[jchtrout1]

Anyone know what the best rated commercial receivers are for rejecting multipath ?

I,m using mainly BT AQD's but they dont seem to handle multipath very well.

Since these are around 3 years old, I,m wondering if any manufacturers have come up with a better solution.

thanks,

 

[AntAltMike]

There won't be any meaningful "ratings" for commercial receivers. Most of us in commercial situations don't need exceptional receiver performance, since we can afford nice antenna arrays, but I see from your other posts that you are not so lucky.


I have been using residential receivers with firm power on and last selected channel memories. I used around 80 CM-7000s, and while they were stable, visually, every once in a while, they would have trouble maintaining audio on certain channels. Then I bought half a dozen iNet SSR1921s, which worked well, but I lost my supplier for those, so now I use Tivax STB-8, which I get from Twister Group for $49 each plus shipping. You might as well try as many CECBs as you can get you hands on, and when one digests your problem signals well, buy a whole bunch for spares, because when they are gone, they are gone.

 

[jchtrout1]

Thanks for the reply. I dont really have a problem with my off air Ct. locals, but I am also pulling in all of NYC and Long Island from 65 miles out and at times, especially when the leaves are out and typical summertime scatter, I get some pretty bad MP on a couple channels.

I have individually cut yagis on a 150' tower and several quad stacks cut to frequency.


When the transition first began, I wouldnt commit to large expenditures and did as you do, bought inexpensive residential receivers and they worked about as well as can be expected. The BT AQD's arent all that bad, especially like the abilty to check and reset remotely, but as always, looking for optimum.


Still waiting for channel 2 WCBS to up their power or activate their translator on LI. When that happens, I will say a prayer.


Thanks

jtrout

 

[AntAltMike]

You might try RL Drake for a demodulator.

http://www.rldrake.com/product-dd860.php

http://www.rldrake.com/product-dad860.php

 

[jchtrout1]

I,ll take a look again at the Drake, they do look a little limited for conversion to 4/3 aspect ratio compared to the BT, but maybe have better co channel and MP rejection.

I do use the Drake DQT 1000 for a couple clear qams now and it has been pretty stable.

Thanks,

 

[AntAltMike]

Have you found any affordable 8VSB modulators? All the headend component manufacturers make devices tha demodulate both 8VSB and QAM, but those produict lines only modulate to QAM. The problem that causes for me is that I'd like to develop digital channels that can be tuned by CECBs, but they won't process the QAM.


Sencore had one listed on their website, but when I contacted them for a current price, they notified me that it had been discontinued.

 

[jchtrout1]

Have you looked at these ?
http://www.blondertongue.com/digital/DHDP_Spec.pdf


I toyed with the idea of just reassigning the 8 vsb's and bought a couple. It worked well in tests, but really not compatible with my system. I have kind of a wierd setup here. I provide the basic tier to all residents, 4500 and the local cable company adds all of their tiers above basic with expanded, digital, voip and internet onto our cable.

Their boxes will not pass the 8vsbs so if a resident subscribes and has anything above expanded basic, they wouldnt see our digitals.

The drawback if you dont have that problem, is bandwidth, still 6 mhz.

 

[AntAltMike]



Quote:
Originally Posted by jchtrout1 /forum/post/18160266


Have you looked at these ?
http://www.blondertongue.com/digital/DHDP_Spec.pdf ...

I use a lot of those, but I have four consecutive broadcast DTV input channels, UHF 33-36, and when I try to convert any one of them, those heterodyne converters do "unintended conversion" of the adjacent channels, a problem you may remember from when we heterodyne converted analog UHF to VHF when there was an adjacent UHF digital channel present. That interference on the channel adjacent to the downconverted, target channel can make it unusable.


In my market, if I always downconvert UHF 36 to channel 5 and UHF channel 33 to 6, then the unintended, downconverted adjacent input signals fall harmlessly between 4 and 5 and above 6, but then, when I downconvert 34 and 35, I have to leave channel 3 vacant so that I can put them on 2 and 4 respectively. In a congested system, I need that twelfth VHF channel, so if I could find affordable 8VSB modulatrs for channels 2 and 4, then I could still use 3, since a modulated 8VSB channel would not degrade adjacent channels.

 

[jchtrout1]

I,m not sure if I,m reading your problem correctly or not, but are you using the mid band channels ?

Those BT's will output to them and the tests that I did with early CSB's did decode on 14-22, although I,m not sure if the tv's will without a box.

I havent run into the problem you describe, I do downconvert 2 adjacent channels 20/21, but run them in analog on channel.

 

[AntAltMike]

No, the problem I am referring to is that the broadcast digital channels that are adjacent to my target input channel do not get completely filtered off and produce interference on the channels adjacent to the target channel. The LG tuners, and the ones in the CECBs that look like Seth Thomas clocks but with two humps, have a lot of trouble processing channels if they are corrupted by the "spill-over" from an adjacent, heterodyne converted channel.


In my market, for example, analog channel 26 was assigned digital channel 27. When we heterodyne converted 26 to 3, some of the digital 27 would pass through the filters and make analog channel 4 look grainy. Since it is not possible to filter UHF channels as tightly as we'd need to, we simply replaced the analog heterodyne converters with modulator/demodulator pairs.


It doesn't cost much to make an 8VSB modulator. I know that because DISH network had one for their model 5000 or 6000 receiver that they sold for a couple hundred bucks. But it looks like there just isn't enough demand for anyone to bother to make one.

 

[jchtrout1]

OK got it.

I have always used the separate demod/mod units. I pretty much am still doing that now. I use a lot of the Olson Technolgy OTR 2500's. They are great with the IF and comp. loops, it makes EAS simple and you could swap and move endlessly, input anything into them, but of course it is still only one analog channel.

I,m filled up right now. I just moved some FM stations to throw a qam on 97, but from here on out, I have to start removing the analogs.

 

[dr1394]



Quote:
Originally Posted by AntAltMike /forum/post/18161541


It doesn't cost much to make an 8VSB modulator. I know that because DISH network had one for their model 5000 or 6000 receiver that they sold for a couple hundred bucks. But it looks like there just isn't enough demand for anyone to bother to make one.

But what was the spectral purity of the Dish 5000 modulator? I'll guess it could have been pretty bad since it was just a single channel application.


A modulator for head-end service needs to be pretty clean, and that costs more (since spectral purity is a function of the analog RF output circuitry, not cheap digital FPGA's).


Ron

 

[Ken H]



Quote:
Originally Posted by dr1394 /forum/post/18164492


But what was the spectral purity of the Dish 5000 modulator? I'll guess it could have been pretty bad since it was just a single channel application.

Would you like one, or two, to test?

 

[AntAltMike]



Quote:
Originally Posted by Ken H /forum/post/18165403


Would you like one, or two, to test?

If I still had mine, I would have made him the same offer.


But notwithstanding the fact that the DISH Network 8VSB modulated output was not deliberately engineered for adjacent channel use, I see no reason why it would cost a manufacturer any more to make a suitable grade 8VSB modulator than it does to make a QAM adjacent channel modulator, and headend grade QAM modulators are now priced at under $1,000. I'd love to be able to 8VSB modulate the digital output from a lobby camera or a house message channel for that price.

 

[bdfox18doe]

Bear in mind the Dish modulator took the transport stream and modulated it to 8VSB,and thus it didn't need an encoder chip & circuitry to convert composite video to MPEG. That's fairly easy and cheap to do. Kinda surprised they haven't put QAM mods in the DVR's yet. Oh, yea.. they won't sell as many 2nd subscriptions that way!

 

[AntAltMike]



Quote:
Originally Posted by bdfox18doe /forum/post/18166078


Bear in mind the Dish modulator took the transport stream and modulated it to 8VSB,and thus it didn't need an encoder chip & circuitry to convert composite video to MPEG. That's fairly easy and cheap to do. Kinda surprised they haven't put QAM mods in the DVR's yet. Oh, yea.. they won't sell as many 2nd subscriptions that way!

The obstacle to either DISH or DirecTV putting in a QAM modulator is that the program providers (ESPN, HBO, etc.) are requiring that the digital signals remain encrypted for most classes of customers. When DISH had an 8VSB modulator, I think the only HDTV programming it had available was its own local-to-local broadcast DTV, which was already unencrypted coming from its source. When we demodulate broadcast 8VSB, the stream is MPEG encoded, so all we need done at that point is remodulation.

 

[Ken H]



Quote:
Originally Posted by AntAltMike /forum/post/18168396


The obstacle to either DISH or DirecTV putting in a QAM modulator is that the program providers (ESPN, HBO, etc.) are requiring that the digital signals remain encrypted for most classes of customers. When DISH had an 8VSB modulator, I think the only HDTV programming it had available was its own local-to-local broadcast DTV, which was already unencrypted coming from its source.

No, until they pulled the plug on the 5000 model, all HD you were subscribed to was output from the 8VSB module, including HBO & Showtime. Somewhere, I still have D-VHS HD recordings of Band Of Brothers and The Sopranos from HBO/Dish 5000 & HD Modulator/Panasonic TU-DST51 & PV HD1000.