screen, with the antennas folded IN so that the antennas are parallel to the screen. Have you tried this orientation? Also, how are you holding the receiver? The receivers should be supplied with lanyards, which must be attached so that the receiver can be worn around the neck. It, too, must be parallel to the screen for optimum reception; placing it in a pocket or cup holder will diminish the reception.
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Harold Hallikainen
Jedi Master Film Handler
Posts: 906
From: Denver, CO, USA
Registered: Aug 2009
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posted 12-20-2013 12:49 PM
Good luck with this! Because of FCC requirements, license-free transmitters have to use very low power. Further, license-free systems have no protection against interference from other users of the same spectrum (which may be your issue, since you're seeing several Wi-Fi signals). Since you have a spectrum analyzer showing you the Wi-Fi signals, can you watch for the Sony transmitter on the spectrum analyzer and choose the Sony RF channel that lands between the Wi-Fi signals? I think you've said that you've tried all the channels, and none of them is great, but this might be a way of finding the best channel you can.
It's interesting that the closed captioning is working and that it is the HI with the issue. Closed captioning, of course, uses a substantially lower data rate, giving more time for retransmission of the data. Sony uses a protocol that is very similar to that which USL uses for closed captions over IR. The information about the next caption (text, time in, time out, etc.) is transmitted repeatedly from the TimeIn of the previous caption until the TimeIn of the current caption. So, captions are transmitted one caption in advance and are transmitted several times (as much as time allows). So, even with marginal reception, at least one of the caption packets gets through. For audio, however, there is not the bandwidth to transmit the audio repeatedly and doing so would also add excessive latency to the audio. So, the audio transmission is more fragile.
Even with reliable coverage, there can be issues with the use of RF in these applications. Because of the limited number of channels, multiplex theaters face channel re-use issues. Users or theater staff have to configure the receiver such that the audience member hears the appropriate HI or VI-N audio, not one from another auditorium. Infrared systems do not face these issues since the signal is confined to the auditorium.
Because the Sony closed captioning and HI/VI-N system is relatively new (it's only been manufactured for a couple years), perhaps the theater has an existing IR system (emitter and headphones) that could be used for HI/VI-N and keep the Sony system to handle the closed captioning. Or, if not, USL would be happy to provide an IR system (of course).
Good luck!
Harold
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Harold Hallikainen
Jedi Master Film Handler
Posts: 906
From: Denver, CO, USA
Registered: Aug 2009
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posted 12-20-2013 03:29 PM
Gordon, sorry to hear about the issue! Since I designed the system, it's my fault! Anyway, the system does not bring up the carriers until there is audio. It holds the carrier up until 30 minutes after audio is last detected.
We transmit HI at 2.3MHz, VI-N at 2.8MHz, and closed captioning as FSK at 1.8MHz. An FM receiver, of course, normally has a hissing sound when no RF is present. If we have the HI carrier up and the captioning carrier up (with a difference of 500kHz), there is a low level intermodulation product generated at 2.3MHz PLUS 500kHz, which lands on 2.8MHz. The intermod product is generated anywhere a circuit is not perfectly linear (and nothing is perfectly linear). The better the linearity, the lower the intermod product. So, a very low level signal is generated by the nonlinearity of the emitter and the nonlinearity of the receiver. IF there is the normal 2.8MHz carrier present, it is much stronger than this intermod product, so there is no problem. But, if there is no VI-N audio (such as during trailers), no carrier is brought up, and the receiver instead gives you this intermod product (and the captioning data sounds fun in your headphones).
I suspect you have IRH-230 headphones. Give us a call about trading them for IRH-280 headphones. These headphones have better selectivity (use of ceramic filters instead of LC networks), have a 1.8MHz trap to attenuate the captioning carrier, AND have a squelch. So, in the absence of carrier, the headphones are silent. In my tests, the headphones remain silent if you are on the VI-N channel, captioning is running, and the VI-N carrier is not up. If you get real close to the emitter, the headphones can still get overloaded, and the sound comes back. But, in most cases, I believe the IRH-280 will solve the problem. Give us a call about a swap!
Harold
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Steve Guttag
We forgot the crackers Gromit!!!
Posts: 12814
From: Annapolis, MD
Registered: Dec 1999
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posted 12-20-2013 04:34 PM
My experiences with the UPC-28c have been mixed.
First off...I've found, using the CP750 as the source, that the VI-N input on the UPC-28c has to be turned down all of the way (1V) on the higher sensitivity setting and forget about using compression or you'll boost the noise.
The other thing is that, as Harold states, you can overload things if you get too close...as in the back rows. I have one theatre where I pointed the panel at the side wall of the theatre to knock it down...still have plenty of coverage in the far corner of the theatre...the IRH-280s are quite sensitive. I was even wondering if there is a way to turn down the intensity of the LEDs for smaller rooms so they draw less current, less heat, last longer and don't overload the system.
In other theatres we mounted the panels in the booth to knock the signal down a bit.
Oddly enough, for the HI track, we take that off of a processors HI output, not from the DCP track...there we turn the compression up to 3:1 (max) and set the sensitivity to .2V since at .3 we have had the carrier not turn on in some locations, depending on the volume setting of the processor and the program material.
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